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THE SCIENTIFIC REVOLUTION

Male Figure showing Muscles, from Thomas Geminus*

Anatomy (1545) after the wood-cut (drawn by John

Stephen of Galcar?) in Vesalius' De Fabrica (1543)

(From A. M. Hind Engraving in England in the Sixteenth and Seventeenth Centuries .
Vol. /, by permission of the Cambridge University Press)

THE SCIENTIFIC
REVOLUTION

15001800

The Formation

of the Modern

Scientific Attitude

A. R. HALL

Lecturer in the History of Science, University
of Cambridge, and Fellow of Christ's College.

LONGMANS, GREEN AND CO

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grato animo

PREFACE

To the historian of science the University of Cambridge offers
riches in its manuscripts, its libraries, and its associations. Among
those who dwell in the places once frequented by Newton, Darwin
and Rutherford there are many who, quietly and unostentatiously,
are making their contributions to the understanding of this age
of science in terms of its long historical evolution. No one who
has lived with them, no one moreover who has been fortunate
enough to learn from Charles Raven, Herbert Butterfield, and
Joseph Needham, can be other than conscious of indebtedness.

To them, and to all those friends who have helped or tolerated
my endeavours, I offer my grateful thanks. One other only I
mention by name, since he is no longer with us, Robert Stewart
Whipple, whose life-long enthusiasm for the history of science is
commemorated in the collection of historic scientific instruments
which he presented to this University.

Above all, this volume could not have been written without
the consistent support of my College, which has given generous
encouragement to the study of the history of science, and the
interest with which the University has fostered the teaching of
this subject.

CHRIST'S COLLEGE, A. R. HALL

CAMBRIDGE

February 1954

vu

CONTENTS

INTRODUCTION page xi

Chapter I Science in 1500 i

II New Currents in the Sixteenth Century 34

III The Attack on Tradition : Mechanics 73

IV The Attack on Tradition : Astronomy 102
V Experiment in Biology 129

VI The Principles of Science in the early Seven-
teenth Century 159

VII The Organization of Scientific Inquiry 186

VIII Technical Factors in the Scientific Revolution 217

IX The Principate of Newton 244

X Descriptive Biology and Systematics 275

XI The Origins of Chemistry 303

XII Experimental Physics in the Eighteenth

Century 339

CONCLUSION 364

Appendices : A. Botanical Illustration 369

B. Comparison of the Ptolemaic and Coperni-

can Systems 370

C. Scientific Books before 1500 371

BIBLIOGRAPHICAL NOTES 375

INDEX 38 I

INTRODUCTION

I HAVE tried in this book to present something in the nature of
a character-study, rather than a biographical outline, of the
scientific revolution. Natural science may be defined suffi-
ciently for my purpose as the conscious, systematic investigation
of the phenomena revealed in the human environment, and in
man himself objectively considered. Such investigation always
assumes that there is in nature a regular consistency, so that
events are not merely vagarious, and therefore an order or pattern
also, to which events conform, capable of being apprehended by
the human mind. But science in this sense is not simply the product
of one attitude to nature, of one set of methods of inquiry, or of
the pursuit of one group of aims. Within it there is room for both
economic and religious motives, for a greater or less exactitude in
observation (though some measure of systematic and repeated
observation is essential to science), and for a considerable latitude
in theorization.

In many of these respects modern science differs markedly from
that of a not very remote past. It demands rigorous standards
in observing and experimenting. By insisting that it deals only
with material entities in nature, it excludes spirits and occult
powers from its province. It distinguishes firmly between theories
confirmed by multiple evidence, tentative hypotheses and un-
supported speculations. It presents, not a possible or even a
plausible picture of nature, but one in which all available facts
are given their logical, orderly places. These are the most impor-
tant characteristics of modern science, which it acquired during
the period of transition conveniently known as the scientific
revolution, and has since retained. Certainly they were long in
gestation, but it is with the period of their coming to fruition and
vindication by success that this volume is concerned. Some topics
I have chosen to omit: mathematics, because it deals not with the
phenomena of nature, but with numbers; medicine, because it
was at this time rather an art than a natural science. It has not

xi

xii INTRODUCTION

been my object to attempt a complete narration of events, nor to
dwell on biographical and experimental details. Perhaps these
omissions may be forgiven in a book designed as an introduction
to the study of the historical processes at work in the development
of science, and of the major stages in that development.

Science began soon after the birth of civilization. Man's attempt
to win an Empire over Nature (in Francis Bacon's phrase) was
much older still; he had already learnt to domesticate animals
and plants, to shape inorganic materials like clay and metals to
his purposes, and even to mitigate his bodily ailments. We do not
know how or why he did these things, for his magic and his
reasoning are equally concealed. Only with the second millen-
nium B.C. is it possible to discern, dimly, the beginnings of
science in the coalescence of these three elements in man's
attitude to Nature empirical practice, magic and rational
thinking.

The same three elements continued to exist in science for many
thousand years, until the scientific revolution took place in the
sixteenth and seventeenth centuries. Reason, in conjunction with
observation and experiment, slowly robbed magic of its power,
and was gradually better able to anticipate and absorb the chance
discoveries of inventive craftsmen, but complete reliance upon a
rational scientific method in man's reaction to his natural environ-
ment is very recent. Magic and esoteric mystery the elements of
the irrational were not firmly disassociated from serious science
before the seventeenth century, at which time even greater stress
than before was being laid on the usefulness to scientists of the
craftsman's practical skills. This in turn was not outgrown until
the nineteenth century, when it became clear that in the future
sheer empiricism and chance would add little to man's natural
knowledge, or to his natural power.

Rational science, then, by whose methods alone the phenomena
of nature may be rightly understood, and by whose application
alone they may be controlled, is the creation of the seventeenth and
eighteenth centuries. Since then dramatic achievements in under-
standing and power have followed successively. In this sense the
period 1500-1800 was one of preparation, that since 1800 one of
accomplishment. And it is convenient to conclude this history of
the scientific revolution with the early years of the nineteenth

INTRODUCTION xiii

century for other reasons. Though profound changes in scientific
thought have occurred since that time, and though the growth of
complexity in both theory and experimental practice has been
prodigious, the processes, the tactics and the forms by which
modern science evolves have not changed. However great the
revision of ideas of matter, time, space and causality enforced
during the last half-century, it was a revision of the content, not
the structure of science. In its progress since 1800 the later
discoveries have always embraced the earlier: Newton was not
proved wrong by Einstein, nor Lavoisier by Rutherford. The
formulation of a scientific proposition may be modified, and
limitations to its applicability recognized, without affecting its
propriety in the context to which it was originally found appro-
priate. We do not need sledge-hammers to crack nuts; we do not
need the Principle of Indeterminacy in calculating the future
position of the moon: 'the old knowledge, as the very means for
coming upon the new, must in its old realm be left intact; only
when we have left that realm can it be transcended.' *

Despite the progressive accumulation of knowledge and elabora-
tion of theory, only the broader extrapolations of nineteenth-
century science would now be described blankly as "wrong,"
though a larger part of its picture of Nature might be described
as "inadequate" or as "true within certain limits." Even in
biology, where ancient and extra-scientific notions lingered long,
where experiment was most tardy in finding its just deployment,
this is still the case. The systematic and descriptive biology of the
pre-Darwinian epoch was not rendered futile by the theory of
evolution. Earlier microscopists were not exposed to ridicule by the
founders of cytology. On the contrary, the revolution in thought
about animate nature incorporated, and was founded on, the
labours of three or four generations. The same could not be said
of science before 1500, or even, without restriction, of the science
of the seventeenth and eighteenth centuries. Its progress in these
earlier times was not by accretion, for it was now and again
necessary to jettison encumbering endowments from the past.
Such science was on occasion simply wrong, both in fact and in
interpretation. Its propositions had to be rejected in toto, not
merely circumscribed, as the result of experiment and creative

1 J. Robert Oppenheimer, in his third Reith Lecture (The Listener, vol. L,
P- 943)-

xiv INTRODUCTION

thinking. In this respect the beginning of the nineteenth century
seems a useful point of demarcation between the scientific
revolution, in the course of which the sciences painfully and in
succession acquired their cumulative character, and the recent
period during which that character has been successfully
maintained.

The cumulative growth of science, arising from the employment
of methods of investigation and reasoning which have been
justified by their fruits and their resistance to the corrosion of
criticism, cannot be reduced to any single theme. We cannot say
why men are creative artists, or writers, or scientists; why some
men can perceive a truth, or a technical trick, which has eluded
others. From the bewildering variety of experience in its social,
economic and psychological aspects it is possible to extract only
a few factors, here and there, which have had a bearing on the
development of science. At present, at least, we can only describe,
and begin to analyse, where we should like to understand. The
difficulty is the greater because the history of science is not, and
cannot be, a tight unity. The different branches of science are
themselves unlike in complexity, in techniques, and in their
philosophy. They are not all affected equally, or at the same time,
by the same historical factors, whether internal or external. It is
not even possible to trace the development of a single scientific
method, some formulation of principles and rules of operating
which might be imagined as applicable to every scientific inquiry,
for there is no such thing. Methods of research in each subject
are too closely bound up with the content and problems of that
subject for the devising of a mechanical method.

Nor can we always exploit any dichotomy between the ideas
and the practice of science, though this dichotomy may be a
useful tool at times. Interpretations without knowledge and
knowledge without interpretations are equally unbalanced and
sterile; any branch of science consists of both. Therefore, since
knowledge arises from practical operations, the history of science
can never be a purely intellectual history (like that of mathe-
matics), nor can it be analysed in a wholly logical manner. For
ideas arise from facts, and the facts of science may be revealed in
an order conditioned by chance, by technical resourcefulness, or
industrial invention. On the other hand, the creative intellect is
always playing upon the materials provided by techniques of

INTRODUCTION xv

experiment, observation or measurement; however subtle these
become, they can never be said to determine the course of a
science, unless in a negative sense.

The dichotomy in science, the fact that its progress requires
both conceptual imagination and manipulative ingenuity, is
particularly apparent in the scientific revolution, and presents
peculiar problems. The reaction against the traditional picture
of Nature derived from the Greeks occurred simultaneously on
the factual and the interpretative levels. The theories of the past were
criticized as being inconsistent, speculative, incomprehensible,
and as involving spiritual qualities rather than the properties of
matter; the facts related in the past were challenged as ill-tested,
spurious, superstitious, and as casually chosen without care in
observation and experiment. The development of each of these
phases of criticism may be traced in the later middle ages, when,
however, they were rarely associated. Even after 1500 many
exponents of a new attitude failed to perceive that doubts of fact
and theory were inter-related; that one could not proceed without
the other. Hence a great part of the force of the "new philosophy"
of the seventeenth century was due to its dual scepticism, its
ambition to challenge fact and theory, sometimes without
consciousness of making a double attack. This duality reinforced
attention to the question of the logical connection between facts
and theories, which had also been examined by medieval critics
of Aristotle. How were the relevant facts to be brought to light?
How, with the facts known, were appropriate propositions
concerning them to be arrived at? How could scientific proposi-
tions be tested by their usefulness in dealing with facts? The early
success of the scientific revolution owed much to the answering
of such questions (pragmatically, rather than philosophically) in
the scientific method combining observation, hypothesis, experi-
ment and mathematical analysis, a method which demonstrates
in itself the essential liaison between the factual and interpretative
levels of inquiry.

If the scientific revolution cannot be completely depicted,
even in its origins, as an intellectual revolt against the traditional
interpretation of Nature, nevertheless such a revolt demands
primacy of place in tracing its antecedents. Few men have, or had,
the sense of supremacy of pure fact demanded by Francis Bacon.
The majority of scientists at all times have sought for facts with

xvi INTRODUCTION

an object in view. Consequently, the scientific empiricists of the
seventeenth century, including Bacon himself, pointed to the
insufficiency of contemporary science before they clamoured for
more facts on which to frame a sounder doctrine. They did not
need these facts to teach them Aristotle's mistakes, for of those
they were already aware; they needed observations and experi-
ments to avoid falling into fresh errors of their own. Cartesians,
too, were as confident that conventional science was untrust-
worthy: because it ignored the method of reasoning from in-
dubitable truths, and was therefore philosophically unsubstantial.
And does not Galileo himself refute Aristotle with reason, before
overwhelming him by experiment? Medieval science, and
especially the Aristotelean doctrines within it, was not so much
swept away by a hurricane of uncomfortable facts, as brought
down by its own internal decay. While the mechanics of Greek
science, the four elements, the bodily humours, the Ptolemaic
system, still commanded allegiance (though becoming less and
less relevant to practical affairs) the Hellenistic view of the cosmos
was becoming increasingly alien to the European mind. From the
fourteenth to the sixteenth century men might teach and work in
science as though they were Greeks of antiquity, but they were not
so in fact, and the community of thought between Europe and
Hellas grew ever more formal. By 1600 it was almost academic.
A demonstration in Greek mathematics or a particular piece of
reasoning could fire admiration, but the universe could be seen
through Aristotle's eyes no more. Even his expositors had trans-
formed him.

In part this was brought about by the rival Christian authority.
No Christian could ultimately escape the implications of the fact
that Aristotle's cosmos knew no Jehovah. Christianity taught
him to see it as a divine artifact, rather than as a self-contained
organism. The universe was subject to God's laws; its regularities
and harmonies were divinely planned, its uniformity was a result
of providential design. The ultimate mystery resided in God rather
than in Nature, which could thus, by successive steps, be seen not
as a self-sufficient Whole, but as a divinely organized machine in
which was transacted the unique drama of the Fall and Redemp-
tion. If an omnipresent God was all spirit, it was the more easy
to think of the physical universe as all matter; the intelligences,
spirits and Forms of Aristotle were first debased, and then

INTRODUCTION xvii

abandoned as unnecessary in a universe which contained nothing
but God, human souls and matter.

Christianity furnished the scientist with God as the First Cause
of things. But if this First Cause had, so to speak, set the universe
to run its course and endowed man with free-will to make his
own destiny, the phenomena of nature could only be the result of
determined processes, manifestations of a mechanistic design, like
an infinitely complex automaton or clock. A clock is not explained
by saying that the hands have a natural desire to turn, or that the
bell has a natural appetite for striking the hours, but by tracing
its movements to the interconnections of its parts, and so to the
driving force, the weight. If God was the driving force in the
universe, were not its motions and other properties also to be
ascribed to the interconnections of its parts? The question, slowly
compelling attention over three hundred years, received a positive
answer in the seventeenth century. The only sort of explanation
science could give must be in terms of descriptions of processes,
mechanisms, interconnections of parts. Greek animism was dead.
Appetites, natural tendencies, sympathies, attractions, were mori-
bund concepts in science, too. The universe of classical physics,
in which the only realities were matter and motion, could begin to
take shape.

CHAPTER I
SCIENCE IN 1500

EUROPEAN civilization at the beginning of the sixteenth century
was isolated as it had not been since the first revival of learn-
ing some four hundred years earlier. Political changes had
severed traditional links between east and west. The heart of the
great area of Islamic culture, from which medieval scholarship
and science had drawn their inspiration, had been over-run by
the Turks; the eastern Christian centre of Byzantium, the last
direct heir of ancient Greece, was destroyed; the learned Moors
and Jews of Spain were expelled by the armies of Castille and
Aragon. The overland route to China, by which many important
inventions had been transmitted to Europe, among them the
new instruments of learning, paper and printing, and over which
Marco Polo had passed, was now barred. Against this loss of a
relatively free interchange of ideas and commodities through the
Mediterranean may be set a developing commercial and scientific
interest in the promise of geographical exploration across the
oceans. The Portuguese had brought spices from the Indies;
Spain had drawn her first golden tribute from Hispaniola. But
the results of the re-orientation of communications southwards
and westwards upon the Atlantic had not yet been assimilated,
and though Europeans were quick to recognize the value of
negroes or American Indians as slaves, they had not yet learnt to
appreciate the magnitude of the civilizations in India and China
with which, for the first time, they came into direct contact.

Fortunately, when these events occurred, European scholars
had already emerged from their tutelage, and Latin literature,
having been enriched with almost everything that Arabic was to
convey to it, had become creative in its own right. The final
dissolution of the Christian empire in the Near East, indeed,
brought to Europe a direct knowledge of classical science with
which it had been less perfectly acquainted through the Islamic
intermediary. At the moment when their intellectual communion
with other peoples was most sharply denied by circumstance, the

2 THE SCIENTIFIC REVOLUTION

humanistic scholars of the renaissance were most engrossed in
studying the pure origins of western civilization in Greece and
Rome. During the next centuries the trend of the middle ages was
to be reversed; Europeans were to teach the East far more than
they learned from it.

In 1500 the fruitful cultivation of science was limited to western
Europe, to a small region of the whole civilized world stretching
from Salamanca to Cracow, from Naples to Edinburgh. Even the
peripheries of this region were illuminated rather by the reflected
brilliance of the Italian renaissance, than by any great achieve-
ments of their own. The northern shift of the focus of learning was
beginning northern Italy had replaced the south and Sicily as the
cultural centre of Europe but the sixteenth is unquestionably the
Italian century in science. Scholars, mathematicians, physicians
everywhere measured their own attainments by Italian standards;
the Italian universities, and the Italian printing-houses, possessed
an acknowledged pre-eminence. Beneath inevitable gradations in
civilization (no less marked in science than in fine art) lay an
essential cultural unity, undisturbed by nationalism or religious
schism. Europe had a common tradition; in matters temporal it
was consciously the heir of Greece and Rome, shaping the texture
and manner of its own life to the model of their golden age; in
matters spiritual a single compass of belief had passed from the
great Councils of the Church through the early Fathers to the
Papacy and the medieval Doctors. If the secular Empire had
become a shadow, the spiritual power of the Church seemed still
firmly founded upon a single theology and a universal orthodoxy
which had triumphed over Albigenses, Wyclif and Hus. Upon
this unified Church all learning was in varying degrees depen-
dent; the universities, themselves papal creations, were religious
institutions. The study of medicine was the only discipline able to
stand, to some extent, detached from learning's prime duty to
theology, and even the teaching and practice of medicine were
subject to a measure of ecclesiastical control. Human dissection,
for instance, was strictly supervised by the Church. Learning had
in Latin its own universal language. The system and content of
education in every school and university were so similar that a
scholar could find himself at home anywhere. In each the student
laboured upon the same texts, graduated by debating similar
philosophical themes, and (if he progressed as a man of learning)

SCIENCE IN 1500 3

found the stimulus to original thinking in problems familiar to all
men of education.

It would be mistaken to suppose that, because the intellectual
life of all Europe at the beginning of the sixteenth century was as
homogeneous as that of the modern nation state, it was character-
ized by a dull uniformity. There were, and there had long been,
distinct and to some extent rival schools, just as there was also a
special development of some type of study at a particular place,
theology at Paris, law and medicine at Bologna and Padua. In
one place men still clung to the pure Aristotelean tradition, at
another they had begun to criticize it; here the Arabic physicians
were more highly regarded than the newer Greek texts, there they
were despised as poisoning the Galenic well of knowledge. Within
the acceptance of a common body of premisses there was vast
uncertainty concerning the way in which the premisses should
be applied. No one doubted that blood-letting was an essential
part of therapy: but there was great dispute over the actual tech-
nique. No one doubted that the world was round: but different
navigators could not agree on the best way to plot a course. No
one doubted that the calendar was out of joint: but the best
astronomers could not join in declaring the remedy. It is indeed
a misleading view of the early stages of the scientific revolution
to see them as involving only the conflict of two types of premiss,
as typically in the antithesis between the Ptolemaic and the
Copernican world-systems. In fact much more was involved, the
practical and successful handling of detailed problems. This is
perhaps most clearly seen in the non-physical sciences, in anatomy
or natural history in the sixteenth century, but it can also be seen
in the practical arts which depended upon the physical sciences.
Ultimately, of course, such an art (or science) as navigation
advanced very considerably through the substitution of the
Gopernican for the Ptolemaic astronomy; but in the sixteenth
century greater accuracy in cartography and oceanic navigation
was independent of the high truths of cosmology.

The unity of learning which the sixteenth century inherited
from the middle ages is a strong mark of its diffusion. Scientific
knowledge in particular showed little differentiation in pattern,
though it varied greatly in quality and method, because it was
not the native product of Christian civilization in Europe,
but imposed upon it. The primitive Germanic tribes had long

4 THE SCIENTIFIC REVOLUTION

submitted to a Romano-Hellenistic culture: first through their
contact with the Roman Empire, then through their conversion
to Christianity and the various efforts towards a renaissance of
learning that had followed; partly assimilated and legitimized
(as in witchcraft or folk-medicine), their original attitude to
Nature had largely sunk to the level of superstition in comparison
with the "literary" science which won its supremacy in the
thirteenth century. As a first approximation, it may be said that
the cultural history of Europe, since the hegemony of the Roman
city-state, is mainly concerned with the diffusion of Hellenistic
influences, Greece itself being the heir to the ancient civilizations
of the Near East. Perhaps the nadir (by either political, economic
or intellectual standards) was reached about the sixth century;
by the ninth efforts were being made to assimilate the flotsam
surviving from the wreck of Roman Imperialism. Islam, em-
bracing many linguistic and ethnic elements, and having its
cultural focus in the eastern portion of the former Roman Empire
which had been less devastated by popular movements than the
West, possessed greater potentialities for immediate development.
The Arabic treatise on the astrolabe which Chaucer translated into
English c. 1390 had been written in the late eighth century; of the
Islamic medical authorities whom he mentions in the Prologue to
the Canterbury Tales, two had lived some four centuries before. In
the first phase of learning among Franks, Saxons and Lombards,
science had been meagrely represented by a few Latin texts
fragments of Plato (the Timteus), of Macrobius, and Pliny and
the degeneration of form and thought from these originals was
rapid. In the second phase, beginning early in the twelfth century,
diffusion was concentrated into a very few channels, for the new
philosophical and scientific literature in Latin was created by its
very few scholars who were able to translate from Arabic, Hebrew,
or more rarely directly from the Greek. The most famous of them,
Gerard of Cremona (c. 1114-87) is credited with making at least
seventy translations, some of them like Avicenna's Canon, or
encyclopaedia, of medicine, of vast extent. Though the lists
certainly exaggerate the personal influence of one individual
upon the Latin corpus, it cannot be doubted that the somewhat
arbitrary selection exercised by a small group of linguists had a
determining effect upon the nature of the material available to the
purely Latin scholars of later generations. And it must be further

SCIENCE IN 1500 5

remembered that the Islamic and Hebrew scientific writings,
upon which the Latin translators worked, themselves represented
a fraction accidentally or consciously chosen from the whole
original literature.

The intellectual life of medieval Europe was rapidly transformed
by this acquisition of a sophisticated method and doctrine in both
philosophy and science. Its influence can be traced in such varied
directions as the use of siege-engines in war, or the theory of
government, as well as in astronomy and physics. At first there
was opposition to the new type of study: the sources, being infidel,
were suspect, and they seemed to encourage a too presumptuous
inquiry into matters beyond human comprehension. But the
simplest Christian attitude, that men should not meditate upon
this world but the next, and that religion, rather than the works
of pagan philosophers, should instil the principles of morality
and ethics, had lost its force. The condemnation of the teaching
of Aristotle's natural philosophy by a provincial council held at
Paris in 1210 proved ephemeral, as did later attempts to limit the
influence of Arabist sources. 1 Even before scholasticism developed
the study of Hellenistic philosophy upon Christian principles the
European mind was awake to the value of the riches laid before
it when refined from theological falsities. Robert Grosseteste
of Oxford in the first, and Thomas Aquinas in the second half
of the thirteenth century were the two foremost exponents of
Aristoteleanism, which as a method of reasoning and a fabric of
knowledge was thus reconciled with Catholic theology. Inevitably
the Hellenistic-Islamic renaissance of the twelfth century emerged
with an even greater homogeneity from this further process of
moulding. To the extent that Aristotle was seen through the eyes
of St. Thomas and his influence was profound for it was he who
made Aristotle the master of medieval thinking the unity of
medieval culture was reinforced by the single Thomist tradition.
Averroism, the extreme rationalist appraisal of Aristotle's thought,
became heresy. Despite Aquinas' deep study of every aspect of the
Aristotelean corpus, he utterly failed to understand the true spirit
and methods of natural science, 'and no scientific contribution

1 George Sarton: Introduction to the History of Science (Baltimore, 1927-48),
vol. II, p. 568. A reputation for profound acquaintance with Arabic writings
was, however, long associated in the popular mind with skill in magical arts,
so that a mass of legend was built up round such a figure as Michael Scot.

6 THE SCIENTIFIC REVOLUTION

can be credited to him.' 1 Against this dogmatic tradition, the
exponents of experiment (Grosseteste, Roger Bacon) and the
mechanistic school of critics (Jordanus Nemorarius, Jean Buridan,
Nicole Oresme) of the same and later times were generally
unavailing, though they are interesting and important as the
precursors of the scientific revolution.

The time of maturation was really astonishingly short. It is a
common delusion that medieval intellectual life was stagnant over
the many centuries that separate the fall of Rome from the rise
of Florence. On a more just assessment the beginnings of intelligent
civilization in Europe may be placed no more than four hundred
years before the Italian renaissance: a longer interval separates
Einstein from Copernicus, than that which intervenes between
Copernicus and the earliest introduction of rational astronomy to
medieval Europe. Within a century of the first translations Latin
contributions to creative thinking were at least equal to those
made in any other region of the globe: by the mid-fourteenth
century the period of assimilation was over, the emphasis lay on
original development and criticism, and the initiative which it has
since retained had passed to the West. The renaissance of the
twelfth and thirteenth centuries was imitative and synthetic; that
of the fourteenth was exploratory, critical, inquisitive. Authorship
began to pass from commentary to original composition, although
still often in the commentatory form. There are signs of true
science: the development of mathematics, now aided by the
" Arabic" numerals which were of Indian provenance; anatomical
research pursued in actual dissection; the development of a new
mechanics employing non-Aristotelean principles and the rudi-
ments of a geometrical analysis. At the same time and there may
be a correlation here which becomes more explicit and conscious
in the seventeenth century there was considerable technological
progress. The magnetic compass was first described in Europe by
Peter the Stranger in 1269; gunpowder was applied to the propul-
sion of projectiles about 1320; the third of the great medieval
inventions, printing, began its pre-history about 1400. But these
are only the most striking examples of a long series: the introduc-
tion, or wider exploitation of new materials like rag-paper, of
processes like distillation, of new machines like the windmill or

1 George Sarton: Introduction to the History of Science (Baltimore, 1927-48),
vol. II, p. 914.

SCIENCE IN 1500 7

the mechanical clock, of new mechanical devices like the stern-
rudder for ships, or the use of water-power for industrial purposes.
Although philosophers and theologians still regarded slavery as a
justifiable social institution, the Latin 1 was the first civilization to
evolve without dependence upon servile labour. From the eleventh
century onwards the rigours of villeinage were mitigated and
servitude disappeared. The phenomenon of the new social fabric
was, that while the general wealth increased, the inequalities in
its distribution tended to become more moderate. In fact the
fourteenth century shows the beginnings of a characteristic of
modern European civilization, the utilization of natural resources
through means progressively more complex, efficient and
economical in the expenditure of human labour. These are the
first signs of an attitude to Nature, and to technological pro-
ficiency, which was to become overtly conscious in the writings
of Francis Bacon but was not to attain its fulfilment before the
nineteenth century. A manuscript of 1335, written by Guido da
Vigevano, a court physician who was no insignificant investi-
gator of human anatomy, already develops the application of
mechanical skills to the arts of war (in this instance a projected
crusade to recover the Holy Land) in a manner typical of the
"practical science" of the Italian renaissance and later ages.
Again, it must be observed that few of the inventions mentioned
above originated in the Latin West. The common principles of
machine-construction were familiar to the later Hellenistic
mechanicians: other discoveries, like the compass and gunpowder,
were transmitted to Europe from the Far East through Islam.
But it was Latin society which was transformed by them, not that
of Eastern peoples: and it was the Latins who, as in the realm of
ideas, alone fully realized and extended their possibilities. In the
end it was the West that rediscovered the East, arriving in the
ports and coasts of India and China with an admitted technical
and scientific superiority.

This is the background to what was once regarded without
qualification as " The Renaissance." The humanists of the six-
teenth century, who created the legend of Gothic barbarity,

1 Since, during the middle ages, not all Europeans were members of the
Roman Catholic, Latin-writing civilization, it seems convenient to adopt the
noun "Latins" and the adjective "Latin" in a general sense as descriptive of
those Europeans who were members of this civilization.

8 THE SCIENTIFIC REVOLUTION

participated in a new phase of the diffusion of Hellenistic culture.
For them the past was not merely a store of knowledge to nourish
the mind, but a model to be directly imitated. Upon them, from
its newly discovered texts, and from its extant relics in Italy and
France, the pure light of the Hellenistic world seemed to shine
directly, and they disdained the reflected splendour of Islam.
Medieval scholarship seemed limited, obtuse, pedantic. It had
embroidered and perverted what it had not truly understood.
Through the perspective of the unhappy and generally, perhaps,
retrogressive fifteenth century, the whole medieval period was
seen in a jaundiced aspect. The decay of medieval society, and of
medieval intellectual traditions, produced a revulsion in the
minds of the first exponents of an art, literature and science which
were at once more authentically classical, and more modern.

The fathers of the Italian renaissance were Petrarch (1304-74)
and Boccaccio (1313-75); they, with other originators of a new
literary and artistic movement, were contemporary with the height
of medieval science. To its exacting discipline and subtle ratio-
cination the new emphasis on taste, elegance and wit was by no
means wholly friendly. In one important aspect the renaissance
was an academic revolt against the tyranny of expositors and
commentators, but the scholars who turned with renewed
enthusiasm to original texts came close to surrendering something
of value, namely the critical analysis and extension of Hellenistic
science due to generations of Islamic and Latin students of
philosophy and medicine. These gains, which the superior texts
of the scholar-scientists of the early sixteenth century would
hardly have recompensed, would have been sacrificed if the
renaissance had abandoned the middle ages as completely as the
academic revolutionaries wished; but such was not the case, and
to a large extent the fourteenth century was assimilated by the
sixteenth.

As this suggests, there are important reservations to be made
concerning renaissance humanism as a force making for innova-
tion in science. For example, it can have had little impact upon
the early printers who published large numbers of medieval books,
nor upon the readers who presumably desired them. And in their
revision of classical authors for the press the scholar-scientists were
if anything less prone to comment adversely upon them than their
medieval predecessors. Among the humanists intense admiration

SCIENCE IN 1500 9

for the work of antiquity led to the belief that human talent and
achievement had consistently deteriorated after the golden age of
Hellenistic civilization; that the upward ascent demanded imita-
tion of this remote past, rather than an adventure along strange
paths. Thus the boundary between scholarship and archaism was
indefinite, and too easily traversecLxSome branches of science
were indeed directed to new ambitions, others were raised rapidly
to a new level of knowledge, but it cannot be said that all benefited
from a single influence favouring realism, or originality of thought,
or greater scepticism of authority. On the contrary, humanism
sometimes made it more difficult to enunciate a new idea, or to
criticize the splendid inheritance from antiquity. Against the free
range of Leonardo's intellect, or the penetrating accuracy of
Vesalius' eye, must be set the conviction that Galen could not
err, or the view of Machiavelli that the art of war would be
technically advanced by a return to the tactics and, weapons of
the Roman legion.

Obviously such rigid adherence to the fruits of humanistic
scholarship did not yield the renaissance of scientific activity
beginning in the late fifteenth century. Rather it sprang from the
fertile conjunction of elements in medieval science with others
derived from rediscovered antiquity. Softin mathematics the
revelation of Greek achievements in geometry provoked emula-
tion, yet the algebraic branch of Islamic origin (for which
humanism did nothing) made equally rapid progress. Ultimately
the union of the two effected a profound revolution. Moreover, to
take a more general point emphasized by Collingwood, 1 the
renaissance attitude to natural events was so different from that
of the ancients that the classical revival inevitably led to some
anomalous results. Thus one may account for the vast interest in
Lucretius' poetic statement of Greek atomism, De natura rerum,
rediscovered in 1417, and the eminence granted to Archimedes
as the archetype of the physical scientist. Already in the fourteenth
century there were clear signs of an approach to a mechanistic
philosophy of nature, and the use of mathematical formulations,
in the physical sciences where such a novel attitude could do much
to liberate the scientist from discussions of the metaphysics of
causation and to lead him to concentrate attention upon the
actual processes of natural phenomena)in this respect the broader
1 The Idea of Mature (Oxford, 1945).

io THE SCIENTIFIC REVOLUTION

interests of humanistic scholarship reinforced a tendency which
they could not have initiated, a reaction against Aristotle. Although
the revival of Greek atomism had an important influence, the
"mechanical philosophy" of the seventeenth century represented
much more than just this.

A more complete access to the works of Euclid, Archimedes
and Hero of Alexandria (among many others) gave a fertilizing
inspiration to physics and mathematics, but it was on the biological
sciences that the superior information of the ancients, resulting
from a more serious attention to observation, had its greatest
effect. Encyclopaedic study by medical men of the complete works
of Hippocrates and Galen, by naturalists of those of Aristotle,
Dioscorides and Theophrastus, played a large part in the scientific
endeavour of the sixteenth century, only slowly overshadowed by
original investigation. Even at the close of the century studies in
the structure, reproduction and classification of plants and
animals had barely surpassed the level attained by Aristotle.
Later still William Harvey could regard him as a principal
authority on embryological problems. Undoubtedly a return to
purer and more numerous sources of Greek science was a refresh-
ment and stimulus; despite the imperfections in the renaissance
scholar's appreciation of the immediate and the remote past, he
rightly felt that such sources laid before him new speculations,
facts and methods of procedure, suggested many long-forgotten
types of inquiry, and disclosed a wider horizon than that known
to the medieval philosopher. To a growing catholicity of interest
printing added the diffusion of knowledge. The tyranny of major
authorities inherent in small libraries was broken for the scholar
who could indulge in an ease of compilation and cross-reference
formerly unthinkable. But it is not to be supposed that the method
of science, or the realization of the problems it was first to solve
successfully, were simply fruits of the renaissance intellect. Nascent
modern science was more than ancient science revived. Through
the revived Hellenistic influence in the sixteenth century, always
diverting and sometimes dominating the development of scientific
activity, the strong current of tradition from the middle ages is
always to be discerned.

In 1500, when Leonardo da Vinci was somewhat past his prime,
the scientific renaissance had hardly begun. Scientific humanism,

SCIENCE IN 1500 ii

the great critical editions, and the first synthetic achievements
under the new influences, were the work of the next generation.
It was once usual to see such men as Nicholas of Cusa, Peurbach,
and Regiomontanus in the fifteenth century as forerunners of a
scientific revival, but more recent estimates of their works serve
rather to emphasize the continuity of thought, than to indicate
an incipient break jvith the past. And though a vast volume of
medieval manuscript was left undisturbed and rapidly forgotten,
the larger proportion of the scientific books printed before 1500
contained material which was familiar two centuries earlier .(The
general stock of knowledge had hardly changed, as can be seen
from such a compilation as the Margarita Philosophica of Gregorius
Reisch (d. 1525), published in I5O3. 1 This was an attempt at an
encyclopaedic survey, perhaps rather conservative, certainly
immensely simplifying the best knowledge of the age, but useful
as a conspectus of scientific knowledge at the opening of the
sixteenth century. The pearls of philosophy are divided under nine
heads which treat of Grammar, Logic, Rhetoric, Arithmetic,
Music (theoretical, i.e. acoustics, and practical), Geometry (pure
and applied), Astronomy and Astrology, Natural Philosophy
(mechanics, physics, chemistry, biology, medicine, etc.), and
Moral Philosophy. There is also (in the later editions) a Mathe-
matical Appendix which deals with applied geometry and the
use of such instruments as the astrolabe and torquetum on which
medieval astronomy was founded. Reisch's design thus corre-
sponds closely to that of the typical arts course in the universities
of the period, which proceeded from the trivium (grammar,
rhetoric and logic) to the quadrivium (arithmetic, geometry,
astronomy and music).

Astronomy was the most systematic of the sciences. The
phenomena of the heavens had long been subjected to mathe-
matical operations, though opinions differed on the most suitable
manner of applying them, and prediction of the future positions
of sun, moon and planets, the groundwork of astrology, was
possible to a limited degree of accuracy. Mathematical astronomy
had been advanced to an elaborate level by the Greeks, and still
further perfected by the mathematicians of Islam, who had also
been patient and accurate observers^ Far cosmology in the modern

^

1 At least nine editions were printed before 1550; others appeared as late as
1583 (Basel) and 1599-1600 (Venice).

12 THE SCIENTIFIC REVOLUTION

sense there was almost no necessity: the universe had been created
at a determined date in the past in the manner described in Holy
Writ, and would cease at an undetermined but prophesied date
in the future. It could be proved, both by reason and by divine
authority, to be finite and immutable, save for the one speck at
the centre which was earth, unique, inconstant, alone capable of
the recurring cycle of growth and decay. As Man was the climax
of creation, so also the earth (though the most insignificant part
of the whole in size) was the climax of the universe, the hub about
which all turned, and the reason for its existence. It was natural
for men who were unhesitant teleologists to believe that the
pattern of events was designed to suit their needs, to apportion
light and darkness, to mark the seasons, to give warning of God's
displeasure with his frail creation. In varying degrees of sophisti-
cation such an attitude is universal and primitive, and there may
be added to it that stage of astronomy, arising immensely later
in the history of civilization, when the alternations of the skies
are seen to be cyclic, and therefore calculable. But in the tradition
of astronomy which prevailed in 1 500 there was a third element,
of purely Greek origin, which provided a physical doctrine
describing the nature of the mechanism bringing about the
appearances. The simple form of this mechanism to which the
Greeks were led by their reflection on the Babylonian knowledge
of the celestial motions was described by Aristotle; the complex
form, capable of accounting for more involved planetary motions,
was due to Ptolemy. The former was a physical rather than a
mathematical doctrine, the latter was mathematical rather than
physical, corresponding to what would now be described as a
scientific model of actuality.

In a debased form, and strongly influenced by Platonic
hylozoism, the simpler Greek theory had never been entirely lost
to the middle ages. The translators brought Ptolemy's Almagest
and many Arabic astronomical texts to Latin science. An abstract
of spherical astronomy, which did not treat of the planetary
motions in detail, the Sphere of John of Holywood, became a
common text in the later middle ages and was printed thirty
times before 1500. The Margarita Philosophica describes the
"mechanism of the world" as consisting of eleven concentric
spheres; progressing outwards from the sublunary region with the
earth as the centre, they are those of the moon, Mercury, Venus,

SCIENCE IN 1500 13

the sun, Mars, Jupiter, Saturn, the Firmament (Fixed Stars),
the Crystalline Heaven, the Primum Mobile, and the Empyraean
Heaven, "the abode of God and all the Elect." The spheres were
conceived as of equal thickness, and fitting together without
vacuities, so that for example the sphere of Saturn was im-
mediately adjacent to that of the fixed stars. Philosophers were
less clear on the physical matter of the spheres (Aristotle's perfect
quintessence as contrasted with the four mutable elements of the
sublunary world) apart from the fact that they were rigid and
transparent; having no dynamical theory they were not puzzled
by problems of friction, mass and inertia. The tenth sphere, the
Primum Mobile, which imparted motion to the whole system,
revolved from east to west in exactly twenty-four hours. The
eighth, bearing the fixed stars, had a slightly smaller velocity,
sufficient to account for the observed precession of the equinoxes.
Between these the crystalline heaven was added to account for a
supposed variation in the rate of this precession. Then, descending
towards the centre, as the spheres became slightly less perfect,
more sluggish and inert, each completed its revolution in a
slightly longer period, so that the sun required 24 hours 4 minutes
between two successive crossings of the meridian, and the moon
24 hours 50 minutes, approximately. This increasing retardation
resulted (as we now know) from a combination of the orbital
velocity of the earth and the orbital velocity of the planet; the
whole heavens revolved round the earth once in 24 hours, but the
sun, moon and planets appeared to move also in the opposite
direction at much smaller, and varying, velocities.

With these motions established, simple spherical astronomy was
taught just as it is today. But this simple theory did not allow of
prediction, it did not take into account the motion of the moon's
nodes, causing the cycle of eclipses, nor the variations in brightness
(i.e. distance) and velocity of the heavenly bodies. It is possible
to derive predictions from purely mathematical procedures, as
the Babylonians did, without making any hypothesis concerning
the mechanism involved. Till modern times the astronomer had
nothing to work with other than angles, angular velocities, and
apparent variations in diameter and brightness. He was unable to
plot the orbit of a planet in space: the best he could do was to
fabricate a system which would bring it to the proper point in the
zodiac at the right time. The Greeks, however, could not renounce

THE SCIENTIFIC REVOLUTION

the system of homocentric spheres altogether, and their geo-
metrical methods based on the circle (in which, it was assumed,
motion was most perfect since it was perpetual and uniform)
facilitated the construction of an analogous, but more complex,
mechanical model. 1 As an example, the system of spheres whose
combined motions are responsible for the observed phenomena of
the planet Saturn is thus described by Reisch. It fills the depth,
represented by the seventh sphere in the simple theory, between
the interior surface of the sphere of fixed stars, and the exterior sur-
face of the sphere of Jupiter, both of which are exactly concentric

with the earth. Taking a
section through the Saturn-
ian spheres in the plane
of the elliptic, A (Fig. i) is
the outer surface of the
largest sphere, concentric
with the earth, B is its interior
surface which is eccentric.
C is a wholly eccentric
sphere, the deferent, carrying
the epicycle F embedded in
it. D is the outer surface of
the third and innermost
sphere, which is eccentric,
and E is its inner surface
which is concentric with the

FIG. i . The Spheres of Saturn.

earth. Within E follow the remaining planetary systems of spheres
in their proper order. The epicycle F, which actually carries the
planet Saturn, rolls between the concentric surfaces B and D.

This is the mechanical model, which requires four spheres,
instead of one, to account for the motions of Saturn. The principles
of Aristotelean physics were observed, since the spheres by com-
pletely filling the volume between A and E admit no vacuum. To
represent the phenomena accurately the astronomer had to assign
due sizes, and periods of revolution, to the various spheres, which
were imagined to be perfectly transparent so that their solidity

1 Both the theories could be represented by actual models. Spherical astro-
nomy and the doctrine of multiple homocentric spheres was illustrated by the
Armillary Sphere , of which the Astrolabe is a plane stereographic projection, the
Ptolemaic theory of planetary motions by the Equatory or computer, which
seems to be a rather late development in both Islamic and Latin astronomy.

SCIENCE IN 1500 15

offered no obstruction to the passage of light to the earth. The
whole system of Saturn (and of every other planet) participated in
the daily revolution from east to west; in addition the spheres AB
and DE revolved in the opposite direction with a velocity of i 14'
in a century this corresponds to the slow rotation of the peri-
helion of Saturn's orbit in modern astronomy. The deferent C
carried round the epicycle in a period of about thirty years, but
its motion was not uniform with respect to its own centre P, or to
that of the earth O, but to a
third point Q so placed that
OP = PQ, called the equant.
By this means the unequal
motion of the planet in its path
was made to correspond more
closely with observation.
Finally, the epicycle itself re-
volved in a period of one year.
The great virtue of the epicycle
which was used by Hippar-
chus before Ptolemy was that
it enabled periodic fluctuations
in the planets' courses through
the sky, the so-called ' ' stations ' '
and "retrogressions" to be
represented (Fig. 2).

The epicycle was essentially
a geometrical device for "saving
the phenomena," and attempts
to make a physical reality of it
were late and unsatisfactory.
Epicyclic mechanisms similar
to that of Saturn were required for all the other members of the
solar system, except the sun itself. Those of Jupiter and Mars were
identical with that of Saturn, with appropriate changes in the
values assigned, while the mechanisms for the inferior planets,
Venus and Mercury, and for the moon, were more complex and
involved a larger number of spheres. 1 In all, the machina mundi

1 There is an obvious and necessary relationship between the sizes and speeds
of rotation assigned by Ptolemy to his circles, and those later adopted in the
Copernican system, but this relationship is not consistent. With Venus and

5-21

FIG. 2. The Geometry of the Epicycle
(Jupiter). E, Earth; J, Jupiter.
The dotted line shows the approxi-
mate path of the planet, whose
"stations" occur about B and D,
and whose "retrogressive" motion
is from D to B.

i6

THE SCIENTIFIC REVOLUTION

described in the Margarita Philosophica required 34 spheres, but at
various times much larger numbers had been used in the attempt
to represent the phenomena more accurately. Once the constants
of each portion of the mechanism had been determined in accord-
ance with observation, it was possible to draw up tables from
which the positions of the heavenly bodies against the background
of fixed stars in the zodiac could be calculated for any necessary
length of time. Unfortunately it was well known by 1500 it was
a scandal to learning that calculations were not verified by
observation. Eclipses and conjunctions, matters of great astro-
logical significance, did not occur at the predicted moments. The
most notorious of astronomical errors was that of the calendar:
the equinoxes no longer occurred on the traditional days, and the
failure to celebrate religious festivals on the dates of the events
commemorated caused great concern. In fact the Julian calendar
assumed a length for the year (365^ days) which was about eleven
minutes too long: the necessary correction was adopted in Roman
Catholic states in 1582. But at the beginning of the century the
causes of these errors in prediction were by no means clear. The
current astronomical tables had been computed at the order of
King Alfonso the Wise of Castille at the end of the thirteenth
century and were out of date. Were the faults of the tables due to
the method by which they were prepared based on the Ptole-
maic system or were they due to the use of faulty observations in
the first place, the method being sound? The fact that Copernicus

Mercury Ptolemy's deferent represents the orbit of the earth in the Copernican
system, and the epicycle that of the planet. With the remaining planets
Ptolemy's deferent represents the orbit of the planet, and the epicycle that of
the earth.

The values of the Ptolemaic constants, and those of their modern equivalents,
may be compared thus:

Ratio of Radii Mean Distances
Epicycle I Deferent (in ast. units)

Mercury 0-375 : J
Venus 0-719 : i

Earth

Deferent I Epicycle

Mars 1*519
Jupiter 5*218
Saturn 9*230

0-387
0-723

i -ooo

1-524
5-203

9-539

Angular Velocities

(deg. per day)

of Epicycle

i -60214
0-98563 [sun]

of Deferent
o 52406
0*08312
0-03349

Sidereal
Mean Daily

Motion
4-09234
i -60213

0*98561

o 52403"
o 08309

0*03346

SCIENCE IN 1500 17

chose the first alternative, that he accepted Ptolemy's observations
and rejected his mechanical system, was to be of great historical
significance.

It is important to realize and the problems became clearer
when the first Copernican tables came into use that the diffi-
culties were not merely conceptual. Suppose that the position of
Mars is to be predicted within an accuracy of one hour: then the
position given, and hence the original observations, must be accu-
rate to less than two minutes of arc, an accuracy quite beyond
astronomical instruments before the invention of the telescope. A
large astrolable, of one foot radius, for example, could not usefully
be divided to less than 5' intervals. For these reasons, certain
oriental observatories had erected huge gnomon-like instruments
in masonry to observe the motions of the sun with greater pre-
cision, and there was a somewhat similar trend towards increase
in scale in Europe during the fifteenth century. With these it was
found, however, that as scale increased new errors crept in, and
the estimated accuracy was not reached. Secondly, mathematical
procedures were highly involved. In the simplest case it was neces-
sary to establish (from the tables) the position of perigee in the
orbit, and then the place of the centre of the epicycle with respect
to this. Then the rotation of the epicycle itself had to be taken into
account, and referred to the equant. Finally the position as seen
from the equant point had to be recalculated as a position seen
from the earth. Real skill was required to compute a planetary
position with any accuracy from the tables, and very few even
in the sixteenth century could confidently undertake the task of
computing the tables themselves.

The earth, considering the relative potentialities of human
knowledge, was much less known than the skies, where the fixed
stars had already been plotted more accurately than any European
coastline. It was essential in the prevailing fabric of knowledge
that the mutable globe and the unchanging heaven be entirely
distinct. It was unthinkable that the same concepts of matter and
motion should be transferred from the sublunary to the celestial
region, and therefore all transient phenomena comets, shooting
stars and new stars were regarded as mere disturbances in the
upper region between the earth and the moon's sphere. This was,
indeed, the region of the element Jire; below it the element air
formed a relative shallow layer above the surface of the globe. The

i8 THE SCIENTIFIC REVOLUTION

earth was composed predominantly of the remaining two ele-
ments, water and earth, but with air and fire as it were trapped in it,
so that when an opportunity for their release occurred they natur-
ally ascended upwards to their proper regions. Conversely, heavy
substances made largely of earth and water sought to descend as
far as possible towards the centre of the cosmos, where alone they
belonged, the water lying upon the earth. It was believed before
the age of geographical discovery that only a sort of imbalance
in the globe enabled a land-mass fit for human habitation to
emerge in the northern hemisphere.

The categories of motion played an extremely important part
in pre-Newtonian science: even Galileo did not succeed in liber-
ating himself from them completely. Perfect circular motion was
an unquestioned cosmological principle, which gave consistency to
the whole theory of astronomy. In the sublunary region natural
motion was invariably rectilinear: away from the earth's centre
in the case of the light elements, and towards it in the case of the
heavy. Since the centre of the earth was a fixed point of reference
the definition of these species of motion occasioned no philo-
sophical difficulties. The earth and its elements were unique, and
as a concept like " heaviness," having no relation to anything but
the sublunary region (to apply it elsewhere would be meaningless)
could only refer to a body's tendency to move away from or
towards the centre of the earth, so also definitions like "up" and
"down" could be quite unambiguous. Violent motion on the
other hand, that is raising that which is naturally heavy, or
lowering that which is naturally light, was unprivileged and could
occur in any direction. Force was required to effect these violent
movements, because they were opposed to the natural order of
the universe, just as force was required to withdraw a piston from
a closed cylinder because nature abhors a vacuum. As soon as
the effective or retaining force ceased, natural motions would
restore the status quo ante. This plausible, though limited, doctrine
was of great importance as the foundation of mechanics. Man was
the agent of the great number of violent motions, and one reason
why mechanics played a minor role in the tradition of science until
the sixteenth century was perhaps just this fact that so much
mechanical ingenuity was directed towards reversing the natural
order it did not contribute to the understanding of nature, but
violated it.

SCIENCE IN 1500 19

A corollary drawn from the classification of motion again
distinguished celestial from terrestrial science. Motion was the
ordinary state in the former, rest natural in the latter. Wherever
the notion of inertia has been perceived, however dimly, it has
been seen most clearly exemplified in the motions of the
heavenly bodies. While natural motion in the sublunary region
exists for Aristotle as a possibility, it is clearly exceptional, except
in connection with the displacements effected by living agents.
In terrestrial mechanics, therefore, attention was most obviously
drawn to the compulsive or violent motions brought about by the
action of a force, and the natural motions which follow afterwards
in reaction, e.g. the fall of a projectile. It was not difficult, once
the question of mechanics was approached in this way, to conceive
of force as producing motion from the state of rest, and as the
invariable concomitant of violent motion. Within itself inert
matter could have no potentiality for any other than its proper
natural movement: and though Aristotle never explicitly formu-
lates the proposition that the application of a constant force gives a
body a constant velocity, it is implied in the whole of pre-Galilean
mechanics. The natural order could not be defied save at the cost
of expending some effort, any more than a weight could be
suspended without straining the rope by which it is hung. As
against this simple principle there was a whole category of
phenomena of motion that had to be treated as a special case, of
which the motion of projectiles was the leading instance.

Observation could not overlook the fact that no form of motion
ceases instantaneously. Effort is required to stop a boat under
way, or a rapidly revolved grindstone. What was the source of re-
sidual force which could impel an arrow for some hundreds of feet
after it had left its mover, the bow-string? The main Aristotelean
tradition pronounced that the force resided in the medium, air
or water, in which the motion took place, the medium being
as it were charged with a capability to move, though it did not
move itself. The medium, indeed, plays a most important part in
the Aristotelean theory of motion, for it is its resistance to move-
ment which is overcome by the application of a constant force,
limiting the velocity which can be attained. If a vacuum in nature
were possible (and this Aristotle denied), a moving body could
attain an infinite velocity since there would be nothing to limit it.
In this special case, then, the medium has a dual function: its

20 THE SCIENTIFIC REVOLUTION

resistance brings the moving body to rest, but its charge of motion
protracts the movement after the effect of the force has ceased.
This apparently contradictory dualism was severely criticized by
philosophers who otherwise worked within the general framework
of Aristotelean science, and an alternative theory of motion was
put into a definitive, and to some extent mathematical, form in the
fourteenth century, principally by two masters of the University
of Paris, Jean Buridan and Nicole Oresme. The principle they
adopted, but did not invent, was that though rest is the normal
state of matter, movement is a possible but unstable state. They
illustrated this conception by analogy with heat: bodies are usually
of the same temperature as their neighbourhood, but if they are
heated above that temperature, the unstable state is only gradually
corrected. A moving body acquired impetus, as a heated body
acquired heat, and neither wasted away immediately. The
impetus acquired was the cause of the residual motion; and only
when the store was exhausted did the body come to rest. 1

Although the idea of motion as a quality of matter was retro-
gressive, and the analogy with heat false, the development of the
mechanical theory of impetus is of outstanding importance in the
history of science. Impetus mechanics was not widely diffused, and
the line of investigators who continued discussion of its tenets
down to the sixteenth century was somewhat thin. It is not dis-
cussed in the Margarita Philosophica, but it was well known to
Leonardo da Vinci, Tartaglia, Cardano and other Italians of the
renaissance period. In its finished form it is absolutely a medieval
invention, which was never displaced by the Hellenistic revival.
The notion of impetus was not inspired by any new observations
or experiments, nor did it suggest any. The facts which it sought
to explain were exactly those already accounted for in the original
Aristotelean theory. But it was the work of truly creative minds.
Before the idea of impetus could be useful, it enforced a revalua-
tion of ideas on the nature of motion and, still more important,
of ideas on the natural order. Ideas of motion, even in Aristotelean
physics, and still more in that of Plato before him and some
medieval philosophers later, had been integrally woven into a

1 Part of the difficulty of the early mechanicians lay in the disentangling of
such concepts as motion, velocity, inertia, kinetic energy, just as much later
the physics of heat was obstructed until the concepts of temperature, heat,
entropy were defined.

SCIENCE IN 1500 21

fundamentally animistic philosophy of nature, to the extent that
in the extremest form motion and change were denied to matter
except in so far as it was pushed, pulled or altered by various ani-
mated agencies. The theory of impetus, attributing to inert matter
an intrinsic power to move, was a decisive step in the direction
of mechanism. In a sense it first conferred a true physical property
upon matter, qualifying it as more than mere stuff, the negation of
empty space. The impetus theory contained the first tentative
outlines of the explanation of all changes in nature in terms
solely of matter and motion which was to figure so prominently
in the scientific philosophy of the seventeenth century. Indeed,
both Buridan and Oresme foreshadow the greatest triumph of
seventeenth-century mechanism, Newton's theory of universal
gravitation. Since the heavenly spheres were perfectly smooth
and frictionless, moving upon each other without resistance and
without effort, they saw that when the whole system had been set
in motion it would revolve as long as God willed, without its
being required that each sphere should be animated by a guiding
intelligence. 1

Although medieval science was ignorant of dynamics in the
modern sense, discussions of motion and the displacement of
bodies form a very important element in its physical treatises.
The other branch of mechanics, statics, although it was of some
practical usefulness, remained in a very rudimentary condition
until the rediscovery of Archimedes' work in the sixteenth century.
His famous hydrostatical principle was known to the middle ages,
but even such an original and profound writer as Oresme failed
to apply it successfully as for instance in his explanation of the
fact that a given piece of wood may weigh more in air than
another of lead, and yet be lighter than the lead in water. 2 Even
the theory of the lever and the balance was imperfectly appre-
hended. In these subjects the classical inheritance was weak; the
authority followed was Aristotle; and the medieval writers had
failed to develop an experimental tradition of their own. In optics
they had a much surer foundation, in the original work of Ptolemy
and its extension by the Arab Ibn al-Haitham (Latine Alhazen,

1 A. D. Menut and A. J. Denomy: "Maistre Nicole Oresme, Le Livre du
Ciel et du Monde," Medieval Studies, vols. Ill, IV, V (1941-3), esp. IV, pp. 181
et seq.

2 Ibid., vol. V, pp. 213-14.

22

THE SCIENTIFIC REVOLUTION

c. 965-1039). Alhazen had actually conducted experiments, and
made measurements, and in the West the experimental and geo-
metrical study of optics was continued by such men as Robert
Grosseteste and Roger Bacon in the thirteenth century. Shortly
after the latter's death a great advance was made in practical
optics with the invention of spectacles. The magnification of
objects by lenses, unrecorded in antiquity, was known to Alhazen;
their ophthalmic use brought the glass-grinder's craft into being.
As a result the Margarita Philosophic^ for example, offers a more

C.H.=Crystfl/f/ne Humour

FIG. 3. Section through the human eye, from the Margarita
Philosophica (translated). Nuca perforata = Iris,Secundina
Choroid, Crystalline Humour = Lens, Spider's Web
? Ciliary processes.

rational and complete account of the phenomena of light than of
any other part of physics though it is to be found under a dis-
cussion of the powers of the "sensitive soul" not in the section on
natural philosophy. Light is defined as a quality in the luminous
body having an intrinsic power of movement to the object, which
may be either the eye or an opaque body thus illuminated. Colours
are somewhat similarly described as potential qualities in the
surfaces of bodies which are made actual by the incidence of light.
Next the structure of the eye is described, with the aid of a good
diagram of a section through the organ, and the functions of the
seven tunics and four humours are explained (Fig. 3). The optic
nerve is said to conduct the " visual spirit" to the brain, and single

SCIENCE IN 1500 23

vision with two eyes is simply accounted for by the union of the
two optic nerves into a single channel. The shining of rotten fish
or fireflies is attributed to the element of fire in the composition
of their substance. 1 Reflection and refraction are quite intelli-
gently treated. The fact that the ray of light passing from a rare
medium to a dense (as from air to water) is refracted towards the
perpendicular is explained by the greater difficulty of penetration.
Examples of the effects of refraction, such as the apparent bending
of a stick in water, are elucidated by simple geometrical figures,
and the apparent enlargement or diminution of the object seen in
accordance with the size of the visual angle at the eye is described.
In another section of the book the appearance of the rainbow is
explained: where tiny drops of water in the clouds are most dense
the sunlight is reflected as of a purple colour, where they are less
dense the colour is weaker and the light appears green, the
blue is the weakest of all. Refraction is not referred to in this
connection. Acoustics also was comparatively well under-
stood, both theoretically and experimentally. Reisch described
the physiology of the ear, the nature of sound as a vibration, and
the transmission of perception to the brain through the nerves
by means of an ' 'auditory spirit." Music of course had its own
peculiar theory and practice, which are carefully outlined in the
Margarita.

Other aspects of the knowledge of material things, which refer
rather to their composition, structure and generation than to the
phenomena which arise from motion of some kind, were broadly
related to the theory of matter derived from Aristotle. That all
substance accessible to human experience is composed of the four
elements, fire, air, water and earth, in varying proportions, seems
to have been a notion to which the earliest philosophers were
favourably disposed: it was accepted among the Greeks in pre-
ference to the single-element theory of Thales, and very similar
ideas prevailed in China and India. It was not required that every
analysis should yield these elements in identical form, nor was
there any means by which such an exact identity could have been
determined; but it is clear that the three ponderable elements
correspond roughly to the three states of matter (solid, liquid,
gaseous), with heat added as a material element. This conception

1 Phosphorescence was studied with much interest in the later seventeenth
century, e.g. by Robert Boyle.

24 THE SCIENTIFIC REVOLUTION

of heat (and electricity) as material though imponderable fluids
elements in fact if not in name had not become an anachronism
even by the end of the eighteenth century. A great deal of learning
was devoted to the question of how mixed bodies are compounded
from the elements, and how bodies generate by a synthesis of
elements, or corrupt by their dissolution. An important philo-
sophic problem was the relationship between the composition of
a substance and its qualities, or properties. Plato's doctrine of
"essential forms," or ideal models, exercised its pernicious
influence indirectly throughout the middle ages. Aristotle and
his followers believed that the elements themselves could be
transmuted from one to another, so that water could be condensed
into earth, or rarefied into air. Again, in a more strictly chemical
form, this conception lingered to the eighteenth century. The four
elements were of undefined figure, and matter was thought of as
being continuous. Ancient atomistic speculation was known to
the middle ages through Aristotle's criticism of it, but that
criticism was regarded as wholly convincing. The conjunction of
elements in a compound body took place without any conceivable
hiatus or division; as Oresme says, they are not mingled like flour
and sand, for every fraction of the infinitely divisible compound
must contain all its elementary constituents.

Regarding this framework of ideas from the point of view of
the chemist or mineralogist, its most important feature was the
latitude it offered for an infinite variety of theorizing on the
nature of change in substances. The only certain definition of a
substance was that it must have form (i.e. fill some volume of
the universe) and substance (i.e. be material), and possess either
gravity or levity. Form and substance are therefore in one sense
(as Oresme remarks) the first elements of matter; the four
elements proper have a secondary role and are transmutable.
Form likewise is obviously mutable: only substance could remain
constant, since its destruction or creation would require a change
in the fixed finite volume of the universe. Consequently, what we
should now call physical or chemical changes could be accounted
for on any of three hypotheses: (i) variation in the proportion of
elements, (2) the generation of elements (fire being the noblest in
the series), (3) the degeneration of the elements. Ex nihilo nihilfit.
The first has in fact formed the main subject of chemistry, but
this limitation was only logically established by Lavoisier. In this

SCIENCE IN 1500 25

period the modern distinction between physical and chemical
changes would have had no meaning, since this differentiation of
properties was not yet established. The analogy, involved in the
use of such terms as "generation," between organic and inorganic
matter was consciously cultivated, being a natural product of the
animistic conception of nature. As the plant grows from earth and
water, so equally well could metals, gems and stones. 1 In the
seventeenth century it was still believed that veins of ore would
grow in a mine if it was left to rest for a time unworked. And by
various natural or artificial processes (the calcination of metals,
the combustion of organic materials) one or more of the con-
stituents could be recovered. A vital principle, though of a
humbler kind, was just as much present in the sand which grew
into a pebble, as in the seed that grew into an oak. Natural history
has only comparatively recently ceased to signify mineralogy as
well as biology, and the apprehension of the problems of formation
and change in the organic world as involving problems of a
different order from those encountered in the inorganic is a
comparatively late product of the scientific revolution. In so far
as it demands a differentiation between organic and inorganic
chemistry it was never appreciated by Robert Boyle. And it must
be remembered that while it was possible to cite as examples of
matter "salt" or "flesh" without any doubt that the two were
precisely comparable, philosophy imposed an even higher degree
of theoretical unity. For the elements figuring in chemical change
were the elements of the sublunary world in cosmological
theory. The structure of explanation had to be consistent
between the macrocosm and the microcosm; the properties
of "fire" or "air" as they were stated in the general picture
of the universe had to recur precisely when these elements
were considered as entering into the composition of organic
matter.

Closely allied to the theory of four elements was the doctrine of
the four primary qualities heat, cold, dryness and humidity. A
combination of a pair of these qualities was attributed to each ele-
ment, fire being dry and hot, air hot and moist, water moist and
cold, earth cold and dry, and from mixtures of these elementary
qualities the secondary material qualities, hardness, softness, coarse-
ness, fineness, etc., were in turn derived, though other qualities
1 But see below, p. 27.

26 THE SCIENTIFIC REVOLUTION

like colour, taste, smell, were regarded as intangible. 1 Thus the
transmutation of elements was accomplished by successive stages
through substitution of qualities: dried water becomes earth,
heated water becomes air, but to transform water to fire it must
be both heated and dried. It was reckoned that with each trans-
formation the volume was multiplied by ten, so that fire had
i/i,oooth part of the density of earth. Meteorological phenomena,
for instance, could be accounted for by the application of these
ideas in detail. The sun's heat turns water into air; the element
air, being light, rises; but high above earth (where it is cold) air is
transformed into water, and water being a heavy element falls
as rain. Similarly air in the caverns and cracks of hills is cooled till
it becomes water, which runs out as a spring. Comets are a hot,
fatty exhalation from the earth drawn into the upper air and there
ignited. The generation of "mixed substances" such as minerals
and metals in the interior of the earth under the action of celestial
heat from the primary elements and qualities was considered as a
more complex example of the same process. Stone is earth coagu-
lated by moisture. Sal-ammoniac, vitriol and nitre are listed in the
Margarita Philosophica as examples of salts formed from the coagu-
lation of vapours in different proportions; to mercury, sulphur,
orpiment, arsenic etc. a similar origin is attributed. The metals
were commonly supposed to result directly from a combination
and decoction of mercury and sulphur though, as the alchemists
insisted, not the impure, earthy mercury and sulphur extracted
from mines and used in various chemical processes. Reisch, while
he admits the theoretical possibility of transmuting metals, points
out the great difficulty of imitating the natural process of their
generation precisely, and seems doubtful of the pretensions of the
alchemists. Indeed, the ambition to tincture the base metals and
otherwise modify their properties so that they should become in-
distinguishable from gold is far older than the Greek theory of
matter which gave it a rationale, and the actual processes or recipes

1 The medieval theory of matter was derived mainly from Aristotle's
De Caelo (III, 3-8), De Generations et Corruptione (Bk. II), and Meteorologies
Cf. De Gen. et Corr. 9 II, 3: * hence it is evident that the "couplings'* of the
elementary bodies will be four: hot with dry and moist with hot, and again
cold with dry and cold with moist. And these four couples have attached
themselves to the apparently "simple" bodies (Fire, Air, Water and Earth) in a
manner consonant with theory. For Fire is hot and dry, whereas Air is hot and
moist (Air being a sort of aquaeous vapour) ; and Water is cold and moist, while
Earth is cold and dry.'

SCIENCE IN 1500 27

traditional in the art of alchemy, some of which can be traced to
pre-Hellenic antiquity, had little reference to the philosophic idea
of metallic generation. But so long as the organic-inorganic analogy
seemed plausible, alchemy could not be dismissed as mere folly.
As for the differentiation between the generation from the
elements of the world of inorganic substances like minerals, and
the generation of living organisms, it is obvious that this could
not be found merely in the principle of growth, or autogenous
development from a seed, for this was really common to both. It
could not be made material at all, and therefore the two broad
kinds of living nature were defined as possessing respectively a
vegetative and sensitive "Soul," man alone having in addition an
intellectual soul which gives him the power of reason. In members
of the vegetative class (plants) the organization of matter was
more subtle than in minerals: they were not passive creatures of
nature, like a stone, for they required to be supplied with water
and rich soil if they were to maintain their existence, they showed
cyclical variations, and they possessed special structures for repro-
ducing their own kind. The fixing of the margin of life is not
simple; our phrase "living rock" is the survival of an ancient
mode of thought, and the alchemists used to distinguish between
the "dead" metal extracted from the ore and the "live" metal in
the veins of the mine. But the need for nourishment, involving
some process of "digestion," and the possession of a reproductive
system were recognized as distinctive of living creatures. It was
certain from theology that these had been created in the beginning,
and perpetuated themselves without change ever since. The func-
tion of the vegetative soul was to control and indeed be the bio-
chemistry of the organism, the whole life of the plant, but only
a part of the life of the animal. For the animal is sensitive: it feels
pain, it is capable of movement, it can manifest its needs and
desires. Therefore it was endowed with a sensitive soul. Man has
both a vegetative soul, since he must digest and reproduce, and a
sensitive soul because he possesses a nervous system, and he alone
being endowed with the power of reflection, of detaching himself
from the mechanism of the body, was credited with the third,
intellectual soul. The matter was everywhere the same, in rock,
in tree, or in dog, for it was well known that certain wells and
caves had the power of transmuting wood into stone, for instance:
the distinction between the animal, vegetable and mineral

2 8 THE SCIENTIFIC REVOLUTION

kingdoms lay in the immaterial organizing principle which brought
the elements into conjunction: nature could make pebbles grow
in streams, but not grass without seeds.

There was one important exception to this rule, founded (un-
fortunately) on the authority of Scripture and Aristotle alike.
A group of organisms, small as Aristotle originally conceived it,
obviously possessing the characteristics of life, seemed to have no
special mechanism of generation, but to develop directly from
decaying matter. Some insects, lichens, mistletoe, maggots were
included in the class of spontaneously generated creatures which
had no specific descent, and to them the middle ages, from sheer
ignorance, added others such as the bee, the scorpion, and even
the frog. Once spontaneous generation had been admitted, it was
a fatally easy alternative to investigation, and the belief remained
unshaken till the mid-seventeenth century. Yet it was less anoma-
lous than it might seem at first sight, for Aristotle was able to
imagine the circumstances in which spontaneous generation might
occur after a fashion that corresponded closely with his ideas on
normal reproduction. Since the whole universe was in a sense, not
the full sense, animated, it was not illogical that some humble,
borderline creatures should be born of it without parents.

Of the excellent descriptive biology of Aristotle and Theo-
phrastus very little was known at the opening of the sixteenth
century. The middle ages had depended only too much on
compilers of the later Roman period and on fables both pagan and
Christian. Such study was excluded from natural philosophy; it
might be just respectable as a form of general knowledge, or
moral as it provided material to illustrate a sermon or emphasize
the minuteness of divine providence, but it offered none of the
sterner food for thought. Botanical or zoological curiosity is of
very recent origin; in most periods most men have been content
to acquire only the minimum of practical knowledge. A very
few in the middle ages, like Albert the Great or the Emperor
Frederick II, had an interest and attend veness far above the
ordinary, but they founded no tradition. Observation was blunted,
and it has been pointed out that naturalistic representation must
be sought not in learned treatises, but in the works of craftsmen,
artists, wood-carvers and masons. Botany was cultivated to a
minor extent as a necessary adjunct to medicine and medieval
herb-gardens included both edible vegetables and medicinal

SCIENCE IN 1500 29

simples. In pharmacology native Germanic lore mingled with
the remnants of Hellenistic botany, so causing much confusion.
Plants named and described by the Greeks were identified with
the different species of western Europe; the nomenclature itself
varied widely from place to place; and there was no system by
which one kind could be recognized with certainty from its
structure and appearance. As the quality of graphic illustration
and of verbal description deteriorated, the herbal became little
more than a collection of symbols, so that the mandrake which was
originally recognizable as a plant becomes a manikin with a tuft
sprouting from his head. Again, on the purely empirical side,
some progress was made in the selection of strains of corn, just as
it is certain that attention was given to the breeding of hawks and
hounds, but in none of these things was the plant or animal itself
the centre of interest. It existed simply to be cooked, or distilled,
or mutilated in man's service, or alternatively to play a part in
symbolisms of endless variety. There are, however, signs of a
more naturalistic outlook from the earliest beginnings of the
renaissance.

Natural history and scientific biology are both modern creations,
stimulated indeed by the rediscovery of Greek sources in the
sixteenth century. But this was not the only fruit of the Italian
renaissance, for naturalism is older in art than in science. It is
unnecessary here to discuss at length a change in the artist's spirit
and ambition which had such important consequences for biology
and medicine. It is at least fairly clear that the medieval draughts-
man was not simply incapable of attaining realism, e.g. in matters
of perspective, but was not interested in perfecting direct repre-
sentation. The element of symbolism was as important to him as
it has been in the twentieth century. No tradition of " photo-
graphic realism" existed which could serve the purposes of science,
such as was assiduously cultivated with the aid of perspective
instruments, camera lucida, and other devices from the seven-
teenth century to the perfection of photography, when art and
science again parted company. Partly under Hellenistic influence,
partly for internal reasons, art moved strongly in the direction
of realism and the faithful representation of nature in the fifteenth
century. Plants and animals became recognizable as individuals
rather than hieroglyphs. The tradition that artists should study
the anatomy of the animals and men they depict came into being,

30 THE SCIENTIFIC REVOLUTION

reaching its peak in Leonardo da Vinci. This development was
powerfully reinforced in its scientific importance by the invention
of printing. Biology is peculiarly dependent upon graphic illus-
tration, and it is essential not merely that the illustration should
be accurate in the first place, but that it should be capable of being
reproduced faithfully. Nothing becomes corrupt more easily
than a picture or diagram repeatedly copied by hand; only a
mechanical process of reproduction, like the woodcut or the later
copper-plate, can maintain faithful accuracy. At the moment
when the technique of visual representation was arousing great
interest in the draughtsman and artist, printing made it possible
for illustrations to be copied in large numbers for teaching pur-
poses, so that the anatomical student and the botanist could
recognize the form of the organ or plant described in the text
when he saw it in the natural state.

The potentialities of the new interests and skills in biology
began to emerge only in the sixteenth century, as living creatures,
in their beauty, in the fascination of their habits, in the variety of
their species and ecological inter-relations, aroused a curiosity
and sentiment which has grown steadily in its extent throughout
the modern period. The faithful imitation of nature the necessary
formal basis of all naturalism was an aesthetic, rather than a
scientific revolution; the romantic nature-lover may not be a good
biologist. It was not until thought began to play upon the new
facts and the faults in the old traditions which passed for natural
history that precise observation could reveal consequences im-
portant for science, or that science could see in the flower not
simply an aesthetically pleasing object, or a symbol of God's
mysterious and benevolent ways, but a challenge to man's powers
of understanding.

Science is an expanding framework of exploration, not the
cultivation of special techniques, or of a pecularly acute apprecia-
tion of the wonder and unexpectedness of the universe in which
we live. Medieval philosophers, who in this respect had a sharp
sense of reality and a just notion of the importance of intellect,
had left natural history to such compilers as Bartholomew the
Englishman (c. 1220-40) whose book is an uncritical compendium
of classical fable and old wives' tale, flavoured with moralizations
and somewhat rarely enlivened by a touch of the countryman's
lore. They judged that the typical was more significant than the

SCIENCE IN 1500 31

freak, unlike some of the scientists of the later seventeenth century
who, in misguided zeal for the principles of Francis Bacon, filled
the museum of the Royal Society with the heads of one-eyed
calves, internal calculi, an artificial basilisk. 1 None of the great
men of the middle ages, with the exception of Albert the Great,
showed more than a cool interest in natural history. As a result,
bestiaries, herbals and encyclopaedias were laborious summaries
of the bald notes available in classical sources, and none of them
carried more than the slightest indication of personal observation.
Heraldic beasts were listed with real animals; the legends of the
crocodile's tears, the pelican killing its brood and reviving them
with its blood, and the barnacle-goose born of rotten wood added
interest to the story: the lion and the fox became popular symbols
of bravery and cunning. Creatures were classified according to
the element in which they lived. The salamander was the only
known inhabitant of fire; birds belonged to air; fishes, whales,
mermaids and hippopotami to water; and the rest to land. Trees
and herbs formed the two kinds of vegetable life, but only the few
species useful to man were noticed. Even common garden flowers
were ignored. Such work of compilation was regarded as a purely
literary task, and the authorities were quoted in wholly uncritical
fashion. Some scholars developed fantastic etymologies, such as
Neckham's Aurifrisius [Osprey] from " Aurum Frigidam sequens."
Roger Bacon pointed out the difficulty of interpreting satisfactorily
the more obscure names of creatures mentioned in the Bible
Biblical exegesis was one of the few respectable motives lor
studying natural history at all. 2 It scarcely existed save as an
appendix to some other branch of study. This is not really sur-
prising, since it is a trait of a sophisticated society to be interested
in things of apparently no concern to humanity. Natural philo-
sophy had for the middle ages an established place in the House
of Wisdom: natural history had yet to establish itself. 3

Francis Bacon wrote of scholastic philosophy that, from
immediate perceptions of nature, it 'takes a flight to the most
general axioms, and from these principles and their truth, settled
once for all, invents and judges of intermediate axioms. 5 Once
fundamental doctrines, the immovable earth, the four elements,

1 Cf. Nehemiah Grew: Musawn Regalis Societatis (London, 1681).

2 C. E. Raven: English Naturalists from Neckham to Ray (Cambridge, 1947).
8 Cf. Appendix A.

32 THE SCIENTIFIC REVOLUTION

or the souls of living organisms, are accepted as unshakably
true, and explanations of the varied phenomena of nature
deduced from them, it is an inescapable consequence that the
structure of scientific knowledge has great cohesion, a logical
unity imposed from above. An empirical science, a science which
sees itself as unfinished and progressive, can tolerate inconsisten-
cies it is for the future to resolve them by some higher-order
generalization. Physicists might have debated for a hundred
years whether light is undulatory or corpuscular in nature, but
the progress of optics did not wait upon a resolution of the argu-
ment. And while it is far from being true that medieval science
was exclusively deductive or exclusively speculative in every
detailed consideration of a particular phenomenon, it is true that
its structure was of the form that Bacon described. The character
of the structure is not changed by the fact that some philosophers
made a few experiments. The structure of modern physics is still
experimental, though some physicists do not make experiments.
The difference is that the theoretical physicist bases his calcula-
tions upon materials obtained by the researches of an experimental
physicist and produces a result which is itself capable of confir-
mation by experiment, whereas the medieval philosopher fitted
the results of his experiments into a theory already firm in his
mind. He knew what "light" was before making experiments on
refraction: he knew the cosmological significance of " weight "
before attempting to determine the speeds at which heavy bodies
fall. Experiment and induction could only modify the minutiae of
science, and these (for example, the numerical value of astro-
nomical constants) were indeed frequently changed in the later
middle ages in accordance with experience. They could not
reflect upon the broad lines of the structure. It might indeed have
happened that Aristotelean science would have been crushed
under the accumulated weight of an adverse mass of experimental
testimony. But modern science did not in fact arise in this way.

This too has its unity, of course a unity derived not from
deduction but from the homogeneity of its procedure and the
wonderful, unforeseeable interlocking of its branches over three
hundred years. Modern science, like medieval science, embraces
in this unity statements of fact, concepts and theories. It could
not function if it were not free to employ terms like "electron"
or "evolution," which are not applicable to crude facts, just as the

SCIENCE IN 1500 33

medieval philosopher could not think about plant-life without
introducing the entity "vegetable soul." Within its own context
of theory the vegetable soul is not less plausible than the electron,
and it cannot be said that one or the other can be disposed of
by a straightforward matter-of-fact test. To do so it would be
necessary to make a complicated inquiry into the value of the
factual information supplied by observation and experiment, to
examine the reasoning involved in either case, to trace the rela-
tionship between the concept and other elements in the fabric of
science, and so forth, and it is because modern science in all such
activities differs from medieval that its fruits are different. From
such intellectual activities modern science yields a system of ideas,
not an unlinked series of factual statements, being in this respect
(despite the immense superiority of its factual content) comparable
to medieval science. And the latter, as a system of ideas, with all
the imperfection of its methods and information, was true science.
It offered a system of explanation, closely related to the facts of
experience and satisfactory to those who used it, giving them a
degree of control over their natural resources and allowing them
to make certain predictions about the course of future events. By
these standards it was relatively vastly inferior to modern science,
just as at each stage in its own development modern science has
been inferior to the science of later stages. But to declare that any
of its tenets was unscientific is to misuse language. Unscientific
is a pejorative term meaning inconsistent with the prevailing
framework of the explanation of natural events and the methods
used to establish this framework; it can have no other meaning
because we do not know that what is scientific now will not be
unscientific in the future. There is no absolute standard. All that
can rightly be said, when we have understood that medieval men
had prejudices, purposes and hopes totally different from our
own, is that they were less inquisitive and self-critical than they
might have been. They were less interested in natural philosophy,
for to them it was but a step forward to higher things. Science was
a means, not an end.

CHAPTER II

NEW CURRENTS IN THE
SIXTEENTH CENTURY

The subtlety of nature greatly exceeds that of sense and
understanding; so that those fine meditations, speculations
and fabrications of mankind are unsound, but there is no one
to stand by and point it out. And just as the sciences we now
have are useless for making discoveries of practical use, so the
present logic is useless for the discovery of the sciences. 1

IN such terms Francis Bacon, in the early seventeenth century,
denounced the existing structure of scientific knowledge as he
knew it. Yet it is clear that the same structure of science had
satisfied the many medieval philosophers of genius who had ex-
pounded it; even those who criticized the learning of their day,
like Roger Bacon, could not depart from its strategic concepts.
Clearly the difference between the men who taught the Aristo-
telean world-system and those who later rejected it was not simply
one of intellectual calibre. Only when the criteria of what consti-
tutes a satisfactory scientific explanation changed, and when fresh
demands were made for the practical application of nature's
hidden powers, could an effective scepticism concerning the
strategic concepts take shape, as distinct from differences of
opinion on matters of detail. 2 When such scepticism arose the
cohesive strength of the science that prevailed in 1500, and on the
whole throughout the sixteenth century, became significant.

In modern science the higher-order generalizations are vulner-
able, but in descending the scale to the substratum of experimental
fact the chances of serious error steadily diminish. In Aristotelean
science the reverse was true: an important dogma, such as the
stability of the earth, might be incapable of experimental proof

1 Novum Organum, Bk. I, x, xi.

2 An important change also took place in the idea of hidden powers, as the
ambition to force "unnatural" operations on nature by esoteric or magical
means gave way to the belief that man could use processes as yet unknown but
still strictly rational or mechanistic.

34

NEW CURRENTS IN THE SIXTEENTH CENTURY 35

or disproof (as Galileo himself confessed), but some of the primary
propositions for example that bodies fall at speeds proportional
to their weights could be exposed as contrary to experience by
very simple tests. To modify the accepted scientific opinion of the
present time it is usually essential to carry out an intricate investi-
gation verging on the frontiers of knowledge; in attacking the
conventional science of the sixteenth century it was possible to
outflank the higher-order generalizations altogether by showing
that the "facts" deduced from them were simply not true. It
could not be a fundamental requirement of the world-order that
changes do not happen in the heavens if the new star of 1572 could
be shown to be far beyond the sphere of the moon by its lack of
parallax. This feature in the structure of Aristotelean science de-
termined a large part of the tactics of the scientific revolution.
Further, since the unity and cohesion of science were imposed
from above, growing out of its majestic axiomatic truths, it fol-
lowed that when the results of any one chain of ratiocination were
impugned the shock was reflected in similar dependent chains.
Once it was known that the liver is not the source of the blood-
stream the whole physiology based on this belief was disposed of
at one stroke. Admittedly the iconoclasts were not always quick
to recognize the necessary extent of their destructive criticism
least of all a Copernicus or a Vesalius which was often jubilantly
pointed out by their opponents. The weakness of conventional
science was also its strength; the whole authority of the magnifi-
cent interlocking system of thought bore down upon an assault at
any one point. How could a mere mathematician assert the earth's
motion when a moving earth was absolutely incompatible, not
only with sound astronomical doctrine, but with the whole
established body of natural philosophy? Logically, to doubt
Aristotle on one issue was to doubt him on all, and consequently
some problems of the scientific revolution, which may now seem
to involve no more than the substitution of one kind of explanation
for another, were pregnant with consequence since they implied
the annihilation of extant learning.

The sixteenth century shows the tactics of the scientific revolu-
tion in two contrasted forms. In the year 1543 were published two
volumes which have become classics of the history of science, the
De Humani Corporis Fabrica of Andreas Vesalius (1514-64) and the
De Revolutionibus Orbium Coelestium of Nicholas Copernicus (1473-

36 THE SCIENTIFIC REVOLUTION

1543). Neither of these books was "modern" in content Vesalius
was no more successful in escaping the limitations of Galenic
physiology than Copernicus in departing from the formal system
of perfect circles but both inspired trains of activity which were
to lead to the substitution of other conceptions for their own within
two generations. The two books and their authors, however alike
in their broad impact upon the scientific movement, are totally
dissimilar. On the Fabric of the Human Body is a work of descriptive
reporting; its value depends upon the trained eye of a great
anatomist and the skill of draughtsman and block-maker, while
Copernicus' treatise is purely theoretical. Vesalius was a young
man whose work, if it was his unaided, shows astonishing pre-
cocity. Copernicus was a dying man, of recognized capacity, who
had nursed his idea for thirty years. Vesalius' material was taken
freshly from the dissec ting-table; Copernicus' was the laborious
digestion of ancient observations. Vesalius was an ambitious and
popular teacher who contributed to the fame of Padua as a centre
for the teaching of medicine which lasted till the mid-seventeenth
century; Copernicus lived obscurely immersed in his ecclesiastical
administration, hesitant to the last over the enunciation of his
great hypothesis. The nature of Copernicus' original contribution
to science is also quite different from that of Vesalius. The former
was the avowed opponent of an idea, that the earth is the motion-
less core of the universe, but his opposition rested in no way upon
his discoveries in practical astronomy, which were negligible, or
on the precision of his measurements, which was not remarkable.
It sprang from a demonstrable truth, that celestial observations
could be equally well accounted for if the earth and planets were
assumed to move about a fixed sun, allied to various wholly non-
demonstrable considerations value-judgments seeming to show
that the astronomical system constructed upon this assumption
was simpler than the older system and preferable to it. Copernicus
criticized the internal logic of prevailing ideas, but to be a Coper-
nican did not add one item to a man's factual knowledge of the
heavens, whereas it did place him in a position which could be
challenged on other grounds. Vesalius, on the other hand, gave
vent to no formidably unorthodox opinions, rather indeed his
passing comments seem to condemn such innovations. Revering
Galen as the great master of anatomy, devoting his energies to
editions of Galen's works, it was with reluctance that Vesalius

NEW CURRENTS IN THE SIXTEENTH CENTURY 37

differed from him. Neither theorist nor philosopher, his book
vastly enhanced the range and precision of knowledge concerning
the structure of the body, an essential foundation for the rational
physiology of which he had himself no prevision. In general his
medical thinking was quite traditional, only his view of what an
anatomical textbook should be provoked controversy. The publi-
cation of Harvey's discovery of the circulation of the blood in
1628 aroused the first serious conflict between ancient and modern
medical theories. Yet it may be said that the beginnings of the
scientific revolution are to be found as truly in De Fabrica, and the
series of illustrated anatomies of which it was the outstanding
member, as in De Revolutionibus. As examples of types of innovation
they are complementary.

The twin advance upon the distinct lines of conceptualization
and factual discovery constantly occurs in science. The former
makes the more interesting history, but it must not be forgotten
that each new observation, each quantitative determination
accurately made, is adding to the stock of knowledge and playing
its part in the genesis of a new idea. Indeed, conceptualization can
only progress and rise above the level of speculation through the
accumulation of fact by the perfection of techniques of experi-
ment and observation. Anatomy is the crucial instance of this
during the early period of the scientific revolution.

In the middle ages it is difficult to distinguish specialized medi-
cal sciences from the general practice of the physician and surgeon.
There was a research interest of a sort in natural philosophy, even
though the research was of a peculiarly narrow kind and its sole
instrument formal logic. The medical sciences were even more
strongly subject to the limitations of the purpose for which they
were cultivated, the training of medical men. Yet some medieval
anatomists were imbued with a disinterested love of knowledge, a
trait which seems to have been stronger in the fourteenth century
than it was about 1 500. The tradition in medicine was at least as
tightly unified as that in natural philosophy. The principal auth-
ority in anatomy, physiology and therapy until the seventeenth
century was well advanced was that of Galen (A.D. 129-99).
Other writers on medical subjects were of course studied: in
clinical matters great respect was accorded to Hippocrates, whose
works were made more fully known by the humanists. Aristotle
was also followed in these subjects, sometimes in preference to

3 8 THE SCIENTIFIC REVOLUTION

Galen, but it is not easy to underestimate the latter's power. A
humanist physician, Dr. John Gaius, as President of the College
of Physicians, could order the imprisonment, until he recanted, of
a young Oxford doctor who was reported as saying that Galen
had made mistakes. When men were educated as logicians and
not as observers it was infinitely easier to detect errors in philo-
sophy than in anatomy or physiology. Admiration for Galen was
so extravagant that anatomists were more apt to attribute their
failure to confirm his descriptions to their own want of skill, than
to his. 'I cannot sufficiently marvel at my own stupidity,' wrote
Vesalius, 'I who have so laboured in my love for Galen that I
have never demonstrated the human head without that of a lamb
or ox, to show in the latter what I could not find in the former/
It was only tardily, and hesitantly, that Vesalius admitted to him-
self the simple truth that the structure then called the rete mirabile,
described by Galen in the human head, was a feature not of
human, but of animal anatomy. 1 Only gradually could anatomists
learn to see the body otherwise than as Galen had taught them,
and the broader influence of his pathology lingered well into the
nineteenth century. Galen was one of the greatest medical scien-
tists who have ever lived, demonstrating in Rome, some six hundred
years after Aristotle, the vigour and quality of Hellenistic science.
He dissected, he experimented and his work, though dominated by
the vitalistic preconceptions of Aristotle, has a strong experiential
foundation. He was also an uncritical teleologist, believing that
it is possible to discover the purpose of every part of the body and
to prove that it could not be more perfectly designed for that
purpose. This profound admiration for the divine plan recom-
mended him strongly to Christian writers of the middle ages.

In many ways Galen epitomizes the typical qualities of the
Greek tradition in medieval science, itself often far superior to the
independent eiforts of the later Latins, but so far imperfect that
even when it was purified and enriched by renaissance scholars
a reaction against it was still necessary before modern science
could take shape. In some aspects the Greek intellect was ' 'modern" ;
but not in relation to medical subjects. Greek medicine never de-
tached itself from teleological arguments, and its anatomy was

1 De Fabrica (1543), P- 642. Quoted by Charles Singer and C. Rabin: A
Prelude to Modern Science (Cambridge, 1946), p. xliv. Doubts on this point had
been expressed earlier by Berengario da Carpi.

NEW CURRENTS IN THE SIXTEENTH CENTURY 39

always firmly subject to a priori physiological theories, not lending
itself to the reverse and correct process. There was a deep-seated
prejudice against human dissection. As a result the study of animal
anatomy without sufficient check introduced numerous errors.
Galen worked extensively on the Barbary ape, he may possibly
have had access to the still-born foetus, but he never dissected an
adult human subject. This lack of experience was scarcely appreci-
ated before the time of Vesalius. Technical nomenclature and
classification were very defective in Greek anatomy, and even had
description been perfect it would have been useless to a later age
in the absence of pictorial illustration. At its best the eye of the
Greek anatomist had often been deceived by his preconceived
notions of the working of the body. As in astronomy, the Greeks
had gone far in the direction of precise and careful research, much
of which proved of enduring value, but the observations they
made were fitted into a scheme of ideas inherited from primitive
times.

The influence of Greek texts upon Islamic physicians had
become considerable by the ninth century A.D., when there was
much activity in translation. Avicenna (980-1037), the greatest
scientist of the Arab world and its foremost physician, reproduced
in his Canon the best features of a Hellenized survey of medicine, as
well as original observation. To some extent, with its important
debt to Galen, the Canon replaced Galen's own writings, even in
the West. Gerard of Cremona in the twelfth century translated it
and a large part of the Galenic corpus, but not Galen's chief
anatomical works which were only Latinized in the fourteenth
century. Other Galenic texts were translated direct from the
Greek by William of Moerbeke, half a century later than Gerard.
Eventually, too, all the more important works in Arabic on
medicine became available, including the Kitab of al-Razi
(c. 850-924), an even larger encyclopaedia than Avicenna's Canon.
Before the sixteenth century the Islamic commentaries upon and
additions to the Greek originals had a decisive influence upon
the European knowledge of Hellenistic medicine.

Human dissection was discouraged in Islam. In Europe the
systematic study of anatomy seems to have begun in the twelfth
century, contemporaneously with the rise of the famous medical
school of Salerno, though the practice of actual dissection was a
north Italian development. The reception of Aristotle's writings

40 THE SCIENTIFIC REVOLUTION

in the thirteenth century, temporarily interrupting the growth of
a purely Galenic anatomy and physiology, was counter-balanced
by a stronger interest in dissection, flourishing under the wider
privileges of the universities. Dissection was given countenance,
partly by the needs of surgery, and partly by legal recognition
(under the influence of the law-school of Bologna) of the value of
forensic evidence derived from the post-mortem opening of the
body. There has been at all times and in all places a universal
revulsion against the dissection of the dead to serve mere curiosity,
and perhaps it was not extraordinarily strong in the middle ages.
At least it is likely that human dissection was comparatively com-
mon at Bologna by the early fourteenth century, the legal post-
mortem having been transformed into a means of instructing
students. Henri de Mondeville, in teaching anatomy at Mont-
pellier in 1304, illustrated his lectures with diagrams probably
copied from those used in the school at Bologna. 1

Shortly afterwards, in Mondino dei Luzzi (c. 1275-1326),
medieval anatomy reached its zenith. He dissected for research,
and he was probably the first teacher since the third century B.C.
to demonstrate publicly on the human body. His Anathomia, which
was printed many times, long remained a popular text. Eager
to reconcile authorities, he did not venture to assert his own views,
and perpetuated many mistakes. Good anatomists succeeded
Mondino (though none escaped his influence) but there was a
general deterioration in the teaching of the subject. Mondino had
expounded while at work upon the body; the standard practice
of a later age is familiar from a number of wood-cuts in early
printed books. The professor sat in his lofty chair, reading and
enlarging upon the Galenic text, while an ostensor directed the
operations of the humble demonstrator who wielded the knife. The
body again became merely an illustration to the words of nobler
men. Anatomy degenerated into the repetition of phrases and
names. No example of the misleading perspective adopted by the
renaissance scholar could be clearer than this: because he knew
that the teaching of anatomy had become a literary exercise in
the fifteenth century, he assumed that it had never been anything
else, and that the only course was to return directly to the works
of Galen.

The curve moves upwards again towards the end of the fifteenth
1 Charles Singer: The Evolution of Anatomy (London, 1925), p. 73.

NEW CURRENTS IN THE SIXTEENTH CENTURY 41

century. One factor in this seems to have been pressure in the
medical schools for more demonstrative teaching; attendance at
dissections had .to be restricted so that all might share in the
spectacle. 1 Another was the official recognition of human dissec-
tion, under clerical licence, by the Papacy. The first printed
anatomies with figures appeared in the last decade of the century
and the first half of the sixteenth shows a whole group of able
practical anatomists at work Berengario da Carpi, Johannes
Dryander, Charles Estienne, Canano of Ferrara, Massa, in
addition to Vesalius. The humanists applied themselves to the
editing of famous medical texts, and others but recently recovered,
such as the De re medica of Celsus (first century B.C.), which
supplemented the medieval corpus. There was a powerful reaction
against the Arabic authorities, and the Arabic technical nomen-
clature was gradually replaced by the classical terminology which
has established itself. Galen's texts were studied in the original
Greek, and re-translated into Latin. English scholars under the
patronage of Reginald Pole had a large share in the edition of
Galen's Opera Omnia printed at Venice in 1525 the connection
between medicine and philosophy was rediscovered. 2 But scholars
were not practical anatomists, their enthusiasm reinforced, rather
than weakened, the medieval attitude to anatomical study. The
pure Galen still held all Galen's faults, for scholarship could
purify a text without touching on the errors in observation held
within it.

Another and more important source of inspiration was of a
different kind, the naturalistic movement in art which has already
been mentioned. Italian artists had been engaged in the study of
anatomy well before the end of the fifteenth century, and from
surviving sketches by, for example, Michelangelo or Raphael, it
appears that they occasionally practised illicit dissection. Leonardo
da Vinci (1452-1519) certainly did so as his interest in the fabric
of the body developed from his first attempts to analyse the
structure of the forms he was portraying. Some of the printed
anatomical figures of the next generation are indeed reminiscent
of Leonardo's famous drawings. The representation of anatomical
structures as seen with the artist's eye and recorded by the artist's

1 Lynn Thorndike: Science and Thought in the Fifteenth Century (New York,
1929), p. 69, n. 22.

2 W. G. Zeeveld: Foundations of Tudor Policy (Harvard, 1948), pp. 53-5.

42 THE SCIENTIFIC REVOLUTION

pencil, which is totally different from the schematized, diagram-
matic illustration of an earlier epoch, and even from the merely
workmanlike but biologically accurate sketches of later professional
anatomists, thus preceded the work of the founders of modern
anatomy. The means for duplicating such drawings already
existed in the technique of wood-cut printing. From this source
the sense of the actual, of the minute, penetrated into academic
anatomy and it is significant that the artists were men who had
no stake in existing theory, and who, in the case of Leonardo at
least, were unschooled in the textual description of organs. But
there are limitations to the artistic impulse and to the naturalism
which is only interested in superficial forms. The artist's drawing
may not be most suitable for the purposes of a text-book; he needs
to know something of the configuration and function of the surface
musculature, of the run of the visible blood-vessels, and perhaps
something of osteology, but he does not normally need to penetrate
to the internal organs or the recesses of the skull. The artist at
the dissecting table would certainly seek to re-create the appear-
ance of the living body from the structure of the dead but he
would not usually be interested in the correlation of function and
the ordering of parts which ultimately lead to the discovery of
physiological processes. Only when naturalism serves an impulse
which is no longer purely artistic and has become the instrument
of scientific curiosity can it have significance for medical anatomy.
Of course it is abundantly clear that the motive which directed
Leonardo to make his perceptive and accurate sketches, to take
casts and prepare specimens by the injection of wax, was of a
truly scientific order. In him, as in Vesalius, artistic imagination
was the servant of science. Yet some even of the most naturalistic
of Leonardo's drawings contain ancient errors, perhaps copied
from the vernacular anatomical text-books which were already
available to him: and to the organization of anatomy as a disci-
pline Leonardo, who had no talent for classification and arrange-
ment, contributed nothing. In any case the influence of his
crowded and ill-ordered note-books upon contemporaries is in
all respects entirely conjectural.

If the historical situation were that teachers of anatomy and
medicine in the universities of France and Italy became them-
selves the pupils of professional artists unlearned in Galen it would
be unique and surprising. But this was not the situation. It was

NEW CURRENTS IN THE SIXTEENTH CENTURY 43

rather that the work of the anatomist reflected, with less artistic
merit, the same general cultural trend towards naturalism which
affected purely aesthetic representation more profoundly; and that
the anatomist made use of the same techniques of draughtsman-
ship and reproduction as the artist, whose stylistic conventions
were impressed upon his illustrations. Naturalism, and the desire
to take advantage of the new faculty of the wood-cut print for
exposition, forced him along the road to observation. If the teacher
of anatomy wished to elucidate the Galenic account of the struc-
ture of the human body by pictures of the features described he
could do so only by dissecting a body and having drawings made
he could not reconstruct a picture entirely from a verbal text,
though the text might influence the instructions he would give
to the draughtsman. As, in so doing, anatomists observed dis-
crepancies between the text and the structures themselves they
departed with greater confidence from the Galenic model and
learnt to rely on observation alone. A few conservative anatomists
were well aware of the danger of illustrated texts; too great a
reliance upon visual images might lead to contempt for Galen's
superior knowledge. So in fact it happened that Vesalius' cuts are
sometimes less traditional and more accurate than his text. The
practice of making realistic not necessarily aesthetically pleasing
drawings elevated instructional dissection to the level of re-
search, but in the circumstances of the time opportunities for
making a recordable dissection were few and hurried. The ambi-
tion to make (for example) an accurate map of the venous system
need not be taken to be ipso facto evidence of a critical spirit,
though it may indicate a more sensitive professional conscience.
As the first men to embark on such tasks were firmly convinced of
Galen's rectitude, there was no reason why they should not take
the liberty to draw what he had already perfectly described. It
was thus with Vesalius himself: not until his preparatory work
for the De Fabrica was well advanced did he realize the extent
to which Galen had transferred animal structures into human
anatomy. This misleading practice, and Galen's specific mistakes,
could not be exposed without an impulse to research which in fact
arose out of the needs of teaching and illustration. The errors in
text-book anatomy could not be discovered through a desire to
amend Galen by reference to nature because no one as yet
believed this to be necessary.

44 THE SCIENTIFIC REVOLUTION

All this has little relation, directly, to aesthetics. The first illus-
trated anatomies were not indeed beautiful books, though they
contained many new discoveries. It may well be that Vesalius'
superbly produced folio cast an undeserved shadow upon the less
splendid efforts of his contemporaries and immediate predecessors.
Perhaps too much emphasis has been placed upon its interest as
an example of the profitable co-operation between scientist and
artist in the sixteenth century; certainly Vesalius' figures were fine
enough to prompt frequent plagiarism. The preparation of illus-
trated anatomies demanded such a collaboration, and provided
an incentive for an original research, but Vesalius was not the first
to attempt a complete pictorial survey, which he began with
youthful energy. When in 1537 he set to work on De Fabrica, and
commenced teaching anatomy at Padua, Vesalius was twenty-
three. He could hardly claim to write with mature knowledge,
and though he had studied medicine at Louvain and Paris, so far
as is known his experience of dissection was still very limited. Nor
was he qualified to stand as an arbiter between Galen and Nature,
for at Paris especially, under medical humanists who were un-
shaken followers of Galen, he had been well grounded in the
renewed Greek tradition. Vesalius' first notable publication was
a revision of Johann Giinther's Anatomical Institutions according to
Galen (1538), and his second, the Tabula Sex, was a series of wood-
cuts to illustrate the Galenic exposition of human anatomy which,
though based on dissection, was still traditional in character and
repeated many ancient mistakes. It was not, apparently, until the
preparation of De Fabrica was well advanced (about 1539-40) that
Vesalius began to doubt whether an anatomy founded on natural-
istic illustration could be reconciled with Galen's descriptions.
Even of Vesalius' finished work it has been said that: 'A few of
his comments reveal an active dissector less experienced than
his contemporaries Berengario da Carpi, Massa and Charles
Estienne.' 1

Creative scientific ability may run strongly in the direction
either of practical work or of theory. To the former talent the
medieval world offered little opportunity in comparison with that
offered by modern experimental science. As mechanics was in the
early seventeenth century the ideal field for the exercise of the

1 Charles Singer: Studies and Essays in the History of Science and Learning offered
to George Sarton (New York, 1947), P- 47*

NEW CURRENTS IN THE SIXTEENTH CENTURY 45

conceptual intellect of Galileo, so anatomy in the sixteenth was a
fruitful subject for keenness of observation and, to a less degree,
ingenuity of experiment. Unconsciously the new developments in
the study of anatomy ran counter to the humanistic endeavour.
At the very moment when humanists were rediscovering the
philosopher in Galen his scientific authority was being under-
mined. As with so much original effort in the first stages of the
scientific revolution, a more perfect anatomical knowledge con-
tributed not to the integration of science but to its disintegration,
in this case to the elaboration of a specialized art of detached
description through which alone accuracy could be attained. The
anatomists who freed themselves, however partially, from their
natural inclination to follow classical masters were framing a new
standard of scientific observation. In no real sense was this the
moment of the birth of some novel, self-conscious method of
observation and experiment in science, but it was the moment
when the accepted narrative of fact and theory was first modified
effectively and permanently by recourse to nature. A body of
original facts relating to a single discipline was for the first time
gathered together for comparison with the traditional account.
Justified only by practical experience, even opposed to the theories
of those who described them, the new discoveries combined to
teach the lesson that the whole doctrine of anatomy must be re-
formed by the use of meticulous observation and independent
thinking. While the facts of experience to which appeal had been
made in the framing of medieval physical theories had mostly
been commonplace, or accidentally revealed, the new anatomy
turned to the systematic exploitation of a specialized and laborious
technique.

The most complete, and the most striking, use of this technique
was certainly in the De Fabrica of Vesalius. All authorities on the
subject agree that Vesalius' exposition of human anatomy is out-
standing in early modern times, basing their judgement on his text
as well as on his still more eloquent illustrations. But he was not
unique in his originality; rather he was the most successful ex-
ponent of a new procedure that was beginning to gain adherents
over all Europe, some of whom Vesalius did not scruple to treat
unfairly. Among his immediate predecessors Berengario, whose
illustrated Commentary on the anatomy of Mondino was published
as early as 1521, was notable for hesitancy in following Galen.

46 THE SCIENTIFIC REVOLUTION

Another, Charles Estienne, was at work on his book On Dissection
by 1532, though this remained imprinted till I545- 1 Estienne was
the first anatomist (after Leonardo) to prepare figures illustrating
complete systems (venous, arterial, nervous) and he discovered
the structures in the veins, later known to be valves, which stimu-
lated William Harvey to the discovery of the circulation of the
blood. John Dryander published two illustrated treatises in 1537
and 1541. Canano's incomplete myology also appeared in the
latter year (or 1540), and nine years after the publication of De
Fabrica, a set of copper-plates to illustrate human anatomy was
finished by Bartolomeo Eustachio (1520-74), which have been
described as more accurate than Vesalius' figures, and almost
equally crowded with new observations. 2 Some of the unillus-
trated treatises on anatomy, such as those of Sylvius and Massa,
are not less remarkable for skill in dissection and acuity in criti-
cism. Moreover, in the application of anatomical knowledge to
physiological theories a subject in which Vesalius was steadily
conservative another contemporary, Jean Fernel (1497-1558),
was far in advance of his time; and, soon after 1543, Serveto,
Colombo and Fallopio were putting forward notions on the dis-
tribution of the blood about the body of which no hint is to be
found in De Fabrica.

When Vesalius is matched against his not unworthy rivals, his
peculiar fame appears all the more enigmatic. He did not lead
the way in making discoveries alien to Galenic anatomy, nor did
he ever intend an onslaught upon it. He had no greater learning,
or more vivid freshness of mind, than his more experienced con-
temporaries. Even when spoken of by his teacher Giinther as 'a
young man, by Hercules, of great promise . . . very skilled in dis-
secting bodies,' the observation for which he was thus praised had
already been anticipated in Italy. The task which he set himself
would seem to require ample time and mature knowledge, but
Vesalius had neither. During the mere three or four years given
to De Fabrica he was busy with other writing, teaching and travel.
His whole study of female anatomy was based on the hasty dis-

1 De dissections partium corporis humani, a large octavo, has fifty -eight full-page
wood-cuts, in which unfortunately the important portions are often too small
to be clear.

2 Charles Singer: Evolution of Anatomy, p. 135. Eustachio's figures, after being
first printed in the early eighteenth century, were thereafter frequently
republished as having contemporary value.

NEW CURRENTS IN THE SIXTEENTH CENTURY 47

section of three bodies not surprisingly, it forms one of the weakest
portions of his work. Comparison of the Tabula Sex with De Fabrica
compresses his development as a scientist into an almost incredibly
brief space of time, if it was entirely unaided. Little is known of
his personality; in comparison the biography of Copernicus is
full. Often abusive, truculent, Vesalius was not a learned man by
the standards of his age, and he reveals little in the way of philo-
sophic depth such as was then expected of a scientist. He was am-
bitious, and apparently ambition prompted his one great work;
after leaving Padua in 1543 to become an Imperial physician his
career in science ended.

It is impossible to fit Vesalius into the conventional picture of
the scientific worthy. But whatever may be the truth concerning
the collaboration of artist and anatomist in the production of De
Fabrica, however serious the charges that may be brought against
Vesalius' character as an author, the book itself stands as a monu-
mental achievement of sixteenth-century science, and in its own
time it was almost immediately recognized as such. De Fabrica was
the implementation, in a manner whose total effect is superior to
that of any contemporary work, of a single conception of what an
anatomical treatise ought to be, and there is no evidence that this
conception was not Vesalius' own. It aimed at a systematic, illus-
trated survey of the body part by part, layer by layer. The skeleton
and the articulation of joints, the muscles, the vascular system, the
nervous system, the abdominal organs, the heart and lungs, the
brain, were described and depicted with a detailed accuracy never
previously attained. The wood-cuts are indeed on occasion better
than the text they illustrate, though in one place it is admitted that
a drawing had been modified to fit Galen's words. In his section
on the heart Vesalius mentions probing the pits in the septum
without finding a passage; broadly, however, he accepted the
Galenic account of the heart's function. Some whole topics (the
female organs, the eye) were less well discussed owing to errors in
observation, due in part to Vesalius' inability to free himself com-
pletely from traditional ideas. In minutiae there was much for the
anatomists of the later sixteenth century to amend.

As a reformer despite himself, Vesalius' attitude to orthodox
instruction was cautious. Where his departures from Galen's texts
are most notable, generally he said little more than others at the
same time were saying.

48 THE SCIENTIFIC REVOLUTION

If it be said that he often corrected Galen it may be rejoined that
much more often he follows Galen's errors. , . . The Fabrica is, in
effect, Galen with certain highly significant Renaissance additions.
The most obvious and the most important is the superb application
of the graphic method. 1

But the graphic method was not invented by Vesalius, and to what
extent its quality was due to the draughtsman employed (who,
according to the art-historian Vasari, was John Stephen of Calcar) 2
will probably never be known. Although Vesalius hotly criticized
Galen for describing human anatomy by analogies drawn from
animal dissection, he was himself led into mistakes resulting from
this very practice. In his interpretation of the functions of the
structures described he followed Galen closely. His boastful narra-
tive of his own achievements, and his claims to originality are not
to be trusted without scrutiny; thus it is obviously untrue that
human dissection was utterly unknown in Italy before he intro-
duced it at Padua. Vesalius seems to have resented, rather than
welcomed, originality in other anatomists. It is true that both his
successors at Padua, Realdo Colombo (who had worked with
Vesalius) and Fallopio, made important additions to knowledge,
but Vesalius himself launched an attack upon the latter's innova-
tions. The tradition of anatomical study was not inaugurated in
northern Italy by Vesalius during his short residence there, for
it had existed for centuries. As for the claim that Vesalius was the
first teacher of anatomy in modern times to carry out dissections
before the students with his own hands the idealized scene is
represented in the frontispiece to De Fabrica the view has recently
been put forward that even as early as 1528, and in the humanistic
medical school of Paris, ' the participation of students and doctors
in the actual process of dissection was recognized.' 3 It seems,
therefore, that if Vesalius introduced any new teaching method to
Padua it was but the method he had known at Paris.

In him there was neither the burning passion of a Galileo to
refine truth from error, nor the remote vision of a Kepler; yet the
work of a man whose spirit is calm, almost plodding, may mark a

1 Charles Singer: Studies and Essays in the History of Science and Learning offered
to George Sarton (New York, 1947), p. 81.

2 This attribution has been disputed and defended; cf. W. M. Ivins in Three
Vesalian Essays (New York, 1952).

3 Charles Singer: Bulletin of the History of Medicine, vol. XVII (Baltimore,

NEW CURRENTS IN THE SIXTEENTH CENTURY 49

turning-point in exact science. If Vesalius was pre-eminent among
early anatomists he must not be made so at the expense of his
contemporaries, who were also men of ability and precision, nor
by neglecting his own faults and mistakes. Although the structure
of De Fabrica was excellent, Vesalius was a poor expositor;
nevertheless, his text inculcated the principles of the new mode of
anatomical study more effectively than any other work, and
brought back the study of anatomy to the dissecting-table. He was
responsible for making many useful innovations in the technique
of dissection which extended its possibilities. He had the merit of
seeing anatomy as more than a catalogue of structures useful to the
physician seeking the proper vein from which to let blood or to
the surgeon tracing the course of a bullet- wound; it was for him
an entrance into knowledge of the living body as a functional
organism. True, he was unable himself to progress far towards
this desideratum, and therefore he was content to rely upon
Galen, but his work was a guide to his successors. De Fabrica must
be judged as a whole, and it is in the preponderance of its virtues
over its defects that the book excels. In a descriptive subject such
as anatomy, especially where the relations between the possibilities
of research and the necessities of teaching are very close, there
seems to exist a critical level of accuracy. Until description has
passed the critical point no steady accumulation of knowledge is
possible because there is no firm orientation to study, no sound
model exists, doubt and duplication lead to wasted effort and
repeated surveys of the same elementary facts. Once the critical
point is passed and the outline is securely drawn, so that the
student can easily identify it with the natural subject, it is possible
to press forward to deeper and finer levels of detail. Vesalius 5
contemporaries had almost attained this point; in particular
studies some passed far beyond it; but De Fabrica passed it in an
extended account of the whole body. The work was far from
impeccable, perhaps its originality and the importance of a high
aesthetic (which is not the same as a naturalistic) quality in its
illustration have been over-emphasized, but it was sufficient. 1
The map was made. It is not enough to say that Vesalius

1 There are some hundreds of figures, not including the initials, in the first
edition of the De Fabrica. Of these, only about a score enter the "aesthetic**
class: they are, of course, the finest wood-cuts in the book, but they do not
compose the whole of Vesalius' graphic teaching.

4

50 THE SCIENTIFIC REVOLUTION

redirected anatomists to the natural facts of bodily structure, for
the work of contemporary anatomists was already in the same
direction, and in any case it was to be long before the meaning of
these facts (like the valves in the veins) could be correctly inter-
preted. The main point is that the De Fabrica was the actual
source from which the method of obtaining the facts of human
anatomy by dissection and experiment was learnt; admittedly
it could still have been learnt had the De Fabrica never been
printed. In the hands of students it was an instrument fit to
measure against nature, to serve as a guide to the complexities
which Vesalius' successors discovered in their turn, and to create
in the exceptional man the critical frame of mind which is the
main-spring of research.

In a sense the possession of this quality belongs to the definition
of modern science. In many instances the reason for the sterility
of conventional science before 1500 was not simply that its
exponents were engaged upon a vain endeavour, nor most
obviously that they were fondly prejudiced, perverse, or unoriginal
of mind. They, like all men, could do no more than accept or
modify according to their powers an intellectual inheritance
which was a part of the age and society in which they lived. Such
an inheritance is never exactly consistent, nor is it wholly dominant
over the individual, but the range of possible variation from it is
always limited. One characteristic of the intellectual heritage of
every medieval philosopher, or physician, was the limited area of
contact between the system of ideas in science and the reality
of nature; on the one hand was a natural philosophy satisfactory
enough to those who knew no other, and on the other the bewilder-
ing complexity of the natural world. A juxtaposition of the two
was not easily effected. If it seemed that philosophy explained the
world, it seemed so because the distinction between the philosophic
view of natural phenomena, and the phenomena themselves, was
not clearly revealed; and since the globus intellectualis and the
globus mundi were so far distant, constructive, purposeful criticism
of the former could hardly emerge from its comparison with the
latter. Hence arises the importance of a new field of experience,
such as magnetism offered to the middle ages, or of a new attitude
to scientific explanation, such as that contained in the mechanistic
philosophy of nature. The effect of every major idea in science, of
every major observation and experiment, has been to present a

NEW CURRENTS IN THE SIXTEENTH CENTURY 51

new juxtaposition of the realm of thought and the realm of facts,
which may in turn demand a far more profound readjustment
than the original innovator could foresee.

It is easier to illustrate this from the history of ideas than from
the history of factual discoveries, easier to see it in Copernicus,
for example, than in Vesalius. It is obvious now that once the
central tenet of the old astronomy was rejected, the incidentals
which Copernicus had retained must also be challenged. Yet it is
important, for the understanding of the process and development
of the scientific revolution, to see how the cardinal observations
and measurements emerged, as well as the cardinal concepts. The
normal development of any established department of science may
be, and indeed usually is, conditioned in large part by its con-
ceptual structure and the nature of the theoretical techniques
appropriate to it, since these furnish the perspective in which the
problems are to be seen. In exceptional situations, however, the
disclosure of a new fact commonly the apprehension of the im-
port of a whole group of facts may force a crisis. Then existing
theory may prove an obstruction. A novel perspective is called
for. In this respect stands the work of Vesalius to that of Harvey
and later physiologists, who revolutionized ideas by applying
experimental procedures to the elucidation of the bare facts
yielded by a more exact anatomy. Through the effort of Vesalius
and his less famous contemporaries there was introduced into
biological science for the first time an acute sense of the importance
of minutiae, of the mastery of special methods, and of the precise
and full reporting of observations. Contemporaries admired the
De Fabrica as the perfection of descriptive art, to this also its claim
to mark a turning-point in the growth of scientific knowledge is
due. But the book is not less notable as entailing the challenge to
Galenic theory which its author scarcely contemplated.

De Revolutionibus Orbium Coelestium has an altogether different
character. Its force springs from the other tactic of the scientific
revolution, accepting the body of observation on which conven-
tional science relied and even the method by which the facts
could be grouped into a theoretical interpretation, but denying
that only the conventional interpretation was possible, or even
preferable to its alternative. Although his name has become more
famous, Copernicus was in many ways less modern than Vesalius,
in particular he had a far less acute sense of the reality of nature:

52 THE SCIENTIFIC REVOLUTION

like many medieval men he was far more concerned to devise a
theory which should fit an uncritically collected series of obser-
vations than to examine the quality of the observational material.
Tycho Brahe, half a century later, was the Vesalius of astronomy.
If one can discern a fundamental motive for Copernicus'
reconstruction of the cosmos, that too seems to be medieval.
The unity of thought had been the goal of medieval philosophy:
the harmonizing of pagan science and Christian religion, the re-
conciliation of authorities, the explaining of contradictions and
discrepancies, had been its unending task. And it seems that the
belief that true knowledge must be unified provoked Copernicus'
first doubts. The early sixteenth century was not a time at which
dogmatism on astronomical problems was easy or profitable. The
popular view that the astronomical science of the middle ages
was simply a matter of applying rigid principles in a determined
fashion is mistaken. Of course the main structure of astronomical
theory was firmly established, but the working out of the exact
details involved constant experimentation, and the best authors
were not themselves agreed on the true values to be attached
to all the constants of the Ptolemaic system. In fact medieval
astronomers were well aware that that system was not meticulously
accurate as a calculating instrument and, though they did not
revolt against its fundamentals, they attempted by adjustments
and additions to bring it to perfection. Wherever astronomy was
actively studied, there was a renewed interest in observation,
in modifications to the machinery of the spheres, and renewed
computation of the constants and tables. The greatest problem of
all was of a different order. No man of learning could ignore the
fact that the system of Ptolemy was something more than an
elaboration of that of Aristotle. To describe as physical the
Aristotelean picture of the cosmos, and to describe the Ptolemaic
as a mathematical hypothesis of planetary motions, is perhaps to
press an analysis of which the middle ages were barely conscious.
Yet, while there was no direct or irresolvable antithesis, it was
always clear that there was something of a hiatus between
cosmological physics and astronomy. There was not merely a
perpetual struggle to reduce the complexities of planetary motion
to mathematical order, but also these complexities were confusing
in physics. The eccentricity of the earth with respect to certain
spheres, and the irregularity of the motion of these spheres about

NEW CURRENTS IN THE SIXTEENTH CENTURY 53

the earth, were assumptions which practical astronomers were
forced to make, without possibility of reconciliation with Aristotle's
physical doctrine. Oresme pointed out another difficulty that
arose from the introduction of epicycles, concluding that Aristotle
was obviously mistaken in his demonstration that the intelligences
controlling the spheres do not themselves move. 1 He seems to
distinguish, too, between what is true "in philosophy" and true
"in astrology," i.e. astronomy. In more practical ways the im-
perfections of astronomy were recognized. The calendar was out
of joint. Even astrologers admitted that their calculations were
uncertain because of the inaccuracy of the tables with which they
worked. Tables for the cycle of moon and tides, essential to seamen,
were unreliable. The observational basis in the celestial coordin-
ates of the fixed stars, and the latitudes of places on the earth, was
equally open to doubt. Humanism added its own confusion: the
conflict between Arabists and Humanists was less spectacular in
astronomy than in medicine, but it was not the less real in the
difference of opinion between those who wished to preserve the
simpler system of Ptolemy, and those who believed that Islamic
elaborations, like the trepidation of Thabit, were necessary.

Already in the fifteenth century Peurbach and Regiomontanus
had applied themselves to the technique of observation, and tried
like their predecessors to bring astronomy up to date by new
determinations and computations. They did not appeal to nature
against Ptolemy, but they sought to refresh his system by a new
draught of observation. The world of learning upon which
Copernicus entered knew that a reform was needful, even though
it did not welcome the shape of that reform in his hands. A world
expecting some new mathematical formula which would u save
the phenomena" along the old lines received instead an unprece-
dented synthesis of philosophy and mathematical astronomy
which attacked much that was orthodox in both. Although united
in the higher realm of ideas, the philosopher and astronomer
had long been professionally divorced. Those who contemplated
the mysteries of the cosmos had done little actual observing or
calculating, while the practical astronomer had lost himself in
mathematical abstractions. Copernicus was a superbly equipped
theoretical astronomer (with some skill in observation, but no
great love for it) who shows at the same time a strong sense of
1 Medieval Studies, vol. IV, p. 169.

54 THE SCIENTIFIC REVOLUTION

physical reality. He was affronted by the Aristotle-Ptolemy
dualism. He thought that some of the devices used by Ptolemy,
especially the equant-point, were cheats counter to sound
philosophy. He found that the physical system failed in mathe-
matics, the mathematical in physics. The only solution to the
dilemma required two steps: the purging from mathematical
astronomy of its needless reduplications, and from physics of
those ideas which were obstacles to a true conception of the
universe. Thus the reform of astronomy demanded a limited
reform of physics, and Copernicus was in fact impelled to dis-
tinguish between those doctrines of Aristotelean physics which he
took to be true, and those which he took to be false. In the end
much was to turn upon the justice of his conception of what is
"right" in nature.

There is good evidence that Copernicus was highly esteemed
by men of learning long before the publication of De Revolutionibus,
which indeed in the eyes of some contemporaries diminished rather
than enhanced his reputation. 1 Rheticus describes him as 'not
so much the pupil as the assistant and witness of observations'
of Domenico Maria da Novara, himself something of a critic of
Ptolemy, at Bologna: and as lecturing on mathematics at Rome
in 1500 (when he was twenty-seven) 'before a large audience of
students and a throng of great men and experts in this branch of
knowledge.' 2 Clearly Copernicus had already become an accom-
plished student of mathematics and astronomy in his earlier days
at Cracow. On his second visit to Italy in 1514 he was consulted
on the question of calendar reform. One of his critical writings,
the Letter against Werner (1524), seems to have circulated in
manuscript, as did the first sketch of his new astronomy, the Little
Commentary which was written, probably, about 1530. There is a
record of Copernicus' ideas being explained to Pope Clement VII
in 1533. In 1539 his fame attracted the Protestant Georg Rheticus
from Wittenberg to Frauenberg, "remotissimo angulo terrae," to
become his pupil, and in the following year Rheticus' First Account,
a review of Copernicus' manuscript of De Revolutionibus, was
published at Dantzig. Some of his readers, who like Gemma
Frisius and Erasmus Reinhold later became firm advocates of

1 Lynn Thorndike: History of Magic and Experimental Science, vol. V (Balti-
more, 1941), pp. 408-13.

2 Edward Rosen: Three Copernican Treatises (New York, 1939), p. in.

NEW CURRENTS IN THE SIXTEENTH CENTURY 55

the heliostatic system, awaited the publication of the whole work
with eager anticipation. In the preface to his book, dedicated to
Pope Paul III, Copernicus particularly mentions, as friends who
removed his reluctance to publish, Nicholas Schoenberg, Cardinal
of Capua and Tiedeman Giese, Bishop of Culm. While his
investigations thus received a measure of countenance at Rome,
it was Luther who was to speak of 'the fool who would overturn
the whole science of astronomy.' 1

Despite this, the new doctrine failed to secure adherents.
Favourable references to it are scarce throughout the sixteenth
century: most are couched in terms resembling Luther's. 2
Admittedly the book was difficult, written only for those who were
skilled geometers and experienced in astronomical calculation,
and it supported a proposition which had been condemned in
philosophy for two thousand years, and no astronomical advan-
tages even if they were genuine could vindicate it. If the
celebrated note by the Lutheran minister Osiandcr which,
unknown to Copernicus, declared that the tenets of the following
book were to be taken only as a mathematical hypothesis, a
calculating device, and not as truth, had any effect in warding
off official censure (which seems doubtful), it certainly did nothing
to weaken the general sentiment that speculation on the earth's
movement was foolish and futile. Those who are known to have
held the opposite view in the years 1543-60 can be numbered on
the fingers of one hand: Reinhold, who calculated the first set
of astronomical tables in accordance with Copernican theory;
Robert Recorde, the English mathematician; John Field and
John Dee, English astronomers; and Gemma Frisius of Louvain,
one of the most famous astronomers of the age. 3 There is nothing,
other than Copernicus' own book, that can be called an exposition
of the heliostatic hypothesis in the later sixteenth century. Until
after the condemnation of Giordano Bruno in 1600 Copernicus'
name was suppressed not by authority, but by indifference.

To understand this, it is necessary to understand in what
measure De Revolutionibus was revolutionary, and effected a
reform in astronomical thought. In the heliostatic principle, and

1 De Revolutionibus Orbium Coelestium (Nuremburg, 1543), sig. iii recto.

2 Dorothy Stimson: The Gradual Acceptance of the Copernican Hypothesis (New
York, 1917).

3 Gf. Grant McGolley: " An early friend of the Gopernican theory : Gemma
Frisius," Isis, vol. XXVI (1937), p. 322.

56 THE SCIENTIFIC REVOLUTION

in its necessary physical consequences, Copernicus opposed the
common sense of his age: in everything else he was conservative.
There was nothing in the method of his madness to arouse
contemporary interest. Moreover his madness took the form of a
familiar heresy: therefore again the whole theory could be lightly
dismissed. A whole stream of references proves that to suppose
that the sixteenth century ought to have reacted violently in
approval or condemnation of the book when it appeared is to
misunderstand a whole facet of medieval astronomy. That certain
of the ancients had supposed the earth to move was as well known
to the middle ages as Aristotle's powerful reasoning against their
contentions. 1 They found the question debated again by their
Arabic authorities. As a result, several scholars of the fourteenth
century exhibit a marked tolerance in their treatment of the idea
when commenting upon Aristotle, among them many members of
the " impetus" or experimentalist school, including William of
Ockham, Albert of Saxony, Jean Buridan, and Nicole Oresme.
Oresme, in his commentary on De caelo, denies that the stability
of the earth is a logical consequence of the movement of the skies:
from the analogy of a revolving wheel he shows that it is only
necessary in circular motion that an imaginary mathematical
point at the centre be at rest. Further he says that local (i.e.
relative) motion need not necessarily be referred to some fixed
point or body: rest is the privation of motion, and is in no way
involved in its definition. For instance, he says, there is imagined
to be outside the universe an infinite motionless space, and it is
possible that the whole universe is moving through this space in
a straight line. To declare the contrary is an article condemned
at Paris, yet this motion could not be considered to be relative to
any other fixed body. Suppose that the skies stood still for a day
and the earth moved: then everything would be as it was before. 2
In another place he gives his judgement, "under all correction,"
that it is possible to maintain and support the opinion that it is
the earth which is moved with a daily motion (axial rotation) and
not the sky, and further that it is impossible to prove the contrary
by any experiment ("experience"), or by any reasoning. This
was just what Galileo was to declare nearly three hundred years
later. Against his proposition Oresme quotes three arguments,

1 McColley: " The theory of the diurnal rotation of the earth," ibid. p. 392.

2 Medieval Studies, vol. IV, pp. 203-7.

NEW CURRENTS IN THE SIXTEENTH CENTURY 57

all*of which were to be directed against the Copernican hypothesis
in the sixteenth and seventeenth centuries. Firstly, the skies are
actually observed to revolve about their polar axis; secondly, if
the earth turned through the air from west to east, a great wind
would be felt constantly from the east; and thirdly a stone thrown
vertically upwards would not fall back at the place whence it was
thrown, but far to the west. Oresme has replies to all these objec-
tions. In answer to the first, he emphasizes the relativity of all
appearance of motion: a man seated in a boat gazing at another
boat cannot tell whether his own vessel is moving, or the other in
the opposite direction, but there is a prejudice in favour of the
stability of one's own immediate frame of reference. As for the
wind, the earth, water and air of the sublunary world all move
together, and so there is no wind other than those to which we are
accustomed. To the third objection Oresme replies that the stone
thrown up in the air is still carried along in the west-east direction
with the air itself, and with ' all the mass of the lower part of the
world which is moved in the daily movement.' It is not quite
clear what this last phrase meant to Oresme, but it holds an idea
of profound consequence. The stone falls back to the place whence
it came, as it would do if the earth were still, and Oresme points
out (again anticipating Galileo) that all the phenomena of motion
appear to be identical in a ship which is moving or a ship which
is at rest. As Oresme puts it, in less precise language, a movement
which is compounded of motions in two directions is not discern-
ible as such when the observer himself participates in one of
them.

Various theoretical or physical arguments against the rotation
of the earth anticipated by Oresme turn upon the idea that it
would be unnatural and out of place in the texture of natural
philosophy. This Oresme also denies. He points out that the
Aristotelean system attributes no movement to the earth as a
whole, though Aristotle himself declared that a single simple
motion was appropriate to each element so that the earth might
well turn in its place, as the heavens do, or as the element fire
does. Oresme agrees that if the earth turns it must possess a "mov-
ing virtue," but this it must have already, since displaced parts of
the earth return to it. To the criticism that the motion of a moving
earth would falsify astrology, he makes a most important riposte.
All conjunctions, oppositions and influences of the sky would take

I THE SCIENTIFIC REVOLUTION

lace as before, and the tables of the movements of the heavenly
Ddies and other books would be as true as they were before, only
would now be recognized that the daily rotation was apparent
[ the heavens, and real in the earth. It has often been alleged
iat Copernicus destroyed whatever scientific basis astrology
dght be supposed to have had. It was not so. The practice of
itrology has been entirely unaffected by it, just as it was (and is)
naffected by the fact that the "Houses" of the zodiac no longer
xrrespond with the constellations after which they were named
ying to the precession of the equinoxes. The predictions of
dicial astrology turn upon the configuration of the skies at any
oment: they are unconcerned with the mechanics of the motions
i which those configurations are produced. And Oresme's dis-
aimer was actually re-echoed in the sixteenth century. To quote
horndike: 'It is a historic fact that the Copernican system was
*st publicly announced, if not precisely under astrological aus-
ces at least to an astrological accompaniment and that such
unifying the future was for long after associated with it in men's
inds.' 1 Two of the leading exponents of the new scheme,
heticus and Reinhold, had no doubts of the virtues of judicial
trology, and Copernicus himself never declared against it.
The authority of Scripture was constantly brought to bear in
vour of the geostatic doctrine, but even this does not silence
resme. Joshua's miracle can be interpreted in the sense that the
n apparently stood still, while the earth was really halted. He seizes
Don the point that if the earth be supposed to move from west to
ist, all the celestial motions will take place in the same sense,
hich he thinks increases the harmony of the system. Also it would
ace the habitable part of the globe on the right or noble side of
.e earth. Again, it will be found that in this way the celestial
)dies which are farthest from the centre will make their circuits
ore slowly (instead of more quickly as in the geostatic theory)
hich seems reasonable; and the principle that God and Nature
) nothing in vain will be more faithfully observed; for example,
iere will be no necessity for a ninth sphere. After all this potent
asoning has been marshalled against the conventional doctrine,
comes as an anticlimax to find Oresme returning to it. c Never-
teless/ he concludes, 'all maintain, and I believe, that the
ravens are thus moved, and the earth not: "for God fixed the orb
1 Op. cit., vol. V, p. 414.

NEW CURRENTS IN THE SIXTEENTH CENTURY 59

of the earth, which shall not be moved," 1 notwithstanding the
reasons to the contrary, for these are not conclusive arguments.
But considering all that has been said, one might believe from this
that the earth is moved, and the sky not, and there is nothing
obviously to the contrary, which seems prima facie as much, or
more, against natural reason as are the articles of our faith.' 2

One might think that the famous cosmological debate of the
seventeenth century had been rehearsed in the fourteenth! 3 There
were, indeed, subtle changes in the background in which Galileo
set the same, or similar, arguments; but if Oresme had been dili-
gently followed the stability of the earth could hardly have been
defended save as an act of faith, not by reason and observation.
The diurnal revolution was again discussed in the fifteenth century,
when it was upheld by Nicholas of Cusa, and in the early sixteenth
before the appearance of De Revolutionibus. This diurnal revolution,
however, and the long argument in favour of it by Oresme, must
be clearly distinguished from the theory of the annual motion of
the earth which was developed by Copernicus, not to speak of the
third motion which he attributed to it to account for the parallel-
ism of its axis in space. A heliostatic theory imposed a far more
severe strain on intellectual adaptability than a geocentric theory
which admitted the diurnal rotation. To have conceived the
annual motion is Copernicus' chief claim to originality, and it was
the annual motion which condemned the Copernican hypothesis
both in the eyes of the majority, and also in the eyes of the Church
because of its heretical consequences.

It can hardly be imagined that the earlier discussion of the
diurnal motion was unknown to Copernicus, and he must have
considered its adoption as the first step to a reform of astronomy
a step which unfortunately did little to solve the problem of
planetary motions and the multiplicity of spheres. It is not unlikely
that his conception of the earth as of the same kind as the heavenly
bodies, and therefore equally suited "by nature" to planetary
motion (being spherical for instance), is an extrapolation from the
reasoning used (by Oresme among others) to support the idea
that the earth is "by nature" suited to axial rotation. Certainly

1 Psalm XCIII, i : 'The world also is stablished, that it cannot be moved.'

2 Medieval Studies, vol. V, pp. 271-9.

3 As was long ago pointed out, with too great emphasis and some misunder-
standing, by Duhem in Revue Generate des Sciences Pures et Applique'es, vol. XX

6o THE SCIENTIFIC REVOLUTION

Copernicus had to abandon the idea of "one element, one motion,"
but this had been virtually abandoned by Oresme. Not, however,
until Copernicus had begun to consider this second, annual
motion could he have begun to see the possibility of results im-
portant to mathematical astronomy in this the middle ages had
done little or nothing to help him. Even Oresme's very correct
remarks on the illusions of relative motion only refer to a geo-
centric system, though they were equally valid as Copernicus
applied them to the heliocentric. Unfortunately, the steps by
which Copernicus proceeded from the first to the second motion,
if that was his course, are totally unrecorded. He relates simply, in
the Preface to his book,

Nothing urged me to think out some other way of calculating the
motions of the spheres of the world but the fact that, as I knew,
mathematicians did not agree among themselves in these researches.
For in the first place they are so far uncertain of the motion of the
Sun and Moon that they cannot observe and demonstrate the
constant magnitude of the tropical year.

Then he goes on to say that there was no consistency of principle
in the devices that had been used some had employed the simple
homocentric spheres, others eccentric spheres, and yet others epi-
cyclic systems. They had passed over the symmetry of the universe,
as though one should put together a body from different members
in no way corresponding to one another, so that the result would
be rather a monster than a man. This uncertainty, he thought,
must prove that some mistake had been made, otherwise every-
thing would have been verified beyond doubt.

Then when I pondered over this uncertainty of traditional mathe-
matics in the ordering of the motions of the spheres of the orb, I was
disappointed to find that no more reliable explanation of the mechan-
ism of the universe, founded on our account by the best and most
regular Artificer of all, was established by the philosophers who have
so exquisitely investigated other minute details concerning the orb.
For this reason I took up the task of re-reading the books of all the
philosophers which I could procure, exploring whether any one had
supposed the motion of the spheres of the world to be different from
those adopted by the academic mathematicians.

Coming across Greek theories which attributed both an axial
and a progressive rotation to the earth, and following the example

NEW CURRENTS IN THE SIXTEENTH CENTURY 61

of his predecessors who had not scrupled to imagine the circles
they required to "save the phenomena," he thought he might
himself be allowed to try whether, by allowing the earth to move,
more conclusive demonstrations of the rotation of the spheres
might be found. And he discovered that if, as he puts it, the
motions of the planets were calculated according to their own
revolutions, with allowance for the circulatory motion of the
earth, then the phenomena of each worked out duly. Even more
important, the orders and sizes of all the celestial bodies, spheres
and even the heaven itself, were so harmonized that nothing could
be transposed in any detail without causing confusion throughout
the universe (Fig. 4). 1

Copernicus was a theoretical astronomer of genius and origin-
ality. He must have noted the suspicious reversal of the constants
of epicycle and deferent between the upper and lower planets: he
must have perceived the unaccountable intervention of the sun's
period of revolution in the calculations for each of the five planets.
Believing that the assumption of an annual motion in the earth
was no more wild than the assumption of a diurnal revolution, he
was capable of taking the celestial machinery to pieces and re-
assembling it in accordance with a different pattern. Working
from irrefutable observations, he proved that the new pattern
gave as good results as the old.

It could hardly give much better results because the parts of the
machine of the world as revised by Copernicus were essentially
of the same dimensions as before, though arranged in a different
order. His determining observations were those of the Greek
astronomers, Timocharis, Hipparchus, Ptolemy, supplemented by
the work of their Moslem successors Arzachel, al-Battani and
Thabit, and his own measurements, few in number and mostly
made about 1515. Sometimes, as in his determination of the length
of the sidereal year, his result was less accurate than an earlier
one (that of Thabit). Copernicus admitted most of the variations
or anomalies which had been introduced to account for the ap-
parent changes in some constants (for example, the variation in the
obliquity of the ecliptic causing an oscillation which was correctly
explained by Copernicus for the first time; and various com-
plexities in the motion of the sun, which he transferred, of course,

1 De Revolutionibus, Preface. The English version in Stimson, op. cit., does not
always make Copernicus' thought fully intelligible.

MOON

Mercury //brotes on the
d/am.(380) of the ep/cyc/e
vftha period of 183 J.

FJG. 4. The Copernican System of the Universe, (a) General arrangement,
(b) Lunar theory, (c) The inferior planets, (d) The Earth. The dimensions
are to scale unless otherwise indicated. (</=days, e~ eccentricity,
r radius.)

NEW CURRENTS IN THE SIXTEENTH CENTURY 63

to the earth). In addition he introduced new elaborations; some,
like the motion of the apse-line of the earth's orbit already sus-
pected by al-Battani, were real and necessary, others, like the
"third motion" of the earth were superfluous or due to the colla-
tion of inaccurate observations, such as the variation which he
supposed to occur in the eccentricity of the earth's circle about the
sun. In fact, mathematically speaking, Copernicus did not create
a new astronomy in the sense of isolating and measuring every
celestial motion afresh; what he did do was to reinterpret the
Ptolemaic structure from the heliocentric point of view, adding
such refinements as he believed to be necessary. His remark to
Rheticus, " If only I can be correct to ten minutes of arc, I shall
be no less elated than Pythagoras is said to have been when he
discovered the law of the right-angled triangle," shows that his
ambition in the matter of precision was very limited. And it proved
in fact that when the first astronomical tables were calculated in
accordance with the new hypothesis, they were little if at all
superior to those which had preceded them. 1

Astronomy remained the doctrine of the sphere, and the imagery
drawn from it which is so prominent in sixteenth-century imagi-
native writing was hardly less appropriate to the new theory than
to the old. Having rejected the prime assumption of cosmology,
Copernicus had no occasion to challenge others. His geometry of
the heavens is still that of rolling orbs, save that the earth has re-
placed the sun in the third sphere. He preserved the fundamental
division between the sublunary region and the celestial, between
the natural laws of earth and sky. He insisted even more severely
than Ptolemy upon the inviolable perfection of circular motion,
repeated again the proof that the alternative methods of eccentric
sphere and defercnt-with-epicycle are identical in their results,
and reduced all motions to combinations of these two forms. The
reality of the crystalline spheres was unquestioned. Apart from
his one great innovation, all Copernicus' astronomical thought
is thoroughly medieval. Truly he reformed the medieval universe,
because he brought its pattern into a new order, but he introduced
no new doctrine concerning its composition or the deeper logic of
its various appearances.

What, therefore, were the merits of the new astronomical
system? What arguments could be adduced to show that in this

1 Cf. Appendix B.

64 THE SCIENTIFIC REVOLUTION

complicated dance of relative movements the stability of the sun
was more real than the stability of the earth? Copernicus dealt
with these two questions as one, but as will be seen they require
separate answers. In the first place, the pattern of celestial motion
described by Copernicus and the methods used to work it out in
detail had several distinct advantages. On the whole, the devices
were rather more economically displayed, though this is a feature
whose importance has been exaggerated and, since the observer's
point of view is geocentric in any case, the geocentric conception
had some advantages in the ease of handling. The fixed stars were
fixed indeed, and with the whole system no more than a point in
comparison with the size of their sphere as Copernicus realized
from the fact that they revealed no annual parallax the problem
of predictive astronomy was properly limited to the planetary
bodies. These now recovered their independence without the
intervention of any extraneous factor in their revolutions, and the
main pattern of the planetary mechanisms could now be made
uniform for all five. Moreover, Copernicus was able to declare,
for the first time, the relative sizes of the planetary spheres, though
because he followed Ptolemy's estimate of the earth's distance
from the sun the whole system was far too small. 1 As the lower
planets, Venus and Mercury, were now placed between the earth
and the centre of the universe the peculiarities of their motions
and their special relation to the sun were explained : clearly they
could never be observed at a greater distance from it than the
lengths of the radii of their spheres. The "stations" and retro-
grade motion of the planets, which had favoured the epicycle
theory, could now be seen as pure illusions caused by the addition
and subtraction of the earth's movement and the planets' relative
to the unchanging background of the starry sphere. The equants
and uneven revolutions of the Ptolemaic system were removed and
the principle of perfect circular motion observed more purely.
Again, the fluctuations in the apparent size of the heavenly bodies
(as the earth approaches or recedes from them) required by the
Copernican geometry corresponded more closely to observation
than those required by the Ptolemaic, particularly in the orbit of
the moon, which Ptolemy supposed to vary by a factor of nearly
two. Most of the advantages that can be obtained by supposing

1 About 5 per cent, of the true value: the dimensions are derived from the
Ptolemaic planetary constants (see above, p. 1 6) .

NEW CURRENTS IN THE SIXTEENTH CENTURY 65

the sun to lie near the centre of all the orbits were actually worked
out by Copernicus in his calculations, which thus removed some
redundancies, and threw light on many obscure points.

On the other hand, it could not logically be claimed that these
advantages proved the sun to be at rest and the earth moving.
An interesting variant of the conventional geocentric theory,
described by Martianus Capella in the fifth century A.D. made the
lower planets revolve about the sun, and there are references to
the same idea to prove it was not forgotten in the middle ages. 1
A natural step beyond this was to suppose all the planets to revolve
around the sun, while the sun turns about the fixed earth, and it
was taken by the great Danish practical astronomer Tycho Brahe
towards the end of the sixteenth century. Mathematically and
observationally the Tychonic system and the Copernican are
indistinguishable, in fact the Tychonic is an exact representation
(in Copernican terms) of what the observer actually sees with
his instruments. Whatever advantages the Copernican pattern of
motion had over the Ptolemaic could equally well be claimed for
Tycho's defence of geocentricity. History has not been kind to
Tycho's hypothesis, and it has seen (with Galileo) the great
cosmological debate as being conducted between Ptolemy and
Copernicus. It is a misleading view. Tycho had enormous
authority, and his system was quoted as the third possible hypo-
thesis until late in the seventeenth century. It reconciled the
combatants without compromising any essential issue; it took all
that was scientifically sound from Copernicus, and for the rest
clung to common sense. If we would understand the power of the
geocentric notion over men's minds we must give it its best
defence, not its worst, and this Galileo naturally did not do. To
dismiss Tycho Brahe's contribution as a rather pointless and
unnecessary obstacle to the advance of truth, or as a conservative
aberration on the part of the creator of modern positional
astronomy, is to misrepresent entirely the scientific situation and
the scientific mind of the sixteenth century. Its importance is
that Tycho pointed out, with absolute justice, that there was no
particle of evidence to be derived from astronomy which could
decide whether the earth moved or not, whereas there was much
good evidence of another kind to lead one to conclude that the

1 Heraclides pf Pontus taught this system, with the addition of the diurnal
rotation of the earth; it is mentioned approvingly by Copernicus.

5

66 THE SCIENTIFIC REVOLUTION

earth does not move- Therefore, while the ingenuity of the
Copernican geometry of the heavens is to be admired, and was in
fact admired by many who opposed his chief premiss, it must be
recognized that for the sixteenth century this was irrelevant to
the main issue, which turned upon different considerations
concerning the earth's mobility.

Taken by themselves, and omitting the mathematical improve-
ments on Ptolemy which are quite neutral in their effect,
Copernicus' arguments in favour of the moving earth were
scarcely compelling in their contemporary scientific setting. Nor
were they very novel. He answered the traditional objections much
as Orcsme did, developing the thesis that the globe is naturally
fitted for circular motion. The earth is absolutely round; it is the
property of a sphere to revolve in a circle, expressing its form in
its motion; ergo the earth revolves. By this reasoning the movement
of the earth is natural, not violent: why then should it fly to
pieces, as Ptolemy supposed? It would rather be much more likely
that the almost infinitely distant sphere of the fixed stars should
disrupt under its own velocity, if it were forced to turn round once
in twenty-four hours, than that the earth should do so. Air and
water move with the earth, so terrestrial phenomena are unaffected.
The absence of measurable stellar parallax is explained by the
immense distance of the stars, and it is argued that it is easier to
believe that the earth moves, than that the whole heaven moves
about it. If, as Aristotle seemed to maintain, the condition of rest
and permanence is more noble and divine than that of change
and instability, Copernicus replies that rest should in that case be
attributed to the whole cosmos, and not to the earth alone. In
discussing the effect of terrestrial motion upon the doctrine of
gravity and levity, he enunciates an idea of surpassing fertility:

Gravity is nothing but a certain natural appetite conferred upon the
parts by the divine providence of the maker of all things, so that they
should come together in a unity and as a whole in adopting a spheri-
cal form. It is credible that this property exists even in the Sun,
Moon, and other planets, ensuring the unchanging sphericity which
we see, and nonetheless they perform their revolutions in many
ways.

Once more Copernicus has emphasized the fact that the earth is
of the same kind as the heavenly bodies; and if it is, as he thinks,
a planet itself, then it must have a progressive circulatory motion

NEW CURRENTS IN THE SIXTEENTH CENTURY 67

as well as axial rotation. Finally Copernicus has this glowing
passage upon the sun:

In the very centre of all the Sun resides. For who would place this
lamp in another or better place within this most beautiful temple,
than where it can illuminate the whole at once? Even so, not inaptly,
some have called it the light, mind, or the ruler of the universe. Thus
indeed, as though seated on a throne, the Sun governs the circum-
gyrating family of planets.

It is an obvious principle of logic that the unknown cannot be
demonstrated from the unknown. Measured by this standard,
Copernicus' arguments in favour of helioccntricity are illogical.
His aim was to prove that the movement of the earth did not
conflict with the principles of physics, which of course meant
Aristotelean physics. But in so doing he interprets these principles
in a sense different from that of Aristotle, and that understood by
most of his own contemporaries. He is forced to allege that
gravity, a tendency to cohere, is a universal attribute of spherical
bodies. He questions whether rest is inevitable to the elemental
earth, and motion to the weightless heaven. Contemporaries can
hardly be blamed if it seemed to them that physics had been
distorted to fit a newly imagined astronomical theory. Copernicus
was not a natural philosopher but an applied mathematician, and
in historical perspective it would have been no weakness in him
if he had failed to subscribe to contemporary physical notions.
In the discussion of cosmological systems two possibilities were
open: either a heliostatic system could be adopted, in which case
Aristotelean physics was palpably false, and it would be necessary
to replace it by a new intellectual framework: or alternatively the
traditional physics might be held to be true, in which case a
geostatic cosmology was enforced. To attempt, as Copernicus did,
to reconcile traditional physics and a heliostatic cosmology was to
choose a course open to fatal criticisms. It was easy enough for
the opponents of the Copernican hypothesis to show that the
reconciliation could not be effected, and that its author's justifica-
tion of it in terms of contemporary doctrine was wholly spurious.
The new astronomy demanded a new physics; and this was
ultimately to prove of great advantage to science. But a new
physics was not Copernicus' creation, and therefore his appeal to
natural philosophy for tolerance of terrestrial motion was an appeal
to the unknown; his arguments could carry no conviction because

68 THE SCIENTIFIC REVOLUTION

they were not derived from the physics in which men believed,
but to an unsubstantiated adaptation of it. In De Caelo et Mundo
Aristotle had welded a unity of explanation and, so long as its
fundamental concepts of motion remained unchanged, this unity
was not to be broken.

Ultimately the decision in controversies upon cosmological
matters which early astronomy was incompetent to decide unaided
turned upon physical considerations, and here Copernicus, with
his thoughts still modelled on Aristotle, barely hinted at a new
approach. Two things make it difficult to view his work dispassion-
ately. In the sheer majesty of its mathematical achievement De
Revolutionibus is traditional, but it is a grandly conceived and
meticulously executed demonstration of the comprehensive powers
of a new hypothesis. To recalculate every motion and every
anomaly from the crude observations in accordance with an en-
tirely original pattern was a task never previously attempted.
Secondly, it is impossible to escape the compelling power of
Copernicus' intuition. Like many other original thinkers, he
uttered the truth for the wrong reasons. His work did not form the
basis of modern positional astronomy, and within a hundred years
the doctrine of the spheres no longer played a part in serious
science; and yet his major premiss was essential to the develop-
ment of both terrestrial and celestial mechanics. His generalship
was medieval, but the fruition of his victory lay in the future.
Lesser men might debate the logic of solar and terrestrial motions
while an imaginative mind could fasten upon the harmony, the
irresistible neatness and dexterity of the Copernican pattern.
Galileo relates that he first relented towards Copernicus when he
found that the Copernicans were usually well informed in their
science, in contrast to their opponents who knew only stock argu-
ments. He read the book and was converted. Men of power and
vision could learn that the new system, though incapable of
rigorous proof in detail, contained a transforming conception.
The constitution of the fertile line of advance at any particular
moment is not always clear in scientific investigation; Galileo and
Kepler found it in the Copernican hypothesis. In their work
Copernicus' intuition that the earth is a planet it can hardly be
called a reasoned judgement was justified.

Even a brief survey of the total scientific activity of the sixteenth
century would require a volume to itself. Here it must be charac-

NEW CURRENTS IN THE SIXTEENTH CENTURY 69

K**
terized in a few sentences. (The scientific renaissance caused no

sudden break in the course ot academic studies, nor did it suddenly
enable a "scientific method" of investigation to prove its value.
Most of the problems that were discussed belong clearly in a
medieval context, and with a few exceptions the procedure and
style of argument conformed to familiar patterns. Experimental
science was not born in the sixteenth century. On the other hand,
the study of pure mathematics flourished exceedingly, and the use
of mathematical methods in science was successfully extended. 1
Arithmetics were published in the vernacular languages and print-
ing also helped to spread and standardize mathematical symbols.
The Greek geometers were edited and their work thoroughly
assimilated. Great advances were made in the formulation and
solution of algebraic equations, and in trigonometry, which in its
modern form was wholly unknown to the middle ages. The calcu-
lations involved in astronomy and in practical arts such as naviga-
tion, cartography, mining, surveying, and " shooting with great
ordnance," became easily practicable, and books instructing in
these various forms of applied geometry appeared in considerable
numbers. When these arts were mathematized, the practitioner
who had given up rule-of-thumb methods required instruments
for the measurement of angles and distances, and the rise of an
instrument-making craft of importance can be traced somewhat
earlier than the middle of the century. In many places it was
closely allied with the domestic clock- and watch-manufacture
which began at about the same time.)

Opinions concerning the pseudo-sciences, astrology and al-
chemy, show no remarkable change during the sixteenth century.
As in earlier times, there were disputes over the merits and sanction
of judicial astrology, but as the general sentiment was strongly
favourable there was no sign yet that the dependance of astro-
nomy on its mother-science was almost concluded. There were
no sixteenth-century alchemists whose authority stood so high as
that of the medieval Latin writer Geber, or the early seventeenth-
century adept who called himself Basil Valentine, 2 but the mystical

1 D. E. Smith: History of Mathematics (Boston, 1923), vol. I, pp. 292-350.

2 The former of these was traditionally an Arabic author, but it now seems
that the works ascribed to him were not composed by the real Jabir (an eighth-
century physician), though they were put together in Latin from Arabist
sources, probably in the late thirteenth century. To the latter also a false
antiquity was traditionally credited.

70 THE SCIENTIFIC REVOLUTION

attitude to chemical operations was powerfully reinforced by the
personality of Paracelsus, though he was not an alchemist in the
conventional sense. Under his influence, strengthened by em-
pirical discoveries such as that of the specific action of mercury
against the "new" disease syphilis (first reported c. 1492-1500),
inorganic chemical remedies were gradually introduced into
medical practice, against strong opposition from the Galenists. 1
The use of chemical compounds in medicine stimulated a more
rational interest in their preparation and properties than that of
the alchemists, but even more important, perhaps, in promoting
a purely empirical attitude to material transformations among
educated men was a new kind of book describing industrial opera-
tions in a practical manner. Works on smelting and assaying were
circulating early in the century; the early masterpieces of tech-
nological description, Biringuccio's Pirotechnia and Agricola's De
re Metallica, appeared in 1540 and 1556 respectively. Mining and
mineralogy, smelting and casting, the extraction of saltpetre and
the manufacture of gunpowder, the making of glass and mineral
acids, the purification of mercury and the precious metals, were
here treated in detail, systematically, and from a thorough know-
ledge of actual practice. Somewhat later similar works on machin-
ery for lifting, pumping, sawing, textile manufacture etc., in a
slightly less realistic vein, likewise did much to place engineering
on a sound basis of description.

In medicine, it is probable that the education of physicians and
surgeons improved considerably, owing to the new accessibility
of the Greek authorities, and to the new anatomical tradition
founded by Vesalius and his contemporaries. There were many
serious problems: war, which has always stimulated the progress
of surgery, presented the new horror of gunshot wounds, and the
rapid growth of towns favoured the spread of disease. Public
health was less a matter of public concern in the sixteenth-century
city and state than it had been in the medieval. While, broadly
speaking, there was no great revolution in the theory and practice
of medicine, there were many advances in detail. Jesuit's bark
introduced from Peru contained quinine as a specific against the
recurring fever of malaria. The pharmacopoeia was standardized

1 The origin of syphilis has been exhaustively investigated. Recent opinion
seems to be against the view that it was introduced into Europe from the
Americas.

NEW CURRENTS IN THE SIXTEENTH CENTURY 71

first in Italy and Germany, not in England until the London
Pharmacopoeia was issued in 1618. Most dramatic of all perhaps
was the influence of the French surgeon, Ambroise Pare, who led
the way in abandoning the use of the fiery cautery, previously
applied to all gunshot wounds (which were believed to be en-
venomed) as well as in cases of amputation. Although Pare still
modelled his practice broadly on that of the Ckirurgia of his great
fourteenth-century countryman, Guy de Chauliac, (which was
itself often reprinted in the sixteenth century) his writings did
much to raise the prestige and skill of the surgeon. Guy, who
himself leaned heavily upon Galen and Avicenna, had taught
that the ' surgeon who is ignorant of anatomy carves the human
body as a blind man carves wood,' and Pare reinforced this
truth by making free use of Vesalius' De Fabrica.

The sixteenth century also saw the current of realism at work
in natural history. Of this something more must be said later
(Chapter X). The best work was still compilatory, and encyclo-
paedic on the vastest scale. It was devoted entirely to the superficial
characteristics and habits of plants and animals, and botany
remained an adjunct of medicine rather than a discipline in its
own right, but much rubbish was purged from the medieval garner
of fact and legend. The humanistic naturalists used a scissors-and-
paste technique upon the authentic texts of Aristotle or Pliny,
and if the range of their reading and collation was wide and
discursive, some of them show for the first time a real eye for
genuine observation, and painstaking endeavour to confirm at
least the external features of their subjects. The first monographs
in natural history have an authentic realism and attention to
specific detail which are entirely new.

On the whole, however, the scientific spirit of the century
developed naturally from the work and progress of the later middle
ages. A hasty reference to the output of the printing-press may
act as a guide to the nature of contemporary taste and estimations;
the most sought after and respected books were still those com-
posed long before the invention of printing. 1 Neither the library,
nor the academic training, of the medieval world were suddenly
outmoded by a vast efflux of novel aspirations and methods. The
mythical " renaissance man" of the early sixteenth century,
though his tastes might be more hedonistic than those of his

1 See Appendix C.

72 THE SCIENTIFIC REVOLUTION

forefathers, though he might be more enamoured of the powers
and potentialities of this world and less regardful of the next, was
still largely limited in his science to the achievements of the
medieval renaissance: his very classicism only attached him more
deeply to the same roots of western learning. The cosmos of
Shakespeare is the cosmos of Dante, save that the former was a far
less philosophical poet: the Fables of Bartholomew, the complex
vocabulary of astrology and alchemy, and the doctrine of the four
humours still enclosed the framework of science which most men
knew. It was not the experimentally minded Dr. William Gilbert,
with his glass rods, magnetic needles and other trivia, who was
most honoured at the court of Elizabeth, but Dr. John Dee, the
astrologer and magus, holding, as it seemed, the keys to far graver
mysteries.

CHAPTER III
THE ATTACK ON TRADITION: MECHANICS

UNTIL the end of the sixteenth century scientific innovations
were put forward with deference and almost a sense of
humility. A great deal of the best work of this period was
entirely non-polemical: to this class belong the first stages of the
Vesalian tradition in anatomy, and much purely descriptive
writing on natural history, mineralogy and chemistry. The works
of Agricola or Rondelet were excellent contributions to science
as positive knowledge, but they created no ferment of new ideas.
It is true that Paracelsus is supposed to have burnt the books of the
masters before his inaugural lecture at Basel in 1527, and that he
declaimed against official medicine:

I will not defend my monarchy with empty talk but with arcana. And
I do not take my medicines from the apothecaries. Their shops are
but foul kitchens from, which comes nothing but foul broths. . . .
Every little hair on my neck knows more than you and all your
scribes, and my shoebuckles are more learned than your Galen and
Avicenna, and my beard has more experience than all your high
colleagues. 1

Paracelsus, whatever his other merits, was a picturesque ranter
and it is futile to portray him as a herald of the scientific revolu-
tion. The texture of his thought in which it is difficult to see any
precise pattern was woven upon a mystical conception of nature
entirely alien to that of natural science. 2 Medicine was indeed
torn by faction: the Arabists and the Humanists, the Paracelsians
and the anti-Paracelsians, the cauterizers and the non-cauterizers
sharpened their wits in vituperative debate as they contended

1 Paracelsus: Selected Writings (edited with an introduction by Jolande
Jacobi), (London, 1951), p. 79.

2 As, for instance, the perennial fallacy that the virtues of herbs are indi-
cated by their structure. * Behold the Satyrian root, is it not formed like the
male organs? Accordingly magic discovered it and revealed that it can restore
a man's virility. . . . And then we have the thistle: do not its leaves prick like
needles? Thanks to this sign, the art of magic discovered that there is no better
herb against internal pricking . . .' etc. (ibid., p. 186).

73

74 THE SCIENTIFIC REVOLUTION

for supremacy within the profession, without aiding the advance-
ment of knowledge. Natural philosophy and natural history were
not similarly divided by quarrels arousing professional passion,
though inevitably personal jealousies were not lacking. More
typical of the relations between old and new were Copernicus
taking leave to speculate afresh on the revolving spheres, Vesalius
adapting his text to follow Galen. As yet, content if they could
show that new ideas were no worse than old ones, men were far
from asserting that the House of Learning was a crazy, rambling
warren that needed to be pulled down and reconstructed. With
the exception of Paracelsus, no scandalous defiance of authority
had been noised abroad; and this was partly because the shape of
authority, the policy and content of conservatism, were themselves
unsettled at this nascent stage of modern science.

When the famous crisis was reached in 161516, it had already
been foreshadowed in the tragedy of Giordano Bruno's life which
must be mentioned in its proper place. Bruno was no scientist,
and his impact, his historical importance, his ultimate influence
upon the development of non-scientific attitudes to science, were
all the more startling for that reason. It must not be imagined
that the ways of the ordinary, common-sensible religious man and
of the critical natural scientist were bound to deviate at the first
novelty, or that the sixteenth century was afflicted by the same
opposition of loyalties and criteria of truth that troubled the
nineteenth. On the contrary, every flaw in the conventional
account of nature was examined not in the hope that it would
profit one philosophy against another, but in the belief that its
examination would advance truth, and that in truth all matters
of importance were ultimately reconcilable. The view that a
man's access to truth might be measured by the nature of his
ideas on celestial mathematics was not known to the sixteenth
century. Copernicus' narrow vision had embraced no more than
the validity of a single hypothesis: it was with the wider philo-
sophical perspective of Bruno, and the wider scientific range of
Galileo, that iconoclasm assumed a massive, threatening character.
Disputes among mathematicians, astrologers or physicians could
be tolerated (these things were not suddenly born at the time of
the renaissance) but criticisms shaking the roots of philosophy
had to be repelled. It was not simply a question of the liaison
between Aristotle and religious doctrine, nor was Catholicism the

THE ATTACK ON TRADITION: MECHANICS 75

only opponent of innovation. 1 The new scientific philosophy of
the early seventeenth century, speaking with a confident voice
that demanded credence, met sheer mental inertia and the weight
of academic omniscience. Men resent admitting that they have
given their lives blindly to the defence of absurdities, and it was a
new generation, not similarly committed, that devoted itself to
the prosecution of Galilean science.

Galileo's greatest fame is as an astronomer, yet in intellectual
quality and weight his one treatise on mechanics almost outweighs
all the rest of his writings. Although his book on cosmology
became notorious, and had a more general public influence, it
had no comparable effect upon the future development of scientific
astronomy, for its polemics were suited only to its own age. The
contradiction here is more apparent than genuine. Though
formally divided between two branches, Galileo's creative activity
in science was a unity, not twofold: it was a unity in laying down
revised principles of procedure in science, and again in its specific
exemplification of these principles, since Galileo saw that the
science of motion and the just appraisal of the results of observa-
tional astronomy were the twin keys to an understanding of the
universe. This is not to say that his comparatively minor (though
in themselves major) researches, into thermometry, the properties
of pendulums, the grinding of lenses, the strength of materials,
the theory of the tides or the measurement of longitude at sea were
not conducted with the same zest for knowledge, or that they were
either irrelevant or auxiliary to his main achievement. Each one
of his minor discoveries would have been notable in a lesser man.
Each has its important place close to the origins of modern
physical science. But Galileo's physical experimentation, like his
turning of the telescope to the heavens, was original and fecund
only in the sense that it was initiatory. Other men took up his
experiments, and even drew more valuable conclusions from them
than Galileo had done, by following and expanding his methods;
and while the initiation of a new kind of scientific activity is itself
an achievement of the first order, it is not of the same dignity
as the induction of fundamental principles which henceforth

1 In the first half of the seventeenth century the " new philosophy" advanced
most rapidly in two Catholic countries, Italy and France. Criticism of its
principal tenets was no less forceful among Protestants (e.g. Francis Bacon).
Cartesian science was very rapidly adopted by men of orthodox religion in
France.

76 THE SCIENTIFIC REVOLUTION

dominate a whole field of science. Besides fulfilling this function
in dynamics, Galileo demonstrated the connection between its
principles, when properly understood, and the disputed points of
cosmology.

Unlike his predecessors Galileo consciously assumed the attitude
of a publicist and a partisan. Writing more often in his native
language than in Latin (for Galileo was one of those who led the
way in abandoning for science the official language of philosophy),
he shaped his arguments to a broad audience. His dialogues were
lively, his irony biting, and he did not scruple to make a merely
debating point. Zealously he magnified the weaknesses of con-
ventional science in order to turn it to ridicule. Almost alone
among the ancients the experimenter and mathematician
Archimedes was singled out for Galileo's commendation; Aristotle
he treated almost as an ignoramus, as though the subtlety and
intricacy of that intellect, preventing vision of the simple truth,
had composed fantastic webs of improbability and artificiality.
He had no doubt at all that the modern way was infinitely superior
to the ancient, and hardly mentioned any contention of the
Peripatetics that he was not prepared to deny. This habit of
opposing conventional ideas was not, apparently, a product of
Galileo's maturity nor of his great discoveries. Rather the critical
attitude which stands out even in his juvenilia was the source of
his original ideas. Born in 1564, by 1589 Galileo was already a
teaching member of the University of Pisa, where he attracted
the attention of the Grand Duke of Tuscany. Two of the most
famous stories belong to these Pisan years: here he observed the
equality in time of the swinging cathedral lamps, and carried out
(as his first biographer relates) the famous experiment of dropping
weights from the Leaning Tower. 1 Unlike most academics of the
time, Galileo remained a layman. The resentment aroused among
his colleagues by his criticisms of Aristotle prompted his removal
in 1592 to Padua, within the anti-clerical Venetian state, where
there was a long tradition of freedom in scientific thought and
where anti-scholastic opinions, if not exactly encouraged, were
at least tolerated. At Padua Galileo studied mechanics, constructed

1 The experiment from the Leaning Tower, told in glorification of his
master by Viviani, has been rejected by many scholars as lacking support in
contemporary documents. At any rate Galileo was not the first to subject
Aristotle's dynamics to this particular test.

THE ATTACK ON TRADITION: MECHANICS 77

his first telescope, and began his long battle on behalf of the
Copernican system. After his growing fame had brought about his
recall to Florence, under the special patronage of the Grand Duke
and with an appointment at Pisa (1610), Galileo was particularly
warned to avoid utterances having a theological implication.
From 1609 to 1633 he was immersed in his astronomical observa-
tions and the polemics they provoked; then after the publication
of the Dialogues on the Two Chief Systems of the World (1632) there
followed his trial and recantation: yet having been condemned to
silence, Galileo published his greatest work at Leiden in 1638.
The significance of his summons to Rome is easily exaggerated.
Galileo did not compel the Roman Church to condemn Coper-
nican astronomy: this intervention in scientific discussion had
already taken place decisively with the decree of 1616, and was a
natural consequence of the condemnation of Bruno. The only
interest in the trial concerns the nature of the judicial process,
which is not impeccably transparent; but though Galileo may
not have broken a private pledge, he had certainly contravened
a general order. 1 Good Catholics were placed in a false position
for two centuries by the decree and Galileo's trial under it, without
these preventing excellent work in practical astronomy in Italy,
or the uninhibited development of other new studies there. Even
the Copernican Alfonso Borrelli was able to make his suggestive
contribution to celestial mechanics (1660) by means of an
ingenious quibble. 2

A reading of the Mathematical Discourses and Demonstrations
concerning Two New Sciences (1638) does not, however, give a true
picture of the revolution in dynamics as Galileo effected it, any
more than the earlier series of Dialogues can now be considered
as a balanced statement of the respective merits of the two
cosmologies. In his book Galileo the polemicist is in full cry after
the absurdities of Aristotelean physics, but in fact it is very

1 However obvious this may now seem, it was not so to the ecclesiastical
censors who affixed the imprimatur to the Dialogues in 1632.

2 The decree distinguished between the annual revolution of the earth,
* utterly heretical because contrary to Holy Scripture,' and the diurnal
rotation, * philosophically foolish.' One of its more curious results, as I learn
from Dr. Joseph Needham, was that Chinese astronomers, being instructed by
Jesuit missionaries, remained ignorant of the Gopernican theory until the late
eighteenth century. Borelli observed its letter by overtly limiting to Jupiter
and its satellites a discussion of planetary motions which he obviously intended
to apply to the earth and moon.

78 THE SCIENTIFIC REVOLUTION

likely that Galileo was never an Aristotelean physicist in the true
sense, and that the original account of motion was never urged
upon him as a true and satisfactory explanation. Much patient
scholarship has been devoted to the origins and development of
Galileo's mechanics; at one stage it seemed as though its godfather
was Leonardo da Vinci, until it was found that Leonardo was
only re-echoing a current of medieval thought. At first these
medieval discussions were regarded as no more than imperfect
gropings at a truth which Galileo apprehended perfectly. Today
the theory of impetus appears as a theory of motion in its own
right, not an uncertain anticipation of Galileo, but a coherent
doctrine which provided Galileo with a firm starting-point. The
theory of impetus could not develop the modern conceptions of
inertia and acceleration by a smooth process of transition and
expansion, but it did provide a more convenient, and more
adaptable, starting point than the ideas expressed in Aristotle's
Physics. Galileo's achievements are more properly measured by
comparing his own science of dynamics not with the absurdities
he discovered in Aristotle, but with the theory of impetus which
was already well formed.

Since it had been handled by Oresme in the fourteenth century
this theory had made little progress up to the time of Galileo.
Remaining a somewhat specialist complexity, it had not sunk to
the popular level of exposition, but it was taught by respectable
mathematicians and philosophers, including Cardano (1501-76),
Tartaglia, Benedetti and Bonamico who was Galileo's own
master. Tartaglia (1500-57), moreover, succeeded in making a
useful application of the impetus theory to ballistics, and was the
first writer to aim at computing the ranges of cannon by means of
tables derived from a dynamical theory, in which task Galileo
later was to believe himself successful. After Tartaglia, if not
before, it was at least clear that in this particular respect a
dynamical theory ought to be quantitative, that is it should be
capable of making exact numerical predictions. Many writers
on gunnery, with varying degrees of imagination, continued to
search for this desideratum within the framework of the impetus
theory until well after Galileo had offered a far better one. This
essential sterility of the impetus theory in the sixteenth century is
an important point. Able men failed to derive from it a mathe-
matical description of the phenomena of motion, yet failed also

THE ATTACK ON TRADITION: MECHANICS 79

to develop concepts which could take its place. It is not, therefore,
the case either that Galileo's ambition to mathematize dynamics
was something unusual in the contemporary scientific milieu, or
that, once this ambition had been framed, it was easy to mould
the necessary modern dynamical concepts out of their crude
impetus forebears. Modern dynamics did not spring from a
modified version of the impetus theory: Galileo was compelled to
return once more to the fundamental concepts of motion.

Towards a new Kinematics

The theory of impetus, the living tradition of dynamics in the
sixteenth century, utilized by Galileo himself in his early treatise
On Motion (1592), had the basic function of explaining certain
phenomena. It had not changed the language in which they were
described. While it gave reasons for the continuation of motion by
a body after the moving agent was withdrawn, and in particular
accounted for the properties of motion shown by falling bodies
and projectiles, it had not produced more accurate or fertile
definitions of force, velocity, acceleration. In the technical terms
of philosophy it dealt with the " accidents" of motion the
decelerating ascent of a projectile was caused by an "accidental
levity," its accelerating descent by an "accidental gravity,"
demonstrated by its having effects on impact equal to those
caused by a body at rest of much greater weight. Impetus as a
causal factor, responsible for the accidents of free motion, being
thus associated with the categories of Aristotelean dynamics, no
mechanician before Galileo attempted to deny the validity of the
substantial distinction between the two kinds of motion, natural
and violent. Hence great difficulties arose when the attempt was
made to describe the path of a projectile, for example, since the
two parts of the problem the ascent and the descent were
qualitatively distinct and subject to different considerations.
Further, progress towards a kinematics through this type of
problem was obstructed by the limitation of the impetus theory
to strictly rectilinear motion. Though both Leonardo and
Tartaglia in the sixteenth century represented the trajectory of a
projectile as a continuous curve, this was no more than a pictorial
device, since their common theory of motion allowed no com-
pounding of natural and violent. In theory the categories of

8o THE SCIENTIFIC REVOLUTION

motion were exclusive, and rectilinear-natural motion could only
occur after the rectilinear-violent was completed. Again, if the
relations between the impetus theory and the later concept of
inertia are examined, it is clear that while in isolated statements
exponents of this theory seem to anticipate the rigorous definition
of inertia, in the full physical context their interpretation of the
phenomena was different. For it was not supposed that a body,
having acquired an impetus to motion, would continue to move
at a uniform velocity. The resistance of the medium ensured that
it would slow down and come to rest; and motion in a vacuous
space was inconceivable when the universe was regarded as a
plenum. Impetus was like heat, an evanescent accident of matter,
of its own nature wasting away. As before, thought on the appli-
cation of these ideas to the special problem of projectiles was
misled by utter deficiency of observation and description. The
impetus mechanicians universally believed that the velocity of a
projectile increased for a space after it had parted company with
the propellant, so that in some strange way its impetus was
actually increased during a part of its free motion. Here also the
theory, instead of leading to universally valid concepts of inertia
and acceleration, required the formation of a special case.

If the scientific tradition inherited by Galileo did not offer any
simple, universal axioms in dynamics, and in its preoccupation
with causation had neglected accuracy in description, it did
provide a suitable mathematical analysis for dealing with changing
quantities, such as the velocity of an accelerated body. It is a
matter of historical record that the geometrization of motion, the
establishment of a formula connecting velocity, time and distance
appropriate to the motion of an accelerated body such as a freely
falling mass, was more easily accomplished than the development
of a framework of kinematics within which such a formula would
be not merely possible but inevitable; the formulation of a true
dynamics involved a still greater effort which was hardly com-
pleted before the eighteenth century. The effect of supposing a
uniform (linear) variation in the intensity of a quality, such as
heat, had been studied by a number of philosophers in the
fourteenth century. They found that the second variable (e.g.
heat) could be related either arithmetically or geometrically to
the first variable (e.g. time). Oresme, for example, had demon-
strated that if a quality be supposed to vary uniformly from the

THE ATTACK ON TRADITION: MECHANICS 81

magnitude represented by the line AB to zero at C (Fig. 5), the first
variable being represented by the line AC, this varying quality is
equal in effect to a uniform quality of
the magnitude AB, since the area of
the triangle ABC is equal to |AB.AC.
He expressly stated that if the varying
quality were velocity, the equivalent
uniform velocity would be that

attained at the mid-point in time (i.e., ^ < .

if AC represents time, of magnitude Fm 5 Geometrical analysis of
|AB) and deduced that any uniformly uniformly varying qualities,
varying quality (or velocity) could be

equated to a uniform quality (or velocity). Somewhat earlier
another master of the University of Paris, Albert of Saxony, had
tried to prove that the motion of a freely falling body could be
treated in this way; he had taught that (i) such a body is uniformly
accelerated, and (ii) that in uniform acceleration the instantaneous
velocity is directly proportional to a first variable which is either
the time elapsed or the distance traversed.

The first of these propositions was supported, from Albert's
time to that of Galileo, by reference to the theory of impetus. It
was asserted that the continually increasing speed of a falling
body was caused by the addition, to the impetus already acquired
by it at any point in its descent, of the constant tendency (conatus)
towards the attainment of its natural place which it always
possessed. If this conatus were suddenly abolished while the body
was actually falling, its impetus would nevertheless bring it down
to the ground at a nearly constant speed, but as this conatus acted
as a cause of motion on a body already in motion, it made it move
ever faster. By an intuitive process, rather than by strict reasoning,
it was argued that the increase of velocity is linear; 1 an argu-
ment not approved by all philosophers. It was not accepted by
Galileo in 1592, for it might be that the rate of increase would
slacken as the falling body moved more quickly.

The second proposition, or rather pair of alternative proposi-
tions, involved even more obvious difficulties. In the first place,

1 Intuitive, because Albert's proposition really implies the true law of
inertia, which he did not enunciate, and also because it is untrue when the
descent occurs in a resisting medium, such as the air. Nor was it logically
certain that the conatus would act in the same way on a body in motion, as on
one at rest.

6

82 THE SCIENTIFIC REVOLUTION

the notion of instantaneous velocity was very imperfectly grasped
no term existed to describe it for while the calculus of varying
qualities could equate these, over a given range, with uniform
qualities, it did not deal with the instantaneous magnitude of the
changing quantity. Moreover even problems on simple linear
relations involve integration, and it was by no means easy to
decide what the integral (the area ABC in Oresme's demonstra-
tion) actually represented. To Oresme it was the total quantity
of a quality over a given range, expressed as a simple product
(p x q) ; but whereas this meaning could be applied to a quality
such as heat, it was hardly applicable to velocity. 1 What is the
"total quantity of a velocity"? In either version of Albert's
second proposition, when the calculus of varying qualities was
applied, this mysterious quantity appeared, but the three useful
terms time, velocity and distance could not be brought to
appear together. The difficulty can be explained, of course, in
modern terms by realizing that the product (\vt) or (\vs) cannot
possibly represent any "quantity of velocity." Galileo was the
first to demonstrate this, by showing that the integral is a measure
of the distance traversed. There was no question here of a purely
mathematical difficulty Galileo's geometry is exactly that of
Oresme he succeeded by attaching correct conceptual signifi-
cance to the mathematical quantities. 2 Thus his originality was
not so much in making a particular calculation, as in interpreting
the answer once he had obtained it.

Finally, the philosophers who followed Albert had to decide
between the alternatives in his second proposition. Was the first
variable time or distance? This was the principal obstacle to
progress in the sixteenth century within the framework of the
impetus theory. And it was so, not because a choice could not be
made, but because it was not even clear that a choice was neces-
sary. Leonardo typified the confusion of thought in his completely

1 This assumes, for example, that a hot iron having a temperature t t falling
to / 2 over time T melts as much ice in that time as an identical iron of constant
temperature J(^ -f- J 2 ). It was only much later that Black cleared up the
confusion between temperature and quantity of heat, analogous to the con-
fusion in mechanics here discussed.

2 His geometry was equivalent to the derivation of the integral (^at z ) from

the differential equation . == at. He realized, correctly, that this represented
the distance traversed.

THE ATTACK ON TRADITION: MECHANICS 83

clear, and completely contradictory, statements in different
passages of his note-books that the velocity of a falling body at
any instant is proportional to the distance fallen, and to the time
elapsed. For the writers on kinematics who preceded Galileo,
what he was to call the supreme affinity between time and motion
was inevitably obscured. They could not measure small time-
intervals. They most naturally stated the problem whose solution
they sought in a form which made time a function of distance,
that is: "If a stone falls x feet in one second, how long will it take
to fall 100 feet?" Even in making experiments on dropping
bodies from different heights, it was more natural to think of
the greater velocity as a function of the greater elevation. It
seemed that the lifting of the stone to a greater height was the
direct cause of its greater velocity on reaching the ground. This
confusion of hypotheses was indeed to trouble Galileo himself,
and some of his brilliant contemporaries. Only one philosopher of
the sixteenth century steered his way unambiguously through it.
This was a Spanish theologian, Dominico Soto, whose commentary
on Aristotle's Physics, fully in the tradition of Oresmc and Albert
of Saxony, was published in 1545. After defining "uniform
difForm" motion (i.e. uniformly accelerated motion) not
velocity as proportional to time, he declared that this kind of
motion was proper to freely falling bodies and to projectiles. 1 He
did not, however, prove these propositions nor did he suggest a
formula relating time, velocity and distance. 2 Though he gave
the definition and application of acceleration correctly, he was
still far from a true kinematics, and his propositions were still
dubiously derived from the concept of impetus. If they were
significant, but limited, anticipations of Galileo's theories on
motion, they were also nothing more than one version of Albert
of Saxony's propositions. And there was no further advance. It
was left to Galileo to perform two functions of highest importance:
to formulate new, clear concepts of motion, and to derive from
them the complete elements of kinematics, using the fragments
provided by those who had shaped his intellectual inheritance.

1 Cf. P. Duhem: fitudes sur Leonard de Vinci (Paris, 1906-13), vol. Ill,
pp. 267-95, 555~ 6 2-

2 i.e., though Soto loosely gives the equivalent of , = at, he did not attempt

to integrate this equation. As will be seen, this was a task that defeated Des-
cartes, and (at first) Galileo.

84 THE SCIENTIFIC REVOLUTION

The Law of Acceleration

During more than two centuries before Galileo's birth the
application of the calculus of varying qualities to the concept of
impetus promised the discovery of the law of acceleration or
rather of two such laws. 1 Dominico Soto had decided correctly
that acceleration was a rate of change of motion (velocity) in
time. He had even struck a blow at the dichotomy of natural and
violent motion by deducing that in the violent motion of ascent
the acceleration is negative. Although Galileo's great achievement
was to be in the mathematical analysis of motion, it was not his
first preoccupation. Instead, in his treatise On Motion of 1592, he
examined the physical nature of acceleration, and criticized the
opinions commonly derived from the concept of impetus. In the
physical sense, he maintained, acceleration was a mere illusion.
His argument at this stage denied the proposition which became
one of the axioms of modern dynamics a constant force gives a
body a constant acceleration for he argued that since the cause
of the natural motion of a body is its weight, each must have a
natural velocity proportional to its weight. He explained the
appearance of changing speed in this way: suppose a heavy mass
projected upwards, the impetus conferred being greater than the
natural conatus to descend. It will rise until the tendency to fall
and the impetus are of equal strength. At this point the body still
possesses a certain degree of impetus and consequently as it begins
to fall back it will increase its speed until all the impetus has
disappeared; after this its motion will have the constant velocity
proper to its weight. In the case of a body falling from rest, he
declared, the impetus acquired by its displacement from the
centre was preserved and the same explanation held. 2

Certainly this novel modification of impetus mechanics one
enforced by allowing notions of the causal functions of impetus to
prevail over its usefulness in kinematics introduced no remark-
able clarity. It may be that Galileo's somewhat unfruitful specula-
tions along these lines had the effect of turning his thoughts in

1 The law relating instantaneous velocity to distance traversed (-T = as)

makes s an exponential function. It was therefore beyond the mathematical
competence of Galileo's age.

2 This theory is discussed in detail by A. Koyre: Etudes Galiltennes (Paris,
1939). PP-

THE ATTACK ON TRADITION: MECHANICS 85

a new direction. The followers of Oresme and Albert had long
abandoned the idea that the speed of a falling body is proportional
to its natural weight, though they did not conclude, as did Galileo
later, that in a vacuum all bodies would fall at the same velocity.
Oresme, for example, opposing Aristotle, held that the uniform
velocity of a body is not proportional directly to the "puissance"
applied (e.g. its weight), but to the ratio between the "puissance"
and the resistance to be overcome. He recognized also that the
natural weight of a body is unaffected by its motion; the only
change is in apparent or effective weight, and it is to this (at any
instant) that the velocity is proportional. 1 Moreover, Oresme
accepted the fact that acceleration may continue indefinitely,
and thus differed in principle from Galileo who assumed in 1592
that the velocity of a falling body tends towards a uniform value. 2
But it is true that the identification of impetus with accidental
gravity involved conceptual inconveniences which Galileo had
correctly appreciated, though he set them into an outmoded
Aristotelean pattern.

The first evidence of a major success already shows that Galileo
had turned from a physical-causal to a kinematical approach. In
1604 he wrote, in a famous letter to Paolo Sarpi, that on the basis
of an axiom sufficiently obvious and natural he had proved that
the spaces passed over by a falling body are as the squares of the
times. The axiom adopted was that the instantaneous velocity is
proportional to the distance traversed; an axiom already rejected
by Dominico Soto. The demonstration of this impossible con-
clusion (which happens to survive) 3 made use of the medieval
calculus of varying qualities. Galileo decided that the integral
(area ABC in Fig. 5, Oresme's "quantity of velocity") represented
the space traversed; but the process by which he derived this
integral from his axiomatic function was entirely false. His
reasoning assumed, in fact, that velocity was plotted against time,
not against distance. 4 Thus the familiar theorem, s = %at 2 , was
first derived by Galileo in a process mathematically correct but
vitiated by a conceptual error. Perhaps the theorem was first
tested about this time by the experiment of rolling a brass ball

1 Oresme, Medieval Studies, vol. Ill, pp. 230-1; vol. V, pp. 179-80.
a In the Discourses Galileo explains that the resistance of the air tends to
limit the velocity of a falling body to a maximum value.

3 Gf. Opere (Edizione Nazionale), vol. VIII, p. 373.

4 Duhem: Etudes sur Leonard de Vinci y vol. Ill, pp. 565-6; Koyr6, op. cit., p. 98.

86 THE SCIENTIFIC REVOLUTION

down an inclined plane described in the Discourses* It is certain,
at least, that from this time Galileo was convinced of its accuracy
as a mathematical description of the motion of freely falling bodies.

In Galileo's scientific method experiments were designed to
give ocular confirmation of reasoning; therefore he could not be
satisfied with his newly discovered theorem as a merely empirical
fact. At this point he was most concerned to prove that his axiom
the false law of acceleration followed logically from an analysis
of the nature of motion, and to establish it as a reasoned premiss. 2
Could it be justified in philosophy? In tackling this question he
must have been aided by the progress of his thought since 1592,
of which unfortunately little is known. Probably he had already
gone far in renouncing that concern for the causation of pheno-
mena shown in his early writing after realizing the confusion into
which it plunged dynamics. In the later phases of his thought
impetus was no longer appealed to as a causal factor but became
a mathematical quantity the product of weight and velocity. As
Galileo's problem became more purely kinematical, he accepted
the facts of gravitation and the fall of heavy bodies without
trying to impose an explanation, although, from his favourable
references to William Gilbert after 1600, it may be presumed that
he approved the notion of gravity as a quasi-magnetic attraction. 3
Already in 1604 he saw acceleration as a fact to be defined, not
explained; but it was not until afterwards that he was satisfied
that the constant effect produced by the constant cause, a force,
is not a velocity but a rate of change of velocity and so resolved
the paradox he had treated very differently in 1592.

With the abandonment of the impetus causation of acceleration
is involved the transformation of this vague conception into the
law of inertia. Mach insisted, logically, that this law is the special
case of the law of acceleration where the force applied is nil, and
therefore no separate statement of it is strictly necessary. 4 His
argument is just, but not historical. Historically the special case
was more readily understood than the general law. It was derived

1 Dialogues concerning Two New Sciences, trans, by H. Crew and A. de Salvio
(New York, 19 14), pp. 178-9.

2 The empiricist would have derived the law of acceleration mathematically
from the law of distances verified by experiment; but this was not Galileo's
method.

3 Dialogues on the Two Chief Systems of the World, pp. 426 et seq,

4 Ernst Mach: Science of Mechanics (Chicago, 1907), pp. 142-3.

THE ATTACK ON TRADITION: MECHANICS 87

from the consideration of motion in a resisting medium: if the
impetus of a body is expended in overcoming the resistance, then
in the absence of resistance its impetus and velocity will remain
infinitely constant. It is in this way that Galileo explains the law
of inertia in his Discourses, and the non-resisted motion of the
celestial spheres had long been described as a peculiar instance of
undiminished impetus, or inertial rotation. The gcometrization of
space, the transference of the phenomena of motion from the real
world of resisting media to an imaginary vacuous space (in which
Galileo had been partially anticipated by Benedetti) and the
restriction of impetus to a kinematic sense virtually necessitated
the transformation of the traditional idea of continued motion
into the idea of inertia, which marks the complete downfall of the
ancient attitude that it is motion, and not rest, which requires
particular explanation in face of the modern notion that only
changes of motion require explanation. In Oresme's natural
philosophy impetus, the motive virtue, had been inevitably a
failing "puissance"; Galilean kinematics required that inertial
motion be uniform because the reason for its retardation had been
removed. The statement of the law of inertia was indeed fore-
shadowed in the treatise On Motion, where Galileo discussed the
motion of a sphere rolling on an infinite horizontal plane, a
motion which is neither violent nor natural and therefore can be
the result of the action of an infinitely small force; or where he
showed that from the abolition of resistance, as in a vacuum, it
did not follow that movement would be infinitely swift. And if,
in such inertial motion, the causal-impetus was conserved, what
could be its function when there was no longer a resistance to
overcome? At this point the conservation of impetus became
redundant: it was only necessary to speak of the conservation of
velocity and momentum. 1

Once the vague concept of impetus had been analysed into two
rigorous statements embodying the law of inertia and a defini-
tion of momentum, the potentialities of the geometric method in
kinematics were vastly extended. With the further addition of an
arbitrary law of acceleration the fundamental theoretical structure
of kinematics was almost complete, and at once the distinction
between "natural" and "violent" motion appeared as an unneces-
sary hindrance. The terms were still used by Galileo, but purely
1 Koyre, op. cit., pp. 71, 93.

88 THE SCIENTIFIC REVOLUTION

for classification, without any causal or dynamical significance.
Natural motion had become, by definition, accelerated motion
in accordance with the normal law: the violent, a motion retarded
in accordance with the same law of opposite sign. Gravitation had
become a force like any other, which might be greater or less than
other forces opposed to it, and the effect of a force was to accelerate
or retard a body whose only physical properties were weight
(which Newton made, more properly, mass) and inertia. Privi-
leged directions with respect to the centre of the universe, intrinsic
lightness and heaviness, causal distinctions between enforced and
unenforced movements, all disappeared once the aptitude of the
law of inertia in perfectly geometrical vacuous space, where all
planes are infinite, all perpendiculars are parallel, and only simple
forces operate, was realized.

It need not be supposed that Galileo had, by 1604, reached the
stage where the distinction between the essence and the accidents
of motion for which he had sought so long, and which was essential
for the elucidation of the true laws of kinematics, was perfectly
clear in his thought. Rather, his erroneous definition of accelera-
tion at that time, together with the imperfect conception of
inertia which he was never to amend, prove that the steps in the
process of reasoning he had followed still lacked clarity and
rigour. Having abandoned the traditional theory of impetus
Galileo's intuition had brought the laws of kinematics almost
within his grasp, at a time when his analysis of the nature of motion
was still far from impeccable. The more adequate reasoning of
the Discourses was to be developed over the next thirty years, yet
even so the ultimate confutation of the false law of acceleration
adopted in 1604 rests upon a paralogism. 1 Powerful and original
as Galileo's thinking already was, and close as it came to the
essential idea of motion, his kinematics of Euclidean space was
still a no more complete theory than impetus dynamics. The false
law of acceleration stated by impetus mechanicians still seemed
plausible, and Galileo was still ignorant of the true law, explicitly
stated by Dominico Soto. Galileo had not yet appreciated the
crucial importance of the distinction between the two possible

1 This was given in the Discourses (Crew and Salvio, op. cit., pp. 167-9),
where Galileo used Oresme's calculus of varying qualities to prove that a body
falls any distance s in the same time if this law of acceleration is adopted. But
this calculus assumed that the variation in velocity was relative to time, and
is therefore quite inappropriate.

THE ATTACK ON TRADITION: MECHANICS 89

hypotheses; an ancient train of thought (strengthened by his
geometrical proclivities) bound him to spatial relations. Was his
statement of the distance fallen as a function of time thus a happy
accident which owes nothing, logically, to the progress of his
ideas after 1592, since the axiom of 1604 was available to him
then? Only in a qualified sense. It is true that the geometric
method of Galileo in 1604 was an attempt to integrate instan-
taneous velocities in Oresme's graphic representation, but
Galileo's calculation is purely kinematical. It is not bound in
terms of explanation to the impetus theory. The quantitative
result could have been obtained in 1592, but it would have
belonged to a different pattern. Secondly, the error which
enabled Galileo to derive a correct function from a false axiom
was not an accidental error. It was probably inevitable that it
would be made by anyone at that stage of thought attempting
the same calculation.

Actually, the identical error was made in precisely the same
fashion independently by Descartes and the Dutch physicist
Isaac Beeckman. 1 Their acquaintance began in 1618, when
Beeckman was already convinced of the perfect conservation of
motion: 'quod semel movetur semper eo modo movetur dum ab
extrinseco impediatur. 5 He also believed (following Gilbert) that
gravitation was the result of the earth's attractive force. Accord-
ing to Descartes, Beeckman proposed the following problem:
'A stone falls from A to B in one hour; it is perpetually attracted
by the earth with the same force, without losing any of the
velocity impressed upon it by the previous attraction. He is
of the opinion that in a vacuum that which moves will move
always; and asks what space will be traversed in any given time.'
Offering certain dynamical axioms, therefore, Beeckman asked
Descartes to furnish him with a mathematical function relating
time and distance. And Descartes replied with a geometrical
construction from which he asserted that if the spaces fallen are as

j, 25-, 4^ 3 8s, etc., the times of fall are as /, , f * J , f J /, etc. 2
When his demonstration of this function is examined it is

1 The story of their collaboration is told by Duhem in Etudes sur Leonard de
Vinci, vol. Ill, by G. Milhaud in Descartes Savant (Paris, 1920) and by A.
Koyre", op. cit., pp. 99-128.

2 By Galileo's theorem they are of course /, A/2/, 2/, 2 Vzt, etc.

go THE SCIENTIFIC REVOLUTION

apparent that Descartes has done exactly as Galileo did taken
the instantaneous velocity as proportional to the distance fallen,
and arrived at a law of acceleration by a process of integration of
these instantaneous velocities which is as mistaken as Galileo's in
1604. Beeckman's interpretation of Descartes' geometry is even
more curious. For Beeckman wrote out a perfect demonstration
that, from his hypotheses of motion, the instantaneous velocity is
proportional to the time, and the distance fallen to the square of
the time, without ever perceiving that it was different from that
given to him by Descartes, in fact he noted this proof as devised
by Descartes. Evidently neither Beeckman nor Descartes was able
to make a clear distinction between the two laws of acceleration:
neither was capable of seeing that the true function relating
distance and time can only be deduced from the one hypothesis.
Thus the investigations of Beeckman, Descartes and Galileo show
the same intellectual difficulty: even when the essence of motion
was justly apprehended in physical terms, its geometrical expres-
sion defeated their initial efforts. The disentanglement of the
velocity-time and the velocity-distance relationship was still
hazardous and the sheer mathematical task of integrating
changing quantities could not be attempted with any assurance
of success.

There is evidence to suggest that Galileo had developed the
correct formulation of acceleration by 1609, but the steps he
followed are unknown. It may have been that first he discovered
the error of his calculation, and so was led to substitute the true
axiom for the false: but it would seem more likely that it was in
meditating further upon the foundation of the law of acceleration
in his essential idea of motion that he realized the 'intimate
relationship between time and motion.' 1 It is doubtful if the
purely mathematical error would have been apparent to him with
any clarity (since he repeated the same kind of error in his own
confutation of his first axiom), whereas he may have reflected
that velocity and rate of change of velocity may be conceived as
changes in time irrespective of spatial considerations. Yet if
Galileo had worked backwards from the relation s ^at 2 , as he
represented it geometrically (Fig. 6), he may have seen that the
areas ABC, ADE, can only represent distances (Jztf) because of
their relative dimensions, and that therefore the dimensions AB,
1 Crew and Salvio, op. '/., p. 161.

THE ATTACK ON TRADITION: MECHANICS

AD must be in time

( being

such moreover that

'AD

\ 2 _ADE\
) ""ABC/'

It may be, indeed, that if the function s = %at 2 is assumed to be
true, it is easier to deduce the true conception
of acceleration, than it is to perform the
inverse and more logical operation (in which
Descartes and Beeckman failed). At all
events, Galileo inserted into the Discourses a
long passage to the intent that the "natural"
idea of velocity is a rate of change in time,
and acceleration therefore a rate of change of
velocity in time, which was written, perhaps,
in 1609, and followed this by the exposure of
the reductio ad absurdum in the alternative pro-
position. What he did not do was to derive the
definition of uniform acceleration from the
action of a constant force: though again it
may be conjectured that Galileo's, and
Beeckman's, progress towards this definition
may have been influenced by Gilbert's
suggestion of gravitation as attraction a
suggestion which from the causal point of
view liberates natural acceleration from spatial considerations.

The law of acceleration and the theorem s \afi derived from
it are the foundations of dynamics, and dynamics exercised a
preponderant influence in the evolution of scientific method
during the seventeenth century. It is no exaggeration to describe
this double discovery, with all the new structure of thought of
which it was the crowning achievement, as the justification of the
new philosophy, as the beginnings of exact science which con-
sciously set itself to proceed by other ways than those of the past,
and which hardly doubted that all the past philosophy of nature
was vain. Yet the law of acceleration had been discussed since the
fourteenth century, and was defined, admittedly not impeccably,
by da Vinci and Soto among the more immediate predecessors of
Galileo. Was the extent of his achievement, then, no more than to
effect the proper integration which would give the law of distances?
If this had been all, it would have been a great feat, for the
perplexities of Descartes and Beeckman show that the law of
acceleration did not prove a ready key even to the most acute and

D Velocity * E

FIG. 6. Time, velocity
and distance.

92 THE SCIENTIFIC REVOLUTION

resourceful of his contemporaries. But this was not all; Galileo,
a less ingenious mathematician, excelled Descartes in a mathe-
matical problem because he understood the conceptual structure
into which the key would fit. In fact the single law of acceleration,
set in the framework of impetus theory, had hardly proved more
useful in the sixteenth century than the crude observation that
falling bodies travel more quickly as they approach the earth. Its
full significance was revealed only when Galileo applied it in a
context of dynamical theory in which the law of inertia had
replaced the idea of impetus, a theory so highly abstracted that
causation, friction, resistance, were no longer considered as
relevant. To Galileo the law was no longer a descriptive deduction
from physical principles (as it was to Soto), or an arbitrary
assumption (as it was to Descartes) but a primary fact, inevitable
in theory and confirmed by experiment. There are many similar
instances in the history of science of the isolated statement of an
anterior phase becoming the core of a comprehensive generaliza-
tion; so comprehensive, in this case, that Galileo obtained from it
knowledge of a whole class of mechanical theories. It is the com-
bined effect of this rapid evolution in thought, requiring clarity
of definition and elaboration of mathematical expression, the
re-thinking of the nature of motion and the statement of functions
making quantitative calculations possible, that determines the
magnitude of Galileo's achievement. The commentary upon
Aristotle's physics had been replaced by the mathematical
scaffolding of a new branch of science.

Galileo and Descartes

The strategic lines of the Discourses on Two New Sciences were
probably sketched out about 1609. The origins of the earlier
dialogues, in which Galileo discussed cohesion and disputed
the doctrine that " nature abhors a vacuum," attacked the
Aristotelean view of the accidentals of motion (that there are
absolutely light bodies, that velocity is proportional to weight,
etc.) and began the study of the strength of materials (the other
"new science") may be traced to a period more than ten years
earlier, when Galileo, in his most Archimedean manner, was
introducing into wider fields the principles of the sciences of
statics and hydrostatics founded by his favourite Greek author.
Certainly the secret of the trajectory of a projectile was known

THE ATTACK ON TRADITION: MECHANICS 93

to Galileo by 1609, of which he wrote later, 'truly my first purpose,
which moved me to speculate on motion, was the discovery of
such a line (which most certainly when found is of little difficulty
in demonstration) ; nevertheless I, who have proved it, know what
pains I had in discovering that conclusion.' 1 The theory of pro-
jectiles, the propositions relating to the oscillations of a pendulum
by which Galileo established its isochronous property, and the
various theorems depending on the principle of the conservation
of vis viva (momentum) are all straightforward deductions from
the complementary laws of acceleration and inertia. Fragments
of this reasoning had been used by Galileo in earlier years; for
example, the experiment of rolling a ball down an inclined plane
assumes the conservation of motion or vis viva. Now the whole was
welded into a single coherent mathematical structure. It was not
a faultless structure, for a number of Galileo's minor theorems were
later found to be false, but its foundations were sound.

With one important exception, the theory of impact and the
partition of kinetic energy between colliding bodies, the whole of
seventeenth-century kinematics springs from Galileo's Discourses.
When, finally, this became the instrument by which Gilbert's
conception of attractive forces could be interpreted mathe-
matically, the classical theory of dynamics was created. But if the
lines of descent are direct, the historical process was complex.
Galileo's intellectual evolution was by no means unique, though
it has chronological priority. An independent " modern" tradition
in dynamics can be traced to the fertile conjunction of Descartes
and Isaac Beeckman. Other writers also, less strikingly, demon-
strate a general tendency for the idea of the conservation of
impetus to be transformed into the conservation of motion. As has
so often happened in science, the decisive advance was made by
one man in accordance with a broad progressive movement.
Moreover, the reaction to the publication of Galileo's dis-
coveries in 1632 was not simply favourable or adverse. 2 In the
later seventeenth century the mathematico-mechanical group of
scientists, the true heirs of Galileo, confided entirely in the essen-
tial conception of motion developed in the Discourses; in England,

1 That is, the trajectory according to the usual assumptions of Galilean
kinematics, in a vacuous, perfectly Euclidean space. Cf. Opere, Ediz. Naz.,
vol. X, p. 229, vol. XIV, p. 386.

2 The elements of kinematics were indicated in the Dialogues, though a full
discussion waited for the Discourses of 1638. See below, p. no.

94 THE SCIENTIFIC REVOLUTION

however, where this group was very strong and produced the
dominating figure of Newton, the Galilean tradition was partly
modified by the companion influence of Francis Bacon in the
direction of more forthright empiricism. Thus Newton completed
the mathematization of the distinction between the ideal laws
of motion, and the real motions of terrestrial bodies. The repre-
sentatives of conservative, anti-Copernican science, such as
Giovanbattista Riccioli, after a vain attempt to dispose of the
Discourses altogether, ultimately accepted the law of acceleration
as a rough empirical truth, a mathematical hypothesis approxi-
mately agreeing with actual experiments, but continued to oppose
the philosophy of motion from which this law was derived. This
attitude was not dissimilar to that adopted by Tycho Brahe with
regard to Copernicus : the innovations could not be philosophically
true, but they could, by twisting them a little, be taken as
quantitatively reliable. Far more important for the development
of science was the position of the Cartesians, who likewise accepted
Galileo's law of acceleration as a quantitative statement, while
opposing Galileo's ratiocination in philosophy.

Descartes himself would never allow any supreme merit to
Galileo as a scientist, and in his later utterances, after the crisis
of 1619-20 in Descartes' intellectual development, he felt himself
far superior because he alone possessed the true method of
philosophy. In general the reception in France of Galileo's new
science of motion was not uncritical: along with Descartes, neither
Mersenne, nor Fermat, nor Roberval would give complete
credence to a natural philosophy which applied such a violent
process of abstraction to the complicated world of experience.
For Descartes this objection was insuperable, and he finally came
to regard Galileo as a mere phenomenalist who, lacking insight
into the total mechanism of the universe, had merely been success-
ful in isolated feats of mathematical description. Of the Dialogues
on the Two Chief Systems of the World he wrote in 1634 that Galileo
philosophized well enough on the subject of motion, but that very
little of his doctrine was wholly true. He admitted that Galileo
was more correct when he opposed current notions, and had
indeed expressed some of Descartes' own ideas it is strange to
find him identifying Galileo's theorem, s = %at 2 , with that which
he had himself devised in 1618. Four years later Descartes'
judgement was more harsh. Although he approved Galileo's

THE ATTACK ON TRADITION: MECHANICS 95

introduction of mathematical reasoning into physical questions
and his criticism of scholastic errors, he added that Galileo had
built without foundation because he did not at all proceed by
order in his investigations, nor consider the first causes of natural
phenomena. The abstraction of Galilean science which has been
its merit in the eyes of many subsequent historians was for
Descartes its cardinal defect. He had now conceived his own model
of the universe, and he found the Galilean model too remote from
reality to be worthy of serious consideration. Its prime requisites,
such as vacuous space and the constancy of gravitational forces,
were assumptions contradicted by a true insight into nature. 1

Descartes was no less convinced of the errors of the past than
Galileo. He was equally a pioneer of the new natural philosophy.
But whereas Galileo had arrived at a new method of procedure by
patient inquiry into particular problems so that his essential idea
of motion was the product of the endeavour to resolve the incon-
sistencies in the prevailing conception, Descartes' method taught
him that it was essential to settle the simplest and most general
ideas first, and then (as in the three treatises appended to the
Discourse on Method] particular applications could be made to
specific problems. What, for instance, is the simplest idea of
matter? Extension, Descartes replied: matter is that which occu-
pies space. To suppose that space could exist without a material
content, that dimension could be conceived without any physical
consideration, was meaningless. God could formally create a
vacuum, but so interchangeable were the ideas of space and matter
for Descartes that if a vessel was imagined to be divinely exhausted
of matter, it meant only that its walls had been brought together
so that there was no space between. Of course he admitted that
vessels could be sensibly exhausted of grosser matter, such as
water or air, when they would remain filled with a purer species
capable of passing through the pores in the coarse material of the
vessel. Similarly with motion: the simplest idea was the translation
of a body from one situation among other bodies to another
situation among a different set of bodies, and motion and rest
were simply states of matter. This definition enabled Descartes
to declare formally that the earth does not move, since despite its

1 (Euvres de Descartes, publiees par Charles Adam et Paul Tannery, vol. I
(Paris, 1897), pp. 303-5; vol. II (Paris, 1898), pp. 380-8. Also J. F. Scott,
The Scientific Work of Descartes (London, 1952), pp. 161-6.

96 THE SCIENTIFIC REVOLUTION

revolution around the sun in the vortex of the solar system, its
environment in surrounding matter is unchanged. Movement,
properly, was displacement; as a body moves, it is forced to
displace other matter from its path, and a corresponding quantity
must occupy the volume which the motion of the body would
otherwise leave vacant. From these considerations Descartes
deduced more specific laws. In the first Beeckman's conservation
of motion became the perpetuation of the state of matter unless it
is acted upon in some way. In Descartes' second law this principle
of inertia was perfected by the statement that all bodies in motion
continue to move in a straight line, again unless they are acted
upon. Thus the necessity for some centripetal lien or force in
circular motion was explicitly recognized by Descartes a funda-
mental contribution to mechanics. The third law of motion was
the fundamental rule for determining the partition of motion
between impacting bodies. It was only later that the mistake in
Descartes' formulation of the laws of impact became significant;
they were, however, essential to the development of his corpuscular
philosophy of matter. The notion of an intangible, incorporeal
force, like Gilbert's attraction, was to Descartes barbarous and
unthinkable. The state of matter could only be altered by the
direct action of other matter, that is, by contact between bodies. 1
Hence what appears as the action of an incorporeal force is in
reality the action of a stream of impalpable particles.

Action at a distance such as the gravitational pull of masses
across empty space was to remain for Cartesians the bitter pill
of Newtonian mechanics. Implicitly its impossibility conditioned
Descartes' reaction to Galilean mechanics. When he declared
that Galileo had not inquired what weight is, when he maintained
that Galileo's description of how bodies fall was vitiated by his
ignorance of why they fall, he meant that in nature there are
no constant forces producing constant accelerations. 'That is
repugnant to the laws of Nature, for all natural forces (puissances)
act more or less, as the subject is more or less disposed to receive
their action; and it is certain that a stone is not equally disposed
to receive a new motion or an increase of velocity when it is

1 Thus Descartes was led into an insoluble problem the nature of the
contact between the soul (spirit) and the matter of the human body. (Cf. M. M.
Pirenne: "Descartes and the Body-Mind Problem in Physiology," Brit, jf.for
the Philosophy of Science, vol. I, 1950.)

THE ATTACK ON TRADITION: MECHANICS 97

already moving very quickly, and when it is moving very slowly.' 1
Descartes' reasoning is quite clear. Terrestrial gravity he believed
to be the effect of a stream of corpuscles of impalpable matter
sweeping towards the centre of the earth. As this stream swept
through bodies of ordinary coarse matter, it pressed them likewise
towards the centre. Clearly this pressure would diminish with the
increasing velocity of the falling body, which would tend towards
a limit, the velocity of the stream itself.

fin 1618, under the influence of Beeckman, Descartes had treated
motion as a geometer, and had made the same sort of mistakes as
Galileo in 1604. I* 1 later years, at the time when Galileo's treatises
were published, he thought of motion in the context of physical
or cosmological theory. Unfortunately, as he penetrated from the
level of description to the deeper level of explanation, Descartes
denied himself the possibility of mathematizing the law of
acceleration: the mechanism, as he framed it, contained too many
unknown variables. 2 The work in which his system of nature is
expounded, The Principles of Philosophy (1644), is in fact almost
completely non-mathematical, although Descartes is one of the
greatest figures in the history of pure mathematics. For all the
originality of its starting point, this was a synthetic system,
blending harmoniously elements derived from the animistic
science of Aristotle with others taken from the mechanistic
philosophy of Democritus and Epicurus; and, like these early
deductive philosophers, Descartes was inevitably preoccupied
with the uncovering of chains of causation, starting from his
initial postulates concerning the nature of the physical world.
When by deductive reasoning the end of the chain was reached,
it was impossible to adopt the reverse process of analysis and
abstraction which alone makes a mathematical science possible
Therefore Cartesian mechanics could never consist of more than
general principles and the false laws of impact. Therefore also
Descartes could never do more than admit that Galilean kine-
matics gave a rough approximation to the real dynamics of the
world of experience.

In Descartes the dichotomy between the mathematical and the
physical attitudes to nature is almost complete, since he could no t

1 Adam and Tannery, op. cit., vol. I, p. 380.

2 Koyre*, op. cit., pp. 126-7; Paul Tannery: Mtmoires Scientifiques, vol. VI
(Paris, 1926), pp. 305-19.

7

9 8 THE SCIENTIFIC REVOLUTION

sacrifice causation to computation. The Cartesians of later genera-
tions were more eclectic and less rigorous. They could not resist
the intellectual charms of Descartes' discoveries both in pure
mathematics and in natural philosophy. In attempting to combine
them they became the illegitimate heirs of Galileo. Having
realized the futility of seeking directly for the descriptive dynami-
cal laws of the actual universe, they sought instead for the correc-
tion which ought to be applied to the ideal laws of Galileo in order
to apply them to a world where bodies move in resisting mediums
and there are no pure forces. No tradition is perpetuated un-
adulterated and the later Cartesians compromised with the pheno-
menalism which Descartes had condemned. While they firmly
maintained his method of philosophizing, his theory of the origin
of the universe, of the corpuscular mechanisms involved in the
phenomena of light and vision, magnetism and electricity, gravity
and the planetary revolutions (none of which, from its very
nature, could be subjected to direct empirical verification), in
discussing any problem of mechanical science descriptively they
turned to the mathematical model of Galileo, to which there was
no alternative. There was a subtle change of perspective: instead
of proceeding from indubitable first principles to the details of
nature and the ultimate descriptive mathematical understanding,
as Descartes had sought to do, later Cartesian scientists followed
a different path, that of working out the modifications required
in transposing a problem from a mathematical model to the
natural scene.

This is most true of the Dutch physicist, Christiaan Huygens,
for many years the mainstay of the French Academic des Sciences.
Certainly Huygens, when still a boy, had worked out a purely
mathematical proof of Galileo's law of acceleration, and certainly
in full age he confessed that his thoughts had been too greatly
influenced by Cartesian fictions. But it is also clear that he could
never have become an entire phenomenalist : he was too great
a Cartesian to be a Newtonian. He has been appropriately con-
sidered in relation to the Cartesian tradition. 1 Much of Huygens'
work was suggested by Descartes' own original thoughts (for ex-
ample, his study of centripetal forces and the laws of impact),
much of his basic theory was Cartesian. Always denying the reality

1 e.g. by P. Mouy: La Dfoeloppement de la Physique Cartesienne (Paris, 1934),
chao. II.

THE ATTACK ON TRADITION: MECHANICS 99

of a physical vacuum, he believed in impalpable matter or aether,
and his theory of gravity was wholly in agreement with Descartes'.
He was never converted to "action at a distance." Yet his particu-
lar investigations are in the highest class of seventeenth-century
mathematical physics, and as an experimenter also Huygens, with
his strong affiliation to the Royal Society of London, was not
negligible. In the actual conduct of his scientific career no one
was more justly an exponent of the Galilean tradition in science
than Huygens who, like Galileo, allied astronomy and physics.
Only on the widest issues did he fall below the example which
Galileo had set, when as it seems, measuring the mathematical
model against the physical model of Descartes, he found his
attachment to the latter unbreakable. The Cartesian mechanical
theory of causation in nature was inevitably the frame of reference
for each of his researches, deeply though his spirit as an inquirer
was akin to that of Galileo.

The example of Huygens sufficiently demonstrates the com-
plexity of intellectual inheritance in the second half of the century.
There was no simple antithesis, uniform at all points, between
conventional science and the new philosophy of the scientific
revolution. There was no pure line of descent in mechanics from
Galileo to Newton, nor among the scientists of the French school
who broadly accepted the framework of Cartesian natural philo-
sophy. The conflict between the Newtonian and the Cartesian
system of the universe which lasted till about 1 740 was indeed
absolute and irreconcilable, but it should not be supposed from
this that the Cartesians had borrowed nothing from Galileo, nor
that the Newtonians had learnt nothing from Descartes. Much of
the application of mathematics to mechanical problems which
had been such a fertile and active field of science during the half-
century between 1638 and 1687 was in fact the work of men who
did not subscribe without reservation to Galileo's philosophy of
science.

In addition, the many lesser contributions to mechanics cannot
be overlooked. Admittedly the main source-books for the later
seventeenth century were the Discourses of Galileo and the Prin-
ciples of Philosophy of Descartes, but other works of the nascent age
of modern science held fruitful suggestion, among them the prac-
tical machine-books and even such a curious confection as Baptista
Porta's Natural Magic. Inventive interest in the development of

ioo THE SCIENTIFIC REVOLUTION

new mechanical devices was a prominent feature in the activities
of the early scientific societies, the Academic Royale des Sciences
enjoying the privilege of examining them and officially approving
those which it found sound and beneficial. Again, though the
progress in statics during the late sixteenth and early seventeenth
centuries was less pregnant with consequence than that in dy-
namicsthere was a profound change in degree rather than a
change in kind this progress too contributed to the methodology
of science as well as to the formation of the whole body of experi-
mental learning. Simon Stevin, whose investigations provided
another part of the foundations of seventeenth-century mechanics,
was a man of wide competence little short of the first rank^In
the history of mathematics he has an important place as, among
other things, one of the leading early exponents of decimal arith-
metic.} With another Fleming, De Groot, he carried out, about
1590, an early experiment on the fall of heavy bodies to test
Aristotle's theory of motion. In statics his work on parallel forces
utilized the important principle of virtual velocities or displace-
ment ; he recognized (like Galileo) that the equilibrium of a system
of pulleys or levers depends upon the constancy of the product
of the weight and the distance moved in each of the balanced
members. Stevin extended the same principle to the action of
non-parallel forces. He showed that unless perpetual motion is
assumed to be possible (and Stevin was one of the first to consider
this ancient fallacy in the light of plain mechanical reason) two
weights resting upon a pair of inversely inclined planes must
balance when they are proportional to the lengths of the
planes. His demonstrations contain the principle of the triangle of
forces, and therefore the first implication of vector-quantities in
statics, just as Galileo's treatment of the trajectory of a projectile
contains the first use of vectors in dynamics. In hydrostatics he
examined the conditions necessary for the stability of a floating
body, and the distribution of pressure in liquids, involving a prob-
lem of integration which he solved successfully. He was the first
discoverer of the so-called "hydrostatic" or "Pascal's paradox,"
that the pressure of a liquid upon a surface varies only with the
area of the surface and the height of the column of liquid above
it, irrespective of its cross-section. This, along with his other dis-
coveries in mechanics, Stevin described in Flemish in 1586. Isaac
Beeckman noted it there, and drew the attention of Descartes to

THE ATTACK ON TRADITION: MECHANICS 101

this strange phenomenon. Descartes without acknowledging his
source discussed its theory at some length. From Stevin too the
paradox passed to Pascal, who analysed it very completely in
1648.!

The essence of mechanistic philosophy in the seventeenth
century was the axiom that all natural phenomena could be re-
duced, by a sufficiently prolonged process of abstraction, to one
single kind of change, the motion of matter. This axiom was the
foundation of Cartesian science, and with limitations and qualifi-
cations it was generally shared by scientific men. Descartes' great
contribution to dynamics, in a sense, is that he made it the primary
science. In so doing he caused research to enter some false paths,
but his idea was to be vindicated in the kinetic theory of the
nineteenth century. Galileo provided the elements of kinematics,
the basic conceptualization and the mathematical procedures
again further elaborated by Descartes in coordinate geometry
which rendered definable the properties of matter in motion. For
the next century a major concern of science was the extent to
which nature could be explained broadly in terms of Cartesian
mechanism interpreted with the aid of Galileo's descriptive
analysis of motion.

1 Milhaud, op. cit., p. 34.

CHAPTER IV
THE ATTACK ON TRADITION: ASTRONOMY

THE period of silence in which comparatively little comment,
favourable or unfavourable, was made on the new celestial
system proposed by Copernicus lasted for about a genera-
tion after the publication of De Revolutionibus. From the later years
of the sixteenth century to the middle of the seventeenth there was
a noisy and not invariably elevated dispute between the adherents
of the new and the old opinions in natural philosophy in which
astronomy was the touch-stone of faith. The triumph of the
innovators did not come rapidly, for it is always easy to exaggerate
the adaptability of the scientific intellect. Books were written
assuming the truth of the geostatic system, astronomical clocks
and armillary spheres were constructed to show a motionless
earth, until at least the end of the seventeenth century. And it is
well to remember that though the ascendancy of the "new
philosophy 55 made modern science possible, the material point
so often at issue was not of long-term importance. It is now recog-
nized that before using words like "motion" and "rest 55 in rela-
tion to the solar system the frame of reference must be explicitly
defined. It was by no means logically essential to the progress of
astronomy that men should believe the earth to have an annual
rotation around the sun. No phenomenon known to the seven-
teenth century required such a motion for its explanation; in
practical astronomy the relative movement of earth and sun
could be equally well interpreted by supposing either to be at
the centre of the other's orbit. Before the celestial mechanics of
Newton's Principia was developed, there was no positive, demon-
strative argument that can be called conclusive either way; only
in the sense that the progress of science demands the liberty to
theorize, to extrapolate beyond the available positive knowledge,
is it true that the Copernicans had enlightenment on their
side.

The first conflict between the innovators in philosophy and
authoritarian learning, which was full of consequence in framing

1 02

THE ATTACK ON TRADITION: ASTRONOMY 103

not only the attitude adopted by the Roman Catholic Church
towards the great astronomical question but also (in part) the
spirit of the scientific movement, at once defensive against sus-
pected allegations of irreligion and hostile to the older kind of
literary scholarship, had strictly no connection whatever with
natural science. This conflict was exhibited in the famous con-
demnation of Giordano Bruno. Bruno was burnt in 1600 because
he taught the plurality of worlds; he was moreover technically an
apostate from a religious order. He believed that beyond the
universe we observe there are other universes similar to our
own, equally of divine creation, equally inhabited by immortal
souls. Speculation of this kind has a natural fascination for some
minds; it had occurred very early in the history of systematic
thought, and had received the strong disapproval of Aristotle. It
had always been regarded as theologically dangerous. Yet Nicole
Oresme, in his Livre du del et du Monde gave considerable attention
to it. He envisaged the possibility of a plurality of worlds in time
or in space so that there might be one world enclosed in another
or separate worlds scattered in space, for example beyond "our"
universe, all the work of one creator. Aristotle's argument that
the earth of another world would be drawn to a natural place at
the centre of this he confuted by rejoining that the natural place
for such earth would be at the centre of its own world. The restric-
tion of the divine creative power to the fabrication of one universe
he regarded as a denial of omnipotence. Further, he was bold
enough to declare that it is natural to human understanding to
believe that there is space beyond "our" finite universe; in this
God could bring other universes into existence. From this dis-
cussion Oresme concluded that reason alone could not eliminate
the possibility of a plurality of worlds, but that in fact there never
had been more than one, and probably there never would be. 1
In the seventeenth century a similar speculation produced the
first scientific fantasies, such as John Wilkins' Discovery of a World
in the Moon (1638).

The allied belief in the infinity and eternity of the whole cosmos
was also ancient.Expounded by Lucretius, who had them from
Democritus, these doctrines were further developed by an im-
portant group of Muslim and Hebrew philosophers of the middle
ages, though little favoured by Christians. Oresme seems to hint
1 Medieval Studies, vol. Ill, pp. 233, 242, 244.

104 THE SCIENTIFIC REVOLUTION

at the infinity of space. Nearer to Bruno's own time the impossi-
bility of conceiving a boundary to space was asserted by Nicholas
of Gusa in the fifteenth century: and it was from him that Bruno
received his inspiration. In his own time the idea was specifically
related to the Copernican hypothesis by the English mathe-
matician Thomas Digges. Digges believed the fixed stars to be
infinitely remote from the earth, a notion he was free to adopt
since it was no longer necessary to suppose them fastened to a
revolving sphere. All that the Copernican hypothesis required,
however, was that the ratio of the distance of the fixed stars to
the earth's distance from the sun should be a large number; had
this number been far smaller than it actually is, the sixteenth-
century astronomer would still have failed to detect any evidence
of the earth's motion in his celestial observations. As for the
infinity of space outside "our" universe, it was perfectly recon-
cilable with Ptolemaic astronomy and not at all a Copernican
innovation. However great the interest of Bruno's ideas in them-
selves, the idea of the plurality of worlds was not inspired by the
scientific renaissance, they were not a logical deduction from
heliocentric astronomy, and they were totally irrelevant to the
progress of science. Bruno was not a scientist, and his dispute with
Rome turned on a purely metaphysical problem.

It is well to attempt to define the contemporary appreciation
of a situation such as this. That the introduction of religious
considerations into a question of quasi-scientific speculation is
quite distinct from a similar intervention in the interpretation of
observations or experiments was perfectly clear to philosophers
of the middle ages and the early modern period alike. A very high
proportion of scientists up to the mid-seventeenth century were
men of unusually profound religious conviction, and none used
science as a lever against religion. Thomas Hobbes won no
countenance from the Royal Society. The furtherance of science
and religion were commonly regarded as inseparable objectives.
The English scientists of the seventeenth century, especially, were
far more complacent than medieval scholastics in their belief that
reason and research properly conducted could never conflict with
religious dogma. The attitude of the middle ages had been that
where reason was incompetent to decide, faith should pronounce:
and that in many instances faith must even prevail against reason.
In the period of the scientific revolution natural theology was still

THE ATTACK ON TRADITION: ASTRONOMY 105

distrusted, and divine modification of the laws of nature in rare
events was a commonplace. A general antithesis between science
and religion was consequently out of the question; a particular
antithesis over a single point could only be due to some misinter-
pretation either of nature or of religious truth. Even for the most
empirical of scientists, like Boyle and Newton, the introduction of
religious considerations into the pattern of scientific investigation
was natural and inevitable. They would not have dreamed of
denying the validity of a universal moral or religious law a
concept to them more binding than scientific law. To the Protes-
tant mind of the seventeenth century the judgements upon Bruno,
and later Galileo, would seem full of human error and expressive
of the bigotedly narrow outlook of the unreformed Church, but
they would agree that it was the duty of the responsible officers
for the time being to enforce the moral law according to their own
enlightenment. 1 No sympathizer with Bruno or Galileo believed
in complete freedom of thought and expression; none would have
asserted that scientific activity and theorizing are completely
outside the range of universal moral law. For the seventeenth
century the burning of Bruno could not be wholly wrong in
principle as it was to the liberals of the nineteenth. Galileo, though
he never surrendered his inner conviction of scientific rectitude,
apparently admitted the right of the ecclesiastical authorities to
pass religious censure upon his arguments. He lived and died in
the Catholic faith; and when compelled to make his formal
recantation, it would seem more reasonable to attribute his
compliance not to lack of courage, but to recognition of the then
universal belief that moral and religious truths are of a higher
order than the scientific. Galileo could only lament that in his
case the moral law had been misapplied.

Although the pronouncements of the Holy Office were not
opposed to any positive scientific knowledge of the time, and in
the case of Bruno only condemned a form of quasi-scientific
speculation, they had a deep effect upon the scientific move-
ment. They were widely interpreted as a final declaration against
the Copernican system, and there is evidence that some (like
Descartes) who were disposed to favour a heliostatic model were
impelled to express their ideas in veiled and guarded terms. It
seemed as though innovations in natural philosophy must lead to
1 As the reformed Church of Geneva had upon the person of Serveto.

io6 THE SCIENTIFIC REVOLUTION

outbreaks of heretical opinion, as reactionaries had long predicted.
Even in England, critics of the newly founded Royal Society did
not fail to assert that its methods were subversive of the Church
of England. An odium, which had not existed in the early sixteenth
century, was for a time attached to any originality in astronomical
thought. But the challenge provoked a powerful reaction in men
like Galileo and Kepler. It created a situation in which the new
doctrines had to be effectively vindicated; it was no longer
possible for the two systems of the world to exist peacefully side
by side.

The pre-Newtonian development of heliostatic astronomy may
be analysed as involving four principal steps. Firstly, the dissolu-
tion of the prevailing prejudice against allowing any motion to
the earth, which involved a careful criticism of all existing
cosmological ideas in order to create a new pattern in which
such a motion would no longer seem implausible, and a broad
discrediting of Aristotle's authority. A necessary auxiliary to this
was the most important second step, in which physical theories
were revised to show the invalidity of objections against the
Copernican hypothesis arising out of terrestrial mechanical
phenomena. Thirdly, the new astronomy was greatly enriched by
qualitative observation, which suggested that the old teaching
was very inadequate. Fourthly, exact quantitative observation
provided new materials for recalculating the planetary orbits,
thereby leading to the abandonment of the ancient preconception
in favour of perfect circular motion, and to the enunciation of
new mathematical laws. Kepler's discoveries might have been
expressed in the terms of the geostatic system; but as Kepler was
a staunch Copernican, his whole discussion of the solar system was
constructed in such a way as to give further force to the heliostatic
hypothesis. The accomplishment of these four steps extended over
a period of roughly half a century (c. 1580-1630), while their
assimilation and particularly the gradual recognition of Kepler's
laws of planetary motion occupied another generation. During
the middle period of the seventeenth century the nature of the
problem was again slightly changed under the influence of
Descartes' natural philosophy, which tended to enlarge the dis-
parity between the natural-philosophical and the mathematical-
astronomical approach which the discoveries of the first third of
the century seemed rather to diminish.

THE ATTACK ON TRADITION: ASTRONOMY 107

The contributions of Galileo to the first three of these steps were
of major importance: to the fourth, quantitative observation, he
brought almost nothing. Galileo was not an astronomer as the
word had previously been understood, he was never interested
in the traditional procedures of positional astronomy, but as a
philosopher he applied new astronomical techniques, mostly of
his own invention, to the examination of cosmological problems.
Before 1609 his studies were very largely, if not wholly, devoted to
physics and mechanics. He must, of course, have been thoroughly
acquainted with elementary astronomy, and it appears that he
had already read Copernicus and become converted to his doc-
trine, which he had at first distrusted. In 1609 Galileo learnt of
the Dutch optical device which made distant objects seem near,
and with this hint and considering the invention as a problem in
optics he constructed his own telescope. During succeeding years
he endeavoured to increase the magnification of this instrument
and to effect improvements in lens-grinding, besides carrying out
celestial observations which were recorded in a series of treatises. 1
Galileo was the first to appreciate the usefulness of the recently
invented telescope in astronomy, and was therefore rewarded by
many discoveries, but within a few years a considerable group had
taken up qualitative investigation in astronomy. The old and the
new branches of the subject remained practically distinct until
about 1670, when the application of the telescope to measuring
instruments became effective; during Galileo's lifetime astronomy
with the telescope brought into being a completely new branch of
scientific investigation. Its first results were striking, and provided
powerful arguments against Aristotle. In January 1610 Galileo
saw four of the satellites of Jupiter, which he called the Medicean
stars and regarded as forming a visible model of the whole solar
system. Later he observed the phases of Venus, from which it
could be deduced that the planet revolves around the sun, and
not between the sun's sphere and the moon's as Ptolemy's hypo-
thesis supposed. He observed the moon itself, and confirmed his
conjecture that it was a body resembling the earth, with valleys
and mountains whose heights he estimated from the lengths of
their shadows. His telescope resolved part of the Milky Way into
a dense cluster of stars. The discovery of sun-spots was made by

1 Sidereus Nuncius ( 1 6 1 o) ; Istoria e dimostrazioni intorna alle macchie solari (1613);
H Saggiatore (1623), an( ^ t ^ le Dialogues of 1632.

io8 THE SCIENTIFIC REVOLUTION

several observers of whom Galileo was one. They are, of course,
sometimes visible to the naked eye; Kepler had failed to recognize
one in 1607 when seeking for a transit of Mercury. Fabricius
probably made the earliest discovery of these maculae)
and Scheiner certainly wrote the largest book on them, but
it was Galileo who realized their importance for astronomical
theory.

To anyone who was prepared to think, the discoveries that
followed upon the invention of the telescope would suggest a
single train of thought which was certainly anti-classical but
equally departed very far from the ideas of Copernicus. It would
seem that celestial phenomena were much more complex than any
extant astronomical system allowed. It would seem that the stars
were not finitely or infinitely remote, but distributed through
space. It would appear also that the heavens, far from being in-
corruptible and unchanging, were undergoing regular and irregu-
lar mutations, as Tycho Brahe had suggested as early as 1572.
The planets, notably Saturn, whose ring-satellite was not yet
fully understood, altered their aspects, and the sun itself was
stained by spots that enabled its revolution upon its axis to be
traced. The image of the moon could be conceived as comparable
to that of the earth seen at the same distance. All this tended to-
wards one general conclusion, that the universe was a physical
structure, not composed of light and a matter totally different
from the matter of the terrestrial region, but rather of two types of
physical body. The first, the stars, were incandescent sources of
light and plainly physical since they were not invariable. The
second, of which more could be learnt, the planets, were physical
bodies practically indistinguishable at this stage from the earth
itself, which could now be placed without hesitation in the class
of solar satellites on physical grounds as well as by reason of its
motion. Physical astronomy was thus a creation of the telescope,
for in the past the sole subject of astronomical science had been the
analysis of the positions and motions of the heavenly bodies with-
out consideration of their nature, which had been resigned to the
speculative discussions of philosophers, while astrology had em-
braced the supposed influences of these bodies upon the terrestrial
region. The concept either of physical astronomy or of celestial
mechanics (which came later) was completely irreconcilable with
the philosophic background of sixteenth-century practical astro-

THE ATTACK ON TRADITION: ASTRONOMY 109

nomy, and it was necessary to reinterpret the Copernican heliostatic
universe in this new light.

This reinterpretation was achieved in Galileo's Dialogues on the
Two Chief Systems of the World (1623) which was, therefore, far more
than a mere defence of the heliostatic principle. At the same time,
it will be seen that Galileo's treatise did not advance beyond De
Revolutionibus in one respect it retained perfect circular motion
as a "privileged case" and in another respect it was even far
inferior, for as a guide to positional astronomy the Dialogues are
worthless. Galileo wholly neglected the complexities of planetary
motion with which astronomical theoreticians had struggled for
two thousand years, and on which his contemporary Kepler was
to spend his life. In astronomy, Copernicus and Kepler set them-
selves against Ptolemy; Galileo's opponent was Aristotle, the
philosopher.

Within a few years after 1609 Galileo's teaching at Pisa as
modified by his discoveries with the telescope had become uncon-
ventional enough to occasion his first encounter with the Holy
Office. The Dialogues were conscious propaganda for the new
philosophy, though the opinions expressed were put in the mouths
of imaginary characters. Galileo did not scruple to indulge in a
certain buffoonery with the Aristotelean Simplicius, whose feeble
defences are mercilessly attacked. The first pages of the Dialogues
contain a delightful battle of wits in which of course the Copernican
is made to score heavily. Galileo examines the reasoning by which
it is argued that the heavens and the terrestrial region are distinct,
both in their motions and their natures. He concedes that the
motions of the heavenly bodies are perfectly circular, since only
by such motion could the pattern of the heavens be preserved
without change, and that rectilinear motion 'at the most that
can be said for it, is assigned by nature to its bodies, and their
parts, at such time as they shall be out of their proper places,
constituted in a depraved disposition, and for that cause needing
to be reduced by the shortest way to their natural state.' 1 But he
denies that terrestrial bodies do, in fact, move along straight lines,
and so the antithesis is not a true one. As for the Aristotelean
contention that the elements move directly towards and away
from the centre of the universe along straight lines, Galileo replies:

1 "The System of the World in Four Dialogues," translated by Thomas
Salusbury in his Mathematical Collections (London, 1661), vol. I, p. 20.

no THE SCIENTIFIC REVOLUTION

If another should say that the parts of the Earth, go not in their
motion towards the Centre of the World, but to unite with its Whole,
and that for that reason they naturally incline towards the centre of
the Terrestrial Globe [a notion distinctly reminiscent of William
Gilbert], by which inclination they conspire to form and preserve it,
what other All, or what other Centre would you find for the World,
to which the whole Terrene Globe, being thence removed, would
seek to return, that so the reason of the Whole might be like to that of
its parts? It may be added, that neither Aristotle nor you can ever
prove, that the Earth de facto is in the centre of the Universe; but if
any Centre may be assigned to the Universe, we shall rather find
the Sun placed in it.

A number of propositions in mechanics are carefully elucidated,
and it is made apparent that the opposition of the Copernican to
the traditional world-picture will depend upon his completely
different analysis of the properties of moving things. Mechanics
in fact is the foundation of cosmology:

. . . none of the conditions whereby Aristotle distinguished! the Coeles-
tial Bodies from Elementary [i.e. terrestrial], hath other foundation
than what he deduceth from the diversity of the natural motion of
those and these; insomuch that it being denied, that the circular
motion is peculiar to Coelestial Bodies, and affirmed, that it is agree-
able to all Bodies naturally moveable, it is behooful upon necessary
consequence to say, either that the attributes of generable or in-
generable, alterable or unalterable . . . equally and commonly
agree with all worldly bodies, namely, as well to the Coelestial as to
the Elementary; or that Aristotle hath badly and erroneously de-
duced those from the circular motion, which he hath assigned to
Coelestial Bodies. 1

That is, if the earth moves, all Aristotle's physical theory of
cosmology is baseless. Soon after this, Galileo makes the general
discussion of the " architectonics" of the world break down on the
argument that hot and cold are not qualities proper to the heavenly
bodies. That sort of dictum (he remarks) leads to ' a bottomless
ocean, where there is no getting to shore; for this is a Naviga-
tion without Compass, Stars, Oars or Rudder. 5 Accordingly the
debate shifts to the evidence for or against the changelessness of
the heavens, in which the new observations made with the tele-
scope are fully discussed, and a detailed comparison is made

1 Salusbury, op. cit. y p. 25.

THE ATTACK ON TRADITION: ASTRONOMY in

between the optical properties of the earth and the moon. From this
their physical similarity is deduced. Incidentally Galileo points
out the futility of the notion that changes in the celestial region
would be impossible because they would be functionless in the
context of human life, the purpose of the heavenly bodies being
sufficiently served by their light-giving and regular motion. Nor
does he pass over the curious judgement which made sterile im-
mutability a mark of perfection: rather if the earth had continued
' an immense Globe of Christal, wherein nothing had ever grown,
altered or changed, I should have esteemed it a lump of no great
benefit to the World, full of idlenesse, and in a word, superfluous.'
By such asides as these, in a strictly scientific argument, the values
of conventional thought were challenged in turn, its texture made
to seem weak and strained.

The second Dialogue opens with caustic mockery of foolish
deference to Aristotle's authority: 'What is this but to make an
Oracle of a Log, and to run to that for answers, to fear that, to
reverence and adore that? ' Those who use such methods are not
philosophers but Historians or Doctors of Memory: our disputes,
says Galileo, are about the sensible world, not one of paper. As for
the motion of the earth, it must be altogether imperceptible to its
inhabitants, c and as it were not at all, so long as we have regard
onely to terrestrial things,' but it must be made known by some
common appearance of motion in the heavens; and such there is. 1
But in so far as motion is relative, the science of motion cannot
decide whether earth or heaven really moves. 2 Consequently
opinion turns on what is "credible and reasonable." It is more
reasonable that the earth should revolve than the whole heaven;
that the celestial orbs should not have contradictory movements;
that the greatest sphere should not rotate in the shortest time; that
the stars should not be compelled to move at different speeds with
the variation of the Poles. On all these points Galileo's view of
what is " reasonable" supposes a different perspective from that
of anti-Copernican philosophers; but Simplicius is not allowed to
argue the matter, and merely remarks that 'The business is, to
make the Earth move without a thousand inconveniences.' The

1 Salusbury, op. cit. 9 p. 97.

2 * Motion is so far motion, and as Motion opera teth, by how far it hath
relation to things which want Motion: but in those things which all equally
partake thereof it hath nothing to do, and is as if it never were.'

ii2 THE SCIENTIFIC REVOLUTION

first group of " inconveniences " to be dealt with includes the usual
mechanical phenomena, the stone falling vertically, the cannon-
ball ranging equally far east and west, which it was thought
would not occur if the earth moved beneath. They naturally lead
Galileo into a long exposition of his new ideas on mechanics, in
which a partial version of the law of inertia is enunciated. Much
of this reasoning against the Aristotelean doctrine of motion had
already been exactly anticipated by the impetus philosophers of
the middle ages. There is a long discussion of the so-called devia-
tion of falling bodies a problem which attracted attention inter-
mittently throughout the seventeenth century as affording a
possible proof of the earth's rotation. It had been alleged, for
example by Tycho Brahe, that if a stone was allowed to fall freely
from the top of the mast of a moving ship, it would not fall at the
foot of the mast, but well aft. Galileo shows that this is inconsistent
with the true principles of mechanics. In spite of Simplicius' cry
4 How is this? You have not made an hundred, no not one proof
thereof, and do you so confidently affirm it for true?', Galileo
places his faith in a priori reasoning to predict the result of an ex-
periment he has never made, though previously he has taken pains
to point out (against Aristotle) that experiment is always to be
preferred to ratiocination. Therefore, since all heavy bodies have
inertia: 'we onely see the simple motion of descent; since that
other circular one common to the Earth, the Tower and our selves,
remains imperceptible, and as if it never were, and there remaineth
perceptible to us that of the [falling] stone, onely not participated
in by us, and for this, sense demonstrateth that it is by a right line,
ever parallel to the said Tower.' 1

In his attempt to analyse the true path followed by a falling
body in space the resultant of its double motion about and
towards the centre of the earth Galileo committed a serious error
caused by his imperfect definition of inertial motion. Though
familiar with the common effects of centrifugal force, he over-
looked the fact that the inertial motion of the falling stone is along
a tangent to the earth's surface, so that in the absence of gravity
it would never describe a circle about the earth's centre unless it
was held to it in some way, but would continue along a straight
line into space. Galileo thought, on the contrary, that its inertia,
impetus or virtus impressa could cause a free body to revolve in a
1 Salusbury, op. cit., p. 143.

THE ATTACK ON TRADITION: ASTRONOMY 113

circle, and so he declared that if a stone fell at a uniform velocity
towards the centre, its compound path would be an Archimedean
spiral. Since the motion of descent is accelerated, however, he
devised a demonstration showing that the true path in space is
probably an arc of circle. Marin Mersenne, who obtained the
accurate law of inertia from Descartes, described this curve cor-
rectly in 1644 as a paraboloid. It is possible that Galileo was in-
duced to make this error, which he never corrected despite its
incongruity with the parabolic theory of projectiles worked out
in the Discourses, because of his preconception in favour of perfect
circular motion. Eager to prove that even the local motions of
terrestrial bodies are truly circular, as further testimony against the
Aristotelean antithesis between circular-celestial and rectilinear-
terrestrial displacements, he also noted that, on his theory, the
absolute velocity in space of the falling body is uniform, accelera-
tion relative to the earth's surface being only apparent. This
being so, the question of finding the cause of acceleration, which
had made Galileo doubtful of the original impetus theory many
years before, could be shown to be spurious; the problem is
solved by denying absolute acceleration in falling bodies alto-
gether, and visualizing the phenomenon of relative acceleration as
the product of the uniform movement of observer and object along
intersecting circular paths.

With one exception the mechanical objections that could be
raised against the earth's diurnal revolution are disposed of by
appeal to the principles of inertia and of the relativity of motion
which Galileo illustrates with a variety of ingenious examples.
Other problems in mechanics auxiliary to the main argument are
touched upon, such as the conception of static moment, the iso-
chronism of the pendulum, and the law of falling bodies, here
quoted by Galileo without proof. In replying to the objection that
the rotation of the earth would hurl down buildings, etc., Galileo
makes the first investigation into centrifugal forces. Using the
idea of virtual forces, enunciated in connection with static
moment, he proves that with equal peripheral velocities the force
is inversely proportional to the radius. He points out that the
angular velocity of the earth is very small, and its radius very
large: therefore the force set up would not be sufficient to over-
come a body's natural gravity. From Galileo's argument ('thus
we may conclude that the earth's revolution would be no more

8

H4 THE SCIENTIFIC REVOLUTION

able to extrude stones, than any little wheel that goeth so slowly,
as that it maketh but one turn in twenty-four hours') it is clear
that he did not realize that when angular velocities are equal, the
centrifugal force is directly proportional to the radius. It was not
indeed till much later that the rotatory stresses in equatorial regions
were detected.

The extensive illustration of the perfect agreement between the
heliocentric theory and a rational natural philosophy is certainly
Galileo's most important contribution to the cosmological debate.
In this there was no conflict of principle between the new philo-
sophy and the old: they were agreed that the science of motion
was the foundation of physics, and that physics and astronomy
must speak the same language. Galilean mechanics was thus the
necessary complement to Copernican astronomy, and though it
is true (as Professor Hcisenberg has remarked) 1 that nothing could
have been more surprising to the scientists of the seventeenth
century than their discovery that the same mechanical laws were
appropriate for celestial and terrestrial motions alike, on the
smallest and largest scale, the coincidence was not fortuitous, for
it followed from Galileo's conscious endeavour to interpret
Copernicus' mathematical model in terms of natural philosophy.
There could be no question as Galileo frequently emphasizes in
the course of the Dialogues of proving that the Copernican
hypothesis was necessarily true; but with the readjustment of
physical ideas effected by him it could be shown to be at least
as plausible as the Ptolemaic. Aristotle's physical theory of the
cosmos, terrestrial and celestial, had been an integral whole; for
Galileo astronomy and physics were so far independent that he
acknowledged the incompetence of purely physical observations
to determine the system of the world, but he had no doubt that
the same laws of motion were universally applicable, to celestial
and terrestrial bodies alike, even to the point of satisfying himself
that if the planets had fallen freely towards the sun from the same
determinate point, they would have acquired, when they had
attained their actual orbital distances from it, the velocities with
which they actually revolve about it. A true mechanical theory,
besides wholly destroying all physical objections to the helio-
centric system, actually created a preponderance of belief in its
favour.

1 Philosophic Problems of Nuclear Science (London, 1952), p. 35.

THE ATTACK ON TRADITION: ASTRONOMY 115

In the Third Dialogue Galileo takes up the arguments for and
against the annual motion of the earth. Beginning with purely
astronomical considerations, he makes plain his distrust of the
quantitative measurements of his own time, from which, however,
he confirms that the new star of 1572 was truly celestial. The
irradiation of light, exaggerating the stars' and planets' apparent
diameters, is next explained, and the observations are proved to
verify the Copernican arrangement. Galileo then discusses, in an
eloquent and lucid exposition, the problem posed by the absence
of a detectable stellar parallax. He was not of the opinion that the
stars are infinitely remote, but he does argue that the size of the
universe is such that its dimensions are beyond human standards
of magnitude. If its immensity can be grasped, then it cannot be
beyond the power of God to make it so immense; if its immensity
is beyond comprehension, it is none the less presumptuous to
suppose that God could not create what the mind cannot compre-
hend. Simplicius objects that a vast region of empty space between
the orbit of Saturn and the fixed stars would be superfluous and
purposeless, so that Galileo can again condemn the introduction
of teleological reasoning into science. 1 He appears to think that
the remoteness of the fixed stars, though vast, is not to be exag-
gerated, and calculates that even if the radius of the stellar sphere
bore the same proportion to the semi-diameter of the earth's
orbit, as that bears to the radius of the earth, a star of the sixth
magnitude would still be no larger than the sun, which is,
according to Galileo's reckoning, five and a half times as big as
the earth. The assiduity and skill of astronomers in making
observations of stellar parallax is in any case doubtful, since these
would demand 'exactnesse very difficult to obtain, as well by
reason of the deficiency of Astronomical Instruments, subject to
many alterations, as also through the fault of those that manage
them with less diligence than is requisite. . . . Who can in a
Quadrant, or Sextant, that at most shall have its side 3 or 4
braccia long, ascertain himself. . . in the direction of the sights, not
to erre two or three minutes?' 2

Galileo's general explanation of the manner in which the
heliocentric theory ' 'saves the phenomena" is modelled on that
of Copernicus, save that he denies the reality of the third motion

1 A teleological argument is, however, used by Galileo himself later.

2 Salusbury, op. cit., vol. I, p. 351.

n6 THE SCIENTIFIC REVOLUTION

which Copernicus had ascribed to the earth in order to account
for the parallelism of its axis. Thus, for instance, the principle of
the relativity of motion solves the appearance of stations and
retrogressions in the planets. But Galileo nowhere indicates that
their orbits, which Copernicus had made eccentric, are other than
purely circular about the sun, nor does he attempt to justify
particular orbits from the records of positional astronomy. He
further differs from Copernicus in making the centres of the orbits
coincident with the body of the sun. It cannot be said, therefore,
that Galileo improved the Copernican argument in terms of
technical astronomy in the Dialogues, except through his use of
the new qualitative evidence derived from the telescope, which
had already been commented upon in his earlier writings. Indeed,
the extremely simple astronomical model described is flatly
incompatible with precise observation. Galileo, it is clear, was
far more confident of the truth of the mechanical principle that
bodies possess the property of inertial rotation in a perfect circle
than of the accuracy of astronomical measurements. It was a
characteristic of his scientific method of abstraction that it could
more easily analyse, and describe in mathematico-mechanical
language, a version or model of the real phenomena which was
less complex than the phenomena themselves; and Galileo was
not always sufficiently conscious of the genuine significance of the
greater complexity. In this instance Galileo was deceived, partly
by his imperfect definition of inertia (only implicitly rectified in
his discussion of centrifugal force) and partly by lingering astro-
nomical ideas. It is noteworthy that, while he does not consider
whether the spheres are real or not, the word itself he uses naturally
and without comment. A perfectly balanced, hollow sphere, or a
circle, could of course be properly imagined to rotate inertially as
a rigid body carrying round with it a planet. It seems, therefore,
that Galileo, whose approach to the problem was kinematic
rather than truly dynamic, did not sufficiently reflect upon the
consequences of taking away the heavenly spheres, and leaving
the stars and planets as free bodies in space if indeed this was
firmly his conviction. Unlike Newton, Galileo never compared
the motion of a planet to that of a projectile; unlike Kepler, he
did not know that the geometry of planetary orbits vitiated any
kind of spherical model.

The scientific work of Johann Kepler (1571-1630) was of an

THE ATTACK ON TRADITION: ASTRONOMY 117

utterly different quality from that of Galileo. The Dialogues, and
to a less extent the Discourses, are popular books. In them Galileo
does not fear to explain many elementary matters with which the
expert would already be well acquainted. Kepler's writings, on
the other hand, are so highly abstruse that the spread of his ideas
was retarded by the difficulty of discovering and understanding
them. They required that the reader be fully trained in the
elaborate mathematics of positional astronomy. As Galileo was
complementary to Copernicus, so the mathematician Kepler was
complementary to Galileo, and there is perhaps no more remark-
able example of the way in which two cognate, yet unlike, minds
can follow parallel paths without interaction. Both Galileo and
Kepler sought to strengthen the Copernican doctrine; they
corresponded, and referred favourably to each other; but there
is no shred of evidence that either was to the slightest degree
deflected from his own course, or impelled to modify his own
ideas, by the other's work. The synthesis of their two distinct points
of view was only effected a generation later; until then Kepler
and Galileo had as little in common as Ptolemy and Aristotle. As
in the traditional, so also in the new science of the early seven-
teenth century this failure to overlap was not due to fortuitous
causes, nor to any lack of sympathy between the two modes of
approach. It was simply that the key by which a synthesis could
be effected was not yet found. A cosmological dichotomy existed
in Hellenistic science because physics and positional astronomy
required similar, but not identical models; a comparable dicho-
tomy existed from about 1630 to 1687 because there was no way
in which the observed celestial motions could be interpreted in
accordance with the kinematical principles of Galileo. The two
lines of progress could only be brought together by a higher
generalization for which dynamics was essential and kinematics
inadequate.

Kepler was the discoverer of the new descriptive laws of plane-
tary motion, but he achieved more than this, for he made the
first suggestions towards a physical theory of the universe adapted
to the necessities of the new description. Although his life was
given over to mathematical drudgery in which he was aided by
the much improved trigonometry of his day, and the invention of
logarithms Kepler was a man of vigorous and original scientific
imagination. The mathematical operations he set himself could

n8 THE SCIENTIFIC REVOLUTION

hardly have proved creative without it. In his first work he sought
for the divine canon in celestial architecture, and this pursuit
ran through all his later computations. But Kepler was no empty
theorist: the divine art of proportion, the harmony of the grand
design of nature, was to be elucidated from the most precise
mathematical observation of the universe. Hence the turning-
point in his career, the necessary foundation for his work, was
Kepler's encounter with the Danish astronomer, Tycho Brahe
(1546-1601), who, after a quarrel with King Christian IV, had
deserted his royally endowed observatory at Hveen to enter the
service of the eccentric Emperor Rudolph II, patron of alchemists
and astrologers, at Prague. Thither Kepler was drawn from Graz
in Styria by the undigested mass of observations, of unparalleled
accuracy, which Tycho had brought with him. Ultimately the
accumulated result of thirty years' labour yielded up the three
laws of planetary motion which, as Kepler framed them, contained
the decisive argument against the geostatic hypothesis so warmly
defended by Tycho.

In many ways the Danish astronomer's role in the early history
of modern astronomy is analogous to that of Vcsalius in anatomy.
Perhaps he was even more fully than the anatomist the iirst
modern exponent of the art of disinterested observation and
description. For if Tycho imported into his astronomical theory
dominant factors which were physical in nature, it cannot be
said (as it may of Vesalius' physiological preconceptions) that the
evidence to confute them lay before his eyes. The problem of
attaining precision was no less real for him than for Vesalius, and
the methods he devised to solve it were probably more original.
And certainly Tycho was unique among early modern scientists
in his insistence upon the crucial importance of accurate quanti-
tative measurement; always a desideratum in astronomy, cer-
tainly, but never previously handled with the analytical and
inventive powers of Tycho, who first consciously studied methods
of estimating and correcting errors of observation in order to
determine their limits of accuracy. The most accurate predecessors
of Tycho were not Europeans, but the astronomers who worked
in the observatory founded at Samarkand by Ulugh Beigh, about
1420. Their results were correct to about ten minutes of arc
(i.e. roughly twice as good as Hipparchus'); Tycho's observations
were about twice as good again, falling systematically within

THE ATTACK ON TRADITION: ASTRONOMY 119

about four minutes of modern values. 1 This result was achieved
by patient attention to detail. The instruments at Hveen were
fixed, of different types for the various kinds of angular measure-
ment, and much larger than those commonly used in the past,
so that their scales could be more finely divided. They were the
work of the most skilful German craftsmen, whom Tycho en-
couraged by his patronage and direction. He devised a new form
of sight, and a sort of diagonal scale for reading fractions of a
degree. In measuring either the longitude of a star, or its right
ascension, it is most convenient to proceed by a way that requires
an instrument measuring time accurately, and Tycho studied the
improvement of clocks for this purpose: but he found that a new
technique of his own by which observations were referred to the
position of the sun was more trustworthy. He was the first
astronomer in Europe to use the modern celestial coordinates,
reckoning star-positions with reference to the celestial equator,
not (as formerly) to the ecliptic. Another innovation in his
practice was the observation of planetary positions not at a few
isolated points in the orbit (especially when in opposition to the
sun), but at frequent intervals so that the whole orbit could be
plotted.

The techniques and standards of precision in astronomy, of
which Tycho was the real founder, were evolved slowly over a
period of thirty years to fulfil a very simple ambition. When he
made his first observations with a home-made quadrant, he found
that the places given in star-catalogues were false, and that events
such as eclipses occurred as much as two or three days from the
predicted times. As the Copernican "Prutenic Tables" were
computed from old observations they had brought in no significant
improvement. The task Tycho set himself, therefore, was very
simple: to plot afresh the positions of the brightest stars, and with
the fundamental map of the sky established to observe the motions
of sun, moon and planets so that the elements of their orbits could
be recalculated without mistake. It does not seem that he under-
took this with any violently partisan intent, but it is likely that he
wished to show the falsity of the Coperni cans' claim to have

1 As was first pointed out by Robert Hooke, the unaided human eye is
incapable of resolving points whose angular separation is less than about two
minutes of arc, so that Tycho's work approximately attains the minimum
theoretical limits of accuracy for instruments such as he used.

i 2 o THE SCIENTIFIC REVOLUTION

increased the accuracy of celestial mathematics, and to bolster
up the geostatic doctrine by publishing unimpugnable tables and
ephemerides calculated upon that assumption. To vindicate the
"Tychonic" geostatic system was the last ambition of his life,
which he charged Kepler to fulfil. However, he was no slavish
adherent to conventional ideas. He did not believe that apparent
changes in the sky were due to meteors in the earth's atmosphere;
he proved that comets were celestial bodies, and that the spheres
could have no real existence as physical bodies since comets pass
through them; and his description of the planetary motions
is relativistically identical with that of Copernicus. 1 As an
astronomer, indeed, Tycho in no way belonged to the past: it
was as a good Aristotelean natural-philosopher that he believed
the earth incapable of movement.

Tycho's observations, including his catalogue of 1,000 star-
places, have not proved of enduring value. The earliest observa-
tions that have an other than historical interest are those of the
English astronomer, Flamsteed, early in the eighteenth century
(error c. ten seconds of arc), for within about sixty years of Tycho's
death the optically-unaided measuring instrument, still ardently
defended by Hevelius of Dantzig, was beginning to pass out of
use. Within a century Tycho's tables had been thoroughly revised
by such astronomers as Halley, the Cassinis, Roemer and Flam-
steed. In the interval, however, Kepler's discoveries based on
Tycho's work had become recognized. To appreciate the relation-
ship between Kepler and Tycho the inventive mathematician
and the patient observer it must be realized that the balance of
choice between Keplerian and Copernican astronomy is very
narrow. Until measurements were available whose accuracy
could be relied upon within a range of four minutes, or even less,
there was no need to suppose that the planetary orbits were any-
thing other than circles eccentric to the sun. Kepler, in plotting
the orbit of Mars, from which he discovered the ellipticity of
planetary orbits in general, was able to calculate the elements of
a circular orbit which differed by less than ten minutes from the
observations. It was only because he knew that Tycho's work was
accurate within about half this range that he was dissatisfied and

1 The point about comets was not noticed by Galileo, some of whose other
arguments cannot be directed against the "Tychonic" version of the geostatic
idea.

THE ATTACK ON TRADITION: ASTRONOMY 121

impelled to go further. Kepler's famous "First Law" was thus the
first instance in the history of science of a discovery being made as
the result of a search for a theory, not merely to cover a given set
of observations, but to interpret a group of refined measurements
whose probable accuracy was a significant factor. Discrimination
between measurement in a somewhat casual sense, and scientific
measurement, in which the quantitative result is itself criticized
and its range of error determined, only developed slowly in other
sciences during the course of the scientific revolution.

While Kepler's discoveries would have been impossible without
the refinement of observation attained by Tycho Brahe, more than
mathematical precision was involved in them. Before the tele-
scope, the only materials available for the construction of a
planetary theory were angular measurements principally deter-
minations of the positions of the planets in the zodiac when sun,
earth and planet were in the same straight line. Consequently the
most that a planetary theory could achieve was to predict the
times at which a planet would return to the same relative situa-
tion, and its position at those times. The mathematical analysis of
the solar system as a number of bodies moving in three-dimensional
space had never been attempted, as such, by the older astronomers,
who had been content to assign such problems to philosophers.
They had never concerned themselves with the real path of a
planet in space, so long as their model predicted with tolerable
accuracy the few recurrent situations in which observations could
easily be made. The whole tendency of the scientific revolution was
to rebel against this view of the astronomer as a mathematician, a
deviser of models to save the phenomena, and to see astronomy
as a science comprehending the totality of knowledge concerning
the heavens and the relations of the earth to the celestial regions.
Copernicus had abolished the equant because it was a mathe-
matical fiction, an unphilosophical expedient. Galileo modified
Copernicus' universe even further in the direction of physical
explicability. Kepler had a true conception of the universe as a
system of bodies whose arrangement and motions should reveal
common principles of design or in more modern language, be
capable of yielding universal generalizations which were to
be demonstrated from the observations, not from physical or
metaphysical axioms. For Kepler the astronomer's task was not
to study the universe piecemeal to construct models for each

122 THE SCIENTIFIC REVOLUTION

separate planet but by studying and interpreting it as a whole
to prove that the phenomena of each part were consistent with
a single design. His aim was to provide a fitting philosophical
pattern for the new discoveries of mathematical astronomy: c so
that I might ascribe the motion of the Sun to the earth itself by
physical, or rather metaphysical reasoning, as Copernicus did by
mathematical,' he remarked in the preface to the Cosmographic
Mystery. Exact science might properly make inroads upon the
established prerogative of philosophy; it was far from being his
purpose to expel natural-philosophical considerations from quan-
titative science altogether.

Indeed, Kepler's scientific work was critically influenced by his
attachment to extra-scientific ideas. He had firm preconceptions,
and he was strongly opposed to mere phenomenalism. Even more
than Copernicus he was infected with Pythagorean mysticism,
and fascinated by the primary, foundational significance of purely
numerical relations. He could elaborately interpret his descriptive
generalizations in astronomy in the terms of musical harmony
genuine "music of the spheres"; draw the analogy between sun,
fixed stars and planets, and God the Father, the Son and the Holy
Ghost; or discuss the aspects of the planets at the moment when
the cosmos was created. Some of the questions which he sought to
answer are, to later minds, absurd or meaningless. Rightly he held
that the question, why are the appearances thus and not other-
wise, requires a scientific (rather than a purely philosophic)
answer, and he was the first astronomer to take a serious grasp of
it, but for him also such a question as, why are there no more and
no less than five planets, was also urgent. As Kepler handled it,
the inquiry involved an unshaken medieval complacency in the
certitude of knowledge. His first explanation was given in the
Cosmographic Mystery (1597), where he adopted the theory that
the design of the universe is modelled upon the series of five
geometrically regular solid bodies. He had tried in vain to find a
rationale for the dimensions of the planetary orbits as calculated
by Copernicus by considering them as mathematical series, or as
circles described round regular polygons. The number five was
certainly accounted for in this theory, and moreover Kepler
found that if the regular solids were supposed to be fitted each
inside a sphere, and these within each other in a certain order, the
dimensions of the six spheres so arranged corresponded approxi-

THE ATTACK ON TRADITION: ASTRONOMY 123

mately to those of the earth and five planets. In the Cosmographic
Mystery Kepler argued trenchantly in favour of the Copernican
system, which he modified in order to make the sun its central
point, instead of the centre of the earth's orbit. Believing that the
imperfect agreement between his theory and Copernicus' determi-
nations might be due to faulty observation, he had good hope of
confirming it with the aid of the more accurate measurements
of Tycho Brahe.

As Tycho's assistant at Prague, Kepler was directed to perfect
the theory calculated in accordance with the observations on
Mars by Tycho's Danish assistant, Longomontanus. The result
was published in the New Astronomy or Celestial Physics, a book sub-
sidized by the Emperor Rudolph II and published in 1609, eight
years after Tycho's death had released Kepler from adherence to
Tycho's geostatic system. His first discovery was that the plane of
the orbit of Mars passed through the sun (a point in favour of
Copernicus) and was invariably inclined to the ecliptic. A major
problem was the planet's unequal velocity in its course. Although
Kepler restored the equant-point, and so could adjust the varying
angular velocity of Mars with respect to the sun in different pro-
portions, he found that no single position of the cquant-point
would give a rate of variation satisfying all the observations. The
same difficulty occurred when the earth's orbit was considered.
Kepler found that its motion was certainly faster when near to the
sun than when most remote from it, but not in such a way that the
angular velocity about any arbitrary fixed point within the circle
was uniform. 1 The problem one after Kepler's own heart was
to find a theorem denoting this variation in velocity, an equation
relating the speed of the planet's rotation at any point to its
distance from the sun. Here Kepler was assisted by a quasi-
philosophical notion that it was a "moving spirit" in the sun
itself which caused the planet's circumgyrations. The further the
planet receded from this spirit, the more weakly its force would
operate, and so the planet's velocity would lessen. This anima
motrix is referred to in the Cosmographic Mystery as hurrying along
the stars (i.e. planets) and comets which it reaches, with a swift-
ness appropriate to the distance of the place from the sun, and the

1 This was the first mathematical proof that the motion of the earth (or,
as Ptolemy would have said, of the sun) is strictly identical with that of the
planets.

124 THE SCIENTIFIC REVOLUTION

strength of its virtue there. 1 The problem Kepler set himself, of
assigning a determinate motion to a body revolving round a fixed
point in an eccentric circle so that it moves through equal in-
finitesimal small arcs in times proportional to its distance from
the point, is one that can be solved by integration. He used a
method similar to that by which Archimedes had long before
evaluated TT, and so arrived at his "second" planetary law, that
the radius-vector between sun and planet sweeps over equal areas
of the orbit in equal times. Though his first proof was open to
criticism, Kepler was later able to satisfy himself that the various
errors in his method cancelled each other, so that the law was
rigorously true. 2

At this stage in his complex and tedious calculations involving
the geometrical analysis of many theoretical possibilities, as well
as the continual checking of the predicted motions against ob-
servations selected from Tycho Brahe's great store Kepler was
already convinced that the orbit of the earth or a planet could
not be a perfect circle eccentric to the sun. As he said:

The reflective and intelligent reader will see, that this opinion among
astronomers concerning the perfect eccentric circle of the orbit in-
volves a great deal that is incredible in physical speculation. . . . My
first error was to take the planet's path as a perfect circle, and this
mistake robbed me of the more time, as it was taught on the auth-
ority of all philosophers, and consistent in itself with Metaphysics.

In calculations of the earth's angular velocity he could assume the
orbit to be circular, because its ellipticity is small (nam insensile
est . . . quantum ei ovalis forma detrahit), but in the orbits of the
other planets the difference would become very sensible. 3 His next
problem, obviously, was to define the nature of this non-circular
orbit more closely. He therefore returned to the investigations on
Mars, in a far more secure position now that he had worked out
the movement of the observer's platform the earth with greater
accuracy than before. Experiment showed that the orbit of Mars
could not, indeed, be circular, for this when compared with the
observations made the motion of the planet too rapid at aphelion

1 Kepler: Gesammelte Werke, vol. I, p. 77.

2 Ibid., vol. Ill, pp. 263-70.

3 The eccentricity of the earth's orbit is only 0-017, that of Mars is about
5 times as great, and of Mercury 12 times. The error which constituted
Kepler's problem increases roughly as the square of the excentricity.

THE ATTACK ON TRADITION: ASTRONOMY 125

and perihelion, and too slow at the mean distances. After many
trials Kepler wrote: 'Thus it is clear, the orbit of the planet is not
a circle, but passes within the circle at the sides, and increases its
amplitude again to that of the circle at perigee. The shape of a
path of this kind is called an oval.' Again, the development of
Kepler's thoughts was influenced by his idea of the physical
mechanism which could produce such a departure from the per-
fectly circular form. He supposed that the oval path was traced
by the resultant of two distinct motions; the first being that due to
the action of the sun's virtue, varying with the distance of the
planet, and the second a uniform rotation of the planet in an
imaginary epicycle produced by its own virtus matrix. The hypo-
thetical orbit would be an oval (or rather an ovoid, since its apses
would be asymmetrical) enclosed within the normal eccentric at
all points save the apses. Kepler spent much labour in vain at-
tempts to geometrize this hypothesis so that it could be compared
with observation. Direct and indirect methods were tried, but
Kepler finally had to confess that the oval orbit and the theory of
its physical causation had "gone up in smoke." It was the acci-
dental observation of a numerical congruity that led him to
substitute for the oval an ellipse, which he found could be made
to fit the area-law exactly. Even at this stage he was much dis-
turbed because he could not give a physical meaning to the
elliptical orbit, until he satisfied himself that such an ellipse as he
required would be traced out by a planet supposed to librate on
the diameter of an epicycle.

The third of Kepler's great descriptive theorems, that the
squares of the periodic times of the planets are in the same ratios
as the cubes of their respective mean distances from the sun,
which solved the problem upon which he had originally embarked,
was announced in The Harmonies of the World (1619). This strange
book, resuming the theme of the Cosmographic Mystery, has the
same concern with esoteric relationships. Kepler compared the
instantaneous velocities of the planets at different points in their
orbits, and expressed these ratios in terms of musical harmony.
He further compared the velocities of the several planets at their
nearest approach to the sun; and finally he was induced to com-
pare, not merely the periods, times and distances of the planets,
which he had already discovered to be without significance, but
the powers of these numbers, and so hit upon the "third law." A

126 THE SCIENTIFIC REVOLUTION

century and a half later, in 1772, a purely empirical formula
connecting the distances of the planets was used by Johann Elert
Bode to predict the existence of an unknown planet beyond
Saturn. His audacity was vindicated by the discovery of Uranus.
The simplicity and directness which these relations introduced
into astronomy need no emphasis. The shapes and dimensions of
the planetary orbits, and the velocities of the planet's motions
within them, could now be calculated with ease and certitude.
Kepler's Laws were the observational axioms upon which
Newtonian celestial mechanics was to rest secure. What is not
obvious is that Kepler's discoveries were displayed in extremely
difficult books, published far from the main foci of scientific
activity in France and Italy, and so were passed over by a genera-
tion that ignored their true importance. Kepler himself regretted
the abstruseness of his subject:

Most hard today is the condition of those who write mathematical
works, especially astronomical treatises. For unless you make use of
genuine subtlety in the propositions, instructions, demonstrations and
conclusions, the book will not be mathematical; if you do use it,
however, reading it will be made very disagreeable, particularly in
the Latin language, which lacks articles and the grace of Greek. And
also today there are extremely few qualified readers, the rest com-
monly reject [such books]. How many mathematicians are there,
who would toil through the Conies of Apollonius of Perga? Yet that
material is of a kind that is far more easily expressed in figures and
lines, than is Astronomy. 1

fn truth Kepler was the last of the medieval planetary theorists,
the last laborious computer and porer over tables. Such methods
were too tedious for his own generation, excited by discovery and
the new philosophy, and to a careless reader Kepler's discoveries
were hidden in the idiosyncrasy of his strange speculation. When
they were appreciated, new mathematics and new techniques were
framing a new astronomy.

But Kepler was more than a mathematician. Perhaps the
importance of his work, apart from the three famous Laws, has
not been sufficiently esteemed. The older historians passed politely
over Kepler's theorizing on physical mechanisms, his love of
analogy, and all that was ancillary to the main mathematical

1 "Astronomia Nova," Ges. Werke, vol. Ill, p. 18.

THE ATTACK ON TRADITION: ASTRONOMY 127

argument, as so much dross that was best left buried. Now it is
not difficult to see that Kepler was as original and stimulating
in his sidetracks as when following the plain mathematical road.
Certainly his ideas on gravity, on the action of forces at distance,
are important factors in the prehistory of the theory of universal
gravitation. The Cartesians ridiculed Kepler's mysterious forces
seated in the sun, and his appetites of matter, just as they later
resisted the notion of gravitational attraction. Kepler does make
odd equivalencies between "soul" or "spirit" and force, never-
theless his cosmological theory was mechanistically designed and
designed to give a far more accurate model than those of either
Galileo or Descartes. It was Kepler who, in the Cosmographic
Mystery, denounced the traditional belief in material spheres
which had been left unchallenged by Copernicus, and on which
Galileo was ambiguously silent:

Neither indeed is to be feared that the lunar orbs may be forced out
of position, compressed by the close proportions of [other celestial]
bodies, if they are not included and buried in that orb itself. For it is
absurd and monstrous to set these bodies in the sky, endowed with
certain properties of matter, which do not resist the passage of any
other solid body. Certainly many will not fear to doubt that there are
in general any of these Adamantine orbs in the sky, that the stars are
transported through space and the aetherial air, free from these
fetters of the orbs, by a certain divine virtue regulating their courses
by the understanding of geometrical proportions.

He went on to ask, by what chains and harness is the moving
earth fastened to its orb? and to point out that nowhere on the
surface of the globe do men find it embedded in a material
medium, but always surrounded by air. Kepler, too, must be
credited, at least as much as Descartes, with the perception that
there must be some source of force, or tension, within the solar
system. It could not be a complex of entirely independent bodies
without mutual interaction. It could not be accidental that the
planes of all the orbits passed through the sun, nor could the
variations of the planet's motion the differences in its velocity
at perihelion and aphelion, for example be explained without
the supposition that some force was acting upon it. For Galileo
the universe was simple and dynamically constant: in Kepler's
far more realistic picture it was highly complex and its dynamical
condition constantly changing. Thus it was the Keplerian picture

128 THE SCIENTIFIC REVOLUTION

that enforced the development of celestial mechanics during the
late seventeenth century. The descriptive and purely empirical
laws of planetary motion presented a problem that natural
philosophy could not escape. Kepler had gone far beyond the
bounds of the astronomical problem of two generations does the
earth move or not? to assert principles of celestial motion, set in
a pattern of theorizing upon cosmic physics, which displaced
traditional doctrines even more thoroughly.

CHAPTER V
EXPERIMENT IN BIOLOGY

"\\7"T HILE *ke ear ty sta g es f the scientific revolution in its
\\ /physical aspects were strongly positive, the first phase
VV in biology seems by contrast indecisive and inconclusive.
The sixteenth century witnessed the promulgation of new ideals
and new methods of study in such fields as botany and zoology,
or anatomy and physiology, but there was as yet no more than the
vague promise of the alternative body of knowledge which the
pursuit of the new ideals and the practice of the new methods
would construct in due course. Though existing doctrines might
be criticized, no others had yet taken shape to displace them.
There were criticisms occasionally of exaggeratedly animistic
patterns of explanation; but the application of mechanistic
philosophy to biological problems was not attempted before
Descartes. As the mind abhors a vacuum, the natural result was
a lag of theory behind observation. The authority of Galen
endured longer than that of Aristotle because it was intrinsically
far more difficult to apply the principles of physics and chemistry
to the investigation of physiological processes than to apply
Galilean mechanics to astronomy; astronomers also had the
advantage over physicians that mechanics was the first science to
enter a modern stage. The effect of the greater subtlety of the
questions handled by the biologist was, so to speak, to distinguish
observation from conceptualization as separate branches of
scientific activity. Many experiments had been carried out in
physical science to confirm or disprove directly the Aristotelean
pronouncements, when as yet the theory of humours or the
Galenic account of digestion were still untested. Experimentation
was not deterred by technical difficulties alone, for imagination
was lacking and the whole framework of ideas which would have
given meaning to such experiments had still to be created. Those
that were planned and successfully carried out such as the well-
known investigation of Sanctorius (1561-1636) into the quanti-
tative gain in weight of the body by ingestion and loss through

129 9

i 3 o THE SCIENTIFIC REVOLUTION

excretion though they produced interesting information, carried
little or no weight for or against the main strategic ideas of
medicine and biology.

In a somewhat similar manner, the advance of the encyclopaedic
naturalists of the sixteenth century towards a modern scientific
method was highly specialized and limited in character. The
naturalist's ideas concerning the origin of organic life, the distri-
bution of plants and animals, and the reasons for their wide range
of structure and form, were still for the most part non-scientific in
origin, or at best derived from very ancient sources. On the other
hand, he was progressing towards modern ways of classifying and
describing organisms and of defining the subject-matter of natural
history. He became less interested in nature-study as an exercise
in morality; he made a partial distinction between the Flora and
the Pharmacopeia. This brought the disadvantage, however, that
as botanists and zoologists became progressively more efficient in
classification and description, they came near to losing interest in
all other problems posed by the organic world. The naturalist was
limited, in the main, to a particular kind of activity ultimately
inherited from the apothecaries' need to distinguish medicinal
herbs partly, of course, because it was one task worth doing
which was within his competence, but partly also because he
lacked the imagination which would have freed him from the
influence of tradition. A different kind of biology, or such crucial
experiments as those of Redi in the seventeenth century on spon-
taneous generation and those of Mendel in the nineteenth on
inheritance, was not technically impossible; it did not necessarily
depend altogether upon laboratories, instruments and the dis-
coveries of other sciences. It did require which is a great deal
intellectual originality. It did require the ability to frame questions
about the living state and ways of proceeding to answer such
questions. This was very different from the compilation of greater
and greater masses of the same type of information.

The vast range of biological and medical science which widened
out during the nineteenth century was, therefore, represented in
the sixteenth only by medicine and natural history: and even
these studies consisted of little more than the endeavour to cure
disease and herbalism, these being in turn closely linked. The
various branches of medicine, such as physiology (the function
of organs in contrast to the arrangement of organs, anatomy),

EXPERIMENT IN BIOLOGY 131

pathology, or hygiene were hardly distinguished save as subjects of
separate treatises by Galen. All parts of medical science, excluding
surgery, fell under the general surveillance of the physician. Or
he might become herbalist or zoologist the former in pursuit of
the medical virtues of plants, and the latter as a comparative
anatomist. Therefore it is not surprising that physicians had a
major creative role in the biology of the sixteenth and seventeenth
centuries, nor that the course of the science was to some extent
directed by medical interests. Among the botanists many were
medical men to name only Fuchs, Cordus, Cesalpino, Bauhin,
Tournefort, and Linnaeus himself. Brunfels, whom Linnaeus
called the father of botany, and John Ray, Linnaeus' greatest
predecessor, were exceptions. All the work in human and com-
parative anatomy, and much microscopy (the famous exception
being Leeuwenhoek) , was carried out by physicians. Surgeons,
being on a lower academic, social and intellectual level, to which
they were firmly suppressed by the energetic corporate interest
of the physicians, had far less opportunity to add to knowledge.
The organization of the scientific movement and the system of
the universities protracted the dual relationship of medicine and
biology long after it had ceased to be real when books were
already being written purely on botany, or zoology, or physiology.
Nowhere was it possible to obtain formal instruction in any of
these subjects, save as part of a general course in medicine, until
the middle of the eighteenth century. Teachers of botany (or of
chemistry) were appointed only to fulfil the needs of the medical
faculty.

To the young physician of the later sixteenth or seventeenth
centuries, ardent for research, many courses were open. He might
venture on original methods in practice, collect case-histories,
perhaps contribute to the growing literature of abnormal observa-
tions and remarkable cures. Or he might, in the humanistic vein,
seek to improve the general understanding of the magisterial
texts. Or he might practise anatomy, in which case he would
certainly dissect many animals. Or he might embark upon de-
scriptive natural history. But the texture of the scientific work
involved in all these courses was far from identical. The humanist-
physician was easily assimilated to the type of the scholar, the
naturalist-physician to the type of the lexicographer admittedly
with the development of specialized powers of observation. Neither

i 3 2 THE SCIENTIFIC REVOLUTION

of these courses, at this time, led naturally to the act of experi-
menting. The problem, however, which comes nearest to the
physician's work, the understanding of the functioning of the
human (and, by analogy, the animal) body in health and disease,
is one that lends itself to observation and experiment. The physi-
cian must observe and classify diseases, he must also experiment
in his therapy. Admittedly the physician found his normal ratio-
cinative background in Galen's ideas, admittedly he proceeded in
accordance with the accepted theory of the nature of disease and
of the measures requisite to effect a remedy; even the ascription
of symptoms to the humoral condition, the amount and timing of
blood-letting and the preparation of drugs were laid down by
rules for his guidance more dogmatically than they are today.
Yet, whatever the teaching, in any age a physician must be some-
thing of an empiric. He must learn to use his own judgement. He
must adapt general principles to particular cases. And in the
sixteenth century the art of medicine was far from static. Apart
from the great variety of herbal medicaments among which the
physician had to make his choice, there were the new inorganic
remedies, such as mercury, and new drugs from the East and West
Indies. There was a great controversy over the correct procedure
in venesection. There were new problems syphilis, gunshot
wounds, scurvy ravaging crews on long ocean voyages, and plagues
flourishing with the growth of cities. A physician's practice could
be guided by principles the use of contraries to restore the balance
of the humours, or analogy (dead man's skull, powdered, in cases
of epilepsy) but he could be no mere follower of the book, if
only because the book was an inconsistent and insufficiently
specific guide. The most important part of medicine was learnt
through experience, and profitable experience depends on
experiment.

Perhaps this lesson was the most enduring contribution made
by Paracelsus to true science. Naturally when Paracelsus writes,
for example, ' From his own head a man cannot learn the theory
of medicine, but only from that which his eyes see and his fingers
touch . . . theory and practice should together form one, and
should remain undivided. . . . Practice should not be based on
speculative theory,' it has to be remembered that "practice" for
Paracelsus meant something very different from the rationalist
practice of the modern physician. He accepted the doctrine of

EXPERIMENT IN BIOLOGY 133

signatures; he taught the doctrine of the microcosm and the
macrocosm that forced the physician to become astrologer; to
him medicine was the study of the occult forces that play upon
the human body. Within his conception of the physician's practice
however, he was empirical. The teachings of Aristotle and Galen
provoked his unmitigated scorn, and he castigated the academic
physicians who relied upon the theories derived from them. He
claimed himself to have learned the art of healing not only from
learned men, but from wise women, bathkeepers, barbers and
magicians. Ideally, for him, the test of a remedy was its efficacy,
though in his devotion to the occult and the esoteric he often fell far
short of this ideal. Believing that experience was the best teacher, he
did not hesitate to experiment with medicaments of which the aca-
demically minded were fearful, and so he became the leader of
the chemical school in therapy. The strongest poisons, he held (no
doubt arguing from the virtues of mercury or opium), contained
hidden arcana, serviceable to the physician initiated into their
mysteries. No doubt the latitude which Paracelsus introduced into
medical practice was usually profitless and frequently dangerous;
but it stimulated a more rationalist empiricism than his own. Not
for the first time, the experimentalism of magic was favourable to
the growth of natural science.

Of course trial-and-error methods do not constitute a new
philosophy of science. Ambroise Fare's use of ligatures and dress-
ings instead of cauterization by fire is not to be put forward as an
example of a conscious experimental science though it was a
genuine revolt against authority, and a genuine instance of em-
piricism. Pare knew no Latin: he was only the royal surgeon. But
it is to a certain degree inevitable that the originally minded men
who adhered to the more practical aspects of medicine, who were
compelled to be empirical (Glauber, after all, must have tested
his sal mirabile), should have moved more naturally in the direction
of experiment than their colleagues whose interests ran otherwise.
From dissection for research to experiment of a limited kind is not
a great step. Anatomical observations on the veins and arteries
suggested simple experiments on the behaviour of the blood in the
living body with which venesection made the surgeon necessarily
familiar. Observations involving vivisection had been made long
before by Galen and Aristotle, and were repeated in the sixteenth
century: wounds occasionally gave opportunities for a glimpse

134 THE SCIENTIFIC REVOLUTION

beneath the surface. There was almost a tradition by which
poisons and their antidotes were tested upon small animals (and
sometimes condemned criminals). Moreover, the Hellenistic tradi-
tion in zoology and physiology offered perhaps the best model of
experimental science that could be found in the whole corpus
of transmitted learning. The Aristotle of the Generation of Animals
and the History of Animals was an experimenter as well as an ex-
cellent observer. In embryology especially again leaving aside
all question of theory the sixteenth-century heritage of experi-
ment is clear. Albert the Great, like Aristotle long before, had
opened eggs systematically. The men of the renaissance had only
to continue a well-defined course of investigation.

Perhaps it is not stretching imagination to see practical medi-
cine playing somewhat the same role in the development of biology
as that of technology in the evolution of the physical sciences. The
physician, engineer and manufacturer had that practical skill in
their encounters with nature which was lacking to the reflective,
generalizing philosopher of the study. They wove a strand of
empiricism into the web of theory. They were equally (if honest
and intelligent men) more interested in the attainment of tangible
results than the discussion of means by which such results ought
to be attainable. And just as experience with cannon or in indus-
trial chemistry had no simultaneous, directly positive effect upon
ideas of motion or the four-element theory of matter, so also
empiricism in medical science could not immediately and pro-
portionately modify the broad theory of physiology or pathology.
The impact of empiricism was in all cases gradual, subject to
variations in emphasis and liable to be different from that which
posterity might deduce merely by treating practical experience
as the "cause," and change in theory as the " effect."

The history of the discovery of the circulation of the blood is
an illuminating instance of the delayed action of observation and
experiment upon biological theory. Harvey had little that was
new in the way of fact available to him. His great merit was to
integrate known but ineffective facts into a new and comprehen-
sive generalization. As he himself constantly reiterates in his
treatise On the Motion of the Heart (1628) for he was one of those
innovators who had little desire to flout authority unnecessarily
many of the observations on which he relied were already known
to Galen. Harvey indeed did not so much contradict Galen as

EXPERIMENT IN BIOLOGY 135

gently convert his doctrines. Other observations must have been
made at almost every venesection if only physicians less intelli-
gent than Harvey had been able to see their meaning. Though
their function was imperfectly understood, the valves in the veins
had been observed more than sixty years before Harvey's dis-
covery of the circulation was made; the tricuspid and mitral
valves in the heart, which were also given a rational function for
the first time by Harvey, had been described by Galen himself. In
many ways, therefore, Harvey's discovery in biology resembled
Galileo's in mechanics in being a new interpretation of familiar
data drawn from common experience, and Harvey, like Galileo,
had numerous precursors.

Harvey, however, made a far more precise appeal to experi-
mental evidence than did Galileo, and his use of a "critical in-
stance" (though there seems to be nothing to suggest that Harvey
was at all influenced by his great patient, Francis Bacon) is not
paralleled in mechanics. The greatest physiologist of the sixteenth
century, Jean Fernel, had not known how to apply the experi-
mental method. Sir Charles Sherrington has expressly pointed the
contrast between him and Harvey:

Fernel, it would seem, in order to do his work, must find it part of a
logically conceived world. His data must be presented to him in a
form which, according to his own a priori reasoning, hangs together.
In that demand of his lies his inveterate distrust of empiricism. " We
cannot be said to know a thing of which we do not know the cause."
And under "cause" he included not only the "how" but the "why."
With Harvey it was riot so. When asked "why" the blood circulated,
his reply had been that he could not say. Fernel welcomed "facts,"
but especially as pegs for theory; Harvey, whether they were such
facts or not, if they were perfectly attested. 1

To Harvey, anatomy offered the elementary facts of physio-
logy; Fernel, however, wrote that 'in passing from anatomy to
physiology that is to the actions of the body we pass from
what we can see and feel to what is known only by meditation.'
He had liberated himself from the occult influence of the stars,
but a mechanistic interpretation of physiological process was still
alien to his thought. For him the origins of bodily actions had
to be sought in the soul, the non-material entity controlling and

1 The Endeavour of Jean Fernel (Cambridge, 1946), p. 143.

136 THE SCIENTIFIC REVOLUTION

directing the operations of the material parts. In this, of course,
he simply followed Galen and the Greek tradition.

The ancients had studied the three most obvious instances of
the involuntary physiological process respiration, the beating of
the heart, and the digestion of food and framed a comprehensive
theory linking and correlating the phenomena. This theory con-
tained all that Fernel, or any other sixteenth-century physician,
knew of the matter. In the first place they discriminated between
three "coctions," the first of which turned the food into chyle,
transported through the veins of the intestine from the stomach to
the liver. This movement of the chyle puzzled Fernel, since he
found the veins full of blood instead of white chyle. In the liver
the second coction transformed the chyle into blood, which issued
forth to the various parts of the body. In these parts the third
coction took place, by which the material absorbed from the
veins by the flesh was made flesh itself. The coctions were assisted,
if not effected, by the natural heat of the animal body, being thus
analogous to ordinary domestic cooking, and each had its specific
cause in a faculty of the soul. 1 The nutritive faculty, working
through the natural spirits, was the agent of the first coction; an
attractive faculty drew the blood from the liver along the veins,
and from the veins into the flesh. The liver was the source of the
blood, and the centre from which it flowed out to the parts, in-
cluding the heart. This flow of blood was not constant, but rather
an ebb-and-flow alternating motion, by which the humours were
uniformly distributed about the body. Thus the Ghost in Hamlet
speaks of the

. . . cursed hebenon

That swift as quicksilver it courses through
The natural gates and alleys of the body. 2

The Galenic theory certainly did not postulate that the blood lay
stagnant in the veins, but references to this ebb-and-flow from the
liver (to which the Latin circulatio was sometimes applied) have
been misinterpreted as allusions to the true circulation (L.
circuitio) of the blood. A principal portion of the output of blood
from the liver passed up the great vein of the body, the vena cava,

1 Fernel, however, likens the second coction in the liver to fermentation;
alchemists similarly spoke of the fermentation of metals.

2 Gates has been interpreted as a reference to the valves, but the alternative
sense of way, path, is equally possible.

EXPERIMENT IN BIOLOGY

137

to the heart, into the right side of which the blood was attracted
by the heart's active dilatation (diastole) (Fig. 7). At the same
time air inspired into the lungs was drawn down the venous artery
(pulmonary vein) into the left side of the heart. During the phase
of contraction of the heart (systole) blood was squeezed from the
right side of the heart into the arterial vein (pulmonary artery) for
the nourishment of the lungs, and also through the median septum
(the thick wall dividing the heart into two main chambers, or

Right Atrium

Right Ventricle

__ Arterial Vein
(pulmonary artery)

Venous Artery
(pulmonary vein)

Left Atrium
Left Ventricle

Septum

Liver

FIG. 7. Diagram of the structure of the heart and lungs, illustrating
the Galenic physiology.

ventricles) into the left side of the heart. This was the seat of a
most important operation, for there the blood, already containing
the "natural spirits" supplied by the liver, was further enriched
by taking up " vital spirits" from the air. The blood and vital
spirits were conveyed about the body from the left side of the heart
by the arterial system. Thus the main function of respiration was
to introduce vital spirits into the body via the arteries, and of the
heart to serve as the organ in which this enrichment of the blood
took place indeed enrichment is an insufficient word, for as
venous and arterial blood were distinguished by their colour and
viscosity, as well as by their supposed difference in physiological

138 THE SCIENTIFIC REVOLUTION

function, it was long denied that they could be the same fluid.
The venous, alimentary blood was virtually transmuted by the
addition of vital spirit into the spirituous arterial blood.

Another joint task of the heart and lungs was to ventilate the
blood and relieve it of its sooty impurities passing along the
pulmonary vein and exhaled in the breath. The greater thickness
of the aorta and other principal arteries was explained on the
grounds that their dense walls had to retain the fugitive vital spirit,
but as Harvey emphasized, Galen had not denied that the
arteries contain blood as well as spirit. The arterial pulse, the
expansion and contraction of the vessels, was not regarded as
caused by the similar action of the heart, for Galen judged, as the
result of one misleading experiment, that the "pulsive force" was
transmitted along the walls of the arteries. Fcrncl added that if
the arteries were swelled by the pulse of blood from the heart they
could not pulsate simultaneously along their length, as they do.
This belief that the arteries have an active diastole and systole of
their own in sympathy with those of the heart was still credited
by Descartes, even though he adopted Harvey's circulation. To
Fcrnel this active contraction of the arteries also served to squeeze
the vital spirit into the surrounding flesh. He also, like Johann
Gunther a little earlier, observed that the phases of the heart and
arteries are opposite, that when the heart shrinks the arteries
swell, and vice versa. Some experiments on this seem to have been
made by Leonardo. The venous system, arising from the liver,
and the arterial system stemming from the heart were thus
structurally dissimilar, and since the physiological functions of
the blood in the veins and the blood and spirit in the arteries
were also different, they were physiologically distinct also. In
this theory the active phase of the heart's action was its diastole,
by which it drew blood, and vital spirit from the air, to itself.

The Galenical theory was universally adopted by subsequent
medical authorities, and became familiar to the Latin West from
the writings of Avicenna and Averroes long before the original
Greek texts were available or thoroughly understood. Therapeutic
directions drawn from the theory varied, but the basic facts were
common to all. The two chief physiological statements of the
theory: (i) that venous blood nourishes the parts, and (2) that
arterial blood supplies the parts with vital spirits, were of course
beyond the experimental inquiry of the sixteenth century. The

EXPERIMENT IN BIOLOGY 139

anatomists were, however, able to check upon the agreement
between the Galenic conception of the blood's motion and the
observed structure of the venous and arterial systems, and of the
heart itself. The operation of the valves in the heart offered no
problem: their opening and closing was perfectly accounted for.
But the density of the septum imposed an act of faith upon
Galenical theorists. Berengario da Carpi recorded that the intra-
ventricular pores in the septum were seen with great difficulty in
man. Vesalius, probing the pits of the septum, was unable to find
a passage, and in the first edition of De Fabrica he wrote: 'none of
these pits penetrate (at least according to sense) from the right
ventricle to the left; therefore indeed I was compelled to marvel
at the activity of the Creator of things, in that the blood should
sweat from the right ventricle to the left through passages escaping
the sight.' In the second edition he expressed his failure to discover
Galen's pores even more firmly, and remarked that he doubted
somewhat the heart's action in this respect. 1 At least one experi-
ment on the heart is recorded by Vesalius, in which the heart-beat
of a dog was restored after opening the thorax by artificially
inflating the lungs. Some anatomists, however, still maintained
that the passages were easy to find in very young hearts, though
concealed in the adult body. Meanwhile, the structures in the
veins, later known as valves, had already been observed by
Estiennc, and from about 1545 were studied by a number of
anatomists, such as Amatus Lusitanus (1511-68) who dissected
twelve bodies of men and animals at Ferrara in 1547 from which
he derived a wholly false theory of their action. As late as 1603
these valves were still misunderstood by Harvey's teacher at
Padua, Fabrizio of Aquapendente.

Attention was concentrated, not so much on the motion of
the blood, as upon the physiological function of the heart. If the
sixteenth-century anatomists had visualized the problem of the
ebb and flow of the blood in mechanical terms, as a problem in

1 De Fabrica (1543), Bk. VI, Gh. xi, p. 589; (1555), p. 734: 'However
conspicuous these pits [in the septum] are, none penetrate (according to sense)
from the right ventricle to the left through the intraventricular septum; nor
do those passages by which the septum is rendered pervious present themselves
to me otherwise than very obscurely, however much they are expatiated upon
by the teachers of dissection, because they are persuaded that the blood flows
from the right ventricle to the left. Whence also it is (as I shall also advise
elsewhere) that I am not a little hesitant concerning the heart's function in
this respect.'

140 THE SCIENTIFIC REVOLUTION

hydraulics, the vascular valves would have given them cause to
think more profoundly; but this was a post-Harveian conception.
The route of the venous blood to the left side of the heart,
whence it could issue to the arteries enriched with vital spirits,
was however open to discovery. Once the impenetrability of the
septum was granted, such blood could only pass via the pul-
monary artery, the lungs, and the venous artery. This is the
so-called "lesser circulation," which is not a circulation at all,
for those who discovered this path had no notion that any blood
traversed it more than once. It was not, apparently, an original
discovery in which Europe has priority. The lesser circulation
was accurately stated by an Egyptian or Syrian physician, Ibn
al-Nafis al-Qurashi, in the thirteenth century in the course of a
commentary on the Canon of Avicenna, in which it was deduced
specifically from the impermeability of the septum. 1 There is no
evidence that his statement was known before very recent years,
so that the sixteenth-century discussions appear to be entirely
independent. It is significant that in two so different circumstances
the same observation elicited the same theory. In Europe the
description of the lesser circulation was first printed by the
Catalan Miguel Serveto in a theological work, Christianismi
Restitutio (1553). Serveto was primarily a theologian and though
he practised medicine it is not certain that he had a medical
degree. In Paris he was associated with the young Vesalius and
the veteran Giinther, who spoke of him as an anatomist second to
none, yet it seems that Serveto's experience in dissection must
have been brief. He was greatly interested in medical astrology
and his whole knowledge of medicine seems to be somewhat
intellectual and literary. There is an element of mystery in the
sudden introduction of a physiological heresy into a work that
was almost completely obliterated on account of its religious
heresy and which was probably written (though not certainly
with the passage on the circulation) as much as seven years before
its publication. Serveto had some knowledge of Arabic, and it
has been conjectured that he may have studied Ibn al-Nafis 5
text, but it seems unnecessary to postulate that he was less original
than the thirteenth-century Syrian. Some scholars judge that
Serveto may have been indebted to the Italian anatomists who
later described the lesser circulation in print: others think that
1 On Ibn al-Nafis, cf. Sarton, op. cit. 9 vol. II-2, pp. 1099-1101.

EXPERIMENT IN BIOLOGY 141

they were indebted to him. This question of priority is not of
great importance. 1

Discussion of the Holy Spirit induced Serveto to write of the
three spirits of the blood, the soul of the body (Harvey also wrote
"Anima ipsa esse sanguis"). He denied that there was any com-
munication through the septum of the heart: instead, 'the subtle
blood, by a great artifice, passes along a duct through the lungs;
prepared by the lungs, it is made bright, and transfused from the
pulmonary artery to the pulmonary vein. Then in that vein it is
mixed with air during inspiration, and purged of impurity on
expiration. 5

The mixture, he said, takes place in the lungs, where the
spiritual blood is given its bright colour, for the ventricle is not
large enough for such a copious mixture, nor the elaboration of
brightness. He imagined channels connecting the artery and vein
in the lung itself, and argued that the artery was far too large for
the supply of the lung alone. His physiological conceptions were
clearly not very different from those of Galen, save that imbibing
of natural spirit by the blood was extended along the pulmonary
vein from the heart to the lung. Serveto did not categorically deny
that blood sweated through the septum: nor, on one interpreta-
tion, had Galen categorically denied that some blood might pass
from one side of the heart to the other through the lungs. Such was
Harvey's understanding of his words: 'From Galen, that great
man, that father of physicians, it appears that the blood passes
through the lungs from the pulmonary artery into the minute
branches of the pulmonary veins, urged to this both by the pulses
of the heart and by the motions of the lung and thorax.' 2 Though
it may be doubted that such an interpretation was accepted in
the sixteenth century, in Serveto original thinking appears to
emerge tentatively from the ideas of the past. His picture of the
lesser circulation was very different from that of Harvey.

The same may be said of intermediate presentations of the same
idea. In spite of the almost complete destruction of Ckristianismi
Restitutio^ there is some record of its being read. It has been argued
that the treatment of the lesser circulation by another Catalan

1 For the two arguments, cf. H. P. Bayon: "William Harvey, Physician and
Biologist," in Annals of Science, vols. III-IV (1938-9); and Josep Trueta:
"Michael Servetus and the discovery of the lesser circulation," Tale Journal of
Medicine and Biology, vol. XXI (1948).

2 Robert Willis: Works of William Harvey (London, 1857), p. 44.

142 THE SCIENTIFIC REVOLUTION

physician, Juan Valverde, in 1554, is imitated directly from that
of Serveto, since he stated, like Serveto, that the pulmonary vein
contains both blood and air (later, in 1560, he wrote that it
contained a copious quantity of blood). Valverde had studied
under Realdo Colombo from about 1545 at Pisa and Rome;
remarking that he had frequently observed the anatomical ap-
pearances with Colombo, he seems to claim no originality for
himself. Colombo in turn had been a pupil of Vesalius, succeeding
him for a short space in the teaching of anatomy at Padua, and it
is possible that the genesis of the idea of the lesser circulation took
place there, and so was made known to Valverde. Colombo
certainly claimed the new idea as his own, and hitherto unknown,
in a treatise published posthumously in 1559, which may well
have been written before Valverde's printed in 1556. Certainly
Colombo's reasoning on the circulation is superior to any that
had preceded it. He made the plain statement that the blood
passed from the right ventricle through the pulmonary artery to
the lung; was there attenuated; and then together with air was
brought through the pulmonary vein to the left ventricle. He relied
particularly upon the observation that when the pulmonary vein
is opened it is found to be full of bright arterial blood.

From this time the circuit through the lungs from the right side
of the heart to the left was described by a number of anatomists,
down to the time of William Harvey. It is important to recognize
that though these physicians are correctly spoken of as precursors
of Harvey (in the sense that this passage of blood through the
lungs played a part in the complete theory of the circulation), the
lesser circulation as it was understood in the sixteenth century
was not a complete fragment of the whole Harveian theory.
Harvey understood the lesser circulation in a manner that differed
significantly from that of his predecessors. For him it was the path
by which all the blood in the body was transferred from the venous
to the arterial system: for them it was the path by which a portion
of the blood formed in the liver and issuing to the parts became
the blood-and-spirits of the arterial system. For him the pul-
monary vein contained nothing but arterial blood: for them it
contained blood and air. The lesser circulation of the sixteenth
century was, as Serveto said, a great artifice for by-passing the
impenetrable septum: it led to no other new conception during
more than sixty years: it did not suggest the general circulation

EXPERIMENT IN BIOLOGY 143

because it was really not a circulation at all. Galen's physiology
was modified, but not entirely displaced. The heart and lungs
were still not perceived as the operative organs in the vascular
distribution and the identity of the arterial and venous blood was
still concealed. The reason for this failure to establish a complete
idea of the lesser circulation in the sixteenth century is that the
earlier anatomists were attempting to solve a different problem
from that of Harvey. They were concerned only to find the route
by which blood and vital spirits entered the arteries in view of
the impenetrability of the septum. Harvey's problem was two-
fold; firstly to account for the function of the valves in the veins
(which, as was realized before his time, obstructed the flow of
blood outwards along the veins), and secondly to dispose of the
large quantity of blood which he knew must enter the heart. The
novelty of his approach was that it ignored the question of vital
spirits altogether, concentrating upon a wholly mechanical, and
partly quantitative, difficulty latent in the accepted doctrine.
This difficulty had occurred to no one before, because no one had
doubted that the contents of the veins and arteries respectively
were absorbed by the parts which attracted them outwards from
the central reservoirs, the liver and the heart. The early theory of
the lesser circulation was, therefore, useful to Harvey in that, at
the proper stage in the development of his own ideas, the transfer
of blood from the right to the left side of the heart could be fitted
in as a partially complete portion of the puzzle; but that theory
in itself was a cul-de-sac so long as it was no more than a variation
on Galen's.

Harvey began his medical studies at Padua in 1597, the year of
his graduation at Cambridge at the age of nineteen. He remained
there till 1602. His teacher was Fabrizio of Aquapendente, a late
member of the great Italian school of anatomists and embryolo-
gists. At this time the lesser circulation was by no means universally
accepted, and the valves in the veins were still explained in a
variety of mechanically improbable ways. Robert Boyle, in 1688,
recorded a conversation with Harvey (d. 1657) in which Harvey
had said that he was first induced to think of the circulation by
these valves (of whose existence he must have learnt at Padua) :

... so placed that they gave free passage to the blood towards the heart,
but opposed the venal blood the contrary way: he was invited to
imagine that so provident a cause as nature had not placed so many

144 THE SCIENTIFIC REVOLUTION

valves without design, and no design seemed more probable than
that, since the blood could not well, because of the interposing valves,
be sent by the veins to the limbs, it should be sent through the arter-
ies and return through the veins. 1

This doubtless presents a very foreshortened view of the truth,
but it does relate Harvey very definitely to the Italian tradition
(as is obvious in many other ways) and it does also indicate
that Harvey's view of the problem was from the beginning a
mechanical one. The fact that in De Motu Cordis the valvular
action becomes one argument among many docs not impugn the
credit of Boyle's statement.

It was natural and fitting that Harvey should have traced the
origin of his discovery to the new anatomy of the sixteenth century,
for the whole discussion of the vascular system down to his time
had been based on advances in observation. While the theory of
the lesser circulation was itself framed in accordance with ana-
tomical observation, it had not been examined experimentally,
nor did it contain any new physiological interpretation. On both
these points Harvey's discovery marks a distinct advance. Firstly,
he showed that if the vascular system was analysed hydraulically,
considering the heart as a pump, the veins and arteries as pipes,
the valves as mechanical valves, the blood itself simply as a fluid,
conclusive experiments on the flow of blood could be made. For
this purpose he disregarded " spirits" altogether, though he still
considered that the heart (not the lungs) restored a spirituous
quality to the blood. Secondly, he introduced a new physiological
conception in which the arterial blood was revivifying and restora-
tive, while the venous blood was the same fluid returning vitiated
and exhausted to the heart where it received its former virtue
again. Blood, in fact, was not itself the aliment of the parts, but a
vehicle carrying the aliment. Harvey's ideas on this were inevi-
tably vague, and conditioned by the knowledge of his time, but
he did conceive of the blood regaining in the heart its c fluidity,
natural heat, and [becoming] powerful, fervid, a kind of treasury
of life, and impregnated with spirits, it might be said with
balsam.* As cold precedes death, while warmth belongs to life,
he saw the heart as the ' cherisher of nature, the original of the
native fire' whence new blood, imbued with spirits, was sent

1 Boyle: Works, 1772, vol. V, p. 427.

EXPERIMENT IN BIOLOGY 145

through the arteries to distribute warmth about the body. 1 On
the passage of the blood through the lungs, Harvey's promise to
explain his conjectures was not fulfilled: but he indicated that he
thought its function was to temper and damp the blood, to prevent
it boiling up with its own excessive heat. All Harvey's thought on
the physiology of the circulation is obviously pre-chemical, proto-
scientific rather than scientific; it does, however, contain the
important seminal idea that there is an exchange by which
"something" is taken up by the venous blood in the heart (really,
of course, the lungs) and given up by the arterial blood to the
flesh. Granting the contemporary lack of chemical knowledge, it
is only open to the criticism that, in eulogizing the heart, Harvey
strangely overlooked the importance of the fact that venous blood
becomes arterial in its passage through the lungs from the right
ventricle to the left, not in the heart itself. Unable to free himself
completely from the error of his predecessors, he could not quite
attain the conception of the heart as a pump only, adding neither
heat nor spirits nor anything else to the blood passing through it.
Thus Harvey's theory is most perfect in its mechanical aspect,
which was fully supported by experiment. His purely anatomical
evidence held little that was new, except perhaps his study of the
heart as a contractile muscle. He also demonstrated the action of
the vascular valves, and the correspondence of the cardiac diastole
with the arterial systole, more forcibly than earlier anatomists.
Even in anatomy Harvey was successful where his predecessors
had failed, in deducing that a mass of discordant observations was
made consistent on the single hypothesis of the circulation of the
blood; as is most clearly seen in his remarks on the foetal circula-
tion. The existence of an intercommunication between the pul-
monary artery and veins, in the mammalian foetus, that disappears
after birth was familiar to all anatomists, but no one before Harvey
had correlated this short-circuiting of the lungs with either the
supposed sweating of blood through the septum, or its passage
through the lungs. It was left to Harvey to show that the foetal
circulation avoids the lungs because they are collapsed and
inactive. He is most original and striking when he uses the
comparative method: 'Had anatomists only been as conversant
with the dissection of the lower animals as they are with that of
the human body, the matters that have hitherto kept them in a

1 Willis, op. cit., pp. 47, 68.

10

146 THE SCIENTIFIC REVOLUTION

perplexity of doubt would, in my opinion, have met them freed
from every kind of difficulty.' 1

His admonition was accepted by a host of biologists in the
later seventeenth century, including Marcello Malpighi who first
observed the blood passing from the arteries to the veins through
the capillary vessels in the lungs of a frog the final link that
clinched Harvey's motion in a circle. Harvey found that the
action of the heart could be most easily studied through experi-
ments on small animals or fishes, as for instance observing the
effect of tying ligatures about the great vessels, in suffusing or
draining the chambers of the heart. He correlated the single-
chambered heart correctly with the absence of lungs, and the
double-chambered heart with the possession of lungs, pointing
out that the right ventricle, which only sends the blood through
the lungs, is slightly weaker than the left which sends it round the
whole body. By experiment Harvey proved that the heart receives
and expels during each cycle of expansion and contraction a
significant quantity of blood, not a few drops only: by calculation
he proved that, on the lowest estimate of the change in volume of
the ventricles, all the blood in the body passed through the heart
more than once in half an hour. Even this was a generous under-
estimate. In his second group of experiments, Harvey further
demonstrated that the blood moves away from the heart through
the arteries, and towards the heart through the veins. These
experiments mainly relate to the human subject, and are such as
would naturally suggest themselves to a physician practised in
phlebotomy. Examining the superficial veins of the arm, he
showed that the limb is swollen with blood when the veins are
compressed, and emptied of blood when the arterial flow is
obstructed. He found that the valves in these veins prevented the
flow of blood away from the heart, and that by arterial manipula-
tion it was impossible to force blood through them except in the
contrary direction. Blood always filled an emptied vein from the
direction of the extremity. Again, he showed that in the jugular
vein the valves were so constructed as to permit a unidirectional
flow towards the heart only, and that therefore their function was
not (as some thought) to prevent the weight of blood falling down
to the feet. The experience of wounds and venesection was cited
by Harvey to the same general effect, and he further alleged

1 Willis, op. cit. 9 p. 35.

EXPERIMENT IN BIOLOGY 147

the experience of physicians as proof that the blood was the
mechanical agent by which poisons or the active principals of
drugs are rapidly distributed about the whole body.

It is today far more easy, by taking the truth of Harvey's
arguments and experiments for granted, to regard his doctrine as
an obvious and straightforward deduction from the anatomical
history of two earlier generations, than to appreciate the nature
of the objections against it. As Galileo remarked in another con-
nection, once this discovery was made its proof was easy: the
difficulty was to hit upon it in the first place. Harvey's discovery,
like Galileo's, was made at a rudimentary level of science, but
the true measure of the intellectual effort involved is the fact that
the discovery had escaped all previous anatomists, was greeted
with incredulity and scorn, and was not universally accepted
even within twenty years. It seems likely that Harvey himself had
worked at the problem for at least ten years before he gained the
solution. Some, as he said, opposed him because they preferred to
endanger truth rather than ancient belief. Others thought that
they had discovered technical anatomical arguments against the
circulation; or that only a portion of the blood circulated; or that
venous and arterial blood could not be the same fluid. Even the
basic anatomy of blood-supply to the chief organs of the body
(especially the liver) was still doubtful, and its physiological
interpretation barely begun; the capillary circulation, and the
change in colour of blood, were to remain mysteries long after
Harvey's death. His originality was that he preferred to face these
new problems, rather than tolerate longer the inconsistencies of
the old system, but in this he was followed by few contemporaries.
As so often in science, one advance was made not by completely
solving an old problem so that no question remained, but by
transposing the problem into an answerable form, creating fresh
problems by the very act of transposition. Harvey asked a question
which, in his precise terms, had perplexed none of his predecessors,
and the answer he worked out was important, not only because
it was correct, or because it challenged prevailing ideas, or even
perhaps because it introduced a new kind of scientific inquiry.
Harvey's influence in this last respect was significant (as much in
his book on generation as in De Motu Cordis) but it was not wholly
unheralded, and some of the new methods exploited by later
seventeenth-century physiologists, such as bio-chemical research

j 4 8 THE SCIENTIFIC REVOLUTION

and microscopy, were altogether unknown to him. Perhaps the
most important of his achievements was to leave unsolved
problems not blind, impregnable problems, but questions that
could be answered in the way he had himself declared. Just as
seventeenth-century mechanics was based upon the unsolved (or
imperfectly solved) problems left by Galileo, so the experimental
problems of biology were inherited from Harvey.

Descartes was not the earliest supporter of the theory of cir-
culation, but he was the first to try to deduce wider implications
from it. He himself practised anatomy, and made anatomical
experiments. He has been accused of plagiarizing from Harvey in
the Discourse on Method what he himself did not fully understand.
But he assigned to "an English physician" the credit for the
discovery of the circulation, and claimed only for himself the
elucidation of the mechanism of the heart. In his Second Disquisition
to Riolan (1649), Harvey had himself commented adversely on the
doctrine of spirits: 'Persons of limited information, when they are
at a loss to assign a cause for anything, very commonly reply that
it is done by the spirits; and so they introduce the spirits upon all
occasions. . . .'

Harvey's attitude to authority seems to have sharpened with
age, and in this passage it seems clear that he meant to take
"spirits" rather as a term in common use, than as having a certain
existence. At any. rate he declared that the spirits in blood are no
more distinct from blood than the spirit of wine from wine itself.
Emphatically, in the Method, Descartes sought to eliminate the old
idea of spirits from physiology altogether. 1 If the human body
were purely material, lacking rational or sensitive soul, other than
natural heat in the heart (which is compared to the heat of fermen-
tation) it would perform all the functions of the human body
except that of thought. Descartes illustrated this deduction by the
motion of the heart, which he imagined to work like a crude
internal-combustion engine. On contraction, a little blood would
be drawn into each ventricle, which being suddenly vaporized in
the hot chamber would cause the whole heart to expand and close
the inlet valves. This expansion of the blood would also open the
outlet valves, so that the blood would pass out into the lungs and
arteries, where it would again condense to liquid and the cycle
would be repeated. The heat of the heart, about which Harvey
1 The word was retained, but with a purely chemical meaning.

EXPERIMENT IN BIOLOGY 149

had written, thus accounted for its purely mechanical cycle of
expansion and contraction. In his speculation on the heart, which
is neither good engineering nor good physiology, Descartes ex-
ceeded Harvey in the functions he assigned to that organ. It
supplied heat to the stomach to concoct food; it completed the
concoction by distilling the blood in the heart 'one or two hun-
dred times in the day' (according to Descartes, the lungs were
the condenser in which the blood was restored to the liquid state) ;
it forced by compression of the blood 'certain of its parts' to pass
through pores specially designed like sieves to admit them into
the various parts of the body where they formed humours; and it
was the hearth where burned a very pure and vivid flame which,
ascending to the brain, penetrated through the nerves (imagined
as hollow tubes) to activate the muscles. In On Man Descartes
developed the theory that the flow of the spirits was controlled in
the brain by the pineal gland, a sort of valve acting under the
direction of conscious volition. According to Descartes' study of the
physiology of behaviour, volition played a minor part even in man,
who was alone capable of abstract thought and true sensation
(that is, sensations capable of objective judgement) , and none in the
activity of any lesser creature. He devoted much attention to the
study of motor mechanisms and reflex actions as for instance
tracing the involuntary mechanisms by which, when the hand
is burnt, the muscles of the arm contract to withdraw it from the
fire, the facial muscles contract in a grimace of pain, tears flow,
and a cry is uttered. 1 He regarded the greater part of bodily
activity as due to mechanical processes of this kind, as automatic
responses to external stimuli effected by the nervous system; but,
though Cartesian physiology was to some extent supported by
anatomical investigation of the relations of nerve, brain and
muscle, it was in the main a purely conceptual structure. Descartes
anticipated some of the conclusions of nineteenth-century
physiology without its careful experimental foundation.

Harvey's work was an important step towards a mechanistic
approach to biological problems, containing a tentative challenge
to the supremacy of spirits founded on a particular experimental
investigation. Descartes' more comprehensive and more specula-
tive writings elevated mechanism to a universal truth, in physics
and biology alike. Soul and material body could have nothing in

1 Cf. De Homine (Leyden, 1662), pp. 109-10. Sherrington, op. cit., pp. 83-9.

i 5 o THE SCIENTIFIC REVOLUTION

common save a single mysterious point of contact; nothing could
be attributed to the soul but thought. The old physiology postu-
lated a variety of non-material souls or spirits each charged with
the management of a set of bodily functions; for Descartes those
functions were the result of mechanistic processes, as much as the
different appearances and movements of an elaborate mechanical
clock. This, he said in the Discourse on Method, would not appear
strange to those acquainted with

the variety of movements performed by the different automata, or
moving machines fabricated by human industry, and that with the
help of but few pieces compared with the great variety of bones,
muscles, nerves, arteries, veins, and other parts that one finds in the
body of each animal. Such persons will look upon this body as a
machine made by the hands of God, which is incomparably better
arranged, and adequate to movements more admirable than is any
machine of human invention.

The body was not maintained alive and active by one or more
life-forces, or spirits, or souls, but solely by the interrelations of
its mechanical parts, and death was due to a failure of these parts.
Therefore, with no non-material factors involved, everything in
physiology was potentially within the range of human knowledge,
since no more was required than the investigation of mechanistic
processes, complex and elaborate indeed. This conception of
Descartes' was of course premature, far beyond the scope of the
scientific equipment of his age, and it led to no immediate physio-
logical discovery. Except perhaps in his work on the eye, the
factual content of his biological theory was wholly misleading.
But the influence of his general conception upon the anatomy
and physiology of the later seventeenth century was profound.
On the whole, those who tried narrowly to demonstrate its truth
in particular applications, like Borelli in On the Motion of Animals
(1680), were least successful, and the attempt to apply mechanical
principles to medicine failed. Ultimately the intractability of
nature prompted a return to more vitalistic ideas. On the other
hand Descartes' justification of experimental inquiry in biology
was of permanent value. Terms like " vital force" might conceal
deep ignorance without endangering the investigation of those
processes through which vital force was supposed to operate. So
long as spirits or the Paracelsian archeus ruled the body, so long as
the functions of its organs had been subject to the influence of the

EXPERIMENT IN BIOLOGY 151

stars and other occult agencies, it had been futile to interpret
physiological phenomena in the light of the purely material
sciences of physics and chemistry. The barrier between organic
and inorganic must have remained for ever absolute. Experiments
from which the mystery "life" was excluded would have been
useless. To have shown that the transformation of venous into
arterial blood can be effected by oxygenation would have been
irrelevant to a "spiritual" theory of respiration. The dead liver
of a corpse could throw little light on the living liver of a man.
Under Descartes' influence, even at the later stage when his
mechanism seemed crude to a degree, all this was changed. An
organ or a limb could be studied as a part of the whole mechanism,
a cog in the works. It could be assumed that what was found to be
true of the part in the laboratory must be equally true of the part
in the living body; that particular results obtainable from certain
experimental processes when observed in the living specimen
must be produced by similar processes in its own organization. The
basic axiom of experimental science is that, circumstances being
unchanged, a like cause will produce a like result because the
"cause" releases a chain of events following an unchanging
pattern. If this is not so, then the experimental method of inquiry
is not one that can usefully be applied to the problem. It was
Descartes' discovery (ratiocinative, not empirical) that this was
true of physiological phenomena; it could be assumed, prima facie,
that circumstances were unchanged (e.g. between the living
body and the chemist's vessel), and that since functions were
automative, like result followed like cause.

The living state was no longer beyond analysis. Descartes'
scientific writings, even more than Harvey's, suggested a host of
inquiries into the nature of physiological process. Those in which
Descartes had been most interested, pertaining to the operation
of the nervous system, made little progress before the nine-
teenth century, though the years immediately after his death saw
important work in anatomical neurology. The mechanism of
respiration was tackled more successfully, and a pregnant analogy
was drawn between combustion and respiration no doubt owing
something to earlier ideas of the heart as the seat of heat. From the
members of the Accademia del Cimento through Robert Boyle to
the eighteenth century a series of investigators studied the effect
of placing small animals in vacuo y in confined volumes of air, or of

152 THE SCIENTIFIC REVOLUTION

various " elastic fluids" (gases). It was discovered that in the
vacuum both combustion and respiration were impossible, and
that life ceased. It was discovered that a combustible or an animal
consumed air (the carbon dioxide being dissolved in the water
which rose up in the vessel), but not all the air, and that the gas
remaining after combustion ceased would not support life, as
that which was left after respiration ceased would not support
combustion. It was further discovered that although vessels could
be filled with "fluids" that appeared to be air they would not
support life or combustion. Robert Hooke showed (1667) that a
dog could be kept alive by blowing into its lungs with a bellows,
even with the ribs and diaphragm removed, from which he con-
cluded that the animal 'was ready to die, if either he was left
unsupplied, or his lungs only kept full with the same air; and
thence conceived, that the true use of respiration was to discharge
the fumes of the blood. 3 Other members of the Royal Society
satisfied themselves by experiment that 'the foetus in the womb
has its blood ventilated by the help of the dam'; and that the
foetal circulation depended directly on the maternal.

For a time, as Hooke's words suggest, there was doubt whether
the presence of fresh air in the lungs was necessary to remove
something from the blood (the "sooty impurities" of Galen's
physiology) or to add something to it. On this point the investiga-
tions of Richard Lower (1631-91), a physician and an experi-
mental as well as theoretical physiologist, threw new light. 1 In
his Treatise on the Heart Lower extended Harvey's discovery and
defended it against the Cartesian perversions: the heart was not
caused to beat by a fermentation of the blood, but by the inflow
of spirits from the nerves, and if the nerves were severed the
pulsation stopped. The blood, not the heart, was the source of
heat, and of the activity and life of bodies in this Lower, more
clearly than either Descartes or Harvey, seems to see the heart as
nothing but a mechanical pump. Nor has the heart anything to
do with the change in colour of arterial blood, for this can be
produced by forcing blood through the insufflated lungs of a dead
dog, or even by shaking venous blood in air:

. . . that this red colour is entirely due to the penetration of particles
of air into the blood is quite clear from the fact that, while the blood

1 Tractatus de Corde (1669): English translation by K. J. Franklin in Early
Science in Oxford, vol. IX (Oxford, 1932), especially pp. 164-71.

EXPERIMENT IN BIOLOGY 153

becomes red throughout its mass in the lungs (because the air diffuses
in them through all the particles of blood, and hence becomes more
thoroughly mixed with the blood)

venous blood in a vessel only becomes florid on the surface. Lower
concluded that the active factor in this transformation of the blood
was a certain "nitrous spirit" (elsewhere called a "nitrous food-
stuff 55 ) 1 which was taken up by the blood in the lungs, and
discharged from it 'within the body and the parenchyma of the
viscera 5 to pass out through the pores, leaving the impoverished
dark venous blood to return to the heart. Respiration, therefore,
was a process whose function was to add something to the blood
(Lower remarked that since "bad air 55 causes disease, there must
be a communication between the atmosphere and the blood-
stream); but the fuller understanding of the nature of this addition
had to await the chemical revolution of the eighteenth century.

The new ideas of blood as a "mechanical 55 fluid, a vehicle
for carrying alimentary substances, constituents of the air, and
warmth around the body, suggested the new therapeutic tech-
nique of blood transfusion, of which also Lower was a pioneer.
The blood had still a semi-magical quality, and as it was thought
that "bad 55 blood could cause debility, frenzy or chronic disease,
it seemed logical to suppose that if the blood of a human patient
could be replaced by that of a healthy animal, an improvement
must result. An Italian who claimed to be the inventor of the
method of transfusion (though he admitted he had never tried
the experiment) even suggested that it would effect a rejuvenation
which should be the prerogative of monarchs alone. Christopher
Wren (1632-1723), when an Oxford student, made experiments
on the injections of fluids into the veins of animals, by which,
according to Sprat, they were 'immediately purg'd, vomited,
intoxicated, kilPd, or reviv'd according to the quality of the
Liquor injected.' 2 Suggestions for transfusions of blood between
animals, and actual attempts to effect it, were made by various
Fellows of the Royal Society in 1665, and Lower went into the
matter thoroughly, successfully reviving a dog which had been
exsanguinated almost to the point of death. Finally, in 1667,
Lower performed before the Society the experiment of transfusing
the blood of a sheep into a certain ' poor and debauched man . . .

1 See below, p. 325.

2 Thomas Sprat: History of the Royal Society (3rd Edn., London, 1723), p. 317.

154 THF - SCIENTIFIC REVOLUTION

cracked a little in his head,' which the patient luckily survived
without any change in his condition. In this Lower had been
anticipated by the French physician Jean Denys, whose practice
soon after caused the death of a patient, which led to a prohibition
of transfusion in France and the abandonment of the English
experiments. Several accounts of this time describe the violent
reactions produced by the introduction of animal protein into
the human blood-stream, which rapidly proves fatal, and doubt-
less much of the apparent success of these early experiments may
be attributed to the clotting of the blood in the tubes used,
preventing the passage of more than a small amount. Experiments
on transfusion were only resumed in the nineteenth century,
when the use of animal blood was abandoned. 1

While one important aspect of the expanding experimental
biology of the seventeenth century was the mechanical and
biochemical study of the blood, whose functions figured so largely
in the therapeutical theories of the time, in another the essential
mystery of "life" was no less involved, and was more directly
explored. This was the investigation of generation and the em-
bryonic development of creatures, including man. Just as interest
in the motion and functions of the blood may be traced to its
prominent place in the Galenic theory of humours, so these
embryological researches return in a continuous tradition to the
work of Aristotle. Of William Harvey himself, certainly one of the
greatest embryologists of the seventeenth century, it has been said
that he did not follow the example of some of his predecessors
in departing from Aristoteleanism, but on the contrary lent his
authority to a somewhat moribund outlook. 2 On one important
matter, however, Harvey contradicted Aristotle altogether: he
was sceptical of spontaneous generation, and if he did not coin
the phrase omne vivum ex ovo, it epitomizes his thought. The partial
discredit of spontaneous generation (not complete, for the idea
was revived in the eighteenth century, when it was refuted
experimentally by Spallanzani, and again in the nineteenth
in opposition to Pasteur) was one of the most important changes
in biological thought of the time; a first step towards modern
conceptions of the living state. Formerly organisms had been

1 Cf. Geoffrey Keynes: History of Blood Transfusion, 1628-1914 (Penguin
Science News 3, 1947).

2 Joseph Needham: History of Embryology (Cambridge, 1934), p. 128.

EXPERIMENT IN BIOLOGY 155

divided into four distinct groups: (i) those that are generated
spontaneously, (2) vegetative, (3) animal, (4) human. The first
had only, as it were, a share of the " world-soul"; the others were
distinguished according to the " souls" of their class. As long as
these distinctions persisted, founded on fundamental unlikenesses
attributed to the structure of the world-order reflecting disparities
in the original created endowment, it was impossible to approach
the modern conception of life-processes depending upon the
nature and complexity of the physiological functioning of the
organism. To make the generalization that the life-process is
transmitted solely and invariably through specific mechanisms of
reproduction was a necessary first step towards a rational under-
standing of the nature of this process, and the differences between
matter in the living and the non-living state: indeed, there seems
something fundamentally irrational in the supposition that the
organization of the living from the non-living might be fortuitous,
and commonplace at that. The crude, superficial differences
between the life of a plant and that of an animal are at least
capable of recognition; but what meaning could be attributed to
the difference between the life of a spontaneously generated
mistletoe or worm, and that of other analogous forms? The
doctrine of spontaneous generation had, moreover, become the
refuge for superstitions and fables of the most absurd character,
wholly inconsistent with any serious study of natural history.

Harvey, it is true, wrote in De Motu Cordis that the heart is not
found e as a distinct and separate part in all animals; some, such
as the zoophytes, have no heart,' and he continued, C I may
instance grubs and earthworms, and those that are engendered of
putrefaction, and do not preserve their species.' If this was not
merely a careless phrase Harvey changed his opinion, for in his
later work On the Generation of Animals (1651), he declared:

. . . many animals, especially insects, arise and are propagated
from elements and seeds so small as to be invisible (like atoms flying
in the air), scattered and dispersed here and there by the winds; and
yet these animals are supposed to have arisen spontaneously, or
from decomposition, because their ova are nowhere to be seen. 1

Before such a statement could be given real force and meaning,
the arts of natural observation, of comparative anatomy, and of

1 Willis' Works of Harvey, p. 321. Harvey, however, did not give up the use
of the term "spontaneous generation."

156 THE SCIENTIFIC REVOLUTION

simple controlled biological experimentation must be developed
to, or beyond, the level which they had reached among the
ancient Greeks. Aristotle's biological knowledge was in many
respects far superior to anything that was available in the sixteenth
century indeed some of his observations were not to be verified
before the nineteenth. It is astonishing to find, for example, that
Aristotle's sensible and penetrating observation of the process of
reproduction among bees which itself was not quite correct
was universally ignored up to modern times, while credence was
given to fabulous tales of their generation in the flesh of a dead
calf or lion which, besides appearing in the works of many Roman
poets and writers on agriculture, were retailed in the sixteenth
century and later by naturalists like Aldrovandi, Moufet and
Johnson, and by the philosophers Cardan and Gassendi. Even the
relatively simple life-cycle of the frog was a mystery, at least to
academic naturalists.

Harvey had conjectured that in some cases the invisible "seed"
of creatures was disseminated by the wind. The man who set
himself to confute the widespread fallacy of spontaneous genera-
tion systematically was Francesco Redi (162678), an Italian
physician who worked under the patronage of the Dukes of
Florence and was an important member of the Accademia del
Cimento. 1 His observations and experiments were varied and
numerous, but the most telling were the most simple. Thus he
was able to prove, by the simplest means, that decaying flesh only
generated "worms" when flies were allowed to settle on it; that
the larvae turned into pupae (which he called eggs) from which
hatched flies of the same kind; and that the adult flies which
infested the putrefying material possessed ovaries or ducts con-
taining hundreds of eggs. Generalizing from such results, Redi
pronounced that all kinds of plants and animals arise solely from
the true seeds of other plants and animals of the same kind, and
thus preserve their species. Putrescent matter served only as a
nest for the eggs, and to nourish the larvae hatched from them.
However, he had to admit that there were some examples of
generation which he could not explain. Intestinal worms and other
parasites puzzled him, and he failed to discover the cause of the
growth of oak-galls on trees, which was traced later by Malpighi.
This led Redi to speculate somewhat loosely on possible perversions

1 See below, p. 189.

EXPERIMENT IN BIOLOGY 157

in the "life-force" of host organisms which might produce para-
sitic developments. Micro-biology was only coming into existence
at the time when he wrote, and its absence set a natural limit to
the range of his investigations.

Nevertheless, Redi's demonstrations, combined with the later
work of such naturalists as Malpighi and Swammerdam, were
generally regarded as sufficiently cogent against the doctrine of
spontaneous generation. The second half of the seventeenth
century was a period in which, partly through animal and vege-
table anatomy, partly through the use of the microscope, and
partly also through experiment, many of the mysteries concerning
the less obvious processes of reproduction were being cleared up.
The sexuality of plants, first asserted by Nehemiah Grew, was
established experimentally by Camerarius before I6Q4. 1 But if
the general tendency was for the exclusion of pangenesis, the
experimentalists were not inclined to hasten towards a purely
mechanistic interpretation. The embryological speculations of
Gassendi and Descartes found few followers. Harvey had written,
* he takes the right and pious view of the matter who derives all
generation from the same eternal and omnipotent Deity, on whose
nod the universe itself depends . . . whether it be God, Nature or
the Soul of the universe, 5 though this did not prevent his studying
the phenomena with all attention. Similarly, John Ray in the
Wisdom of God (1693) related his discussion of the fallacy of spon-
taneous generation to the fixed, created nature of species. Ray's
world was a machine in the sense that he doubted from the
cessation of creation on the sixth day the divine institution of
new species (or the endowment of matter with life de novo) but for
him life was transmissible only through the recurring generations
springing from the original ancestors; since the power of living
was confined to the whole group of creatures extant at any
moment, it could not be born of any conjunction of purely
mechanical circumstances.

Despite the limitations in philosophic outlook, which denied to
many experienced naturalists and to Harvey in particular any
vision of the ultimate potentialities of the admittedly crude

1 When his Letter on the Sex of Plants was published. There were ancient and
popular forms of this idea artificial fertilization of the date-palm had been
practised in pre-classical antiquity but it had not acquired any previous
scientific validity.

158 THE SCIENTIFIC REVOLUTION

physico-chemical speculations of the time, the history of embryo-
logy offers a useful example of the critical application of observa-
tion and experiment to the consideration of scientific concepts
of a complex order. This was possible for a variety of reasons,
which point to some significant analogies between the situation
in this science, and that in the physical sciences where so much
progress was made. It was important in this branch of biology
that there were ideas to be challenged or confirmed, problems
that demanded inquiry, far more obviously than in the purely
descriptive departments. What were the respective contributions
of the male and female parents to their offspring? Were the parts
"formed" or did they merely "grow"? What was the function of
the amniotic fluid, or the foetal circulation? How was the embryo
nourished, or enabled to breathe? Aristotle's systematic account
had attempted to deal with such questions; his exactness in
biological observation and his acuteness in biological reasoning
were examined no less thoroughly in the sixteenth and seventeenth
centuries than were his doctrines relating to the physical sciences.
As Galileo had wielded the method of Archimedes against
Aristotle, so in effect Harvey and Redi applied the methods of
Aristotle as observer against the conclusions of Aristotle as theorist.
In embryology there was as effective a classical tradition to focus
attention on the critical points as in cosmology or mechanics. Of
course the strategic gains were far less there was no dramatic
scientific revolution but the tactical advance in method and
analysis was no less real. Though to later minds some of the
questions asked by the seventeenth-century embryologist are
meaningless, though the teleological cast of his thought has
proved fruitless, the tradition of investigation has continued
unbroken, and some descriptions of observations made at this
time have never been surpassed. The difficulties to be overcome
in any analytical department of biology were far greater than
those which the new mechanics solved, while in addition the
biologist lacked the logical procedures of physical science. Serious
limiting-factors in the development of those subjects were to
disappear only in the nineteenth century: in the late seventeenth,
however, their techniques were greatly enriched by the use of the
microscope, which will be discussed in a later chapter.

CHAPTER VI

THE PRINCIPLES OF SCIENCE IN THE
EARLY SEVENTEENTH CENTURY

CONSCIOUS reflection on the relations between man and his
natural environment can only be a product of an advanced
state of civilization in which abstract thought flourishes.
Greek philosophers seem to have been the first to discuss the
problem, how can reason be most successfully applied to under-
standing the complex phenomena of material things? and in so
doing they introduced the generalizing of ideas that is essential
to science and distinguishes it from the ad hoc solving of practical
problems undertaken in man's struggle with nature. It is generally
agreed that the foundations of scientific knowledge cannot be
settled, or even verified, by the normal processes of science itself.
If such questions are asked as, what is the status of a scientific
theory? or, what is the meaning of the word "explanation" in
science? or, to what extent is science a logical structure? they
cannot be answered without transcending the framework of
science. The scientist must have some idea, which is essentially
philosophical, of how he is going to set about acquiring an
understanding of nature before he can apply himself to this task.
He may in practice be entirely uninterested in philosophy, pre-
ferring to regard himself as a compiler of demonstrable facts;
nevertheless, he cannot escape the implications of adopting a
definite scientific method, which teaches him to record particular
kinds of facts, by using certain recognized procedures. Thus the
nature of science in different periods has been determined by the
methods employed in collecting facts and reasoning about them,
and by the prevailing approach to the study of natural pheno-
mena. For example, when the mechanistic philosophy of the
seventeenth century replaced the teleological outlook of earlier
times the change in the character of scientific explanation was
profound: it was no longer sufficient to ascribe the pattern of
events to divine purpose or the necessary conditions for human
existence.

i6o THE SCIENTIFIC REVOLUTION

Consequently, when comparing the scientific achievements of
one epoch with those of another, it must be recognized that the
aims and methods of scientific activity may themselves vary. The
fundamental philosophy of science is neither fixed, nor static, nor
inevitable. It cannot be claimed that any scientific method is
correct, without considering the nature of the objects it seeks to
achieve. Both may be subjected to criticism, for it may be asked
whether scientists have the proper aims, or whether they are using
fit methods; and, indeed, from the thirteenth to the seventeenth
centuries there was continuous and effective criticism of science
from each of these points of view. During the eighteenth and
nineteenth centuries, however, there was a tendency for practising
scientists to feel a confident complacency concerning their aims
and methods, and to envelop themselves in an impenetrable
detachment from any attempt to interpret their activities philo-
sophically. They were scientists, devoted to a peculiarly rigorous
pursuit of knowledge, not natural philosophers. They despised
metaphysics and logic. Their limited outlook, and their often
shallow pragmatism, would have been intolerable to the Greek
founders of scientific method.

In essence, the Greek notion of scientific explanation (passing
into the European tradition through the medieval dependence on
the philosophy of antiquity) did not differ from that of modern
science. When a phenomenon had been accurately described so
that its characteristics were known, it was explained by relating
it to the series of general or universal truths. The most important
distinction between Hellenistic science (including that of the
middle ages) and modern science is in the constitution of these
universals, and the methods of recognizing them with certainty.
For Platonists the universal truths were Ideas, the principal task
of their philosophy it cannot properly be called science being
the elucidation of the ideal world of perfect Forms of which the
tangible world was a clumsy model framed in imperfect matter.
Aristoteleans, on the other hand, denied the separability of Idea
(or Form) and Matter (or Substance), but nevertheless were
concerned with the processes by which Forms, the generalizations
of their science, were detected in the materials provided by sense-
perception. Phenomena were then explained by comprehending
them within the a priori scheme of Forms. This procedure required,
not additions to the already bewildering variety of fact, but the

SCIENCE EARLY SEVENTEENTH CENTURY 161

exercise of reason upon the facts requiring organization; thus in
the Physics, for example, proceeding from the known facts of
motion and change, Aristotle discusses the logical meaning to be
attached to the idea " motion/ 5 and then from the idea of motion
deduces the properties of moving things. In this method experience
and observation are adduced, less to provide bricks to construct
the fabric of the argument, than to give examples of the author's
meaning. As Aristotle declares in the opening of the Physics:
'Plainly in the science of Nature, as in other branches of study,
our first task will be to try to determine what relates to its first
principles,' principles however whose validity was tested by the
rule of reason not that of experiment. As when (to cite the Physics
once more) he denies the existence of a vacuum on the ground
that bodies would move in it at an infinite speed, he makes use of
the logical impossibility of a body being in two places at the same
time. Aristotle derived his universal truths before the application
of intensive inquiry to the phenomena themselves, a procedure
which Francis Bacon contrasted with his own inductive method:

There are two ways, and can only be two, of seeking and finding
truth. The one, from sense and reason, takes a flight to the most
general axioms, and from these principles and their truth, settled
once for all, invents and judges of all intermediate axioms. The other
method collects axioms from sense and particulars, ascending con-
tinuously and by degrees so that in the end it arrives at the most
general axioms. This latter is the only true one, but never hitherto
tried. 1

In building up a body of scientific knowledge other series of
steps than those of Aristotle were used by the Greeks. One was
a logical process, akin to that of mathematics, applied where
mathematical analysis of the phenomena was feasible. This began
with a series of axioms or postulates, defining the conditions of
equilibrium in statics, or the geometrical character of the propa-
gation of light in optics, then deduced the consequences of these
axioms in the same way that the Euclidean geometry of space is
deduced from definitions of point and line. The validity of the
postulates was purely experiential, not deriving from any more
fundamental truths, so that should it be found, for instance, that
equilibrium could be produced in other conditions than those

1 Novum Organum, Bk. I, xix.

r6 2 THE SCIENTIFIC REVOLUTION

envisaged the science of statics would be false or incomplete; and
in the same way the validity of their consequences might be
illustrated from experience. Other Greek writers, notably the
successors of Aristotle at the Lycaeum, founded their doctrines
firmly on a discussion of experimental data a method which
Aristotle had used in his biological works. 1 A large group of later
Greek scientists were far from merely speculative in their interests
and confined themselves strictly to the discussion of facts, which
they sought to extend and enrich by experiment and observation.
In this way "the sciences," to contrast them with natural philo-
sophy, came into existence. But their works, though permitting
quantitative comparisons with experience (as in Ptolemy's
astronomy), were fragmentary in scope and did not combine into
a systematic interpretation of the universe as a whole. For this
the middle ages turned to the Aristotle of the Physics and On the
Heaven.

As a consequence of his authority the universal truths of
Peripatetic science, originally formulated by sorting out and
abstracting with the aid of logic the confused information im-
parted by sense-perception, tended to become the unquestionable
arbiters of thought. However, though the attempt to rationalize
the phenomena of nature by reference to them might often be
productive of nothing more than intricate mental gymnastics, it
could occasionally lead to a more factual inquiry. Nor were "the
sciences" of the later Greeks wholly neglected by a line of the
more critical and heterodox medieval philosophers. Thus arose a
problem of method: how were the fruits of the mathematico-
logical or experiential procedures in investigating nature to
be reconciled with the knowledge gained by deduction from
Aristotle's universals? How did knowledge of a phenomenon, in
terms of its relationship to Aristotle's theory of nature, differ from
knowledge of the same thing in terms of the complete description
of the chain of events producing it? The interest of such questions
was doubtless heightened by the technological progress of the
middle ages, which literary men did not disregard. There was
much new knowledge to be systematized (in the field of chemistry,
for example), new properties of bodies like magnetism to be
explored. And though the main medieval opinion echoed Plato

1 On Strato, of. Benjamin Farrington, Greek Science (Penguin Edn., vol. II,
pp. 27-44).

SCIENCE EARLY SEVENTEENTH CENTURY 163

and Aristotle in its definition of knowledge as " understanding "
(passive knowledge) rather than "power to control" (active
knowledge), a minority foreshadowed a less contemplative, more
practical view of science. Yet the evidence for actual experimenta-
tion by medieval philosophers is not massive, even in optics, and
some of the warmest advocates of the experimental method, like
Roger Bacon, were guilty of misstatements of fact which the most
trifling experiment would have corrected. More successfully, they
discussed the intellectual problem of the relationship between
facts and theories, modifying Aristotle's teaching with regard to
the acquisition of knowledge, the nature of causation, and the
character of the proof of a proposition. It has been suggested that
the middle ages witnessed the philosophical development of the
experimental method, through whose systematic application the
dramatic changes of the scientific revolution were effected. 1
Attention has been drawn to the empiricism of such philosophers
as William of Ockham, who regarded as "real" only that which
could be perceived by sensation, and to the notion of explaining
an event by giving a history of its antecedents, among other signs
of the future onslaught upon the foundations of Aristotelean
physics. But traditional ideas continued to satisfy the majority
until the seventeenth century, and the philosophic conception of
empiricism was a very different thing from its application to
scientific problems.

No important re-statement of scientific method was made
during the sixteenth century. The medieval tradition continued
to run strong, yielding wider divagations from Peripatetic ortho-
doxy in Leonardo or Copernicus, or the philosophers Cardan and
Telesio, but there was no philosopher independent enough to
transfer the weight of scientific authority to completely new bases.
Instead, it may be noticed that a number of the more interesting
developments in the science of the period signify that science was
outgrowing its cradle, philosophy. They bear the mark of the
practical hand of a Vesalius or an Agricola. Since no true science
can remain permanently at the level of simple description, the
first half of the seventeenth century witnessed further efforts at

1 e.g., A. C. Crombie: From Augustine to Galileo (London, 1952), p. 217,
etc.: 'The development of the inductive side of natural science, and in fact the
thorough-going conception of natural science as a matter of experiment as
well as of mathematics, may well be considered the chief advance made by the
Latin Christians over the Greeks and Arabs.'

164 THE SCIENTIFIC REVOLUTION

rationalization. Of these two were properly philosophic and
systematic: Francis Bacon aimed at an exclusively experiential
method of scientific inquiry, while Descartes fabricated a new
logical key to nature. The third was Galileo's conscious reforma-
tion of the processes of scientific reasoning in mechanics, which was
less a philosophy of science applied to the solving of particular
problems than a reconstruction of a department of science which
necessitated the introduction of far-reaching philosophic principles.
The types of question which a scientist may ask which the
method he uses enables him to formulate, and possibly to solve
may of course be infinitely varied. But here it is useful to single
out two groups among them. The first kind may begin with such
words as "How can we demonstrate that . . .", "How may it be
proved that . . .". These questions are defined, for the investigator
has an idea, however vague, and seeks to test it. The second kind
are undefined, taking such a form as "What are the factors in-
volved in . . .", "What is the relationship between . . .", "What
are the facts bearing upon . . .". Here the investigator has hardly
arrived at the stage of ascertaining and ordering the relevant facts,
much less examining a hypothesis. Copernicus' problem falls into
the first of these groups, and the problems of seventeenth-century
chemistry and physiology into the second. Part of Bacon's signifi-
cance in the history of science resides in his realization of the
insufficiency of the first aspect of scientific method alone, and
though he made a notable contribution towards it, the second
aspect attracted his main interest. He found the theory of scien-
tific explanation that he encountered insufficient, partly perhaps
because his education in renaissance humanism gave him little
acquaintance with the natural philosophers of the late middle
ages; but still more warmly, he condemned inattention to the
methods by which the range of scientific facts could be enlarged,
or the facts themselves tested and more closely knit together. It
was one of his favourite themes that for many centuries genuine
contributions to solid knowledge had been the work of artisans
rather than of philosophers, of the weavers of speculation. Bacon's
writings have often been described as though his criticisms and
proposals were directly and solely the result of his social sense; as
though, because he believed that progress in material civilization
was a worthy end (a belief shared by both Galileo and Descartes),
he reasoned that the single function of science was to enhance

SCIENCE EARLY SEVENTEENTH CENTURY 165

man's command over natural forces. He has thus been depicted
as the first philosopher to appreciate the potentialities of science
as the servant of industrial progress. The truth seems to be rather
more complex. It is not even true that Bacon was the first to see
science as a powerful agent in improving material welfare, for this
point had been made by the empiricists of the middle ages and was
part of the common descent of magic and science. Nor was Bacon
merely a philosophical technologist; if he wrote

the true and lawful goal of the sciences is none other than this: that
human life be endowed with new discoveries and power,

he also declared, more emphatically, that as

the beholding of the light is itself a more excellent and a fairer thing
than all the uses of it so assuredly the very contemplation of things
as they are, without superstition or imposture, error or confusion, is
in itself more worthy than all the fruit of inventions . . . we must
from experience of every kind first endeavour to discover true causes
and axioms, and seek for experiments of Light, not for experiments of
Fruit. 1

Many passages in Bacon's writings indicate that he had a philo-
sophic appreciation of the value of knowledge for its own sake,
not merely for its utilitarian applications. The test by works, in
Bacon's thought, assumed a particular importance not because
works were the main end of science, but rather because they
guaranteed the rectitude of the method used. A discovery or
explanation which was barren of works could hold no positive
merit not because it was useless to man, but because it lacked
contact with reality and possibility of demonstration. Since
Bacon's science was to deal with real things, its fruits must be real
and perceptible.

Measured by these standards, Aristotelean science was a hol-
low structure, dealing with abstractions rather than real things,
justified by no fertility in works. Bacon did not deny that there
was truth in the content of orthodox science he was quite as
certain as Aristotle of the stability of the earth but these truths
were buried in a misleading and sterile philosophy. His remedy
was to return to a consideration of the bare facts, and above all
to increase vastly the range of facts available. Only when all the

1 Novum Organum, Bk. I, Ixxxi, cxxix, Ixx.

i66 THE SCIENTIFIC REVOLUTION

material upon a particular phenomenon, or natural process, had
been collected, classified and tabulated could any general con-
clusions be drawn from it and generalizations be framed. The
facts might be collected from experience, from reliable reports,
from the lore of craftsmen, but above all from designed experi-
ment. For Bacon clearly conceived of experiment not merely as a
trial "to see what happens," but as a way of answering specific
questions. The task of an investigator was to propose questions
capable of an experimental answer, which could then be recorded
as a new fact appertaining to the phenomenon under study. In
this way the lists of "instances" were to be built up, as Bacon
attempted himself to construct tables of instances of heat and
motion. Other aids were then required in the intellectual process
of finding order in the mass of fact compiled, for which also Bacon
made suggestions. In the New Atlantis the work of the fact-gatherers
is separated altogether from the work of the fact-interpreters, and
this has been criticized as a defect in Bacon's system. Yet in
practice in science it has often happened that a new generaliza-
tion in theory has interpreted a mass of evidence assembled by a
line of earlier experimental investigators.

Some comments on science have denied categorically that there
is any such thing as a specific "scientific method," by saying, for
example, that science is organized common sense. Bacon's method
at least seems to suffer from excessive formalization and a top-
heavy logical apparatus. Even in his own ventures into scientific
research Bacon did not observe his complex rules very strictly,
and hence the once popular notion that he invented and described
the method of experimental science is no longer acceptable.
Modern science was not consciously modelled upon Bacon's
system. Mathematical reasoning especially, so freely and success-
fully exploited from the earliest stages of the scientific revolution,
he never understood so that its essential role was hidden from
him. It has also been said, with less justice, that the integration
of theory and experiment typical of modern research was not
allowed for in his system and that he did not foresee the importance
of hypothesis in the conduct of an investigation. In fact Bacon did
envisage the situation where reflection on the facts suggests
several possible theories, and discussed the procedure to be
adopted for the isolation of the correct one by falsification of the
others. And certainly he understood the decisive nature of a

SCIENCE EARLY SEVENTEENTH CENTURY 167

" crucial experiment" in judging the merit of an idea taking shape
in the investigator's mind. It should not be forgotten, too, that
pure fact-collection (the first stage in Bacon's system) has been a
most important fraction of all scientific work up to the present
time. Even the routine verification of measurements, or the
establishment of precise constants, has been productive of original
discoveries. It is true that the main course of physical science in
the seventeenth century ran in a very different direction, that
in the new mechanics of Galileo the plodding fact-gathering
imagined by Bacon had little significance; elsewhere in science,
however, where the organization of ideas was less advanced and
the material far more complex and subtle, the straightforward
acquisition of accurate information was a more fruitful endeavour
than premature efforts at conceptualization. This is most
clearly true of the biological sciences; no Galileo could have
defined the strategic ideas of geology or physiology which only
emerged from the wider and deeper knowledge of facts obtained
in the nineteenth century. Bacon's advice that solid facts, certified
by experiment, should be collected and recorded was sound and
practical; this task occupied chemistry and biology till towards the
end of the next century. But in the long run the great generaliza-
tions in these fields did not follow from the kind of digestion and
sublimation of fact that Bacon had described.

While Bacon's works gave a useful impetus to the growing
interest in science, especially in England, his attempt to define
the intellectual processes involved in the understanding of nature
was limited and only partially helpful. Empiricism alone is an
insufficient instrument in science. The history of the scientific
revolution shows the fertility of the critical examination of con-
cepts and theories, even when the modification of the simple
account of the facts is insignificant (as with Galileo's new concepts
of inertia and acceleration) . Bacon's views were characterized by
his approach to science, which was that of a philosopher rather
than that of an experienced investigator. His own ventures in
research are notoriously uninteresting and unproductive, for
except in his leaning towards an atomistic materialism he was out
of sympathy with the progressive ideas of the time, and remarkably
indifferent to those developments which posterity has found most
significant. His logical system was for the most part ignored by
those who were finding how to make discoveries regardless of

i68 THE SCIENTIFIC REVOLUTION

logical systems, and consequently modern science did not so much
grow up through Bacon as around him.

Galileo offers a very different picture. On the one hand he was
mainly occupied with purely scientific matters and the discussion
of specific problems. He did not construct a methodical philosophy
of science, though the elements of such a philosophy may be
extracted from his works. On the other hand he may properly be
described as a philosopher, for his conscious reflection on the
obstructions to be overcome in arriving at a clear and confident
understanding of nature is explicit in a number of passages and
implicitly conditions the revolution in ideas that he effected. Like
other major critics of Aristotle, Galileo was faced with two
inescapable problems: on what foundations was the intellectual
structure of science to be built, and what criteria of a satisfactory
explanation were to replace those of Aristotle? With Galileo these
questions were not answered in prolonged metaphysical or logical
analyses though it seems clear that his ideas were shaped by just
such analyses carried out by his predecessors but the answers
were given as they became necessary in the progress of his attack
on the prevailing ideas of nature. As scientist Galileo's aim might
be to detect Aristotle's errors in fact or reason, while as philo-
sopher he demonstrated more fundamentally how these errors had
arisen from weaknesses in method that were to be avoided by
taking a different course. The negative exposure of an isolated
mistake by means of experiment or measurement was not, in
Galileo's view, the sole advance of which the new philosophy was
capable.

Galileo's two greatest treatises are polemics. They do not relate
how certain conclusions were reached, instead they seek to prove
that these conclusions are certainly true. Their arguments are
therefore synthetic, and the texture of reasoning and experience
is so woven that experience appears less as a peg upon which a
deduction depends, than as an ocular witness to its validity. It is
universally the case that the methods by which a discovery is
made and expounded differ, in varying degrees, and Galileo
rarely used the direct technique of reporting and inference, so
much favoured later by the English empiricists. In the Dialogues
and Discourses the foundations of scientific knowledge are shown to
reside in phenomena and axioms conjointly. By its attention to
actual phenomena Galilean science was made real and experien-

SCIENCE EARLY SEVENTEENTH CENTURY 169

rial; by its use of the capacity of the mind to apprehend axiomatic
truths its logic was made analogous to that of mathematics. The
latter were indeed generalized from the former, but the process
might involve historical as well as philosophical elements. Thus
a fundamental axiom of the Dialogues is that heavenly bodies
participate in uniform circular motion, while in the Discourses
successive propositions in dynamics are deduced from the axio-
matic definition of uniform acceleration. Such axioms, illustrated
and confirmed by experiment, become the starting-point for
arguments through which their implications are unfolded (in the
manner of Euclidean geometry or Archimedean statics) and again
in turn verified by experience, or applied to specific problems,
such as the isochronism of the pendulum.

Galileo's remarks on the procedure to be adopted in arriving at
these principal generalizations are therefore of special interest.
The most important step is that of abstraction. The essential
generalizations are not to be taken as the end-product of the
logical examination of an idea, in the manner of Aristotle, but
are obtained by abstracting everything but the universal element
in a particular phenomenon, or class. So far Galileo agrees with
Bacon, though he offered no comparable set of logical rules for
effecting this operation. He went on, however, to insist emphati-
cally that by abstraction it is learnt that the real properties of
bodies are purely physical, that is, size, shape, motion, propin-
quity, etc., not colour, taste or smell so that as he stated in the
Saggiatore, the " accidents, affections and qualities" attributed to
them are not inherent in the bodies at all, but are names given to
sensations stimulated in the observer by the physical constitution
of that which he perceives. Galileo noted that this failure to ab-
stract from sensations to the underlying physical reality had given
rise to much confusion in the study of heat; physically considered
(he says) there is no mystery in heat, which is merely a name
applied to a sensation produced by the motion of a multitude of
small corpuscles, having a certain shape and velocity, whose
penetrations into the substance of the human body arouse such
sensation. 1 In these opinions the influence of Epicurean atomism
is evident; one might say that this whole approach to the question

1 // Saggiatore (Bologna, 1655), PP- I 5~3- Bacon also agreed that 'heat is
an expansive motion restrained, and striving to exert itself in the smaller
particles.' (Novum Organum, Bk. II, xx.)

170 THE SCIENTIFIC REVOLUTION

of primary and secondary qualities is determined by a mechanistic
notion of the composition of matter. The explanation of a scientific
problem is truly begun when it is reduced to its basic terms of
matter and motion the transformation which remained the ideal
of classical physics. The name heat could not be a cause, since as
Galileo pointed out there is nothing between the physical pro-
perties of bodies with the varying motions and sizes of their com-
ponent particles and the subjective perceptions of the observer.
He found other instances in conventional science of this tendency
to believe that matters could be explained by juggling with
abstract names, as when in the Dialogues gravity is defined as only
the name of that which causes heavy bodies to fall; naming does
not contribute to understanding. Of course Galileo did not mean
that there is no purpose in classifying phenomena; his argument
is that classifications based on superficial characteristics and naive
analyses are misleading because they conceal physical realities.
They had concealed the universal generalizations on motion,
whether caused by gravity or any other force, which it was
Galileo's main achievement to reveal. 1

( In the process of abstraction an important aid was mathematics.
If the elements of a problem were capable of statement in numeri-
cal terms then the most exact definition had been framed and the
most general case considered. Moreover, by transposition into
mathematical language the conditions of the problem could be
exactly prescribed, in order to remove the imperfections and
minor variations that always occur in actual experience. As in
geometry the areas of triangles can be calculated more precisely
than they can be measured, so in mechanics the properties of the
lever, the inclined plane, the rolling sphere could be calculated
by reducing these physical bodies to geometrical forms whose
behaviour could be established by abstraction from that of their
physical counterparts. Galileo knew that this was a function of the
imagination; a calculus may solve a problem, but the due con-
ditions must be postulated before the calculation can begin. The
motion of a perfect sphere on a perfect plane must be inferred
imaginatively from the motion of physical spheres on physical
planes, or the motion of an ideal pendulum from that of actual

1 Similarly, a chief problem of the early botanical taxonomists was to
penetrate below the superficial differences and similarities in plants to more
"real" morphological distinctions.

SCIENCE EARLY SEVENTEENTH CENTURY 171

oscillating bodies, but this, for Galileo, was strictly analogous to
Euclid's abstraction in the definition of space, or Archimedes'
assuming that the cords hanging from the ends of a balance are
geometrically parallel. Mathematics, serving as a guide to the
imagination as well as handling the abstracted properties, could
yield further statements which, through reference to experience,
might confirm the process of abstraction and the generalizations
derived from it. In this ideal world of abstraction, without
resistance or friction, in which bodies were perfectly smooth and
planes infinite, where gravity was always a strictly perpendicular
force and projectiles described the most exquisitely exact para-
bolas, the principles of Euclidean geometry held absolutely. The
world of Galileo's imagination in mechanics was in fact Euclid's
geometrical space with the addition of mass (later defined pre-
cisely by Newton), motion and gravity. The secret of science, in
Galileo's outlook, was to transfer a problem, properly defined, to
this abstracted physical universe of science which, as ever greater
complexities are added to it, approximates more and more closely
to the actual universe. For the architecture of the real world is no
less mathematical than that of Euclidean space, the book of nature
being written 'in mathematical language . . . the letters [being]
triangles, circles and other geometrical figures, without which
means it is humanly impossible to comprehend a single word.'
As Galileo elsewhere declared, there is no distinction between
"real truth" and mathematical truth. On this account he has
been called a Platonist, whereas perhaps he was rather a Euclidean
in mechanics, never cultivating the mathematical mysticism that
distinguished Kepler. Moreover, Galileo recognized that while
mathematical logic is infallible, it may rest on false assumptions,
like those of the Ptolemaic system, which e although it satisfied an
Astronomer meerly Arithmetical, yet it did not afford satisfaction to
the Astronomer Phylososphical* It was but too easy to mistake one of
nature's circles for a triangle.

By the method of abstraction, moreover, the scientific concept
of " laws of nature" was simply and neatly accommodated. This
concept, unknown both to the ancient world and to the Far
Eastern peoples, seems to have arisen from a peculiar interaction
between the religious, philosophic and legalistic ideas of the
medieval European worldjjlj, is apparently related to the concept
of natural law in the social and moral senses familiar to medieval

172 THE SCIENTIFIC REVOLUTION

jurists, and signifies a notable departure from the Greek attitude
to nature. The use of the word "law" in such contexts would
have been unintelligible in antiquity, whereas the Hebraic and
Christian belief in a deity who was at once Creator and Law-giver
rendered it valid. The existence of laws of nature was a necessary
consequence of design in nature, for how otherwise could the
integrity of the design be perpetuated? Man alone had been given
free-will, the power to transgress the laws he was required to
observe; the planets had not been granted power to deviate from
their orbits. Hence the regularity of the planetary motions, for
example, ascribed by Aristotle to the surveillance of intelligences,
could be accounted for as obedience to the divine decrees. The
Creator had endowed matter, plants and animals with certain
unchangeable properties and characteristics, of which the most
universal constituted the laws of nature, discernible by human
reason. This conception is clearly capable of association with a
mechanistic philosophy, and irreconcilable with animism; as
Boyle put it:

God established those rules of motion, and that order amongst things
corporeal, which we call the laws of nature. Thus, the universe being
once framed by God, and the laws of motion settled, the [mechanical]
philosophy teaches that the phenomena of the world are physically
produced by the mechanical properties of the parts of matter. 1

If this transcendental status be granted to the laws of nature
so that one may inquire what they arc, but not why they hold
the question may still be asked, "How may a given proposition
be recognized as a law of nature? " In other words, how gloes a law
of nature differ from any other generalization which happens to
be true because no instance to the contrary has yet been dis-
covered? Modern philosophers of science, having deprived the
laws of nature of their transcendental status, present their own
answers to this problem. Galileo, and after him Newton, obtained
an answer to it by application of the method of abstraction. When
Galileo created by abstraction the essential model of the pheno-
mena of motion which he studied, he transformed the pragmatic
validity of a generalization appropriate to the world of experience
into the absolute validity of the law of nature in the intellectual

1 The Excellence and Grounds of the Mechanical Philosophy ', in Philosophical Works,
abridged by Peter Shaw (London, 1725), vol. I, p. 187 (condensed).

SCIENCE EARLY SEVENTEENTH CENTURY 173

model. Thus Newton, following Galileo, formulated his laws of
motion as laws of nature having complete applicability within the
fabric of mathematical physics, whose conclusions as a whole can
be confirmed by direct observation. In this way the difficulty that
the perfect universality of the laws of nature cannot be established
by experience of countless instances was overcome. For Galileo
and the later scientists who adopted his method such laws had a
greater force than descriptive generalizations could attain, because
they had acquired a fundamental systematic status in the scientific
picture of the universe.

Hence laws of nature could be considered in theory as being
rigorously exact, although the ascertainable correspondence be-
tween laws and experience in the physical world is limited by
probability-factors in experiments and by the intervention of a
multitude of complications. Such limitations were discovered, for
example, by the early experimenters in mechanics who discovered
that Galileo's theorems on motion could not be rigorously con-
firmed when applied to the movements of physical bodies. Galileo
had clearly appreciated the exceptional usefulness of the concept
of laws of nature in which they were taken to represent that which
the intellect, aided by scientific abstraction, conceives as the
essence of certain phenomena, but it fell to others to demonstrate
more satisfactorily the precautions which the scientist must take
in relating the laws to the crude evidence of the senses.

When abstraction has played its part, when attention has been
given to the really existing physical properties of bodies, when the
mathematization of the phenomena has been fully explored and
a theoretical science begins to take shape, how is the investigator
to determine whether his image or model of things in the ab-
stracted universe represents faithfully things as they are according
to experience? Galileo's answer to this problem, prepared for him
by earlier logicians, was the appeal to experiment. If theoretical
examination suggests that in specified conditions the event B will
follow the event A, then the reasoning can be tested by creating
those conditions, and making the observation. This doctrine is not
explicit in Galileo's writings, but it is implicit in their texture.
Thus the difference between Galileo and Bacon in this respect is
that the former emphasized mainly the role of experiment in test-
ing a theory, or determining its constants, while the latter stressed
the role of experiment as a means of obtaining information. In

174 THE SCIENTIFIC REVOLUTION

Galileo's view the questions which the investigator can ask nature
are most useful when they are not random questions, but are so
designed that a single unambiguous response can be elicited from
the experiment. This is probably the cardinal feature of modern
scientific method, of which numerous examples are to be found in
Galileo's writings, such as the use of the experiment with the in-
clined plane to verify the law of acceleration. It would be erroneous
to suppose that it had never appeared in earlier scientific research,
but it is with Galileo that it becomes its main pillar. It must be
observed, however, that the experimental method is capable of
bearing different connotations. With Bacon the appeal to experi-
ment is a remedy for ignorance:

Let further inquiry be made as to the comparative heat in different
parts and limbs of the same animal; for milk, blood, seed and eggs
are moderately warm, and less hot than the outward flesh of the
animal when in motion or agitated. The degree of heat of the
brain, stomach, heart, and the rest has not yet been equally well
investigated. 1

With Galileo experiment is a test of knowledge, confirming a
necessary deduction in the development of a sound theory, so that
he can even declare: " If you were to perform such an experi-
ment then you would obtain such a result," although he has never
made the experiment himself. Or in other passages he refers to
his readers' experience of the reflection of light from mirrors, the
motion of bodies in a ship under way, the passage of fluids between
vessels; a possible experiment is described, but none is reported
circumstantially. The function of these " thought-experiments"
in the argument of the Dialogues or Discourses is not to demonstrate
a new fact so much as to guide the imagination into perceiving the
agreement between experience and the ideas put forward. As
Galileo had framed his concepts, not in the laboratory but by a
correct analysis of the common evidences of motion, so in exposition
reversing the process he teaches the reader to analyse his own ex-
perience of motion by means of these thought-experiments. He
was well aware that experimentation is a double-edged weapon,
deceiving those who use it crudely, as when he writes of the
"sublime wit" of Copernicus, who

did constantly continue to affirm (being perswaded thereto by reason)
that which sensible experiments seemed to contradict; for I cannot
1 Novum Organum, Bk. II, xiii.

SCIENCE EARLY SEVENTEENTH CENTURY 175

cease to wonder that he should constantly persist in saying, that
Venus revolveth about the Sun, and is more than six times further
from us at one time, than at another; and also seemeth to be alwayes
of equal bigness, although it ought to shew forty times bigger when
nearest to us, than when farthest off. 1

Sheer empiricism, therefore, could not uncover physical reality,
which could only be glimpsed through the alliance of analytical
reasoning (especially of the mathematical kind), scientific imagina-
tion, and experimental caution.

From the critique of empiricism it emerges that in Galilean
science experiment is incompetent to confirm the whole intellectual
structure, whose conceptual elements transcend experiment. For
example, the concept of acceleration which science owes to Galileo
cannot be proved in the laboratory, though its applicability in
representing phenomena can be illustrated. For the definition of
acceleration involves the further concepts of time and velocity, the
latter a function of time and the concept distance. There is perio-
dicity in nature, and there are intervals in nature, but nature offers
no ready-made dimension-theory embracing the concepts of time
and distance. These can have no other status than that of ideas or
mental constructs which help to form the world-picture, having
the advantage that unlike concepts of beauty and justice they can
be understood in the same sense by all men. But their definition is
of mind, not innate in the fabric of the universe. The concept time
gives order to certain kinds of experience, the concept distance to
others, and from these arise velocity and acceleration rationalizing
others still, so that the first test^br a definition of acceleration must
be its assimilability in logic to existing dimension-theory; more-
over, in a second test, by experiment, the usefulness of the new
construct cannot be distinguished from the usefulness of the exist-
ing constructs, time and distance, so that effectively the whole
system of constructs must be tested together, if at all. Though the
Galilean scientist seeks to penetrate ever deeper into physical
reality, the nodes of his exposition of nature can never be more
than mental constructs, time, acceleration, the chemical element,
or the electron, which give order and significance to the experi-
mental data. This incidentally provides the justification for
Galileo's thought-experiments; the constructs are equally valid
when they give order to the facts of experience, duly analysed, as
1 Dialogues (trans. T. Salusbury), p. 306.

176 THE SCIENTIFIC REVOLUTION

when they apply to the most delicate determinations of the
laboratory.

If the theoretical part of science, leaving aside its practical
success in operating with materials and instruments, is a frame-
work of mental constructs giving order to experience, then it
follows that the only kind of explanation that is possible is one
that arranges the constructs in a logical pattern; as when the
properties of the molecule are traced to its atomic structure, and
the properties of the atom to its electrons. The sole method of
assigning a cause to any particular phenomena is to invoke the
constructs applicable to it, that is, the generalizations derived
from the study of less complex phenomena. In this way Galileo
used his concepts of motion to describe and account for the tra-
jectory of a projectile, as a modern physiologist more elaborately
uses the concepts of cytology, biochemistry and even the physical
notions of matter and energy to describe and account for the
functioning of a part of the body. That it is never possible to touch
any cause more fundamental than a construct or generalization
derived from the description of some definite phenomenon, and
that therefore explanation and description have no really distinct
significance in science, was the great methodological discovery upon
which the scientific revolution flourished. In Galileo's works its
full powers appear for the first time, but it was only gradually
extended from mechanics to the non-physical sciences. In the Dis-
courses (Third Day) Galileo disposed of the causes of the accelera-
tion of freely falling bodies imagined by philosophers as fantasies
unworthy of examination: 'At present it is the purpose of our
Author merely to investigate and to demonstrate some of the
properties of accelerated motion (whatever the cause of this
acceleration may be).' This does not mean that in replacing the
question why by the question how Galileo has excluded the study
of phenomena in terms of cause and effect it was his pupil
Torricelli who proved that the cause of the horror vacui (so called)
was the pressure of the air. Mere simple description, like that of
anatomy, was not the sole end of the new sciences Galileo created,
for the formulation of constructs and generalizations is a necessary
feature of the full description of a class of events, e.g. accelerated
motion. Galileo seems rather to be making the minor point that
if the cause of B is called A, the first subject of study must be B
itself (since it is from B that the very existence of A is wholly or

SCIENCEEARLY SEVENTEENTH CENTURY 177

in part inferred), and the more serious point that to describe and
account for the A-B relationship, the investigator must be able to
make a number of statements concerning A independently of B
in order to establish its character. In other words, since causation
and full description are synonymous, the "cause" of B (accelera-
tion) is a property of A (gravity), not of B, and can be sought only
in the description of A. This is Galileo's attitude throughout the
Discourses, as it is Newton's throughout the Principia. The explana-
tion of phenomena at one level is the description of phenomena at
a more fundamental level, that is, one nearer to the primary
realities of classical physics, matter and motion.

Following the example of Galileo, the scientist may as it were
work either upwards or downwards; he may seek for a more
fundamental construct (like the law of inertia, or the laws of
thermodynamics) or he may examine the applications of the con-
struct to the details of a complex phenomenon (like the isochron-
ism of the pendulum). In either case he may have to handle
constructs which are not reducible to the ultimate physical reali-
ties, as was the case for instance with Newtonian mechanics where
the law of gravitation had to be taken as descriptively correct,
though gravity was not explicable in terms of matter and motion.
For Galileo there was no anomaly in recognizing that certain
constituents of the physical world had to be accepted as axio-
matic; descriptive analysis can only advance gradually from the
coarse to the refined, from the lower to the upper levels, each with
its appropriate generalizations. In the period between Galileo and
Newton, however, the validity of the purely descriptive generaliza-
tion (which rests upon scepticism concerning the possibility of
arriving at a final indubitable truth serving as the single origin of
scientific thought) was challenged in the philosophy of Descartes,
and rejected by the systematists who expounded Cartesian ideas.
The chief difference between Galileo and Descartes lay in this,
that while the former believed that a body of knowledge successful
in organizing sense-perceptions (duly refined and analysed) and
in framing generalizations based on them gave an adequate under-
standing of nature, the latter believed that there was no reliable
test of the significance of sense-perceptions other than that which
issues from a deeper metaphysical certainty. The mind, being
extra-nature, was capable of doubting anything external to itself
in nature.

12

i?8 THE SCIENTIFIC REVOLUTION

\As Descartes relates in the Discourse on Method (1637), after
completing a thorough education, in which, ' not contented with
the sciences actually taught us) I had read all the books that had
fallen into my hands, treating of such branches as are esteemed
the most curious and rare, '(he found himself involved in many
doubts and errors, persuading him that all his attempts at learning
had taught him no more than the discovery of his own ignorance.
In philosophy, despite all the efforts of the most distinguished
intellects, everything was in dispute and therefore not beyond
doubt, and as for the other sciences 'inasmuch as these borrow
their principles from philosophy, 5 he reasoned that nothing solid
could be built upon such insecure foundations.

In this perplexity,fbescartes proposed to himself four "laws of
reasoning" which he applied in the first place to the study of
mathematics: }

In this way I believed that I could borrow all that was best both in
geometrical analysis and in algebra, and correct all the defects of the
one by the help of the other. And, in point of fact, the accurate ob-
servance of these few precepts gave me such ease in unravelling all
the questions embraced in these two sciences, that in the two or three
months I devoted to their examination, not only did I reach solutions
of questions I had formerly deemed exceedingly difficult, but even as
regards questions of the solution of which I remained ignorant, I was
enabled as it appeared to me, to determine the means whereby, and
the extent to which, a solution was possible.

Mathematical ideas, then, could be understood with perfect
clarity and mathematical demonstrations accepted with absolute
confidence. These principles, to which Descartes held firm in all
his scientific activities, ally him with Galileo in the attainment of the
ideal of mathematization throughout science. Indeed, Descartes'
most valuable contribution to the scientific revolution was the
co-ordinate geometry described for the first time in the same
volume as the Method. But his grasp of a starting point for the
comprehension of fact, rather than the abstractions of mathe-
matics, depended upon a form, of psychical crisis from which he
emerged possessed with the metaphysical force of the statement'
/ think, therefore I am:

I thence concluded that I was a substance whose whole essence or
nature consists in thinking, and which, that it may exist, has no need
of place, nor is dependent on any material thing; so that "I," that is

SCIENCEEARLY SEVENTEENTH CENTURY 179

to say the mind by which I am what I am, is wholly distinct from the
body, and is even more easily known than the latter, and is such, that
although the latter were not, it would still continue to be all that is.

This led Descartes to inquire why he had found Cogito, ergo sum
an infallible proposition, whence he convinced himself that all
things clearly and distinctly perceived as true, are true, 'only
observing that there is some difficulty in rightly determining the
objects which we distinctly perceive.' Further, he declared that
since the mind is aware of its own imperfection, there must be a
being, God, which is perfect and that since perfection cannot
deceive, those ideas which are clearly and distinctly perceived as
true are so because they proceed from perfect and infinite Being.
So much more certain are the fruits of reason, says Descartes, that
we may be less assured of the existence of the physical universe
itself, than of that of God, 'neither our imagination nor our senses
can give us assurance of anything unless our understanding
intervene . . . whether awake or asleep, we ought never to allow
ourselves to be persuaded of the truth of anything unless on the
evidence of our reason.'

After this denunciation of empiricism, this declaration that all
knowledge of truth is implanted by God, this assertion that the
task of the scientist is to frame propositions as clearly and distinctly
true as those of geometry, what suggestions can be made for the
deciphering of the enigma of nature? According to Descartes, it
is necessary to follow exactly that procedure which Bacon had
condemned in Aristotle, that is, to establish the prime generaliza-
tions that are 'clearly and distinctly true.'

I have ever remained firm in my original resolution ... to accept
as true nothing that did not appear to me more clear and certain than
the demonstrations of the geometers had formerly appeared; and yet
I venture to state that not only have I found means to satisfy myself
in a short time in all the principal difficulties which are usually
treated of in philosophy, but I have also observed certain laws estab-
lished in nature by God in such a manner, and of which he has im-
pressed on our minds such notions, that after we have reflected
sufficiently on these, we cannot doubt that they are accurately
observed in all that exists or takes place in the world.

Thus the science of Descartes is a centrifugal system, working
outwards from the certainty of the existence of mind and God to
embrace the universal truths or laws of nature detected by reason,

i8o THE SCIENTIFIC REVOLUTION

and then from the "concatenation of these truths" revealing the
mechanisms involved in particular phenomena. It is systematic,
unlike the "new philosophy" of Bacon or Galileo, because its aim
is not to enunciate a correct statement here and there as it becomes
accessible to intellect, but to provide an unchanging fabric whose
relevance to particulars is the sole remaining subject of inquiry.
In this respect, despite his contempt for scholasticism, Descartes
sought for himself the commanding authority of a new Aristotle.
Indeed, among Cartesian scientists, and still more among Car-
tesian philosophers of later generations, a new scholasticism
flourished through the dissection, embroidering and expansion of
Descartes' doctrines, until they, like Aristoteleanism in the six-
teenth and seventeenth centuries, were in turn regarded as a
bulwark against dangerous innovations and as the philosophic
justification of religious orthodoxy. 1

(Apart from his researches in optics and mathematics by far
the portion of the whole which proved of greatest value to science
Descartes preferred to express his ideas in the form of a model,
whether of a man or of the universe. Superficially this procedure
seems to resemble the Galilean process of abstraction, but in
reality it is very different. Having settled his principles, Descartes
believed that to philosophize about mathematical abstractions
was to promote delusions; his object was the real world, but as he
did not know from experience what the mechanisms of the real
world, or the actual human body, are, he was forced to imagine
what they must be to accord with the principles and such know-
ledge as he had. He did not claim that in describing the model he
was describing the real world, only that from the identity of their
properties the real world could be understood in terms of the
model. Its mechanism was absolute, since it followed from the
dualism of mind and matter that all the phenomena of nature
resulted from the properties of matter, especially its motion, which
in turn were fixed by natural law. The laws of nature, including
the definition of matter by extension and the impossibility of a
vacuum, the law of inertia, and the laws of impact between
particles, were derived by Descartes as ideas 'clearly and dis-
tinctly perceived to be true.' Thus Descartes and Galileo agreed
that the only physical reality which science can study is that of
matter in motion; unlike Galileo, however, Descartes did not
1 Cf. A. G. A. Balz: Cartesian Studies (New York, 1951).

SCIENCE EARLY SEVENTEENTH CENTURY 181

hesitate to extrapolate far beyond the limitations of mathematical
analysis or experimental inquiry. In the end, elaboration of the
principles, guided only by the criteria of "clear and distinct/'
yielded.)) in Cartesian cosmology, chemistry and physiology
nothing other than subtle scientific fantasy.

Again, with regard to the functions of experiment Descartes and
Galileo adopted antithetical positions. The pillars of Cartesian
science were " clear and distinct" ideas formulated as laws of
nature; it was to fit these, and not experimental evidence, that its
subsidiary theories were shaped. It was essentially deductive from
these natural laws, and if knowledge did not supply the requisite
materials, then they had to be invented with the aid of reasoned
deduction, as the celestial vortices carrying the planets about the
sun, the three kinds of matter and the variously contrived pores
of substances were invented in accordance with the exigencies of
experience and reason. Of course, experience was respected in the
sense that Descartes sought to explain in his model the sum of the
phenomena of nature as he knew them, for it is obvious that he
could not have deduced magnetism within his system had he not
known of its manifestations. But Descartes made no attempt to
confirm his mechanisms in detail by experiment. The foundations
of knowledge, he thought, were best settled without it:

for, at the commencement, it is better to make use only of what is
spontaneously represented to our senses, and of which we cannot
remain ignorant, provided we bestow on it any reflection, however
slight, than to concern ourselves about more uncommon or recondite
phenomena; the reason for which is, that the more uncommon often
mislead us so long as the causes of the more ordinary remain
unknown. . . .

Experiments indicating some conclusion detached from a deduc-
tive system Descartes distrusted; hence nothing that Galileo did
had value for him, because Galileo did not know the cause of
gravity. This must not be taken to mean that either Descartes or
his successors were totally blind to the merits of experimentation,
though it could only be an adjunct when the application of clear
and distinct ideas failed, or in an obscure inquiry. In his own
experimental researches Descartes revealed great talent, and those
who were influenced by him, like the Dutch physicist Christiaan
Huygens, included some of the great exponents of experimental
science of the later seventeenth century though indeed they owed

182 THE SCIENTIFIC REVOLUTION

much less in this respect to Descartes, than to the empirical temper
of the age, and the emulation of Galileo's example in mechanics.
It was Huygens who later described Descartes as the author of
c un beau roman de physique.' Though its doctrines were recited
into the mid-eighteenth century the Cartesian system of science
proved sterile, and it may be doubted whether the Cartesian
philosophy of science ever produced a single useful thought, save
in the mind of its originator. 1 The optimistic metaphysical belief
that what is clear and distinct must be true proved unfounded.
The deductive method, subjected to the destructive criticism of
the neo-Baconians of the Royal Society, was again convicted of
fostering works that were shallow, speculative and remote from
real things. Clearly when Descartes devoted himself to systematics
his status as a scientist diminished. But the importance of his
systematic works especially the Principles of Philosophy (1644), the
text-book of the Cartesian school for nearly a century must not
be underestimated, for in the mid-seventeenth century the intel-
lectual appeal of Descartes throughout France, Britain and north-
western Europe was immensely greater than that of Galileo, while
Bacon was almost unknown to continental scientists. The very
fact that Descartes wrote as a philosopher gave his scientific ideas
greater currency, and to many places where Aristotelean and
humanistic conventionality lingered untroubled, Cartesian notions
brought the first breath of a new outlook, a fresh vitality in natural
philosophy. Thus Oxford, because Descartes was read there, was
regarded about 1650 as being much in advance of Cambridge.
His was undoubtedly the pre-eminent intellect in the swelling
movement, ebullient with ideas and discoveries, that made Paris
the scientific focus of Europe from about 1630 to 1670. Even
among those who cannot be enrolled with the expositors of Des-
cartes' science, there were many who, like Boyle or Newton,
though they learnt through the use of an empirical or Galilean
method to criticize his theories, had found in those same theories
their point of departure; indeed, the main activities in physical

1 It may be remarked that Descartes' metaphysic of scientific discovery, as
described in the Method, is essentially individualistic, i.e. it shows how each man
may learn to frame his own idea of nature. But, just as those sects which claimed
to be founded on the free interpretation of the Bible imposed the sternest disci-
pline in order to safeguard the interpretations of their founders, so the later
Cartesians instead of going through this process of discovery adhered rigidly to
the idea of nature developed by Descartes himself.

SCIENCE EARLY SEVENTEENTH CENTURY 183

science for more than a generation after Descartes' death can be
interpreted, without gross distortion, as a commentary upon
Descartes' works. And if the Principles of Philosophy proved ephe-
meral compared with Newton's Mathematical Principles of Natural
Philosophy even the title suggests a reaction its influence in
leading later seventeenth-century science to entertain ideas of
mechanism, of the corpuscular structure of matter, of the im-
portance of "natural laws," was creative of further progress.

Perhaps it may justly be said that Descartes' successes in science
were due less to any peculiar merits in his method, than to his
native genius for investigation. There is one point, however, both
in the method and the texture of his thinking on scientific subjects
that deserves to be singled out. Descartes well understood the
importance, in any work of research, of scientific imagination, a
faculty with which he himself was so well endowed that he hardly
perceived its limitations when controlled by reason alone without
cautious experimentation. Bacon had recognized that imagination
or intuition might surmount an inconvenient obstruction; Galileo
also admitted that in demonstrative sciences a conclusion might
be known before it could be proved:

Nor need you question but that Pythagoras a long time before he
found the demonstration for which he offered the Hecatomb, had
been certain, that the square of the side subtending the right angle in
a rectangle triangle, was equal to the square of the other two sides:
and the certainty of the conclusion conduced not a little to the investi-
gating of the demonstration. . . , 1

In Descartes there is a more overt appreciation of the function
of directed imagination, playing on the problem in hand, in
formulating hypotheses to be tested by experiment or other means:

. . . the power of nature is so ample and vast . . . that I have hardly
observed a single particular effect which I cannot at once recognize as
capable of being deduced in many different ways from the principles, and
that my greatest difficulty usually is to discover in which of these
ways the effect is dependent upon them; for out of this difficulty I
cannot otherwise extricate myself than by again seeking certain
experiments, which may be such that their result is not the same
if it is in one of these ways that we must explain it, as it would
be if it were to be explained in another. 2

1 Dialogues (trans. T. Salusbury), p. 38.

2 Discourse on Method, Part VI; my italics.

184 THE SCIENTIFIC REVOLUTION

Here experiment is put forward, not as by Bacon to uncover the un-
known, or as by Galileo to confirm the known, but as a means of
eliminating all but one of the mechanisms suggested by imagina-
tion as the explanation of a particular phenomenon. And as
Descartes correctly stated, the imagination is directed because it
is referred to certain known principles (or constructs), and further
because the mechanisms suggested must be susceptible in the
first place of deductive check, since science does not admit of
idle guessing. If Descartes had realized that even when only a
single hypothetical mechanism seems deductively feasible it
remains a hypothesis until confirmed by experiment, and if he
had applied this test more meticulously, his thought would have
been less liable to run into speculation. In any case the liberty to
frame hypotheses (in spite of Newton's famous dictum), with the
rigorous attention to the findings of experiment and observation
which Descartes himself neglected in his encyclopaedic survey of
nature, was to prove a creative factor in the accelerating progress
of science.

The scientific method of the seventeenth century cannot be
traced to a single origin. It was not worked out logically by any
one philosopher, nor was it exemplified completely in any one
investigation. It may even be doubted whether there was any
procedure so conscious and definite that it can be described in
isolation from the context of ideas to which it was related. The
attitude to nature of the seventeenth-century scientists especially
their almost uniform tendency towards a mechanistic philosophy
was not strictly part of their scientific method; but can this be
discussed except in connection with the idea of nature? In large
part the character of the method was determined by the mental
range of the men who applied it; hence Bacon's method bore
fewer fruits in his own hands because his conception of the facts
of nature was still Aristotelean. The influence of Descartes, too,
was so great because he produced a mechanistic world-system of
infinite scope (enriched with some genuine discoveries) which was
welcomed by his age, not because he outlined a remarkably clear
or satisfactory way of proceeding in scientific research. Even
Galileo's observations on method were probably less important
than direct imitation of the kind of mathematical analysis he
initiated in mechanics. Over the broad area of scientific activity
the influence of content on form was more significant than the

SCIENCE EARLY SEVENTEENTH CENTURY 185

reverse effect. Methods changed, because different questions were
asked, and a new view of what constitutes the most useful kind of
scientific knowledge began to prevail. Perhaps this is most effec-
tively revealed in the biological sciences, where the century
witnessed a progressive change in the content of investigations
unaccompanied by conscious discussions of the methods to be
employed. Here there was no parallel to the criticism of the
methods of Aristotle and the scholastics in physics, though of
course the medieval neglect of the descriptive sciences was often
commented on adversely. The far-reaching inter-action between
the content and the techniques of science was also uncontrolled
by any very explicit conceptions of method. This interaction had
a profound effect on the quality and extent of the information
available; but Bacon alone explicitly recognized the importance
of accurate fact-gathering in science. It seems most natural to
believe that in any effective step the method, the philosophy and
the discovery itself were carried along together in the subsequent
impact, for though there is nothing that can reasonably be called
a specific method of science to be found in the works of Harvey,
or Kepler, or Gilbert, these men changed the character and form
of future studies. Who, for instance, could ignore the challenge of
the phrase with which Gilbert opens his Preface to De Magnete:
' Clearer proofs, in the discovery of secrets, and in the investigation
of the hidden causes of things, being afforded by trustworthy ex-
periments and by demonstrated arguments, than by the probable
guesses and opinions of the ordinary professors of philosophy. . . .'
Yet the meaning and weight of experimental testimony was still
open to discussion a century later. A scientific approach to prob-
lems must be the sum of its many aspects experimentation,
mathematical analysis, quantitative accuracy, and so on varying
according to the nature of the problem; and this the seventeenth
century drew from many varied sources. Its implied implementa-
tion in practice was more important than its explicit formulation,
with the somewhat curious result that scientific method, shaping
itself to the needs of practising scientists and vindicated rather by
results than by preconceived logical rigour, has remained some-
thing of an enigma to philosophers from Berkeley onwards. In the
long run the obstinate empiricism of a Gilbert or the unpredictable
intuition of a Faraday have successfully broken the rules of both
inductive and mathematical logic.

CHAPTER VII
THE ORGANIZATION OF SCIENTIFIC INQUIRY

EA.CH phase of civilization tends to produce its own institutions
of learning. In the ancient empires science was attached to
the temples of religion; Greece saw Plato's Academy, the
Lycaeum founded by Aristotle, and the vast library of Alexandria;
the middle ages created the common school and the university in
a structure of education which has not wholly vanished. Lastly,
in the modern era, the learned society, with its international
affiliations and specialized journals, has profoundly influenced
the stratigraphy of research. Neither the learned society nor the
learned journal (the terms are convenient, if pompous) was
altogether the creation of the scientific revolution, but in both
cases the course of events was very much determined by the
necessities of the scientific movement, and scientific organization
was taken as a model by those who worked in other fields of
knowledge. From the end of the seventeenth century the majority
of active men of science were members of some active scientific
group; publication in one of the ever more numerous journals
gradually became the recognized manner of announcing the
results of investigation; and the national scientific society was
accepted as the vehicle for the state's concern in scientific matters.
Although the Fellowship of the Royal Society, for example, was
much less indicative of intellectual distinction in the eighteenth
century than it has since become, as institutions the Royal Society
or the Academic Royale des Sciences enjoyed a prestige even
greater than that of the universities in humane studies. Indeed, the
evolution of modern science outside academic walls was the main
cause of the lack of cohesion, and of the difficulty in the communi-
cation of ideas, whose correction was one of the principal objects
of the founders of the scientific societies. In the unity of medieval
learning the scholar enjoyed communion with others of similar
interest in the university of which he was almost invariably a
member, and wherever his studies might lead him. The* sixteenth
century saw the new phenomenon of scholars, literati and

1 86

ORGANIZATION OF SCIENTIFIC INQUIRY 187

scientists whose interests were no longer embraced in the work of
the university, and who were also more uniformly distributed
throughout a highly cultivated society. The landed gentleman,
the country physician or clergyman, the apothecary, the soldier
and the lawyer, played a new and important part in the advance-
ment of knowledge or the patronage of literature. Expecially in
northern Europe, where the universities were less numerous and
more conservative than those of Italy and France, intellectual
leadership passed to a class which was not merely outside the orbit
of the university, but was apt to regard academic learning as old-
fashioned and sterile.

Oxford and Cambridge are our laughter,
Their learning is but pedantry:
These Collegiates do assure us,
Aristotle's an ass to Epicurus.

wrote the "wit" who composed the Ballad of Gresham College about
iGGy. 1 From the first, the connection of the new scientific move-
ment with practical arts rendered it in some degree independent
of the universities. As the friends of the "new philosophy" became
increasingly critical of Aristotle and conventional education, they
found their opponents the more firmly entrenched behind
academic walls; hence the innovators tended to seek a more con-
genial intellectual environment elsewhere. 2 Scientific knowledge
was no longer in the mid-seventeenth century limited to the
religious and medical classes, but was widely diffused through a
diversified and exuberant society. Many biographies relate the
feeling of confidence, the depth of intellectual satisfaction, the
release of a creative drive that was experienced by members
of the new class of laymen, educated and leisured, when they
passed from the confines of academic disputation to the methods
of experimental science.

Scientific discovery is (or was, until recent times) an act of the
individual, with of course a greater or less indebtedness to his in-
tellectual inheritance. So, equally, in the seventeenth century, was
the adoption of the novel scientific outlook, critical of orthodoxy,

1 Gresham College, founded in 1598 by the merchant-financier Sir Thomas
Gresham, was the first meeting-place of the Royal Society, whence the Fellows
were known as the "Gresham philosophers."

2 In Europe, this was partly due to the control of education exercised by
certain religious orders, but everywhere the university was deeply committed
to Aristotelean thought.

i88 THE SCIENTIFIC REVOLUTION

which can be seen almost as a conversion in many instances,
as when Galileo became an adherent of the Copernican system.
But since men naturally assemble to indulge a common taste, and
since wits are sharpened by contact, the groups of intellectuals
who collected in a tavern, a lecture-room, or about an enterprising
patron tended to assume a more formal character, to look for
recognition and privilege. The first of such groups to acquire an
organization and a history were products of Italian humanism.
Their interests were literary rather than scientific. About a century
later the first national academy, the Academic Franchise founded
by Richelieu in 1635, was also a literary institution: its main task
was the conservation of the purity of the French language. The
early literary societies met for discussion and criticism; their object
was rather the extension of knowledge and the refinement of taste
than anything resembling research or analysis, and there was
nothing foreshadowing the modern presentation of papers. The
first scientific societies, which also originated in Italy, followed the
same pattern. Occasional meetings of groups of experimenters,
like that which is supposed to have collected about William Gilbert
at his London house, or that centred about Giovanbattista Porta
in Naples (the so-called Accademia Secretorum Naturae) were
hardly societies at all. 1 The first assembly emphatically of this
character was the Accademia dei Lincei in Rome, of which Galileo
was a member, which lasted with one break through the first
thirty years of the seventeenth century. The Lincei 2 rose to a
membership of thirty-two, and planned to set up branches every-
where, equipped with printing-presses, botanic gardens and
laboratories. The patron of the society was Duke Federigo Cesi,
a naturalist, and much of its activity was diverted to natural
history. One member, Francesco Stelluti, published the first
zoological studies made with the aid of the microscope. Two of
Galileo's early books were published by the Lincei, but the society
did not approve his later cosmological ideas.

The Accademia dei Lincei, like earlier literary societies, and some
later scientific groups, did not engage in any form of corporate
activity. The members followed their own investigations, whose

1 Baptista Porta (d. 1615) was the author of Magia Naturalis Libri IV (1558,
enlarged edn. 1589: Englished as Natural Magick, 1658), and a great exponent
of esoteric experimentation.

2 So called, because the Lynx symbolized the clear-sightedness of science.

ORGANIZATION OF SCIENTIFIC INQUIRY 189

results they discussed at the meetings. However, the great Floren-
tine society of the mid-seventeenth century, the Accademia del
Cimento, followed the alternative plan, which had already been
described by Francis Bacon in the New Atlantis. The object of
Bacon's model organization was not merely to bring men together,
but to set them to work in common on the tasks most important
for science, so that it resembled a scientific institute more than a
modern scientific society. The vast realm of natural knowledge,
he felt, was too vast for one man to tackle single-handed, while
concentration on a single problem or set of problems was likely
to produce a myopic picture of single trees, not a survey of the
forest. To the efforts of individual pioneers, as Sprat put it later
in speaking of the Royal Society, 'we prefer the joint Force of
many Men.' Other advantages of the Baconian plan were that,
as it ensured that due attention was always paid to each division
of science, so it made certain that none could be carried on in
complete isolation from the rest; and it also provided a means by
which, it was hoped, a quantity of necessary apparatus beyond
the means of a private purse could be gathered together.

In Bacon's view, the assembling of pure information, the
preliminary to the elucidation of natural truths, was such a
formidable task that it could only be tackled by a co-operative
endeavour. Otherwise science was likely to be for ever deluded
by theories enunciated on the basis of an insufficient mass of
digested fact. 1 Later the Royal Society was for a short time to
embark on such a project of fact-collection. The Accademia del
Cimento, on the other hand, was not committed to this Baconian
conception of procedure in science. It concerned itself with the
experimental development of the scientific ideas of Galileo, and
of his two most successful pupils, Torricelli and Viviani, while the
nine members also pursued their own problems independently.
One large fraction of their total activity was directed to the proof
of the theorems on motion that Galileo had demonstrated mathe-
matically, and another to the study of the barometric vacuum

1 Thomas Sprat, in his History of the Royal Society (1667), echoed the then
typical opinion that in Bacon's writings were 'everywhere scattered the best
Arguments, that can be produced for the Defence of experimental Philosophy,
and the best Directions, that are needful to promote it,' but he did not hesitate
to confess that Bacon's natural histories were far from accurate, because Bacon
seemed 'rather to take all that comes, than to choose, and to heap, rather than
to register ' (1722 edn., pp. 35-6).

igo THE SCIENTIFIC REVOLUTION

discovered by Torricelli. Though the business of the society was
experiment, it was not by any means empirical experimentation
alone. Reports of its work, which spread slowly throughout
scientific circles in Europe, did much to shape the course of
experimental science elsewhere, and created new confidence in
the Galilean experimental method. Part of the success of the
Accademia del Cimento in spite of its short duration often years
from 1657 to 1667 was due to the richness of the apparatus at its
command, for it made use of what was really the first physical
laboratory in Europe. 1 The academy was founded by the Grand
Dukes Ferdinand II and Leopold of Florence, who used the
remaining wealth of the Medicis to buy the services of the finest
instrument-makers, to procure the most perfect lenses, and equip
their colleagues with a most elaborate series of barometers,
thermometers, time-measuring devices and whatever else was
required for their work.

The book in which this was described the Saggi di Naturali
Experience (i667) 2 was almost the first piece of pure experimental
reporting in the history of science. Interpretation of the results
gained was limited strictly to the range of the evidence, and
elaborate speculation was avoided. The experiments recorded
are various as well as numerous. Attempts were made to verify
Galileo's theory of projectiles, and the time-keeping properties of
the pendulum were studied without, however, leading to its
application to a mechanical clock, which was made by the Dutch
physicist Christiaan Huygens. Various forms of the thermometer,
hygrometer and barometer were tested, and the design of optical
instruments improved. Experiments were made on the "radia-
tion" of cold from a lump of ice; on the thermal expansion of
many substances; on the incompressibility of water; on the force
of gunpowder; and on capillary attraction. The researches of
Torricelli and Pascal, showing that the observations formerly
explained by the statement that nature abhors a vacuum should
be attributed to atmospheric pressure, were confirmed. It was
proved that neither combustion nor respiration were possible in
a space exhausted of air, that magnetic attraction was transmitted
through it but not sound, and a rather unsuccessful attempt to
construct an air-pump was made. In this field of activity the

1 Many of the instruments are still preserved in Florence.

2 Translated by Richard Waller as Essayes of Natural Experiments (1684).

ORGANIZATION OF SCIENTIFIC INQUIRY 191

Accademia was largely repeating work that had already been
done by Robert Boyle at Oxford, and described in his Physico-
Mechanical Treatise on the Spring of the Air (1660).

Naturally the benefits to be derived from closer co-operation
among those interested in the new scientific movement were not
perceived in Italy alone. In both England and France informal
groups had existed for many years before the Accademia del
Cimento was founded. The generation of Frenchmen which in-
cluded Descartes, Gassendi, Fermat, Desargues, Roberval, Pascal
and Mersenne (c. 1630-60) was particularly active, fertile both in
new ideas and new experiments. Paris was their centre, and there
was a continuous tradition of scientific gatherings which was
ultimately formalized in the Academic Royale des Sciences. One
of the earliest groups was held together by the personality of Marin
Mersenne, a Minim friar of the convent in the Place Royale,
which was not only a meeting place at which important discussions
took place, but also the centre from which Mersenne conducted
his vast correspondence, maintaining communication between his
colleagues even more effectively than the actual gatherings. It is
a significant historical fact that, since the late sixteenth century,
transport facilities and postal organizations had much improved,
rendering possible regular and frequent exchanges of letters. 1 By
this means news of the latest developments could be spread more
rapidly: problems could be exposed for general consideration: and
criticism could be provoked and collated. In the mid-seventeenth
century a number of men occupied a prominent position, less
on account of their own intellectual capacities, than because of
their indefatigability as correspondents. Their function was to
be acquainted with everyone of importance in science, to gather
information and to re-distribute it to those of their friends who
were likely to be interested. Of these Fabri de Peiresc at Mont-
pellier was one, and Mersenne in Paris another. Later Henry
Oldenburg, first Secretary of the Royal Society, carried on the
same role, his talent as a "philosophical merchant" (as Robert
Boyle called him) greatly strengthening the bonds between
English and continental scientists. Even in the eighteenth century
the private correspondence of a great public figure in science (like
Sir Joseph Banks) was still of international importance.

1 Tycho Brahe was one of the first scientists to leave an important mass of
material of this kind, which has been edited byj. L. E. Dreyer.

i 9 2 THE SCIENTIFIC REVOLUTION

Jta London, ox in Firm, informal groups preceded a formal
scientific society. These seem to have had a stronger common
interest in the mathematical sciences than in moral and natural
philosophy, partly because geometry and astronomy were well
represented at Gresham College (the natural focus for scientific
pursuits in London), partly in continuation of the Elizabethan
tradition of developing the practical sciences (navigation, sur-
veying, cartography, etc.).') While there was little evidence of
English concern for the ideas of Bacon, Gilbert and Harvey until
near the close of the first half of the seventeenth century, there
was considerable activity in the field where science and technology
overlap. Cornelius Drebbel, an ingenious engineer as well as an
experimenter of some repute, was acclaimed at the court of
James I, 1 whose successor, besides patronizing Harvey's researches
in embryology, established an experimental workshop at Vaux-
hall. Even the mathematician Napier of Merchistoun, inventor
of logarithms, in a fit of Protestant fervour invented a series of
terrible war-like devices, the plans for which he destroyed on his
death-bed. On the whole, the more important exponents of pure
science in England at this early period, like Thomas Harriot
(d. 1621) and Jeremiah Horrocks (d. 1641), though by no means
isolated, had slender contact with the great scientific movement
on the Continent. 2 Dilettanti, philosophers and literary men (such
as Thomas Hobbes, Sir Charles Cavendish and Sir William
Boswell) did more to make its literature known in England.
Indeed, the " grand tour" was a serious and necessary education,
as may be seen in the life of Robert Boyle.

The history of the emergence of the Royal Society from these
groups has been told many times. It now seems probable that
there were two at least of these, whose members became the fathers
of real science in England; some men entered more than one
circle, but there was far from complete unity of ideas. In the
London of the Commonwealth and Protectorate men of antagon-
istic religious and political persuasions could have very similar

1 Who paid a state visit to Tycho Brahe's observatory at Hveen, and received
the dedication of Kepler's Harmonices Mundi.

2 Harriot was an inventive algebraist, and perhaps an independent dis-
coverer of the usefulness of the telescope in astronomy. He was closely connected
with the Elizabethan explorers. Horrocks, in a very short life, proved himself a
theoretical and practical astronomer of genius. He was an early student of
Kepler, with whom he had some correspondence.

ORGANIZATION OF SCIENTIFIC INQUIRY 193

scientific aspirations. 1 Something, at least, of Bacon's influence
may be detected in all; many wished to see some sort of specifically
scientific institution established, not a few were firmly convinced
that civilization could be powerfully advanced through scientific
knowledge. These last were particularly evident in the group that
Boyle called the "Invisible College" in 1646, who apparently
devoted especial attention to agriculture, as well as to natural
philosophy and mechanics. The leading figure in this group was
Samuel Hartlib, a Polish refugee, a man of great learning and
wide connections, an enthusiast for the union and defence of the
Protestant churches. Hartlib was a great advocate of the applica-
tion of science to technology, but no scientist himself. His hopes
broken by the restoration of the monarchy, he appears to have
played no part in the foundation of the Royal Society that soon
followed. Another group included men of greater weight. As
John Wallis, the mathematician, recollected the events of 1645:

We did, by agreement, divers of us, meet weekly in London on a
certain day and hour, under a certain penalty, and a weekly contribu-
tion for the charge of experiments, ... of which number were Dr.
John Wilkins . . . Dr. Jonathan Goddard, Dr. George Ent, Dr.
Glisson, Dr. Merrett (Drs. in Physick), Mr. Samuel Foster . . . Mr.
Theodore Haak . . . (who I think first suggested these meetings)
and many others.

Haak was another German refugee, probably the most im-
portant of Mersenne's English correspondents. All those named
by Wallis (including himself), except Foster who died in 1652,
were Original Fellows of the Royal Society. The group met in
term-time at Gresham College, and Wallis's list of topics in the
"New or Experimental Philosophy" which came up for discussion
recalls the subjects treated by the Accademia del Cimento:

Some were then but New Discoveries, and others not so generally
known and embraced as now they are, with others appertaining to

1 Thus, a circle close to the government included the poet Milton, Olden-
burg, probably John Pell (mathematician), Lady Ranelagh (Boyle's sister).
In touch with this was another group (Boyle's "Invisible College"?), which
included Hartlib, Boyle, Drury, Oldenburg, Plattes, Dymock, Petty, and
evidently others. Then Wallis's group at Gresham College, also deeply com-
mitted to the republican regime, was linked with the universities and the
"Invisible College." Finally, the Royalists (Evelyn, Brouncker, Moray) seem
to have maintained amicable relations with individuals (at least) in these
groups.

13

i 9 4 THE SCIENTIFIC REVOLUTION

what hath been called the New Philosophy which from the times of
Galileo at Florence, and Sir Francis Bacon in England, hath been
much cultivated in Italy, France, Germany and other parts abroad,
as well as with us in England.

It is interesting to note that the Copernican hypothesis was still
debated by these philosophers. About the year 1649 they were
divided, some moving to Oxford, where they formed the Oxford
Philosophical Society, which was joined by Boyle on his removal
there in 1653. In Oxford they were reinforced by some brilliant
students, among them Christopher Wren and Robert Hooke.
Thus there is considerable evidence that before the restoration
there existed an extensive ramification of personal connection
among at least thirty men, many of whom were prominent in
academic and public life, and that their common interest was in
mathematics and science, not in the promotion of a religio-political
movement. The arch-royalist Evelyn could even visit Wilkins,
Cromwell's brother-in-law. Few were too deeply committed to the
republic to adjust themselves to the restoration of the monarchy,
which provided an opportunity for effecting the formal organiza-
tion long discussed among these amateurs. 1 Charles IPs dilettante
interest in science was well known, and his scientifically minded
courtiers, Sir Robert Moray 2 and Viscount Brouncker (later first
President of the Royal Society), were able to win his patronage.

The Royal Society of London for the promotion of Natural Knowledge,
which received its first charter in 1662, was a wholly private
creation, very different from other major societies of the century.
Royalty gave patronage, but nothing more. The Fellows enjoyed
neither privilege nor pension. They were granted no buildings or
funds. Therefore the Society remained, to the nineteenth century,
impoverished and inadequately housed. It has never possessed

1 In addition to the proposals of Bacon, Comenius and Hartlib, plans were
made by Evelyn, Petty and Cowley. In the latter's plan sixteen resident pro-
fessors were to teach * all sorts of Natural, Experimental Philosophy, to consist
of the mathematics, mechanics, medicine, anatomy, chemistry, history of
animals, plants, minerals, elements, etc.; Agriculture, Art Military, Navigation,
Gardening. The mysteries of all trades, and improvement of them; the Facture
of all merchandises, all natural magic, or Divination; and briefly all things
contained in the catalogues of natural histories annexed to my Lord Bacon's
Organon.* (A proposition for the Advancement of Experimental Philosophy, in Cowley's
Works, 1 680, pp. 43-5 1 ) .

8 Moray was a close friend of Huygens, and like Oldenburg he had attended
sessions of the Montmor academy in Paris.

ORGANIZATION OF SCIENTIFIC INQUIRY 195

laboratories, or other than honorary means of promoting research,
and was never able to implement the Baconian conception to
which many of the Founders were attached. For over a century
and a half the qualifications for a Fellowship included wealth and
influence as well as scientific merit, because without such support
the Society would have collapsed. On the other hand, it had a
corresponding sovereignty over its actions. It was independent of
government, and though the specialist knowledge of the Fellows
was often placed at the service of the state (especially in the
eighteenth century), state officials guided neither its elections nor
its business. By contrast, in France the Academic Royale des
Sciences was the creation of the first minister, Colbert, who
arranged the appointments and suggested problems in accordance
with political interests. The members were pensionaries when
occasion demanded, they became civil servants. That the Dutch
physicist Huygens, who retained his Fellowship of the Royal
Society throughout the Anglo-Dutch wars, found his position in
the Academic des Sciences inconsistent with Louis XIV's anti-
Dutch policy, and resigned from it, sufficiently indicates the
difference in character between the two institutions. And these in
turn correspond to the different social and constitutional structures
of the two states.

The middle-class intellectuals, who in England combined to
form their own clubs in which they met as equals, were in France,
as in Italy, more dependent on the good offices of a patron. Thus,
at the beginning of the seventeenth century, one of the groups
most notable in Paris for literature and learning met regularly
at the residence of the historian de Thou. His patronage, which
included the use of his valuable library, was continued by his
relatives the brothers Dupuy to about 1662. Less exalted gather-
ings met at the Bureau d'Adresse managed by the journalist
Renaudot. At these, as at the Cabinet of the Dupuys, literary and
political news was more eagerly awaited than discussion of
scientific topics. Mersenne's circle, however, confined its attention
almost entirely to mathematical and scientific affairs: it was he,
for example, who made the discoveries of Galileo and his pupils
known in France, who gave currency to the Cartesian system, and
publicized Pascal's problem on the cycloid. 1 After Richelieu's

1 i.e. the calculation of the area bounded by the curve and a straight line,
which proved to be three times the area of the generating circle.

196 THE SCIENTIFIC REVOLUTION

foundation of the Academic Frangaise there was some feeling among
those who cultivated the sciences that encouragement ought to be
given to a similar non-literary institution. Among their number
was Habert de Montmor, a man of great wealth who had offered
his patronage to both Descartes (who declined it) and Gassendi.
Not long after the death of Mersenne in 1648 weekly meetings
were taking place in his house, presided over by Gassendi. Their
discussions were not limited to science, and it was required only
that those who took part should be c curious about natural things,
medicine, mathematics, the liberal arts, and mechanics.' The
Montmor Academy, which gave itself a formal constitution in
1657, soon became a fashionable resort; at the meeting in 1658
when Huygens' paper announcing his discovery of Saturn's ring
was read, there were present 'two Cordon Bleus . . . both Secre-
taries of State, several Abbes of the nobility, several Maitres des
Requetes, Conseilleurs du Parlement, Officers of the Chambre
des Gomptes, Doctors of the Sorbonne,' after which the amateurs,
mathematicians and men of letters seem rather insignificant. 1
Science, even the most abstruse mathematics, had become respect-
able, and apparently interesting, even in the upper levels of
Parisian society. The new philosophies of Descartes and Gassendi
were victoriously allied against Aristoteleanism. But the course of
the Academy was not altogether smooth; the amateurs were
more ready to discuss the latest marvels in science than to work
for its advancement, and there were sharp clashes of personality.

Mazarin, who had shown far less concern for the intellectual
eminence of France than his master Richelieu, died in 1661 and
the supreme power was then committed to the young King,
Louis XIV. There was thus the possibility of acquiring for science
the greatest of all patrons. Since the Royal Society had begun to
take shape in 1660 the Montmor Academy had followed its
fortunes with some envy, and had even to some extent modelled
its own proceedings upon the Royal Society's example. The links
between the two bodies were close, for Oldenburg corresponded
with several members of the Montmor Academy. Huygens and
Sorbire (the Secretary of the Academy) were members of both
societies, and a number of the Parisians visited London.

The works of Boyle and other Englishmen were carefully

1 Saturn's ring had been seen in very distorted form by other astronomers,
but Huygens first interpreted its nature correctly.

ORGANIZATION OF SCIENTIFIC INQUIRY 197

studied in Paris, where the usefulness of the empirical attitude was
gradually more highly esteemed. While the Royal Society had
grown from its own independent and varied origins, the Academic
des Sciences was certainly inspired by its success. In 1663 Sorbiere
sent to Colbert, who was virtually Louis' Minister for Internal
Affairs, a copy of his memoir on a proposed reform of the Montmor
Academy. He regarded an experimental organization without
royal support as hopeless; soon afterwards the Academy did indeed
cease to exist, partly as a result of tension between the experi-
mentalists and the philosophers. Meetings continued, however,
at the house of Melchisedec Thevenot, 1 who also found the
expense of providing for experiments too great, and appealed to
Colbert. In a situation where co-operation between the Cartesians,
the Gassendists, the amateurs, the mathematicians and the experi-
mentalists in a joint undertaking seemed increasingly impossible,
the latter group turned to the monarchy. Their first scheme,
planned in an ample Baconian fashion, was severely pruned by
the minister. Ultimately the Academic des Sciences consisted of
two classes only, mathematicians (including astronomers and
physicists) and natural philosophers (including chemists, physi-
cians, anatomists, etc.), meeting jointly on Wednesdays and
Saturdays in two rooms assigned to their use in the Royal Library.
Appointments of the academicians were made during 1666, and
sessions began at the end of that year.

Most of the active members in the English groups preceding the
Royal Society became Fellows, 2 but few of those associated with
earlier Parisian assemblies were received into the new Academic.
The systematic Cartesians were carefully excluded; on the other
hand, three foreigners, Huygens, Cassini and Roemer, were
among the most distinguished of Colbert's appointments. Thus
the Academic des Sciences was not strictly a continuation of any
previous body, nor did it include the amateurs and dilettanti
admitted by the Royal Society. No rules or constitution exist
earlier than the reorganization effected by the Crown in 1699,
but it is evident that as in England the precepts of Bacon were not
without weight. Huygens, especially, advocated the preparation

1 (1620-92), traveller, linguist, author, student of many sciences, and
inventor of the familiar spirit-level.

2 The few who did not seem to have retired into obscurity for political or
religious reasons, as Milton did; the election of John Ray (1667) shows that the
Royal Society exercised considerable latitude in these respects.

198 THE SCIENTIFIC REVOLUTION

of a complete Natural History, and the examination of new
inventions was an important aspect of the Academic's work.
Having sketched a common programme, the pensionaries pro-
ceeded to their experiments and discussions in concert. These
proceedings were strictly secret. As in London, the private
researches of the academicians gradually assumed a greater
significance than their co-operative undertakings. Yet the
Academic, thanks to its greater wealth, was able to attempt
ventures beyond the resources of the Royal Society. Two of them,
the measure of a degree of a great circle about the earth, giving
an accurate estimate of its diameter for the first time, and the
expedition to Tycho Brahe's observatory at Uraniborg, were
conducted by the astronomer Picard. A third, the expedition to
Cayenne (in which it was discovered that the length of the
pendulum beating seconds was less in southern than in northern
latitudes) had as its object the measurement of the earth's
distance from the sun by means of simultaneous observations on
Mars. 1

Indeed, the study of astronomy by the members of the Acade-
mic was particularly successful. They developed the telescope of
very long focal length to its useful limit, the application of the
telescope to measuring instruments, and the use of the telescope
micrometer. Cassini's observations on Saturn, and Roemer's on
Jupiter (from which he correctly deduced the finite velocity of
light) won great fame. Some of these observations made at the
Paris Observatory provided important evidence for the system of
the universe which Newton was to substitute for that of Descartes.
They were made possible by royal generosity in equipping the
Observatory, built in 1666, which became an experimental insti-
tution as well as an astronomical observatory in the modern sense,
fitted with the finest instruments. For astronomy was the first of
the sciences to reach the stage where the results obtained bear a
definite ratio to the expenditure permitted. The Royal Society, by
contrast, was far less well provided for. It was not placed in control
of the Royal Observatory at Greenwich (founded in 1675), though
it was granted some vague surveillance over it. 2 The equipment at
Greenwich, provided in the first instance by John Flamsteed, the

1 The result obtained was about 6 per cent, too small.

2 This somewhat anomalous situation provoked a serious conflict between
Flamsteed and the Society early in the eighteenth century.

ORGANIZATION OF SCIENTIFIC INQUIRY 199

Astronomer Royal, and his friends, was limited though good of its
kind. He himself was forced to take a country living for support,
and could never afford proper assistance. His main work in de-
termining the positions of the stars was not available for more than
thirty years, but he supplied observations on the moon used by
Newton in his gravitational theory. The credit for Flamsteed's
great achievement in reducing the errors of astronomical measure-
ment to a new low order, despite all the obstacles he had to over-
come, clearly attaches to himself alone. The Royal Society had
other observers of note, such as Robert Hooke and Edmond Halley
(Flamsteed's successor at Greenwich), but these had to do what
they could with their own resources. In fact the Society could offer,
at this period, no fit facilities for scientific work of any kind, apart
from its library and museum.

Everywhere in Europe the formation of scientific societies illus-
trates a dual tendency, on the one hand towards the crystallization
of a specifically scientific organization out of informal groups
having broader and more superficial intellectual interests, and on
the other towards the preponderance of the experimentalists within
the organization. In Italy, France and England there was a transi-
tion from the discussion of natural-philosophic systems or hypo-
theses to the verification and accumulation of fact; as the course
of the scientific revolution laid more emphasis on deeds than on
words, on the laboratory rather than the study, and as the prepara-
tion of commentaries and criticisms of ancient texts gave place to
the writing of memoirs describing the results of systematic investi-
gation, so the characteristics of scientific organization changed
accordingly. In the first half of the seventeenth century the func-
tion of a scientific assembly had been to promote discussion and
dissemination of the new idea of science, and to provide a forum
in which, not merely before an audience of enthusiasts, but before
the broadest cross-section of educated and literate society, the
original thought of a Galileo or a Descartes could challenge con-
ventional opinions in science. Patrons like the Medici brothers, or
a newsgatherer like Mersenne, amassed the accumulative weight
of innovation against the science of colleges and text-books. They
presented the total case for the "new philosophy," in an intel-
lectual environment whose dogmatic traditions were already
disintegrating, to a new learned class freed from the sterner disci-
pline of the old professional scholar, ready to admire acuity of

aoo THE SCIENTIFIC REVOLUTION

wit, subtlety of reasoning and fertility of imagination more than
allegiance to orthodox "sound" views. If the "new philosophy"
was obstructed in the university, there was appeal through the
scientific assembly to the more tolerant, eager and wealthy in-
tellectual circles of court and capital. But the alliance between
modern science in its early stages and the whole turbulent current
of cultural development in the seventeenth century was inevitably
incomplete and of short duration. Important, creative scientific
work rapidly outdistanced the dilettante and virtuoso: rarely, for
example, does the name of John Evelyn occur in the proceedings
of the Royal Society printed by Birch in his History. A man of
general culture could not see the point of detailed scientific labours,
for whereas he might enjoy a debate on Descartes' concept of the
animal as machine, he tended to find the naturalist grubbing in
ditches for insects' eggs merely comic. The exploitation of the
shift of intellectual perspectives, so fascinating in general outline,
inevitably sank to tedium and pedantry in the eyes of those who
sought entertainment and striking novelty. As a result, the Mont-
mor Academy broke up, and the Royal Society failed in wide
appeal after its first fifteen years.

Consequently, in the second half of the seventeenth century the
role of the scientific society changed considerably. Having become
a thoroughly professional body, it served as a focus for the discus-
sion of works rather than ideas. Its aim was to develop the sciences,
rather than promote a "new philosophy." Opposition from Aris-
totelean university teachers, or the medical profession, was hardly
serious any longer. The scientific movement required countenance
less than means buildings, apparatus, money for the maintenance
of research, and methods for exchanging its results. It was found,
for instance, that as scientific books became more truly technical,
more fully devoted to describing research (rather than useful text-
books or practical manuals), the publishing trade refused to handle
them unless large sums were laid down. Or again, while there was
an expanding commercial market for ordinary watches and clocks,
navigational instruments, and even telescopes and microscopes,
financial encouragement alone would induce craftsmen to hazard
their profits in efforts to improve instruments for the advancement
of science. In short, the task before a scientific society .was less to
secure the scientific revolution, than to maintain its momentum
and to reap its harvest. The founders of the Academic des

ORGANIZATION OF SCIENTIFIC INQUIRY 201

Sciences were perhaps the first to appeal to national interest in
this connection. 1 Earlier exponents of the utility of scientific dis-
covery had rather looked to the improvement of the condition of
mankind to a shift in the precarious balance between human
powers and the forces of nature. As Bacon had put it, the ambition
to exalt one's state was a degree less noble than the ambition of the
natural philosopher to elevate mankind. But in the proposals put
forward by Leibniz, for example, to establish a scientific academy
in Germany, there seems to be a clearer statement of the case for
investment in science as a national benefit. There the first scientific
academy, founded at Berlin in 1700, did not develop from the
efforts of earlier groups of amateurs. 2 The capital of Brandenburg-
Prussia was indeed far removed from the main centres of culture
in Germany, its university not being founded until more than
a century later, but Leibniz had in the Elector (later King)
Frederick I a patron willing to realize his long-matured plans. These
had always aimed at furthering the interests of the German nation
and raising its technological standards through the encourage-
ment of the vernacular language and the reform of education in a
practical direction. To attain these objects a national academy
which should concern itself with practical applications as well as
with the pure sciences was the first necessity. In Leibniz' view
Germany had once enjoyed pre-eminence in useful arts, especially
in mining and chemistry, 3 but also in horology, hydraulic engin-
eering, goldsmith's work, turnery, forging etc. Astronomy was
restored by the Germans, and the " Nieder-Deutschen " (Nether-
landers) had invented the telescope and mastered navigation.
The only remedy for the subsequent deterioration was the generous
encouragement of science, which Leibniz coupled with the en-
forcement of a strictly mercantilist economic policy, by which the

1 'Sans exclure de son programme cT6tudes les sciences pures et specu-
latives, Colbert essaie de Porienter vers les sciences appliquees a Pindustrie et
aux arts." P. Boissonade: Colbert (Paris, 1932), p. 28.

2 There were already active scientific groups in Germany in the late
seventeenth century such as the Collegium Nature Curiosorum, founded by
Lorentz Bausch in 1652 and dealing with the medical sciences, and the
Collegium Curiosum sive Experimental , founded by Christopher Sturm of the
University of Altdorf in 1672 and dealing with physical sciences. Neither was
a national academy of science in any sense.

3 'Denn weil keine Nation der Teutschen in Bergwergssachen gleichen
Konnen, is auch Kein Wunder, dass Teutschland die Mutter der Chimie
gewesen.' L. A. Foucher de Careil: CEuvres de Leibnitz (Paris, 1859-75),
vol. VII, pp. 64-74.

202 THE SCIENTIFIC REVOLUTION

state should become self-sufficient. 1 As he put it in a letter to
Prince Eugene, discussing the proposed scientific academy in Vienna:
Pour perfectionner les arts, les manufactures, Tagriculture, les deux
esp&ces d'architecture [i.e. civil and military], les descriptions choro-
graphiques des pays, le travail de mini^res, item pour employer les
pauvres au travail, pour encourager les inventeurs et les entre-
preneurs, enfin pour tout ce qui entre dans f&conomique ou mecanique de
Vetat civil et militaire, il faudrait des observatoires, laboratoires, jardins
de simples, menageries d'animaux, cabinets de raretez naturelles et
artificielles, une histoire physico-m6dicinale dc toutes les annees sur
des relations et observations que tous medecins salaries seraient
obligez de fournir. 2

Leibniz, historian, mathematician, philosopher, diplomatist and
confidential adviser of princes, in his dual devotion to science and
Germany saw the scientific academy as a necessary instrument of
the modern state, through which science could be made to play
its due part in social and economic policy. He had little patience
with those who ' considerent les sciences non pas comme une
chose tres importante pour le bien des hommes, mais comme un
amusement ou jeu,' and criticized the Academic des Sciences
for this reason. 3 Science as a factor in creating national prestige,
its role in war and in the commercial rivalry of states, were
appreciated in England and France as well as in Germany; but
no one who could claim high rank as a philosopher and scientist
announced the importance of scientific organization to jealous
statesmen more clearly than Leibniz.

Thus, one alleviation of the obstructions to scientific progress
was sought through the conversion of Bacon's appeal to the inter-
ests of humanity into an appeal to the interests of the state. 4 One

1 On mercantilism, cf. E. Hecksher: Mercantilism (London, 1935). The
Berlin Academy was intimately linked with Leibniz* typically mercantilist
project for the establishment of a silk industry in Brandenburg. (Foucher de
Careil, loc. cit., pp. 280 et seq.)

2 Ibid., p. 317, italics inserted.

3 Letter to Tschirnhaus, January 1694 (G. I. Gerhardt, Mathematische
Schriften, in Gesammelte Werke hrsg. von G. H. Pertz, vol. IV, p. 519).

4 In the later seventeenth century gunpowder was still quoted as one of the
great discoveries of the modern age. War was accepted by scientists, as by all
men, as an inevitable human evil, and the development of the war-like potential
of the state did not provoke moral condemnation, perhaps because this genera-
tion experienced warfare which was more technically efficient than that of
previous generations, but which the lessening of religious fanaticism had
rendered less horribly destructive. Many scientists, however, commented that
it was more noble to advance the arts of life than those of death.

ORGANIZATION OF SCIENTIFIC INQUIRY 203

other must be briefly treated. The Royal Society approved a step
which was calculated to increase its support in a rather different
way, by the publication of its Philosophical Transactions, begun in
1665. Partly a profit-seeking venture on the part of the Secretary-
editor, Henry Oldenburg, the Transactions were also intended to
attract the "curiosi" and "virtuosi" to the work of the Royal
Society, and to stimulate the submission of original reports. The
publication consisted of discourses read by Fellows at meetings
of the Society, of letters on scientific subjects (translated, if neces-
sary, and printed more or less verbatim), both from Britain and
abroad, most of which also had been read at meetings, and of
book-reviews. The modern scientific " paper," of which the first
examples appear in the Philosophical Transactions, has in fact a
double origin. One of its ancestors exists in the interchange of
scientific correspondence discussing original work, which may be
traced back to the late sixteenth century. Very many of Olden-
burg's articles were letters with hardly more than the "Dear Sir"
and "your obedient servant" deleted: but they were letters in-
tended for publication. The other ancestor was the formal essay
or discourse read to scientific groups from the early seventeenth
century onwards. At the time, this form of presentation required
the development of a new art of composition, for no suitable liter-
ary or academic models existed and its perfection, leading to the
complex machinery for scientific reporting existing today, is an
event of historical importance. At the end of the century, however,
the learned journal was still far from being the accepted means
for the announcing of discoveries. Huygens, for instance, though
he stated his results in bald (or even enciphered) language to
the societies of London and Paris, published them completely
only in full treatises which sometimes appeared many years
later.

Nevertheless, the Philosophical Transactions was immensely suc-
cessful. Latin translations were produced at Amsterdam, and
the Academic des Sciences prepared its own French version.
Though Antoni van Leeuwenhoek, the great microscopist, never
visited London and knew no language other than his native Dutch,
he sent the accounts of his astonishing discoveries for publication
in English in the Transactions. Oldenburg had created a new field
of literature, which was rapidly extended; for if the Transactions
was not the first journal to appear in regular numbers, it was the

204 THE SCIENTIFIC REVOLUTION

first to print original communications. Its predecessor by two
months, the Journal des Sfavans, surveyed the whole field of
learning, devoted much space to summaries of books, and merely
reported the business of the scientific societies. The series of
original Mgmoires of the Academic des Sciences was begun only
after the reorganization of 1699. Many other reviews, of which
the most famous was Bayle's Nouvelles de la republique des lettres
(1684) followed the broad pattern of the Journal] a few others (the
Miscellanea published by the Collegium nature curiosorum from 1670,
and the Ada Eruditorum founded by Leibniz in 1682, the former
restricted to the medical sciences and the latter embracing many
aspects of learning) printed communications, but none was so
purely descriptive in its content as the Philosophical Transactions.
While the reviews enjoyed a steady repute among intelligent
readers, and gave a superficial picture of the total scientific
activity in Europe, private communication in correspondence,
and the frequent exchange of their respective publications, was
for the leading figures far more important.

From the preceding account, it will be clear that during the
mid-seventeenth century there was a tendency for all effective
scientific activity to be focused upon some society or group. In
the small area of England a single organization embraced every-
one, but in France and Germany, both before and after the
foundation of national academies, less magnificent societies
flourished, as they did also in the Italian and other small states.
Each of these had its own character and major preoccupations.
Naturally also each proclaimed, with varying degrees of emphasis,
the principal tenets of the scientific revolution. Strategic concepts,
like that of natural law, gradually gained a universal validity; the
practical benefits to be expected from the cultivation of natural
science were canvassed in all parts of Europe; Aristotelean
philosophy was everywhere condemned, and the virtues of
mathematical analysis everywhere exalted; nearly all the societies
embarked on elaborate programmes of experiments. The societies
differed in character, and individual members of the same society
differed in their opinions; in France Descartes, and in England
Bacon, were regarded as peculiarly magisterial figures, but it is
commonplace to find members of different societies working on
the same or allied problems in similar ways, or to discover the

ORGANIZATION OF SCIENTIFIC INQUIRY 205

reaction of some discussion in Gresham College upon the work of
the Parisian academy, and vice versa. Only to a strictly limited
degree did local or personal traditions bar the complete amalga-
mation of the new scientific spirit.

Perhaps this may best be illustrated in the development of a
mechanistic view of nature during the seventeenth century. This
proceeded at three different levels. In the first place, a mechanistic
theory of the universe was fully described by Descartes in 1644
(in the Principles of Philosophy] , to be supplanted by the far more
perfect theory of Newton's Principia (iGSy). 1 Spheres and intelli-
gences were finally banished, and the secrets of the heavenly
motions were traced to the properties of matter and the rule of
laws of nature. Secondly, in biology, the theory of the organism
as a machine was taken up by the Cartesian school, and exercised
a wide influence; this theory, of course, was the product of a shift
in philosophical outlook. Newtonian mechanism could be shown
to satisfy all the minutiae of evidence; biological mechanism was
a profound hypothesis, but no demonstration of it in physiological
terms as yet existed, or was possible. In the third place, mechanistic
views in relation to physics and chemistry fall into an intermediate
category. They could not be demonstrated completely, but they
could be applied successfully in a number of particular instances.
They were certainly philosophical in origin, and not deductions
from definable experimental investigations, but they were
applicable in a wide area of experimental research.

At each of these levels, the attitude of the mechanistic scientist
to the complexity of nature enabled him to cope with different
fundamental problems. Pure and celestial mechanics, the most
highly mathematical branches of science, treated of the nature
offerees and motion. Mechanistic biology gave a new interpreta-
tion of the nature of life, of growth and of sensation. In relation to
physics and chemistry, the problem to which the scientist sought
an answer was the nature and constitution of matter, in so far as
these sciences dealt with the properties, changes and transforma-
tions of inorganic substance. The distinctions between the three
states of matter; differences in density and mass, hardness and

1 The Principia exposes, of course, no mechanistic theory of the nature or
cause of gravitational forces. Newton's conjectures, on various occasions, make
it plain that he leaned strongly towards some form of mechanistic interpreta-
tion. See below, pp. 272-3.

206 THE SCIENTIFIC REVOLUTION

brittleness; the nature of magnetism, electricity, gravity and heat;
hypotheses of light and colour, all seemed to require interpretation
in the light of some general theory of what matter is, which would
account for the variations in observed properties between different
kinds of material substance. Similarly the philosophical chemist,
studying solution, volatilization, fusion, and the analysis and
synthesis of substances effecting striking qualitative changes in
macroscopic properties, necessarily tried to form some picture of
what was happening to the very nature of the materials in his
vessels. Starting from the axiom that matter is neither created nor
destroyed, what internal modification was implied by a change
in observable qualities?

During the sixteenth and seventeenth centuries there was, as
might be expected, a sharp reaction against the answers which
Aristotle had furnished to this type of question. In the period of
the foundation of the Royal Society and the Academic des
Sciences various versions of a mechanistic, particulate theory of
matter were widely entertained. As in other matters, there was a
tendency for the scientific revolution to revert to a Greek view of
nature older than Aristotle's. Medieval philosophers had, very
largely, respected Aristotle's condemnation of atomistic doctrines,
but the scholars of the renaissance and the scientists of the seven-
teenth century, with the full text of Lucretius' exposition of Greek
atomism in their hands, 1 preferred its use of the concepts of
structure and physical texture in matter to Aristotle's theory of
forms and qualities. The Greek atomists had explained the com-
plexities of substances without making any assumptions of a
non-material nature; indeed, if Lucretius was right in his declara-
tion that the only realities are atoms and the vacuum in which
they move, qualities were mere illusion, the perceptual registration
of physical reality. 2 This was a virtue of the "mechanical" or
"corpuscular" philosophy particularly attractive to Galileo, for
example, who sought to penetrate by means of the process of

1 There were about thirty editions of De Natura Rerwn (editio princeps, Brescia,
1473) before 1600. There was a French translation in 1677, and an English
in 1683.

2 By contrast, in the older philosophy, forms and qualities were real, existing
entities. If it was said that snow had the "form of whiteness," this did not
describe the snow, but explained its optical properties. Similarly for the
alchemists the "form of gold" was something that could be separated from the
"substance" of gold and transferred to the "substance" of another metal,
e.g. lead deprived of its own distinctive "form."

ORGANIZATION OF SCIENTIFIC INQUIRY 207

abstraction from the evidence of sensation to the basic reality of
nature.

Before Descartes' influence became significant a number of
writers had expounded or commented on ancient particulate
theories, drawing on the texts of Democritus, Epicurus, Lucretius
and Hero of Alexandria. The earlier ones treated the atomistic
doctrine purely as a theory of matter, which they freely combined
with Aristotelean physics. Pierre Gassendi, from about 1625, was
the first writer to attempt to develop a completely mechanistic
physics founded on Epicurus and rejecting Aristotle, but his
success was hardly greater than that of Lucretius, whom, except
in matters touching on religion, Gassendi very closely followed.
Physical properties were simply traced to the imagined size and
shape of the component particles. In Galileo and Bacon, on the
other hand (as already mentioned), are found the beginnings of
a true kinetic theory, especially in relation to heat. As Isaac
Beeckman stated it, c all properties arise from [the] motion,
shape, and size [of the fundamental particles], so that each of
these three things must be considered.' 1 For both Bacon and
Galileo an important aspect of the "new philosophy" was its
endeavour to establish, through experimental study, a theory of
particulate mechanisms to replace the doctrines of forms and
qualities, yet neither of them were atomists in a narrow sense.
Bacon, indeed, wrote that the proper method for the discovery of
c the form or true difference of a given nature, or the nature to
which nature is owing, or source from which it emanates ' would
not lead to 'atoms, which takes for granted the vacuum, and
immutability of matter (neither of which hypotheses is correct),
but to the real particles such as we discover them to be.' 2 In
short, there is ample evidence that in the early seventeenth century
the conception of matter as consisting of particles, whose aggregate
might be a solid, a liquid, an air or a vapour, was commonplace
and generally acceptable and that the properties of the aggregate
were attributed to the nature and motions of the particles.

In considering the development, extension and diversification
of this generalized concept in the second half of the century, three
traditions may be distinguished. The first is that of the strict

1 Journal tenu par Isaac Beeckman de 1604 a J ^34> e ^. Cornells de Waard (La
Haye, 1939-45), vol. I, p. 216 (1618).

2 Novum Organum, Bk. II, Aphorisms i, viii.

2o8 THE SCIENTIFIC REVOLUTION

atomists, adhering firmly to the indivisibility of the ultimate
particle and the absolute reality of the vacuum between atoms.
They were the followers of Gassendi. Next, Cartesian scientists
continued the peculiar corpuscularian doctrine of Descartes, which
admitted the infinite divisibility of matter, and denied the vacuum.
Finally, the experimentalists refused to commit themselves to any
precise body of philosophic preconceptions. They learnt from both
Gassendi and Descartes : the form of their particulate theory was
closer perhaps to that of Gassendi, but in its application to physics
it borrowed much from Descartes' concrete imagination. This
experimentalist tradition in corpuscularian physics grew most
rapidly in England, and was especially fostered by the works of
Robert Boyle. Never a dogmatic system, it was a late development
which played an important part in the relations between the
French and English scientific societies. It was, in fact, a major
product of the impact of French scientific ideas upon Englishmen
about the middle of the century an impact which conditioned
the nature of the scientific achievement of the Hooke-Boyle-
Newton generation.

Starting from the assumptions that in nature there are no occult
forces, like gravity or magnetism, and that the universe is continu-
ously and completely filled with matter, Descartes developed in
the Principles of Philosophy (1644) an extraordinarily elaborate
mechanistic and corpuscularian "model" of the physical universe.
His particles, of which there were three species, were not atoms,
because he imagined them as divisible, though in nature not
normally divided. The first element was a fine dust, of irregular
particles so that it could fill completely the interstices between the
larger particles. The second element (matiere subtile or aether) con-
sisted of rather coarser spherical particles, apt for motion, and the
third element of still more coarse, irregular and sluggish particles.
These three elements corresponded roughly to the Fire, Air and
Earth of Aristotle, and as they were composed of the same matter,
the elements could be transformed one into another. This was
regarded by the Cartesians as no arbitrary hypothesis, but as a
truth (according to Rohault) 'necessarily following] from the
Motion and Division of the Parts of Matter which Experience
obliges us to acknowledge in the Universe. So that the Three Ele-
ments which I have established, ought not to be looked upon as
imaginary Things, but on the contrary, as they are very easy to

ORGANIZATION OF SCIENTIFIC INQUIRY 209

conceive, and we see a necessity of their Existence, we cannot
reasonably lay aside the Use of them, in explaining Effects purely
Material. ?1 The nature of a substance was mainly determined by
its content of third element, its properties by the second. Since
Descartes denied that the third-element particles had intrinsic
weight or attraction, hardness (the cohesion of these particles) was
attributed to their remaining at rest together, fluidity to their
relative motion; but this motion also was not intrinsic but im-
parted by the first and second elements. Thus in solution the
grosser particles of the solvent by their agitation dislodged those
of the dissolved material; if however the particles of the solvent
were too light, or the pores of the solid material too small to admit
them, the latter would not dissolve. When the pores between the
third-element particles were large enough to admit a large quan-
tity of the second element, the substance was an "elastic fluid"
(gas), whose tendency to expand was caused by the very free and
rapid motion of the second-element particles. Flame itself con-
sisted of matter in its most subtle form and under most violent
agitation, and was therefore the most effective dissolvent of other
bodies, while the sensation of heat increased with the degree of
motion in the particles of the heated body. Rohault notes that,
when filed, copper grows less hot than iron because, copper being
the softer metal, its particles do not require such violent agitation
to separate them as do those of iron. 2 The greater motion associ-
ated with heat was also the cause of thermal expansion. Light
was thought to be c a certain Motion of the Parts of luminous Bodies
whereby they are capable of pushing every Way the subtil Matter
[second element] which fills the Pores of transparent Bodies, ' and
secondary illumination was attributed to the tendency of this
matter to recede from the luminous body in a straight line. Trans-
parent bodies had straight pores through which the matiere subtile
could pass, opaque bodies blocked or twisted pores. If this exertion
of pressure by the luminous body were confined or resisted, it
would grow hot. Refraction and reflection of this pressure (or

1 John Clarke (trans.) : Rohault's System of Natural Philosophy Illustrated with
Dr. Samuel Clarke's Notes Taken mostly out of Sir Isaac Newton's Philosophy (London,
1723), vol. I, pp. 115-17. Jacques Rohault (1620-72) was the greatest of all
expositors of Cartesian physics; his Traitt de Physique appeared first in 1671.
Clarke's Notes strongly oppose Newtonian corpuscularian ideas to those of
Descartes.

2 Ibid., p. 156.

4

2io THE SCIENTIFIC REVOLUTION

rather pulse) which is Light were explained by analogy with the
bouncing of elastic balls. 1 In dealing with magnetism Cartesians
were careful to emphasize that 'though we may imagine that
there are some Particular Sorts of Motion which may very well
be explained by Attraction; yet this is only because we carelessly
ascribe that to Attraction, which is really done by Impulse'; as
when it is said a horse draws a cart, whereas it really pushes it by
pressing on the collar. 2 Magnetic effects were actually caused by
streams of screw-like particles, entering each Pole of the earth and
passing from Pole to Pole over its surface, which passed through
nut-like pores in lode-stone, iron and steel, and thus were capable
of exerting pressures on these magnetic materials.

By theorizing in this way on the different motions of the three
species of matter the Cartesian physicists tried to account for all
the phenomena of physics as known in the second half of the
seventeenth century. They had some striking contemporary dis-
coveries on their side: for instance, the discovery that the rising
of water in pumps and analogous effects were not due to horror
vacui or to attraction, but simply to the mechanical pressure of the
atmosphere. They also explained gravitation mechanically as a
result of pressure, and extended their corpuscular ideas to chemical
reactions. The idea of particulate matter-in-motion was therefore
the very foundation of Cartesian science, the basis of a homo-
geneous system of explanation. The fact that (in Rohault's words)
' the few Suppositions which I have made . . . are nothing com-
pared with the great Number of Properties, which I am going to
deduce from them, and which are exactly confirmed by Experi-
ence' was a strong reason for believing 'that That which at first
looks like a Conjecture will be received for a very certain and
manifest Truth.' 3 As expounded by Descartes and his successors
this "mechanical philosophy" was illustrated by many qualitative
experiments; but these could hardly be said to prove the Cartesian
system, which always remained, in addition, entirely non-
mathematical.

Nevertheless, Cartesian science had a great influence upon the
Fellows of the Royal Society. Just as, in the past, Aristotle's teach-
ing was the inevitable starting-point for scientific thought, so they

1 Clarke, op. cit., vol. I, pp. 201 et seq.

2 Ibid., vol. II, p. 1 66.

8 Ibid. 9 vol. I, p. 203; vol. II, p. 169.

ORGANIZATION OF SCIENTIFIC INQUIRY 211

often found their point of departure in Descartes. For Boyle,
indeed, 'the Atomical and Cartesian hypotheses, though they
differed in some material points from one another, yet in opposi-
tion to the Peripatetic and other vulgar doctrines they might be
looked upon as one philosophy.' While older philosophers had
given but superficial accounts of natural phenomena, relying on
an incomprehensible theory of forms and qualities, the moderns
agreed in explaining 'the same phenomena by little bodies
variously figured and moved.' The differences between the
modern schools were rather metaphysical than physical, and did
not greatly affect the study of the world as it actually is. 1 Appar-
ently the English experimentalists who formed the Royal Society
already held eclectic opinions: 'they found some reason to sus-
pect,' wrote Hooke in his Preface to Micrographia (1665), 'that
those effects of Bodies which have been commonly attributed to
Qualities, and those confess'd to be occult, are perform'd by the
small machines of Nature.' Over this wide and in many ways
strategic area of scientific thinking the English and French socie-
ties spoke the same language and shared a common inheritance
of ideas. The differences between Cartesians and Gassendists were
found in both alike, and the appeal to a particulate theory of
matter was as common in England as in France.

Though the experimenters of Gresham College were far from
being pure empiricists, in giving high praise to Descartes' system
they did not forget their other allegiances to Bacon, Galileo and
Gilbert. Few were dogmatic or literal followers of Descartes.
Accepting the general form of the "mechanical philosophy," they
measured Cartesian science rigorously by the experimental test.
Hooke challenged its theory of light and colours, Boyle its theory
of elastic fluids, and Newton its cosmology. Yet even the last of
these suggested a space-filling aether, and questioned whether the
most subtle effects of nature were not obtained by purely mechani-
cal means. The very titles of Boyle's works indicate the tendency
of his thought: The Excellence and Grounds of the Mechanical Philo-
sophy] The Origin of Forms and Qualities, an introduction to the same;
The Mechanical Origin of Volatility and Fixedness] The Mechanical
Production of Electricity] The Mechanical Origin of Heat and Cold] with
many more in a similar vein. And during the greater part of his

1 Certain Physiological Essays (publ. 1661 but written some years earlier).
Works, ed. T. Birch (London, 1772), vol. I, p. 355.

212 THE SCIENTIFIC REVOLUTION

scientific career, from about 1655 at least, he devoted himself to
trying 'whether I could, by the help of the corpuscular philo-
sophy . . . associated with chymical experiments, explicate some
particular subjects more intelligibly, than they are wont to be
accounted for, either by the schools or [by] the chymists.' 1 In his
Excellence and Grounds of the Mechanical Philosophy Boyle defined his
position exactly:

God, indeed, gave motion to matter; ... he so guided the motions
of the various parts of it, as to contrive them into the world he de-
signed to compose; and established those rules of motion, and that
order amongst things corporeal, which we call the laws of nature.
Thus, the universe being once fram'd by God, and the laws of motion
settled, and all upheld by his perpetual concourse, and general provi-
dence; the [mechanical] philosophy teaches, that the phenomena of
the world, are physically produced by the mechanical properties of
the parts of matter, and that they operate upon one another accord-
ing to mechanical laws. 2

Here Boyle appeals for justification of his natural philosophy to
the divine plan of creation (thus withdrawing himself from the
atheistic connotations of Epicureanism, and from the evolutionary
suggestions of Descartes) ; seeing the world as a machine indeed,
but a machine whose complex processes are continually supervised
by a divine providence. Though his world-picture transcended
the evidence of experimental science, Boyle was convinced that
the details of the mechanism of nature could only be revealed
through experimental study. It might even be more useful not to
attempt at this stage to relate observed physical phenomena to
the 'primitive and catholick affections of matter, namely bulk,
shape, and motion,' but rather to intermediate physical proper-
ties such as hardness, temperature and so forth. Therefore he did
not hesitate to doubt the necessity of Descartes' rectitude. He
doubted whether the air in an exhausted vessel was really replaced
by a matiere subtile, of whose existence he was generally sceptical. 3
He attributed the elasticity of air to the springiness of its particles.
He was much more vague in his pronouncements on the basic

1 Some Specimens of an Attempt to make Chymical Experiments useful to illustrate
the Notions of the Corpuscular Philosophy. Works, 1772, vol. I, p. 356.

2 Peter Shaw: Works of Boyle abridged (London, 1725), vol. I, p. 187.

3 The matiere subtile (or aether) in an exhausted space was used by Cartesians
generally to explain the transmission of light, and by Huygens to account for
effects of surface tension in vacuo.

ORGANIZATION OF SCIENTIFIC INQUIRY 213

structure of matter than Descartes, indicating only that he thought
it composed of fundamental particles, and larger aggregates of
these, the real corpuscles. The particulate theory was related by
Descartes to the Aristotelean four-element doctrine, but not by
Boyle. He was sceptical also of the Cartesian interpretation of mag-
netism and electricity. He carried through a far more thorough-
going mechanistic attack on the doctrine of " forms" than the
Cartesians. Moreover, while the Cartesians sought to illustrate a
theory of nature by experiments, Boyle sought to interpret his
experimental researches in the light of the corpuscular philosophy.
The distinction is perhaps subtle, but it is real. For besides his
sense of the ultimate truth of a mechanistic view of nature, Boyle
was also imbued with Bacon's conception of the scientist's com-
piling histories of nature, and promoting the progress of material
civilization. In the last resort his devotion to the corpuscular
philosophy seems to have been grounded less on an opinion that
it was a key to the final understanding of nature, than on the con-
viction that it provided a broad framework of ideas within which
scientific research could most rapidly progress towards this final
understanding.

If Boyle presented the corpuscular philosophy more elaborately
than any other Englishman, the influence of Newton on non-
Cartesian particulate theories of matter was perhaps of even longer
duration. His successors did not hesitate to read the Queries ap-
pended to Newton's Opticks (1704) as though they were state-
ments of his considered opinions. Newton's views on the structure
of matter are indeed shadowy. The famous Hypotheses non jingo is
not to be taken too literally, but he certainly would not have ac-
cepted Rohault's easy dictum that a conjecture agreeing with the
properties of things may be taken as very probable. The questions
which Newton felt impelled to ask, and the answers to them at
which he hinted, were indeed only made public because Newton
knew that his scientific career was over. The experiments needed
to gain further insight into these problems he would never per-
form. Yet Newton had confidence enough in his opinions to
declare:

It seems probable to me, that God in the Beginning form'd matter in
solid, massy, hard, inpenetrable, movable Particles, of such Sizes and
Figures, and with such other Properties, and in such proportion to
Space, as most conduced to the End for which he form'd them. . . .

214 THE SCIENTIFIC REVOLUTION

These, then, were true atoms; endowed with 'a Vis inertia,
accompanied with such passive Laws of Motion as naturally result
from that Force/ and with 'certain active Principles, such as is
that of Gravity, and that which causes Fermentation, and the
Cohesion of Bodies.' Such principles were not occult qualities,
like those of the Aristoteleans, because they were made precisely
known by experiment; only the causes of them were hidden. 1 Of
the particles Newton asked, have they not also 'certain Powers,
Virtues, or Forces, by which they act at a distance, not only upon
the Rays of Light for reflecting, refracting, and inflecting them,
but also upon one another for producing a great Part of the
Phaenomena of Nature?'

He confessed that these " Virtues" might be veritably performed
by impulse, but their cause was only to be unfolded through study
of the "Laws and Properties of the Attraction." 2 To attraction
between particles he attributed cohesion and the strength of
macroscopic bodies, the force being very strong in immediate
contact, but reaching ' not far from the Particles with any sensible
Effect.' Thus the particles were compounded (as Boyle had sug-
gested) into corpuscles of weaker attractive force, and so success-
ively into the largest aggregates 'on which the Operations in
Chymistry, and the Colours of Natural Bodies depend, and which
by cohering compose Bodies of a sensible Magnitude.' 3 Newton
was the first to point out that in any apparently solid body the
volume of matter is small compared with the volume of space
between the particles, and to think of each particle as surrounded
by a field offeree. Again, he asked:

Is not . . . Heat . . . conveyed through the vacuum by the vibra-
tions of a much subtiler Medium than Air, which after the Air was
drawn out remained in the Vacuum? And is not this Medium the
same with that Medium by which Light is refracted and reflected. . . .
And is not this Medium exceedingly more rare and subtile than the
Air, and exceedingly more elastick and active? And doth it not
readily pervade all Bodies? And is it not (by its elastic force) expanded
through all the Heavens?

But this Newtonian aether was very different from the Cartesian.
As the cause of gravity Newton imagined it as being more rare

1 Sir Isaac Newton: Opticks (with Introduction by Sir E. T\ Whittakcr,
London, 1931), pp. 400-1.

2 Ibid., pp. 375-6. 3 Ibid., pp. 389, 394.

ORGANIZATION OF SCIENTIFIC INQUIRY 215

in solid bodies than in free space; where it must be of the order
one million times less dense than air, but more elastic in the same
proportion. 1 With regard to the theory of light, it seems futile to
try to harmonize the different notions referred to in the Queries.
Newton's views involved a compromise between the "undulatory "
and "corpuscular" theories, and in different passages he seems,
as it were, to be operating at different depths of thought. But
whether he spoke of light as a vibration in the aether, or as a
stream of particles issuing from the luminous body, he was at
once mechanistic and anti-Cartesian. Similarly he gave a purely
mechanical account of the physiological nature of vision.

The Queries are highly suggestive. The reader half-glimpses
entrancing vistas of the territory to be conquered by the " me-
chanical philosophy." In the early eighteenth century a number
of rather unfruitful attempts to take Newton's ideas further were
made, especially in relation to chemistry with the notion of
corpuscular attraction as a precursor of affinity. He has been
regarded as one of the founders of nineteenth-century atomic
theory, and perhaps the very fact that the mighty Newton had
speculated in this way made atomism more respectable at a time
when the Cartesian system of science had passed into oblivion,
and many matter-of-fact chemists distrusted John Dalton as a
weaver of idle fancies. Certainly the less specialized corpuscularian
and mechanistic concepts had the best chance of survival;
Cartesian mechanism, the dinosaur of seventeenth-century
scientific thought, could not adapt itself to a new intellectual
environment. It was committed dogmatically in too many points
of detail where it proved to be false.

Only with the passage of time, and usually in relation to points
of precise detail, did the development of scientific activity in
Britain after the foundation of the Royal Society begin to follow
this definitely less specialized course, yielding a mechanistic
philosophy that was ultimately anti-Cartesian. More than two
decades passed, after the death of Descartes in 1651, before his
works acquired their greatest fame and authority, and before the
character of his system became rigid. Meanwhile, the prestige of
Gassendi was falling in France, and that of Descartes in England
especially through the success of new ideas concerning light
and gravitation. The Academic des Sciences became, before the

1 Ibid., pp. 349-52.

2 i6 THE SCIENTIFIC REVOLUTION

end of the century, more deeply committed to Cartesian thought;
the Royal Society more ready to criticize it. It is important to
realize that the somewhat singular character of the Royal Society
during its first half-century was due, not solely to the Fellows'
greater assiduity or success in experimentation emphasis on the
purity of their empiricism is certainly to be suspected but to
experimentation combined with a definite eclecticism of outlook,
within the broad framework of a mechanistic, corpuscularian
science which was becoming almost a commonplace. The intel-
lectual tension between the English scientific groups, on the one
hand, and the French and German on the other, certainly in-
creased between about 1665 and 1720, the substantial difference
between Cartesians and non-Cartesians being exacerbated by the
adventitious dispute between Leibniz and Newton over the inven-
tion of the calculus, but this should not be allowed to conceal the
fundamental similarity of their attitudes, on which Boyle had
insisted, and of their approach to scientific research. Although the
national organization of science facilitated a deplorable kind of
national partisanship most vicious in the early years of the
eighteenth century, beneath this there existed a fundamental
community of thought and activity. Broadly, the tendencies
of science were everywhere in the same direction, and in the
later eighteenth century, in a different situation, the friendly co-
operation between scientific societies was once more of the
greatest importance.

CHAPTER VIII

TECHNICAL FACTORS IN THE
SCIENTIFIC REVOLUTION

t 1 ^HE renaissance of science in the sixteenth century, and the
I strategic ideas of the first phase of the scientific revolution,
JL owed little to improvements in the actual technique of
investigation. Before the beginning of the seventeenth century
there is little evidence, except perhaps in anatomy and astronomy,
of any endeavour to control more narrowly the accuracy of
scientific statements by the use of new procedures, still less to
extend their range with the aid of techniques unknown to the
existing tradition of science. Even the refinement of observation,
begun in anatomy by Vesalius and his contemporaries and in
astronomy by Tycho Brahe, hardly involved more than the natural
extension and scrupulous application of familiar methods. Since
the apparatus and instruments available were crude and limited
the means were not at hand for gaining knowledge of new classes
of phenomena, or eliciting facts more recondite than those already
studied. Though greater reliance was placed on observation and
experiment, the change in the content of science could not be
dramatic and other sources of information were, at least till the
latter part of the sixteenth century, largely traditional. Aristotle,
Pliny, Dioscorides, Theophrastus and Galen were still very highly
respected. Gradually, however, the tendency to supplement this
book-learning, checked by personal examination where possible,
by the experience of various groups of practical men gained
ground. The wealth of fact was augmented by admitting the
observations of craftsmen, navigators, travellers, physicians, sur-
geons and apothecaries as worthy of serious consideration, and thus
the status of purely empirical truths, hardly inferior to that of the
systematic truths of physics or medicine, was in time enhanced.
In this respect, as in others,tfthe work of Galileo gives a useful
indication of a turning point, displaying in various ways the opera-
tion of the new technical, as distinct from conceptual, factors
in the development of science. His practical, almost materialistic

217

2i8 THE SCIENTIFIC REVOLUTION

intellect, stripping from natural philosophy the vestiges of its
metaphysical connotations, led him to admire the technological
achievements of his time and to appreciate the scientific prob-
lems suggested by them. By revealing the value of mathematics
as a logical instrument in scientific reasoning, he transformed,
if he did not actually create, an important method of inquiry.
His exploration of the potentialities of the telescope and other
instruments shows his concern for the enlargement of the scope of
observation and experiment through newly invented techniques.
It is typical of the evolution of the apparatus of science during the
seventeenth century that Galileo's results were more notable for
their qualitative originality than for quantitative accuracy, since
the necessity for precision in measurement was less apparent than
the strange novelties which the new techniques unfolded. Though
the perspective in which science regards nature changed markedly
in the sixteenth century, it was only in the seventeenth that a sig-
nificant qualitative change occurred in the image itself, to which
the technical resources used by Galileo contributed profoundly.

It has already been pointed out that the ideal of social progress
was also a commonplace among seventeenth-century scientists,
and that with varying degrees of assurance the attainment of this
ideal was linked with the application of scientific knowledge to
technology. Conversely, it is clear that scientific research is itself
dependent upon the level of technical skill, especially when the
endowment or organization of science compel the experimenter
to rely upon the skills acquired by the craftsman in the normal
course of his trade, as was the case before the nineteenth century.
Perhaps, in the early stages of a science, it is even more important
that the investigator should be amply provided with both prob-
lems and the materials for solving them by the technological
experience to which he has access. This is partly a question of
attitudes the ability to receive the stimulus from a merely
practical quarter partly of the richness of the techniques. Galileo
makes Sagredo remark, on the first page of the Discourses:

I myself, being curious by nature, frequently visit [the Arsenal at
Venice] for the mere pleasure of observing the work of those who, on
account of their superiority over other artisans, we call " first rank
men." Conference with them has often helped me in the investigation
of certain effects including not only those which are striking, but
also those which are recondite and almost incredible. At times also

TECHNICAL FACTORS 219

I have been put to confusion and driven to despair of ever explaining
something for which I could not account, but which my senses told
me to be true.

It can hardly be doubted that the dialogue of the First Day in this
work was influenced by such practical observation, and it was
from a workman that Galileo learnt of the break-down of the
horror vacui theory when the attempt was made to lift water through
more than thirty feet by means of a suction pump. Bacon also
wrote of the knowledge concealed in skilled craftsmanship. In the
next generation Boyle thought that only an unworthy student of
nature would scorn to learn from artisans, from whom knowledge
could best be obtained; for

many phenomena in trades are, also, some of the more noble and
useful parts of natural history; for they show us nature in motion,
and that too when turn'd out of her course by human power; which
is the most instructive state wherein we can behold her. And, as the
observations hereof tend, directly, to practice, so may they also afford
much light to several theories. 1

Such opinions did not spring from theoretical reasoning alone.
They express the new philosophy's concern for realia, but they also
recognize a genuine historical fact, that many of the ordinary
operations of household and workshop were quite beyond the
reach of scientific explanation. To remedy this, Galileo began the
theory of structures and Boyle the study of fermentation in food-
stuffs. Many of the problems suggested by the " naturalist's insight
into trades" could not, of course, be very profitably handled in
the seventeenth century and some of the most intractable like
fermentation were in any case very old. On the other hand, the
inquiry into geomagnetism begun in the late sixteenth century is
an example of a branch of science originating in the recent
observations of practical men and followed up with profit to both
theory and practice. Time-measurement also was both a scientific
and a commercial problem, especially in relation to navigation.
More obviously, skill in glass- and metal-working, especially
grinding, turning and screw-cutting, could be readily applied to
scientific purposes. Improvements in such arts were sought
by scientists and craftsmen together, as when Robert Hooke
collaborated with the famous clock-maker, Thomas Tompion.

1 Considerations touching the Usefulness of Natural Philosophy; Shaw's Abridge-
ment, vol. I, pp. 1 29-30.

220 THE SCIENTIFIC REVOLUTION

In three related sciences, chemistry, mineralogy and metallurgy
the pre-eminence of art over science was very marked at the
opening of the sixteenth century. In natural philosophy there was
a rudimentary knowledge of the classification of gems, earths and
ores together with a wholly useless theory of the generation and
transformation of substances. The pseudo-science, alchemy, had
its own theory of the nature of metals and their ores, and contained
some sound information on chemical processes and the preparation
of simple inorganic compounds. But during the previous three
centuries its originally useful content had become garbled and
obscured through the growth of esoteric mysticism and the
propagation of absurdities in its name. By contrast, great progress
in chemical industry, at a time when this represented almost the
only rational body of chemical knowledge, was scarcely reflected
at all in scientific writings before the mid-sixteenth century. There
were changes, permitting the use of new materials, economy of
manufacture, or the improvement of the product, in a long list
of trades, all of which depended on chemical operations, such as
the extraction of metals and the refining of precious metals, glass-
and pottery-making, the manufacture of soda and soap, the re-
fining of salt and saltpetre and the manufacture of gunpowder,
the preparation of mineral acids, and distillation. Other chemical
arts, like dyeing and tanning, were probably less improved; some
later innovations, like sugar refining, immediately aroused scien-
tific interest. The knowledge of the craftsmen concerned was, of
course, wholly empirical; they were uninterested in theory, and
given to superstition and prejudice. Part of their skill may have
derived from the Greek scientific tradition through Islamic
sources the art of distillation was clearly derived in this way,
but it was perfected by artisans, not by philosophers or alchemists.
Much of their skill was the tardy fruit of long experience. Taken
altogether, craft knowledge in chemistry and related sciences im-
plied a far greater acquaintance with materials and command over
operations than were available to the philosopher or the adept.

By the end of the sixteenth century something like a rational
chemistry was coming into existence, though sixty years later
Boyle could still write:

There are many learned men, who being acquainted with chymistry
but by report, have from the illiterateness, the arrogance and the
impostures of too many of those, that pretend skill in it, taken

TECHNICAL FACTORS 221

occasion to entertain so ill an opinion as well of the art as of those
that profess it, that they are apt to repine when they see any person,
capable of succeeding in the study of solid philosophy, addict himself
to an art they judge so much below a philosopher . . . when they
see a man, acquainted with other learning, countenance by his ex-
ample sooty empirics and a study which they scarce think fit for any
but such as are unfit for the rational and useful parts of physiology
[science]. 1

In the course of that century a number of books had appeared
which, although primarily concerned with technological processes,
had a significant influence on the chemical group of sciences.
Avoiding theory, they threw off the air of mystery. They described
in a matter-of-fact way how mineral substances were found in
nature, extracted, and prepared, and how further commercial
products were obtained from them by the operations of art. The
processes described required mineralogical and chemical know-
ledge, manipulative skill, and often a complex economic organi-
zation. Some of the German mines already absorbed heavy
capital expenditure, and some processes, like the manufacture of
nitric acid needed for the separation of gold from silver, were
conducted on a considerable scale.

The first of these treatises was a small German work known as
the Bergbiichlein, printed at Augsburg in I5O5. 2 Before this, in the
fifteenth century, there had been in circulation manuscripts
written in German dealing with pyrotechnics, the preparation of
saltpetre and the manufacture of gunpowder, but these were never
printed and seem to have been unimportant in science. Possibly
there were similar "handbooks," earlier than the invention of
printing, dealing with mining and metallurgy. The Bergbuchlein
describes briefly the location and working of veins of ore, and is
followed in the Probierbiichlein (first printed about 1510) by an
account of the extraction, refining and testing of gold and silver.
Their usefulness is proved by the many editions published. The
same subjects were treated by Biringuccio in 1540, by Agricola in
1556, and by other German authors later in the century. The best
informed of these was Lazarus Ercker, superintendent of the mines
in the Holy Roman Empire, whose Treatise on Ores and Assaying

1 Works (cd. Birch, 1772), vol. I, p. 354.

2 A. Sisco and C. S. Smith: Bergwerk- und Probierbiichlein (New York, 1949).
Cf. also Anncliese Sisco in Isis, vol. 43, 1952.

222 THE SCIENTIFIC REVOLUTION

(Prague, 1574), was translated into English as late as
Ercker's thoroughly practical book is chiefly concerned with the
precious metals, but has chapters on working with copper and
lead, on quicksilver, and on saltpetre. The Pirotecknia of Vanoccio
Biringuccio and the De re Metallica of Agricola both cover a wider
range of topics. 2 Biringuccio, for instance the only Italian author
of an important work of this type describes the blast furnace,
bronze- and iron-founding, and glass manufacture, but the tech-
nical information is somewhat unspecific. Agricola's book, mas-
sively detailed in its account of geological formations, mining
machinery and chemical processes is justly regarded as the master-
piece of early technological writing. Agricola [germanice Georg
Bauer] was a scholar, corresponding with Erasmus and Melanch-
thon, writing good Latin, enriching his observations with appro-
priate quotations from classical authors. He wrote also On the
Nature of Fossils and on other scientific subjects. His knowledge of
mining and industrial chemistry was gained through long resi-
dence, as a physician, in the mining towns of Joachimsthal in
Bohemia and Chemnitz in Saxony. About the first third of De re
Metallica is given to a discussion of mining methods. Then Agricola
passes on to describe the assaying of ores to determine their
quality, and the operations of preparing and smelting them.
Iron, copper, tin, lead, bismuth, antimony and quicksilver are
considered as well as the precious metals. The testing of the base
metals for gold and silver content is the next topic, followed by
an account of the separation of precious and base metals, and
of gold from silver. Here the various processes of cupellation,
cementation with saltpetre, liquation with the use of lead, amal-
gamation with mercury, refining with stibnite, and extraction
with what Agricola calls aqua valens are described at length. This
last was, apparently, a mixture of mineral acids prepared by
distillation of different mixtures of vitriols, salt, saltpetre, alum
and urine. The last section of the work treats of the preparation
of "solidified juices" salt, potash and soda, alum, saltpetre,
vitriols, sulphur, bitumen and glass. Here Agricola was on less
firm ground and was guilty of some confusion and error.

1 Modern translation by A. Sisco and C. S. Smith (Chicago, 1951).

a The former translated into English by M. Gnudi and C. S. Smith (New
York, 1943); the latter by H. G. and L. H. Hoover (London, 1912; New York,
1950).

TECHNICAL FACTORS 223

This series of technical books reflects a tradition in applied
science that had grown slowly in the later centuries of the middle
ages, that was still gradually increasing in skill, and was capable
of producing new techniques for handling the unprecedented
richness of the South American mines. The authors, like the
contemporary anatomists and herbalists, took full advantage of
the art of wood-cut illustration. They did their work so well that
it lasted into the early eighteenth century, when a new era of
technology was beginning; it was over Agricola's great folio that
Newton pored when he was investigating the chemistry of metals.
Chemical industry did not merely furnish the chemists of the late
sixteenth and seventeenth centuries with the materials in their
laboratories; it supplied them with a factual account of the
occurrence of minerals in the natural state and the methods of
their preparation. More than this, the technical treatises provided,
in contrast with the fanciful symbolic language of the alchemists,
a precise account of basic chemical operations and reactions.
Besides the works already mentioned, the philosophical chemist
and virtuoso could turn to the Distillation-book of Hieronymus
Brunschwig (1512) and its successors for instruction in this most
necessary, and most difficult, of chemical arts. The alchemists,
even when honest, wrote on the principle that if the reader had
not been admitted to the secrets he would fail to understand, and
if he had he would scarcely need further guidance. These writers,
however, set forth the best of their knowledge as plainly as
possible; and it was likely to be sound, for as Boyle remarked,
' tradesmen are commonly more diligent, in their particular way,
than any other experimenter would be whose livelihood does not
depend on it.' Only in its practical applications, stripped to its
bare essentials of preparing this from that, was chemistry on a
really solid foundation, independent of the misleading implica-
tions of false, and often fantastic, theories. But the chemical
operations of industry were not merely qualitatively reliable and
instructive. The application of quantitative methods to a chemical
reaction was the essence of assaying, for example in calculating
the quantity of gold in an alloy by carefully drying and weighing
a precipitate.

The assayer deserves as much credit as the observational astronomer
for providing numerical data and establishing the tradition of accu-
rate measurement without which modern science could not have

224 THE SCIENTIFIC REVOLUTION

arisen. Though more of a craftsman than a scientist and more con-
cerned with utility than with intellectual beauty, the assayer never-
theless collected a large part of the data on which chemical science
was founded. 1

When, in the eighteenth century, the balance was recognized as
an invaluable tool in research the chemist was only extending
a technique whose specialized usefulness in assaying was long
familiar. Even the law of the conservation of mass was no more
than a theoretical statement of a truth on which the operations
of this craft were founded.

Boyle once spoke of German as the "Hermetical language,"
because so many alchemists had used it. It is perhaps a more useful
observation that rational chemistry began with accounts of the
elaborate chemical industry in Germany, and was continued by
German experimenters, some of them inspired by Paracelsus,
himself a German-Swiss. Here there seems to be a clear case for
believing that the development of a technical art to the necessary
point in complexity and achievement provided much of the basis
of fact and method from which experimental sciences could
arise. Of course, the roots of modern chemistry, mineralogy and
metallurgy are also to be found in alchemy, in pharmacy, and in
philosophy. To the formation of chemical theories in the seven-
teenth and eighteenth centuries the description of practical opera-
tions contributed very little. Ideas were derived from different
sources; and there was even a muddled, wrong-headed tradition
of laboratory work in alchemy parallel to operations on the in-
dustrial scale. Yet in many ways the outlook of Black or Lavoisier
resembles that of a practical assayer more than it does the esoteric
perspective of Raymund Lull, Paracelsus or " Basil Valentine."
The influence of the artisan, conceived as closer to the realities
of nature than the abstracted philosopher, was an important
element in many of the nascent sciences, but nowhere more
than in chemistry, which most of all required an alliance of sane
thought and reasoned activity.

In the seel aspect- 64Se role of technical factors in the
scientific revolution, the technique of mathematical analysis offers
a good example of a factor internal to science itself influencing
the progress of certain branches, in this instance mechanics and

1 Smith: Lazarus Broker's Treatise on Ores and Assaying (Chicago, 1951), p. xv.

TECHNICAL FACTORS 225

astronomy! In a similar manner chemistry was another internal
factor affecting the progress of physiology, but this was scarcely
realized as yet.frhe ambition to formulate theoretical propositions
and experimental results in the form of mathematical functions,
nourished in some men by reflections of Platonic OP Pythagorean
philosophy, was commonly entertained in the seventeenth century,
even by those little learned in mathematics. As Boyle foresaw, 'A
competent knowledge in mathematics is so necessary to a philo-
sopher that I scruple not to assert, greater things are still to be
expected from physics, because those who pass for naturalists have
been generally ignorant in that study.' 1 The singularly happy
synthesis^ of mathematical reasoning and experiment in geo-
metrical optics and mechanics was regarded as a model to be
imitated in other parts of science, and it was recognized that a
mathematical demonstration has a rigour, and sometimes a
generality, not easily obtained in other arguments. The study of
mathematics, for the sake of its beneficent effect upon the intel-
lectual powers, as an introduction to natural and moral philo-
sophy, and as a necessary preliminary to certain professions, was
by degrees granted a more prominent place in education} It was
readily seen that the practical sciences navigation, cartography,
surveying, gunnery owed their origin to the combination of
mathematical method with more exact instrumental measure-
ment. They had thus gained a certainty impossible with rule-of-
thumb procedures. (About the middle of the seventeenth century
it was found that the vagaries of chance, in the throw of a die or
the odds in betting, were not immune to the laws of mathematics.
The calculus of probabilities was begun. Closely connected with
this were the first essays in statistical analysis, by John Graunt and
Sir William Petty in England, which proved that even the hazards
of human life were not beyond computation. From such crude
beginnings developed an impressive mathematical apparatus of
immense importance to theoretical physics in the nineteenth
century.

These analogies, of very different kinds, suggested that where
quantitative observation and experiment were possible, a mathe-
matical formulation ought to be adopted. Galileo had shown the
splendour of the prize that might be won. If the workings of nature

1 Usefulness of Natural Philosophy; Philosophical Works, abridged by Peter Shaw,
vol. I, p. 1 1 8.

15

226 THE SCIENTIFIC REVOLUTION

were regular and uniform, should not they ultimately reveal a
mathematical harmony Jas Kepler thought? In the study of acous-
tics, during the seventeenth century, it was indeed found that
harmonies pleasing to the ear were produced by the vibrations of
different strings when their lengths, thicknesses and tensions agreed
with simple mathematical ratios. More generally, Cardano in the
sixteenth century had reviewed the physical applications of the
rules of proportion, while Petty examined, in a paper in the Philo-
sophical Transactions , the special significance of the quadratic ratio

in nature ( that is, functions of the type a = kb 2 , a = ) . Again,

r ...

if (the mechanical philosophy was justified in its belief that the
physical properties of macroscopic bodies result from the shape,
size and motion of the particles composing them, ought not all
these properties of the particles to be susceptible of mathematical
discussion, which was already making great progress with the
study of motion? And, indeed, by making certain measurements
in connection with the phenomenon of optical interference, and
examining them mathematically, Newton was able to make
quantitative statements about the nature of light. Furthermore,
mathematical analyses enabled him to prove that some conse-
quences of the Cartesian theory of matter were quite incompatible
with observation.

The limitations to the extension of the mathematical method,
flourishing in dynamics, to the whole of physics and a fortiori to
still less "exact" parts of science were obviously of two kinds. The
first lay in the ability of physicists and others to design experi-
ments and produce results of a form suitable for mathematical
analysis; the experimental physicist had to discover in what ways
mathematics could help him before he could become a mathe-
matical physicist. This kind of limitation had vitiated all attempts
towards a mathematical theory of projectiles before the time of
Galileo. 1 The second limitation is in the nature of mathematics
itself, in its ability to perform the operations required.) For ex-
ample: Boyle's experiment on the compression of a volume of air
in one limb of a U-tube by a column of mercury poured into the

1 The parabolic trajectory of a projectile in a vacuum was first established
by Bona ventura Cavalieri in Lo Specchio Ustorio (1632), six years before Galileo's
much fuller treatise appeared. The problem was easily solved mathematically
with the aid of Galileo's theorem on acceleration.

TECHNICAL FACTORS 227

other (described in A Defence of the Doctrine touching the Spring and
Weight of the Air, 1661) gave quantitative results which could be
simply interpreted to yield "Boyle's Law" (pv = k). It was also
found that the height of the mercury column in a barometer falls
as the instrument is carried progressively higher above sea-level,
because the weight of the atmosphere above decreases. The cele-
brated experiment was carried out by Perier, on the suggestion of
Pascal, in I648. 1 From a combination of these facts, it was realized
that it should be possible to frame a mathematical theory which
would enable the vertical distance between two stations, to be
calculated from the difference in atmospheric pressure found from
simultaneous readings of two barometers. To make a rough ap-
proximation is sufficiently easy, but an accurate calculation
involved purely mathematical difficulties which were not fully
overcome in the seventeenth century.

Discussion of the first group of these factors limitinguhe applica-
tion of the mathematical method to science must, naturally,
belong to the history of the separate branches of science. It would
be necessary to discuss, in each case, the steps by which experi-
ments were designed and instruments invented to obtain quanti-
tative results of various types, and the methods followed in the
formulation of a variety of theoretical postulates, before materials
suitable for mathematical study were assembled. Till the nine-
teenth century no parts of science, other than mechanics and
astronomy, were so highly organized and coherent that the appli-
cation of mathematics was possible, otherwise than in elementary
computations. But with regard to mechanics and astronomy the
second limitation latent in the resources of mathematics itself
becomes significant; the great achievements which signalized the
triumph of the scientific revolution would have been impossible
in the absence of the enormous elaboration of pure mathematics
which took place, and was to some extent inspired by realization
of the fact that it was essential. Nearly all the great mathematicians
of, the sixteenth and seventeenth centuries, from Tartaglia and
Stevin to Cavalieri, Descartes, Newton and Leibniz, were at least
partly interested in the physical sciences. One of the unexpected

1 Pascal deduced that the atmospheric pressure would fall progressively
above sea-level from his own repetition of Torricelli's experiments with the
barometer. The deduction was confirmed by P6rier's ascent, with the instru-
ment, of the Puy-de-D6me, in Auvergne.

228 THE SCIENTIFIC REVOLUTION

discoveries of the time was that a number of regular mathematical
curves (some long familiar), such as the ellipse, the parabola and
the cycloid, or the algebraic functions which Descartes associated
with such curves, appeared in the investigations of the astronomer
and the physicist, so that their study proved to have a double
interest. The calculations performed by the physical scientist fre-
quently required the calculation of an area bounded by a curve
of some type, and so in turn stimulated investigation of the opera-
tion of integration in which perhaps the success of seventeenth-
century mathematicians was most striking. A number of their
advances in method were first denoted by the solution of some
problem in mechanics, which offered from about 1650 onwards
a most rewarding opportunity for the display of mathematical
inventiveness, formerly more commonly devoted to the improve-
ment of the mathematical procedures in astronomy. 1

The progress made in mathematics in the seventeenth century
can be very easily illustrated from the fact that, about 1600, it
had hardly as yet reached a form intelligible to modern eyes. The
writing of Arabic numerals was indeed nearly stabilized in the
modern style, but the Roman were still commonly employed,
especially in accounting. The use of the modern symbols for the
common operations of multiplication, division, addition and so
forth was standardized only in the second half of the seventeenth
century. Previously mathematical arguments were set out in a
diffuse rhetorical form. Algebraic notation was settled at about
the same time, the practice of employing letters to denote un-
known or indeterminate quantities having been introduced by the
French mathematician Viete shortly before 1600. Arithmetical
operations, particularly those involving long division or the hand-
ling of fractions, were still performed by cumbersome methods,
and "reckoning with the pen" (rather than with the abacus
or other aid) was still regarded as a somewhat advanced art. One
of the earliest calculating-devices, the so-called "Napier's bones,"
was designed to obviate the memorization of multiplication tables
and the labour of handling long rows of figures. Again, at a higher
level, tables of functions were very deficient. In trigonometry, the

1 It has been pointed out that almost all the progress made in the theory of
structures, for instance, before about 1 770, was made as a by-product of sheer
mathematical ingenuity. The same might be said of the applied science of
ballistics, which also had a negligible experimental foundation before 1 740.

TECHNICAL FACTORS 229

Greeks had known tables of chords alone; during the late middle
ages tables of sines and tangents became available, and during the
sixteenth century other trigonometrical functions were tabulated.
But the methods of computing and of using the tables were both
very tedious. From an attempt to facilitate calculations involving
these functions developed the invention of logarithms, perhaps the
most universally useful mathematical discovery of the seventeenth
century, as it was certainly the least expected. Napier's tables,
published in 1614 (Mirifici logarithmorum canonis descriptio), gave
logarithms of sines which are effectively powers of a base e~ l , the
reciprocal of the base of modern Napierian logarithms. 1 A table
of logarithms to the base 10 for the first thousand numbers was
published by Henry Briggs in 1617. Logarithms offered a com-
pelling instance of the utility of the decimal system of fractions,
of which Stevin had been a most forceful advocate some thirty
years earlier.

Sincefthe Greeks had excelled in geometry and trigonometry,
little more than the assimilation, with some slight extension, of
their methods in these branches of mathematics had been accom-
plished by 1600. Renaissance scholarship had devoted itself to the
recovery of the pure classical tradition in this as in other depart-
ments of learning, with the result that the texts, particularly those
describing the more advanced Greek studies of geometrical analy-
sis and the conic sections, were far more completely available by
the middle of the sixteenth century than before. Here, at least,
pure scholarship caused an immediate rise in the level of com-
petence. Even in the mid-seventeenth century the practice of
"restoring" a lost or fragmentary work by means of the methods
presumably used by the ancient author did not seem absurd, and
when Newton wrote the Principia the synthetic geometry of the
Greeks was still held to be a more reliable form of mathematical
demonstration than the recently developed analytical method.

Algebra, on the other hand, represents a native European de-
velopment from Hindu and Islamic sources made known to the
Latins by medieval translators. Considerable progress in the
sixteenth century, for example in the solution of equations of
higher powers than the quadratic, was unaffected by humanistic
influences; indeed, Greek geometric procedures for solving equa-
tions were supplanted by algebraic methods. Operations with
1 Hence log N = 2 30259 Iog 10 fl.

23 o THE SCIENTIFIC REVOLUTION

proportions and series, also known to the Greeks solely in the
geometric form, were similarly transformed into the more con-
venient algebraic symbolism. Islamic mathematicians (notably
Omar Khayyam, c. noo) had recognized a partial equivalence
between algebra and geometry, that is, that certain geometrical
problems could be represented by algebraic functions; and this
equivalence was more thoroughly exploited by the European
mathematicians of the sixteenth and early seventeenth centuries.
The next step, upon which analytical geometry is founded, was
the representation of any function graphically by the use of
rectangular co-ordinates. Graphs with such co-ordinates had been
used in the middle ages for a few special purposes (e.g. to repre-
sent the motions of the planets), and Oresme's calculus of varying
qualities was itself an elementary form of co-ordinate geometry.
Far more general and precise methods had been sketched in
private by the English mathematician Harriot, and by Pierre
Fermat, before the publication of the first treatise on the subject
by Descartes the Geometric annexed to his Discourse on Method
(1637). In this he showed that a constant relationship exists be-
tween the co-ordinates x and y of any point on a regular mathe-
matical curve which can be expressed as the algebraic function
y =f(x) 9 and that certain patterns of function corresponded
uniformly with certain classes of curves."N

This discovery was capable of immediate and fruitful applica-
tion to mechanics, in which many problems could be most easily
postulated in an initial geometric form, and then analysed with
the aid of the appropriate algebraic functions. Thus, to cite a
simple instance, in ballistics it was no longer necessary by the
end of the seventeenth century to work out a range by supply-
ing the necessary constants in the geometric construction used
by Galileo, since it could be obtained directly from the function

gx*

y = x tan e

^

appropriate to the parabolic trajectory, from which all the
theorems established by the elaborate geometry of Galileo and
Torricelli are readily deduced.Such functions can, of course, be
derived far more easily bymSe of the differential and integral
calculus than by the application of algebraic notation to conven-
tional geometrical reasoning, and the usefulness of the "calculus"
to the engineer and technician as well as to the mathematical

TECHNICAL FACTORS 231

scientist has therefore been clearly recognized since about the
middle of the eighteenth century. Both Kepler (1616) and
Cavalieri (1635) made use of infinitesimals in integration, the
former in connection with practical problems such as the calcula-
tion of the volumes of casks. Thus Cavalieri imagined that the
area of a surface was made up of an infinite number of lines, and
the volume of a solid of an infinite number of superposed surfaces,
calculating these quantities by the summation of an infinite
number of their geometric elements. Such methods had a certain
practical value, but the concepts were badly defined and of
doubtful validity. In co-ordinate geometry the problems for
which they were designed were first set out in the modern syste-
matic form. Perhaps even more important were the methods for
finding the maximum and minimum values of curves (or the
equivalent functions), and for drawing tangents to them, dis-
covered by Fermat (1638) and others about the middle of the
century, for they used operations identical in principle with what
was later known as differentiation.^ Barrow, for example, in his
method of tangents, obtained by geometrical means the derivative

( Jr ) f tne function (j> =/(#)) represented by the curve, and

equated this derivative to zero.

(Before 1670, therefore, the crude components of new mathe-
matical processes for dealing with quantities having a non-linear
variation were already in existence. The priority in time in
perfecting them undoubtedly belongs to Newton (whose Method
of Fluxions was written in 1671), but a more useful notation and a
somewhat clearer presentation of the matter were later developed
independently by Leibniz, whose first essay on the calculus was
published in 1684. The charge maintained by a group of English
mathematicians, with considerable covert assistance from Newton
himself, that Leibniz had plagiarized Newton's ideas from un-
printed manuscripts which had circulated privately provoked in
the early years of the next century a sordid and bitter dispute
between them and most continental mathematicians. Its only
significance is that the transmission to England of continental
discoveries in pure and applied mathematics was inhibited for
over a century, until soon after 1830 the Newtonian method of
fluxions was replaced by the virtually equivalent differential and
integral calculus which had advanced very far from Leibniz'

232 THE SCIENTIFIC REVOLUTION

original invention. 1 In principle, both Leibniz and Newton were
successful in the same task: they generalized the methods of
differentiation and integration which were already in existence,
recognizing that the latter operation was the inverse of the former;
they developed the new notation required for these new opera-
tions; and they greatly clarified mathematical thinking about
their nature?\Both succeeding in solving by the new methods
problems which had been nearly intractable to the old.

The first coherent treatise explaining the calculus was only
written at the close of the seventeenth century, and its general
extension to mechanics and physics was the work of more than
one succeeding generation. Consequently its full impact on science
was not immediate, though Newton referred in passing to his
method of fluxions in the Principia and the mathematical demon-
strations he offered would have been impossible without it.
Nevertheless, mathematical methods tending towards those of the
generalized calculus, or even anticipating it, were widely applied
in mechanics from about 1650 onwards, along with other new
developments in advanced algebra (for example, the study of
series) . Huygens offers perhaps the neatest instance of a physicist
making by means of co-ordinate geometry many complex calcula-
tions that would now be dealt with by means of the calculus,
through the development of his own methods which were virtually
equivalent to differentiation and integration} In this way Huygens
was able to investigate some of the properties of motion in a
resisting medium, which were also examined (rather more
thoroughly) by Newton in Book II of the Principia with the aid of
fluxions. It seems that, with the exception of celestial mechanics,
the development of no branch of science was seriously obstructed
by the absence of a suitable mathematical technique, even before
the formulation of the true calculus. Some known problems
remained unsolved, naturally, partly owing to imperfect concep-
tualization, but partly also owing to the fact that their solution

1 The truth seems to be that Leibniz was in close contact with men who
understood something of Newton's new ideas; that he saw some of Newton's
manuscripts; but that he could have learned little in this way that he could not
have gathered from other sources, and that his ideas were already at the
significant time shaping towards the form in which they were later formulated.
Leibniz has long been cleared of the charge of plagiarism; any historical
obscurities that remain are of little significance. (For bibliography cf. D. E.
Smith: History of Mathematics, vol. II, p. 691.)

TECHNICAL FACTORS 233

required difficult approximations involving constants which had
not yet been determined experimentally. On the contrary, it
seems rather that the nature of the possible mathematical processes
exercised a powerful guiding influence at least over the science of
mechanics. Even had ideas been more precise, and the experi-
mental material more complete, it would have been impossible
for the seventeenth-century physicist to work out a mathematical
corpuscular theory of matter because he lacked the necessary
technique of statistical analysis; but mechanics acquired an
increasingly theoretical character because its problems could be
stated mathematically, and solved by known procedures. The
propositions of the Principia are not less certain, although they
may not be the result of mathematical analysis applied to a mass
of experimental data; but it must be recognized that Newton's
method was to deduce, by mathematics, the consequences of
selected axioms and then to show by reference to observation or
experiment that these consequences are actually confirmed in
nature. Already in Galileo's writings it is apparent that in science
the mathematical and experimental approaches are far from
identical, though they may be closely correlated. He himself
attached greater importance to his mathematical theories than to
his experimentation (which is never precisely described, and often
appears casual). The early researches of the scientific societies laid
a greater emphasis on exactitude and consistency in experiment;
but mechanics was again sublimated into the regions of higher
mathematics in the last years of the century !)The consequence of
this may be illustrated by Huygens' ingenious proof that a pendu-
lum is perfectly isochronous when describing a cycloidal arc a
discovery, made with the object of perfecting the mechanical
clock, which proved completely irrelevant to the experimental
search for a scientifically reliable time-keeper; or by the history
of the industrial revolution, which was scarcely at all promoted by
the elaboration of theoretical mechanics during the eighteenth
century. There was, in fact, a strong tendency for the first truly
mathematical branch of science to lose touch with its roots in
experiment by becoming no more than a specialized department
of mathematics.

rit may perhaps seem surprising that seventeenth-century
mathematics progressed so opportunely as to satisfy, very largely,
all the demands that science made upon it. Only the activity of

234 THE SCIENTIFIC REVOLUTION

a number of highly original mathematicians made this possible,
and obviously their activity was not wholly fortuitous (it is re-
markable, for instance, that there was so little interest in the theory
of numbers) . It was inspired, to some extent, by knowledge of the
usefulness in science of advances in certain directions. But it is
generally true, of other periods as of this, that the mathematics
required for any particular step in science has been available.
Greek science was never near to exhausting the subtlety of the
Greek mathematician. In recent times the mathematics of the
theory of relativity was in being well before Einstein. Perhaps this
empirical fact, more than anything else, justifies the qualification
of mathematics as a scientific technique. When a class of facts, or
concepts, is first subjected to its use, the mathematics involved
will tend to be relatively simple, if only for the reason that the
innovator will probably be a scientist, more familiar with the
science than with the most recent advances in mathematics itself.
Galileo was not a great mathematician. But as the mathematical
theory develops, its continuance will increasingly depend upon
the activity of men who have been trained as mathematicians to
digest and analyse the results of experiment, even to suggest and
perhaps carry out the experiments and measurements necessary
for the prosecution of the theory. Yet it will rarely happen that
the mathematician who applies his skill in this way penetrates to
the very frontiers of pure mathematics. While the application is
perfected, mathematics itself is not standing still. And the appli-
cation is made because the mathematical theorist perceives that
the particular technique is appropriate, or adaptable, to the
problem. The conjunction of the highest mathematical with the
highest scientific ability, as in Archimedes or Newton, is extremely
rare; the fabrication of scientific theory by the use of well-known
procedures has, on the other hand, been a frequent occurrence

The invention of numerous scientific instruments during the
seventeenth century, and their fertile use in many capacities, has
long been associated with the revolution in scientific thought and
method. The idea of science as a product of the laboratory (in
the modern sense of the word) is indeed one of the creations of
the scientific revolution. In no previous period had the study of
natural philosophy or medicine been particularly linked -with the
use of specialized techniques or tools of inquiry, and though the

TECHNICAL FACTORS 235

surgeon or the astronomer had been equipped with a limited
range of instruments, little attention was paid to their fitness for
use or to the possibility of extending and perfecting their uses.
More variants of the astrolabe, the most characteristic of all
medieval scientific instruments, were designed during the last
half-century of its use in Europe (c. 1575-1625) than in all its
preceding history. The Greeks had known the magnifying power
of a spherical vessel filled with water, but the lens was an inven-
tion of the eleventh century, the spectacle glass of the thirteenth,
and the optical instrument of the seventeenth. Navigational
instruments also were extremely crude before the later sixteenth
century. It was not that ingenuity and craftsmanship were wholly
lacking (for many examples of fine metal-work, for artistic and
military purposes, prove the contrary); rather the will to refine
and extend instrumental techniques was absent. On the other
hand, it has justly been pointed out that the early strategic stages
of the scientific revolution were accomplished without the aid of
the new instruments. They were unknown to Copernicus, to
Vesalius, to Harvey, Bacon and Gilbert. They leave no trace in
the most important of Galileo's writings, in which he reveals
himself driven to measure small intervals of time by a device
considerably less accurate than the ancient clepsydra. It is clear
that, great as was the influence of the instrumental ingenuity of
the seventeenth century upon the course of modern science, such
ingenuity was not at all responsible for the original deflection of
science into this new course.

Thus it would seem that the first factor limiting the introduction
into scientific practice of higher standards of observation and
measurement, or of more complex manipulations, lay in the
nature of science itself. Only when the concept of scientific re-
search had changed, as it had by the end of the first quarter of
the seventeenth century, was it possible to pay attention to the
attainment of these higher standards. A number of the new instru-
ments of the seventeenth century were not the product of scientific
invention, but were adopted for scientific purposes because the
new attitude enabled their usefulness to be perceived. The balance
was borrowed from chemical craftsmanship. The telescope was
another craft invention, initially applied to military uses. The
microscope was an amusing toy before it became a serious instru-
ment of research. The air pump in the laboratory was an improved

236 THE SCIENTIFIC REVOLUTION

form of the common well pump Otto von Guericke, its original
inventor, had at the beginning exhausted vessels by pumping out
water with which they had been filled. And inevitably the tech-
niques used in the construction of the new scientific instruments
were those already in existence; they were not summoned out of
nothing by the unprecedented scientific demand. Some instru-
ments were only practicable because methods of lathe-turning
and screw-cutting had been gradually perfected during two or
three centuries, partly owing to the more ready availability of
steel tools, others, because it was possible to produce larger,
stronger and smoother sheets or strips of metal. The techniques
of glass grinding and blowing which provided lenses and tubes
might have been turned to scientific use long before they were.
The established skill of the astrolabe-maker could be devoted to
the fabrication of other instruments requiring divided circles and
engraved lines, that of the watch-maker to various computers and
models involving exact wheel-work, and so on. Common crafts-
manship held a considerable reservoir of ingenuity, when scientific
imagination arrived to draw upon it.

On the other hand, once interest in the kind of result that could
be obtained from the employment of specialized instruments had
been created, particularly as this employment began to extend
under a more disciplined direction towards a greater qualitative
depth of information and a greater quantitative accuracy of
measurement, the limitations of normal craftsmanship were soon
reached. Then it was necessary to begin a more conscious exami-
nation of the instruments themselves. Descartes was virtually the
founder of the scientific study of the apparatus of science, in his
investigation of the causes of the distortions present in the images
of crude microscopes. (At the same time, purely empirical measures
were also being adopted to remedy their defects.) Descartes con-
cluded that lenses should be ground to a non-spherical curvature,
which would introduce greater complexity into their manufacture.
Some scientists (including the astronomer Hevelius, and the
microscopist Leeuwenhoek) became masters in the art of grinding
the lenses they required for their work; others, like Newton,
experimented with an alternative form of optical instrument.
Towards the end of the century a scientist wishing to have a
really good telescope or microscope could no longer simply make
use of craftsmanship; he had to direct the work in accordance

TECHNICAL FACTORS 237

with a pre-determined specification. Astronomy had already at
the end of the sixteenth century reached the point where further
advances in precision involved great effort. Devices like the
vernier scale and the tangent screw were major steps, and the
attachment of telescopes to instruments for measuring angles
reduced sighting errors. But the advantages gained by increased
complexity in mechanical construction were all dependent on
progressive refinement in workmanship, and the forethought and
supervision of the scientist. The astronomer, in fact, had to
consider his observatory as an exercise in design; he had to build
walls, duly orientated, that would not settle; to design quadrants
that were rigid, yet light, and true; to ascertain the probable
errors of divided scales; to collimate his telescopes and rate his
clocks. He had become aware that the limitations to his work
were imposed by factors that were, in the main, technical and
mechanical. As such, they deserved, and received, increasingly
meticulous attention.

From the historical point of view, instruments may be divided
into two classes: those which render qualitative information only,
and those which permit of the making of measurements. Naturally,
these uses of an instrument are not necessarily exclusive, in fact a
little consideration makes it obvious that in their evolution most
early scientific instruments tended to move into the second class.
Thus, devices like the micrometer could be added to telescopes
and microscopes so that very small or very distant objects could
be measured; or alternatively these optical systems could be added
to other measuring instruments to improve their performance.
But the first use was purely qualitative. Similarly, in the eighteenth
century, the electrometer designed in the first place for the detec-
tion of charges, was later applied to their comparison and measure-
ment. The balance was first used in chemistry to establish a simple
loss or gain in weight; its employment to determine accurately
the masses involved in a chemical reaction came much later.
It is therefore a natural and plausible proposition that the quanti-
tative potentialities of a new instrument or piece of apparatus are
generally appreciated less readily than the qualitative, and this
was particularly the case in the seventeenth and eighteenth
centuries. The invention of instruments, therefore, did not have
that immediate effect of inducing greater rigour, and greater
interest in refined measurement, which might be anticipated a

238 THE SCIENTIFIC REVOLUTION

priori. The barometer, for example, was invented by Torricelli
in 1643. ^ was use d originally to demonstrate the existence of
atmospheric pressure, and secondly as a means of exhausting a
small chamber formed at the top of the tube in which experiments
could be made. Only about 1660 was the correlation between
barometric pressure and climatic conditions discovered, and only
after this were attempts made to improve the readability of the
instrument and collect a " history of the weather." Later still,
Boyle employed the barometer as a gauge to measure the quality
of the vacuum formed by his air-pumps, and the amount of "air"
evolved from fermentations. The thermometer has an even longer,
and more surprising, history as a merely qualitative instrument.
The thermoscope, an instrument in which the expansion of air in
a bulb moved a column of water in a narrow tube upwards when
heat was applied, was invented by Galileo about 1600. Liquid
thermometers were introduced about the middle of the century,
and were extensively used by the Accademia del Cimento, but
none of these was calibrated. The first suggestions for systematic
calibration with the use of two fixed points were made about 1665;
Fahrenheit's scale was devised about fifty years later, and the
modern centigrade scale only in 1743. Thus the first century of
thermometry yielded no quantitative measurements which can
now be interpreted with any degree of confidence. 1

While seventeenth-century astronomers, continuing a long
tradition, effected a refinement of angular measure which bore
fruit in Flamsteed's Historia Coelestis Britannica (1725), in physics
and biology qualitative results were far more significant. Even the
allied science of terrestrial angular measure (in surveying and
geodesy) remained rather crude until vernier scales and telescopic
sights were introduced at the close of the century. Consequently
it can scarcely be maintained that technical limitations to accuracy
of measurement were significant in any other branch of science
than astronomy before the early part of the eighteenth century.
Certainly it has been argued that chemistry would have pro-
gressed faster, and the science of heat have been more systematic,
if greater attention had been paid to the quantitative aspects of

1 The tubes of the early thermometers were of course divided, so that
comparative readings could be taken, but without reference to any standard
scale. Thus, extensive observations were rendered useless by the fact that they
depended on the arbitrary divisions of a unique instrument.

TECHNICAL FACTORS 239

experiment; but the reasons for the neglect of these aspects are to
be sought rather in the nature of scientific activity in the seven-
teenth century, than in instrumental deficiencies. The importance
of accurate measurements was not adequately understood, and
therefore they were rarely made; so that it was the texture of
science that hindered the effective exploitation of devices already
in being, rather than vice versa.

On the other hand, with regard to the two qualitative instru-
ments which most strikingly opened up great new fields of activity,
the telescope and microscope, it is plain that technical limitations
rapidly became serious, and that the nature of these limitations
was well understood. Both instruments began in very crude form.
Systems of convex lenses replaced the concave-convex combina-
tion (the so-called Galilean arrangement) only gradually from
about 1640, when rules for working out the appropriate focal
lengths and apertures were better understood. The first true com-
pound microscopes date from about this period, and the new
(Keplerian) telescope brought more detail of the solar system into
visibility. Additional satellites were discovered; the mysterious
appearance of Saturn was accounted for; transits and occultations
could be observed with higher accuracy. But the great desideratum
of seventeenth-century astronomy an observational proof of the
earth's rotation was not accomplished. To increase magnifica-
tion without a corresponding vitiating increase of the aberrations
the astronomer was compelled to use very long focal lengths and
small apertures. The light-gathering power of such instruments
was poor, and a practical limit to length (about 100 feet) was soon
reached. Non-spherical curvatures for lenses were theoretically
desirable, but technically impracticable. Newton's optical theory
explained the nature of chromatic aberration without suggesting
an appropriate remedy, for he found that the separate colours
into which white light can be resolved could not be brought
to a single focus by a simple lens. The reflecting telescope, free
from chromatic aberration, was suggested by James Gregory
and first constructed by Newton, but it was hardly of serious
value to astronomers before the later years of the eighteenth
century.

Similar problems were encountered in the microscope. Simple
glasses, with a magnification of about ten diameters, were used
early in the seventeenth century; by Harvey, who observed the

240 THE SCIENTIFIC REVOLUTION

pulsation of the heart in insects, and by Francesco Stelluti who
published in 1625 a microscopic study of bees. The small tubular
" flea-glass," with the lens mounted at one end, and the object set
against a glass plate at the other, became popular among the
virtuosi. Towards the middle of the century the compound micro-
scope attracted renewed interest, being now constructed with a
bi-convex objective and eye-lens, with a plano-convex field lens
placed between to concentrate the rays. In the improved design
of Hooke (described in Micrographia y 1 665) the body, containing
extensible draw-tubes, was mounted so that it could be tilted to a
convenient angle; a long nose-piece engaged in a large nut, so that
the body could be brought to focus on the object by screwing it in
or out. The lead-screw and slide method of adjustment was in-
vented later by Hevelius. To illuminate opaque objects Hooke
used an oil-lamp and bull's-eye lenses; before the reflecting-
mirror was fitted (about 1720), transparent objects were examined
by placing a lamp or candle on the floor beneath the instrument,
which was often pierced through the base. The compound micro-
scope was complicated and expensive, but it was easy to handle,
and in mechanical design became steadily more efficient. Optically
it was less satisfactory. Magnifications exceeding 100 diameters
could be obtained, but the uncorrected lenses, made of poor glass,
gave low resolution. As a result, the point was soon reached where,
though the object could be made to appear larger, no finer detail
in it could be seen. From 1665 until about 1830, when satisfactory
corrected lenses became available, the compound microscope
made comparatively slight advance in optical properties. The
limitation imposed, on biological research in particular, is obvious.

Nevertheless, the compound microscope was eminently a scien-
tific instrument, and Hooke's Micrographia the first treatise on
microscopy. Since his objects were fairly coarse (insects, seeds,
stones, fabrics, a razor's edge, leaves, wings, feathers, etc.), and
since he did not seek to penetrate into anatomical structure by
dissection (though he examined the compound insect eye, and
discovered the cellular composition of cork) he was able to produce
a series of admirable illustrations despite the limitations of his
microscope. Most of the discoveries of the time in minute ana-
tomy, associated with the names of Malpighi, Swammerdam and
Grew, such as the capillary circulation of the blood, could also be

TECHNICAL FACTORS 241

demonstrated with the compound instrument. 1 For the very finest
observations, however, another technique was required, in which
the Dutch microscopist Antoni van Leeuwenhoek excelled. The
compound microscope had stimulated the grinding of very small
bi-convex lenses of short focal length for use as objectives. It was
found that better results could be obtained by mounting such high-
power lenses, or even tiny fused glass spheres, as simple micro-
scopes than by using them as elements in an optical system that
multiplied the aberrations. For considerable magnification the
lenses had to be less than one-tenth of an inch in diameter; they
were proportionately difficult to grind and manipulate, and they
imposed severe eye-strain. But Leeuwenhoek reported, in his
letters to the Royal Society, observations obtained by this means
which were only repeated with the achromatic microscopes of the
nineteenth century. His skill as an optician is further shown by the
fact that one of his few surviving lenses has been proved, by recent
tests, far superior to any other known simple lens; others of his
own make are good but not outstanding. This skill enabled him to
study more thoroughly than any other observer spermatozoa and
the red corpuscles in the blood and to become the first to discern
protozoa and bacteria. Despite some contemporary incredulity,
aroused by the great number and disparity of Leeuwenhoek's
original discoveries, and the difficulty of confirming them, his
work was astonishingly accurate. He was also creditably free from
the tendency to theorize, or to allow his imagination to play with
his microscopic images. At the end of the century Leeuwenhoek
was alone in his investigation of microscopic creatures, although
others were engaged on the study of the microscopic parts of
larger creatures; his results, therefore, remained largely isolated
curiosities. In the eighteenth century the description of various
animals, visible to the naked eye but capable of being studied only
with the aid of the microscope, was taken up both in England
(Baker, Ellis) and in France (Reaumur, Bonnet, Lyonet) . Tremb-
ley, whose monograph on the hydra has become a classic, worked
in Holland and was closely associated with both the English and
the French groups of naturalists. All these worked with the simple
microscope but at a much lower magnification than that frequently
employed by Leeuwenhoek. This instrument thus became estab-
lished in familiar use among zoologists and botanists for much the

1 See below, p. 286.

16

2 4 2 THE SCIENTIFIC REVOLUTION

same purposes as it serves at the present time, when the higher-
powered compound microscope, given a beautiful mechanical
construction by the English instrument-makers, was still of little
scientific value. The continuation of the sciences of histology and
cytology, begun by Malpighi and Leeuwenhoek, depended upon
the perfecting of lenses which proceeded swiftly in the early
nineteenth century.

It would be possible to develop other, comparable, instances
of the way in which, after an initial seventeenth-century invention,
a long interval followed before, in a stage of higher proficiency
in instrumental techniques, observations or measurements of a
different order became practicable. The Newtonian reflecting
telescope, with Herschel's improvements, for the first time enabled
the astronomer to escape the confines of the solar system. If the
" chemical revolution" of the eighteenth century was effected
without profound modifications of apparatus, on the other hand
the chronology of electrical science was fixed by the discovery of
instruments for the creation, and the measurement, of charges and
currents. These in turn induced new chemical techniques, such
as electrolysis. During that century a considerable literature grew
up dealing with the manufacture and use of scientific instruments
of all kinds, and teaching the technique of making experiments
and observations, while the actual manufacturers strove intelli-
gently to improve their wares. John Dollond, the practical man
who solved the problem of making achromatic telescope objectives
which had baffled mathematicians, was an instrument-maker.
The marine chronometer, in the perfecting of which so much was
due to another practical man, John Harrison, imposed a close
collaboration between watch-makers and astronomers. Science,
therefore, entered into a promising situation with the early nine-
teenth century, being able to call upon the services of a skilful
and progressive specialized craft, and realizing far more perti-
nently than hitherto its own dependence upon its material equip-
ment. In nearly every respect its progress was involved in that of
some instrument, or in that of a variety of laboratory techniques.

Because a three-fold division of function may exist in science,
between the instrument-maker, the laboratory worker' and the
theorist, it has always been possible, and still is, for the strategic
thinking in science to take place outside the laboratory, away from

TECHNICAL FACTORS 243

the instruments (though it may still be controlled by the accessible
mathematical techniques). Thus Tycho's instruments were made
by the metal-workers of Augsburg; he himself managed their use
with consummate skill; and his results were interpreted by the
mathematician Kepler. But the third function without the second,
and the second without the first, can clearly yield only diminishing
returns. The progress of science demands originality at all three
levels; more than this, it may demand the existence of resources
of industrial magnitude, of a glass-industry, a gas-industry, of the
great plants required to produce antibiotics and radio-active iso-
topes. If it seems increasingly likely that the major advances of
the future will come from large institutes, freely endowed, and as
the result of co-operative labours, it is no more than a fresh step
in that growth of complexity, and of an increasing reliance on
techniques and tools of investigation, which was typical of the
scientific revolution. In a sense it is the fulfilment of Bacon's
foresight.

CHAPTER IX
THE PRINCIPATE OF NEWTON

IT might be misleading to suggest that the career of Isaac
Newton represents the peak of the scientific revolution, the
point at which the transition from renaissance to modern
science became complete. The qualifications to be added to such
a generalization are obvious. Profound changes in the methods
and theories of the non-mathematical sciences, upon which the
impact of Newton was negligible, were deferred to future times.
He showed no interest in biology; perhaps, indeed, to his highly
organized intellect its structure was wholly alien. It could be
argued that Newton's essentially physical approach to chemistry
was no less a departure from the traditions of that science than
Lavoisier's theory of chemical combination, but Newton's ideas,
despite their surviving historical interest, proved unconstructive.
Their ingenuity was premature, and Newton, like Boyle, in his
treatment of chemistry as a branch of corpuscular physics more
nearly resembled an ancient philosopher than a nineteenth-
century chemist. The clear light shining through his mathematical
and physical researches did not illumine other, darker quarters of
Newton's mind and character. The author of the Principia was
also the compiler of millions of words of extracts from the most
obscure alchemical writers; the great mathematician laboriously
computed the generations that had passed since the creation of the
world. Despite his genius, despite his rapid and sure mathematical
invention, despite his experimental precision, science was always
for Newton a detached intellectual pursuit, not an activity, a
cause, close to the emotional core of his being. Strangely, to
modern ways of thinking, alchemy seems to have given him a
greater sense of the ultimate mystery than his unfolding of the
celestial system. To many of the critical issues of the scientific
revolution he was insensitive. Unlike Descartes or Boyle he felt
impelled to utter no fundamental pronouncements on the trinity
of God, Nature and Man. Cutting neatly and narrowly through
the froth swelling up from the intellectual ferment of his age,
withdrawing himself from idealists and propagandists, the social,

244

THE PRINGIPATE OF NEWTON 245

religious and philosophic implications of the scientific revolution
scarcely touched him. Newton saw the ideal of scientific truth se-
renely, as an end attainable by the application of methodical prin-
ciples; it provoked in him no warm revulsion against established
errors, no enthusiasm for a hopeful shift in the course of civilization.

Even Newton, therefore, cannot be described without reserva-
tion as a "modern scientist." His own attitude to nature still bore
traces of the medieval; he faced some problems which the modern
world considers unworthy of serious consideration, and by con-
trast philosophized sometimes in such a fashion as to gloss over
other problems which have since become important. Nevertheless,
Newton's contributions to those branches of physical science that
were studied in the seventeenth century mark a peak of achieve-
ment. At the same time they disclosed fruitful prospects for the
future advance of science, but where the influence of Newton was
most profound in the theory of gravitation, in the theory of
light, and in the particulate theory of matter his own example
was so commanding, and his own explorations were of such range,
that for about a century no investigation passed the limits of the
Newtonian framework. Newton may be pictured as establishing
developing sciences at a new level, less by seeing the problems in
ways unimagined by his contemporaries than by the exercise of
his greater ability and mathematical skill. At about this level they
remained until the nineteenth century was well advanced, while
the major creative impulse was transferred to the less organized
departments of science, to chemistry and biology, and in physics
to the study of heat and electricity. The comparative stagnation in
the eighteenth century of those aspects of physics which had seen
most revolutionary developments in the seventeenth is a measure
of Newton's success in extracting the quintessence of knowledge
from those scientific procedures which the seventeenth century had
developed most highly; for long it seemed that in those aspects
no other procedures, and no greater knowledge, were possible.

The Newtonian theory of light was severely shaken by Young
and Fresnel about 1820, and at the same time a notion of electrical
attraction among the ultimate particles of matter was gradually
replacing the Newtonian idea of a gravitational attraction. These
were the first checks to the established structure of physics, while
serious doubts of the inviolability of Newtonian or classical
mechanics only arose at the very end of the nineteenth century.

246 THE SCIENTIFIC REVOLUTION

Throughout a long period of more than 150 years Newton's
scientific thinking in mathematical science appeared practically
infallible; other aspects of his intellect were still almost completely
hidden, partly owing to the caution of his literary executors and
editors, who carefully marked so many of his manuscripts as
"Not fit to be printed," partly owing to Newton's own reticence in
publication. 1 Before 1684 Newton was a comparatively unknown
professor of mathematics in the University of Cambridge; his
optical experiments and construction of a reflecting telescope,
with his mathematical discoveries which were known only to a
limited circle, had given him a certain repute, but he had won
no striking acclaim. The publication of the Mathematical Principles
of Natural Philosophy in 1687 immediately gave him enormous
prestige. The Royal Society recognized something of its majesty
even before the book was printed; foreigners, though more reluc-
tant to accept Newton's theories, were quick to perceive the genius
which had given them a mathematical dress. The tone was set by
Edmond Halley's opening ode to the volume whose publication
he generously undertook :

. . . Talia monstrantem mecum celebrate camaenis,
Vos o caelicolum gaudentes nectare vesci,
Newtonum clausi reserantem scrinia veri,
Newtonum Musis charum, cui pectore puro
Phoebus adest, totoque incessit numine mentem;
Nee fas est propius mortali attingere divos. 2

A somewhat fulsome adulation was maintained by English writers
to recent times (e.g. in Brewster's Life of Newton, 1855); others
were more critical in equally sincere admiration. Even today the
distinction between that which was of permanent value in
Newton's scientific thinking, and that which was stamped with
the character and preconceptions of his age, is not always very
clearly indicated. The fact is (as might be expected) that in their
manifold and complex aspects Newton's contributions even to

1 Most of his works appearing in his life-time, other than the Principia, the
papers in the Philosophical Transactions, and the Opticks (delayed until after
Hooke's death), were first printed without his consent.

2 *O you heavenly ones who make merry on nectar, celebrate with me in
song the revealer of these things, Newton to the Muses dear, Ne\yton who
unlocked the barred treasure-chest of Truth: Phcebus is in his pure breast, and
enters his mind with all his own divinity. Nearer the Gods no mortal may
approach.'

THE PRINCIPATE OF NEWTON 247

mathematics and mathematical science were not all equally useful,
though all were important. Newtonian mechanics, and his
celestial system, have stood firm within limits which are now
clearly defined; but of the remainder of Newtonian science the
last century has left scarcely a vestige.

Clearly Newton, like most great men, was fortunate in the hour
of his birth: in 1642, the year of Galileo's death. His adolescence
was accompanied by the foundation of scientific societies, the
practice of systematic experiment, the gestation of modern mathe-
matics. In 1665-6 the rather unpromising, and certainly ill-
grounded student upon whom Barrow had enforced the study of
Euclid's Elements was in the "prime of his age for invention."
How much the fruit of his originality owed to the ground from
which it sprang, to Barrow, to Wallis, Slusius, Kepler, Borelli,
More, Boyle, Descartes and others whom he read in those early
Cambridge years! 1 How many, and how rich, were the threads
which these giants led to the hand of so able a spinner of theorems,
so close a weaver of theories! The genius that was frustrated by the
dense mysteries of chemistry reaped a splendid harvest in the
riper fields of mathematical science in which its fullest powers
could be exercised. It is no detraction from Newton's originality
to point out that all his discoveries were firmly rooted in the science
of the time that like a helmsman he was borne along by the
stream that each of them has a quality of inevitability in its
contemporary context. Newton, in fact, won such immediate
esteem because he saw clearly the things to which others were
groping, because he was so fully in harmony with his age. Not
scientists and mathematicians alone, but philosophers and theo-
logians could find in Newton exactly that of which they wished to
be assured. Even in his political allegiance to a limited Protestant
monarchy, in his ambition to rise in the great world of affairs,
and in his shrewd financial sense, Newton was a good and success-
ful citizen of Augustan England, a bon bourgeois when the middle
classes were rising to luxury and power.

There are no singularities in Newton's early years. As a student
in Cambridge, he was fashionably inclined to scepticism of the

1 One would naturally like to add the name of Galileo to this list, but there
seems to be no evidence that Newton met Galileo in the original, at least at
this time.

248 THE SCIENTIFIC REVOLUTION

Cartesian system, looked favourably upon hypotheses of atoms
or corpuscles, and developed a mild academic interest in the
empirical method represented by Boyle. Starting rather late, he
rapidly assimilated the latest mathematical knowledge, but
although his notebooks show him at the age of twenty-three
already deeply interested in science, they contain no sketch of
an original contribution, no hint of a sudden revelation of the
importance of natural knowledge. He was always apt, much later
in life, to regard science as an importunate mistress, to work with
immense concentration and speed upon a problem when the
passion to solve it fell upon him, because a part of himself doubted
the problem's cosmic significance. Then, for the better part of
two years after he had taken his degree, Newton was forced into
retirement at his country home in Lincolnshire by the plague
which raged in the towns and villages during 1665 and 1666. He
had already begun his optical experiments (which seem to have
been prompted by undirected curiosity, rather than by any
clearly perceived ambition), and his mind was turning towards
new conceptions in mathematics. In the winter of 1664-5 he had
found the method of infinite series, and shortly after discovered the
binomial theorem; in Lincolnshire during the following summer
he calculated a hyperbolic area to fifty- two places of decimals;
in November of the same year he had formulated the direct
method of fluxions (differentiation), and in May 1666 he began
upon the inverse method (integration) . During the whole of 1 665
he must have been working at his optical experiments, and trying
to grind lenses of non-spherical curvature, and early in 1 666 he
"had the Theory of Colours." This quickly directed him to the
construction of his first reflecting telescope. 'And the same year/
wrote Newton long afterwards, 'I began to think of Gravity
extending to y 6 orb of the Moon, & (having found out how to
estimate the force with which a globe revolving within a sphere
presses the surface of the sphere), from Kepler's rule ... I deduced
that the forces which keep the Planets in their Orbs must [be]
reciprocally as the squares of their distances from the centers
about which they revolve.' To this period belongs the famous
story of Newton and the Apple, told at first hand by Newton's
younger friend, William Stukeley:

After dinner, the weather being warm [the date was 15 April 1726],
we went into the garden and drank thea, under the shade of some

THE PRINGIPATE OF NEWTON 249

appletrees, only he and myself. Amidst other discourse, he told me,
he was just in the same situation, as when formerly, the notion of
gravitation came into his mind. It was occasioned by the fall of an
apple, as he sat in a contemplative mood. Why should that apple
always descend perpendicularly to the ground, thought he to himself.
Why should it not go sideways or upwards, but constantly to the
earths centre? Assuredly, the reason is, that the earth draws it. There
must be a drawing power in matter: and the sum of the drawing
power must be in the earths center, not in any side of the earth.
Therefore does this apple fall perpendicularly, or towards the center.
If matter thus draws matter, it must be in proportion of its quantity.
Therefore the apple draws the earth, as well as the earth draws the
apple. That there is a power, like that we here call gravity, which
extends itself thro the universe. l

When the plague had subsided, Newton returned to Cambridge,
presumably in the hope (which was soon fulfilled) of becoming a
Fellow of Trinity College; in 1669 he succeeded Isaac Barrow in
the Lucasian Professorship of Mathematics. He was now com-
fortably established in a life that was to be his for nearly thirty
years. Professorial pupils were few, though Newton must have
done some college teaching; he had ample leisure for his experi-
ments in optics and chemistry, and for his mathematics. In 1672
letters written to Oldenburg, describing the new theory of colours,
brought him into the Royal Society but the disputes and criticisms
which followed during the next four years (aggravated by the
officiousness of Oldenburg) persuaded Newton virtually to cut off
this connection. His interest in alchemy and chemistry quickened;
the wooden staircase leading from his first-floor rooms to the
furnace in the little garden below was shaken by his eager tread.
It was Halley who brought Newton back into the scientific move-
ment, who encouraged his interest in mathematical matters, and
was the godfather of the Principia. The book was begun towards
the end of 1 684, and was finished by the spring of 1 686. Thereafter
Newton's life became more full of incident, and more empty of
science. He took part in the resistance to the Catholic policy of
James II; sat (silently) as a Member of Parliament; and sought

1 William Stukeley: Memoirs of Sir Isaac Newton's Life, ed. by A. Hastings
White (London, 1936), pp. 19-20. Stukeley was forty-five years junior to Newton,
who was in his eighty-third year in 1 726, and did not compose his memoir until
1752. His expressions, therefore, cannot be taken very strictly as interpreting
Newton's state of mind in 1665-6.

2 5 o THE SCIENTIFIC REVOLUTION

to become Provost of King's College. 1 His fame, and his new
acquaintance with John Locke, made him known personally to
men who possessed political power and influence. The prospect of
exchanging academic seclusion in a provincial town for an office
of honour and profit in London was welcome. The initial frustra-
tion of this ambition, working in a mind intolerant of opposition at
a time when it was strained by overwork, caused a serious break-
down during 1693. After some months Newton recovered his full
intellectual powers, but it is to be doubted whether his judgement
of men's actions ever regained a normal balance. 2 This illness
brought his creative scientific work to a close. Honours and fame
came later; in 1696 Newton left Cambridge to become first
Warden, then Master of the Royal Mint; in 1703 he was elected
to the Presidency of the Royal Society, which he held for the rest
of his life; in 1705 he was knighted. In the Augustan Age Newton
and Pope ruled the intellectual world with a sway more absolute
than that of the Queen herself.

That branch of science in which Newton had first published
original discoveries was also the last to be enriched by his mature
reflections. The bulk of the Opticks of 1704 had long been written,
but the Queries with which the book concludes represent Newton's
final contribution to science, and perhaps the sum of his perception
of nature. In the Queries optical phenomena are discussed in order
to throw light on the ultimate particulate structure of matter:

Have not the small Particles of Bodies certain Powers, Virtues, or
Forces, by which they act at a distance, not only upon the Rays of
Light for reflecting, refracting and inflecting them, but also upon
one another for producing a great Part of the Phenomena of
Nature? 3

1 Newton's extraordinary mastery of detailed argument is well revealed in
the legal briefs that he drew up for the royal benefit to confute the contentions
of the Fellows of King's. His claim brought him into touch with Christiaan
Huygens, whose brother Constantyn had come to England in the service of
William III. It is pleasant to think of these two great, and very different,
scientists setting off in a coach to petition their common sovereign to promote
Newton in the academic hierarchy.

2 Newton's mental illness was a definite paranoia, in which he accused his
closest friends of persecuting and calumniating him. Locke, in 1705, privately
described him as 'a little too apt to raise in himself suspicions where there is no
ground'; this mental trait, which he always had, was played upon by men of
greater ambition than discretion in the quarrel with Leibniz, wherein INewton
lost all sense of proportion and probity.

8 Opticks, Bk. Ill, Qu. 31.

THE PRINCIPATE OF NEWTON 251

Newton, indeed, for the first time made optics a branch of physics,
by his demonstration that the theory of light and the theory
of matter were cognate and complementary. Before the mid-
seventeenth century the science of optics was almost wholly geo-
metrical, and it is interesting that progress was achieved through
renewed attention to its qualitative aspects. Since the character-
istic colours of bodies and pigments had long been regarded as
true Aristotelean qualities, confusion followed upon the challenge
to Aristotle's philosophy in the time of Galileo. The prismatic
colours also had long been familiar; in the middle ages an increas-
ingly more perfect account of the formation of the colours in the
rainbow had been given by the Latin writers who, following
Alhazen, regarded them as produced by the refraction of sunlight
in shining through rain-drops. The geometrical optics of the rain-
bow were further perfected by Descartes, who also put forward a
new and more definite corpuscular hypothesis of light. In his view,
light was a sensation caused by pressure of the matiere subtile on the
optic nerve, set up by the tendency of this matter to expand in all
directions from its concentration in the luminous source; colours
were caused by rotations of the particles of the matttre subtile.

This was, like all the science of the Principles of Philosophy, an
unsupported hypothesis. Descartes assumed that light travels
more rapidly in a dense medium (such as water) than in air, and
from this the sine-law of refraction could be deduced; but the same
law could also be deduced from the contrary assumption. There
was no method of proving either by experiment. The explanation
of what happens to "light" itself when a beam of white light is
converted into a beam of one or more colours was vague and
wholly speculative. In all theories before Newton's, a qualitative
change in the nature of the beam was suggested, a modification
of the physical entity of light, which at least in imagination could
be reversed, so that as red light can be derived from white, white
ought to be derivable from red. The same potential reversibility
is implicit in the more ingenious theory of colours described by
Robert Hooke in Micrographia (1665). Hooke was the first investi-
gator of the colours produced by optical interference in the form
known, somewhat unjustly, as "Newton's rings," which he ob-
served in the laminations of mica, and in plates of glass pressed
together, finding that the manifestation of the colours depended
upon the existence of a very thin refracting medium, each colour

252

THE SCIENTIFIC REVOLUTION

corresponding to a determinate thickness. According to Hooke,
the sensation of light is caused by a very rapid, short vibrating
motion in the transmitting medium, every pulse or vibration of
the luminous body generating a sphere 'which will continually
increase and grow bigger, just after the same manner (though in-
definitely swifter) as the waves or rings on the surface of the water
do swell into bigger and bigger circles about a point of it, where,
by the sinking of a stone the motion was begun.' Therefore, each
successive pulse or vibration may be considered as being at right

angles to the direction of pro-

AIR , natation radially from the

(less easy transmission) . , T

' ' centre, and in a narrow beam

of light each pulse as a plane
surface perpendicular to the
beam. 1

Hooke next investigated
geometrically the results of the
passage of the beam from one
medium into a second which
is capable of transmitting the
pulses more, or less, easily than
the first. He reasoned that if
the light falls obliquely upon
the surface separating the two
media, one "edge" of the
pulse (treated as a plane)

WATER
(more easy transmission)

FIG. 8. Hooke's Theory of Refraction.
aaabbb, incident ray; cccddd, refracted
ray. ab, ab perpendicular pulses, cd,
cd oblique pulses.

would enter the second medium before the other, and would
therefore be accelerated or retarded before the latter, in turn, had
started to travel through the second medium (Fig. 8). He assumed
(without proof) that when the second medium transmitted the
pulses more easily the beam would be refracted towards the per-
pendicular, and consequently that water transmits more easily
than air. 2 This refracted ray, moreover, would be distinguished
from the incident ray in that the pulses would now be oblique,

1 Micrographia, pp. 55-7.

2 In this Hooke followed Descartes. Fermat had already demonstrated that
refraction towards the perpendicular occurs when the velocity of light in the
second medium is less, i.e. when like water or glass it transmits light less easily
because it is more dense than air. Huygens, in the Traitt de la Lumtire (1690)
wherein he follows Fermat, by introducing the conception of the wave-front
into the pulse-theory showed that the sine-law of refraction followed from it.

THE PRINGIPATE OF NEWTON 253

not perpendicular to the ray, due to the acceleration or retarda-
tion of the "leading edge" of each pulse. 1 To this obliquity of the
pulse Hooke traced the sensation of colour, on the grounds that in
a whole beam of light there would be some confusion of the oblique
pulses, and that one "edge" of each pulse would be weakened or
blunted through having to initiate the vibration in a medium at
rest; thus:

Blue is an impression on the Retina of an oblique and confus'd pulse
of light whose weakest part precedes, and whose strongest follows.
Red is an impression on the Retina of an oblique and confus'd pulse
of light, whose strongest part precedes, and whose weakest follows.

For example, in Fig. 9, towards a the leading edge of each oblique
pulse, being adjacent to the un-
disturbed medium, is weakened,
whereas towards d the lagging
edge pulse is weakened for the
same reason. Hence the colour
blue will be seen about a, and red
about d. Hooke thought that
the intermediate colours of the
spectrum 'arise from the com-
position and dilutings of these

two' produced by the confusion , _ u ,

~ * . r FIG. 9. Hooke s Theory of Colours,

ot the two primary types of

oblique pulse towards the middle of the refracted beam. He
further showed by a very ingenious analysis that when a ray
passes through a very thin medium a similar succession of strong-
weak or weak-strong pulses is created, according to its thickness,
producing colours.

In this theory of light, Hooke devised a subtle mechanism by
which colours might be derived from white light considered as a
train of uniform and homogeneous pulses. It accounted for the
association of heat, light and motion in a crudely sketched kinetic
theory; for the fact that refraction is always accompanied by
coloration; for the order of the colours as produced by refraction
or by interference; and for the fact that the spectrum produced by
one prism can be re-converted into white light by a second. On

1 Huygens (see note 2, above) avoided this supposition of obliquity by
different reasoning on the formation of the refracted wave-front.

254 THE SCIENTIFIC REVOLUTION

the other hand, it was not very clearly conceived in detail, and it
explained only a selection of the known facts. Hooke seems to
have observed that the two sides of a refracted ray are not parallel,
but makes no mention of the fact (cf. Fig. g). 1 Probably no experi-
ments on homogeneous coloured light were made by him, since
he seems not to have known that further refractions have no effect
upon such light; this would certainly have been difficult to recon-
cile with his theory. The most serious objection against its broad
form was that it failed to account for the rectilinear propagation
of light. If a ray was a train of pulses, why did not these spread out
into the surrounding medium, as sound-waves do? This was, in-
deed, for long a profound objection against any pulse or undula-
tory theory, having been thoroughly discussed by Newton in the
Opticks.

So far the theory of light had been illuminated by few new
experiments, and none that were decisive. The ideas of Descartes
and of Hooke could have been as well propounded in the four-
teenth century as in the seventeenth. The new experimental evi-
dence, relating to interference (Hooke) and diffraction (Grimaldi,
also 1665) seemed to favour the pulse hypothesis, but though the
two opposed theories were equally mechanical in character, they
were nevertheless ad hoc hypotheses, entirely lacking in the demon-
strative solidity on which the "new philosophy" was supposed to
be founded. By introducing imaginary mechanical qualities of
pellucid matter, the old Aristotelean theory of colour as a quality
had only been pushed back to a further remove. Newton's experi-
ments began where the theories of Descartes and Hooke, with
which he must certainly have been acquainted, ceased in new
experiments. His papers in the Philosophical Transactions, containing
his new theory of prismatic colours, are hardly more than the
statement of experimental results. The deductions he drew were
simply those enforced by the new evidence.

His first paper begins with the observation that a parallel beam
of white light diverges into the spectrum when it is refracted by
a prism. The spectrum is longer in one direction, not of the same
shape as the aperture through which light is admitted. This must
have been noticed often, and disregarded. Both in the Opticks,
and in his note-book, however, Newton first describes another

1 This is shown in Fig. 2 of Schem. VI of Micrographia, where, however, the
incident ray is shown as convergent though Hooke purports to be using sunlight.

THE PRINGIPATE OF NEWTON 255

experiment, in which he observed a continuous line, painted in
two colours, through the prism and found that the image of the
parti-coloured line was no longer rectilinear. Perhaps this gave him
the first clue to what followed. These simple experiments taught
Newton that 'y e rays which make blew are refracted more y n y c
rays which make red,' 1 or as he phrased it after many more ex-
periments described in the Opticks, 'the Sun's light is an hetero-
geneous Mixture of Rays, some of which are constantly more
refrangible than others.' Any refracting agent, such as a prism,
simply acted like a filter to distinguish the infinite components of
white light according to their refrangibility. Therefore, he thought,
it was necessary to give up all hope of contriving a lens which
would refract all colours equally, and so yield an achromatic
image. Newton was careful to prove that monochromatic light has
all the optical properties that were " vulgarly" attributed to white
light, and that there could be no question of the white ray being
actually shattered by refraction it was merely divided, and it
could be reassembled. Each pure coloured constituent, however,
was homogeneous and indivisible.

This doctrine appeared very shocking to contemporaries. The
simple nature of white light had always been accepted as axio-
matic. The proof that all the colours of the spectrum are equally
primary and necessary in white light cut directly across notions
which supposed them the product of mixtures of red and blue, or
blue and yellow. While some theorists of empiricism welcomed
Newton's Baconian use of experiment, many who prided them-
selves on their knowledge of optics were hostile. The reactions of
the critics, Hooke and Huygens amongst them, are interesting.
When Newton's first paper appeared in the Philosophical Transac-
tions, they judged initially that he was merely speculating, and
tried to answer with irrelevant arguments. Then they denied that
the experiments gave the results described by Newton, or main-
tained that if the experiments were correct the conclusions drawn
from them were false. Finally, it was alleged that if Newton's ideas
were justifiable, they were not original. Neglecting the minor
critics, it may be doubted whether either Hooke or Huygens
two of the leaders of the scientific movement ever succeeded
entirely in adjusting their thinking in accordance with the evidence

1 Cambridge MS. Add. 3996: cf. the author's note in Cambridge Historical
Journal, vol. IX (1948), pp. 239-50.

256 THE SCIENTIFIC REVOLUTION

of Newton's experiments. The former never understood that his
own pulse-theory could not account for them. The latter, in his
Traite de la Lumiere (1690), tactfully omitted the subject of colour
completely. Their failure is not more surprising than that of other
scientists in more recent periods who have equally resisted an
innovation which has inevitably overwhelmed their criticism.
Newton's propositions were revolutionary, not only in their con-
tent, but because they were founded straightforwardly on new
experimental evidence. It is, in one sense, an indication of the
superficiality of the change in spirit effected by the scientific revo-
lution that such obvious conclusions drawn from such easily
repeatable experiments should have been treated as matters for
argument. Empiricism that is, in this instance, Newton's reti-
cence in his original papers on the question of what light is, and
the reasons for the properties exhibited by a lens or prism was
still obstructed by the inertia of established theory, which could
prevent an accurate factual description being estimated at its true
worth. In another sense, the dispute carried on in the pages of the
Philosophical Transactions was the product of a confusion between
facts and their interpretation which is perhaps inevitable in
science at its growing point. Of this there are many examples, in
the incredulity with which Lavoisier, Darwin, Joule or Pasteur
was heard. Major scientific advances have not been made simply
by uttering the statement that, in certain conditions, "The red
line is higher than the blue," or " the thermometer reading was #."
Newton did not make such a purely descriptive statement, for he
added that the red was higher than the blue because the constituent
coloured rays of white light are not equally refrangible. If un-
comfortable experiments have stuck in the throats of those wedded
to established ideas, it is owing to their indissoluble connection
with a heterodox theory. In such circumstances, the new theo-
retical attitude may seem to leave incomprehensible more than
it seeks to explain, and then the question arises: "Is it worth
while to alter the balance which is already struck between the
mysteriousness of nature and human understanding?"

The most important of Newton's discoveries, because they were
most unconventional, aroused in many of his contemporaries the
feeling that the accepted conception of natural processes was being
wantonly disturbed in order to account for phenomena that
could equally well be treated without such intellectual upheavals.

THE PRINGIPATE OF NEWTON 257

It is, in the last resort, the function of cumulative experiment and
observation to prove that such supposed alternatives in explana-
tion are unreal; triumphantly to defend the old, or vindicate the
new. In the course of the scientific revolution, the dominant
antithesis had been between old and new methods and ideas,
broadly divisions among the "moderns" were trivial. Towards the
end of the seventeenth century this antithesis was becoming lifeless,
and other divisions between the moderns themselves became far
more critical. The appeal to experiment and observation had
played a useful part in resolving the former antithesis, but the
appeal to a new conception of what science should be, to a new
image of nature, to a new mathematics and structure of reasoning,
in short to a new appraisal of familiar facts, had achieved far
more sweeping results. In many ways, genuine observation and
experiment had been the pivots of seventeenth-century biology
far more than they had been of its mechanics and physics. With
the empiricist reaction against Cartesian science, which had
seemed for a moment almost to sum up the whole revolt against
tradition, and especially with the discoveries of Newton, came the
test of the ability of the heirs of Copernicus and Galileo to resolve
their own internal contradictions. If these were not in turn to lead
to endless debate, such as had embroiled the heirs of Aristotle, it
could only be by a more rigorous attention to the criteria of
experiment. The fundamental significance of Newton's scientific
method was that it achieved this exactly; it did not show merely
that a theory roughly agreed with a selected group of facts, but
that a group however limited and restricted of theoretical
propositions could be associated with a range of experimental
facts, carefully checked and often repeated. Confidence could be
granted to such a group of propositions because it was unique,
and the minimum necessary; because it claimed only to compre-
hend a limited range of phenomena that had been exactly studied,
and not to extrapolate from a few particulars to universal truths.
Against such a method the kind of criticism directed towards
Newton's theory of colour was unavailing in the long run; as was
that directed against Lavoisier or Joule. If, with regard to Newton,
expressions of incredulity were less well founded, it was perhaps
because his precise use of the experimental method was not yet
understood.

Of course Newton did not restrict himself entirely to such

17

258 THE SCIENTIFIC REVOLUTION

theoretical propositions as were firmly based on experiment. Too
much has been made of his celebrated obiter dictum, " I do not frame
hypotheses." Scattered through his works, and more freely through
his unpublished papers, are numerous comments suggestive of a
deeper penetration into the mysteriousness of nature than exact
science could yet achieve. Newton framed many hypotheses
which, he was inclined to think, might account for natural
phenomena, like gravitation or refraction, hardly as yet illumi-
nated by experimental inquiry; but he was always careful to
distinguish between such hypotheses and an experimentally
established theory. With him this distinction totally ignored by
Descartes becomes fully self-conscious; hence the form of the
Queries in the Opticks. In these Queries Newton sketched out an
interlocking but not wholly consistent body of ideas relating to
the nature of light and matter which he regarded as possible, or
probable, but unproven. The most influential portions of this
discussion were those in which Newton considered the relative
merits of the undulatory (or pulse) and the corpuscular theories
of light. He has been generally regarded, with some truth, as the
classical advocate of the latter. But he was not wholly decided.
For example, in Query 13 the suggestion is made that the colour
of a ray depends upon the "bigness" of its vibration, the shortest
vibrations corresponding to violet, and the largest to red, just as
the pitch of sound corresponds to the " bigness" of the vibration
in the medium. 1 Again, in Query 16, Newton asks, 'considering
the lastingness of the Motions excited in the bottom of the Eye by
Light, are they not of a vibrating nature?'; and in Query 17 he
suggests that when a ray of light is reflected or refracted, vibrations
are set up in the medium which, radiating from the point of
incidence, c overtake the Rays of Light, and by overtaking them
successively, do they not put them into the Fits of easy Reflexion
and easy Transmission described above? ' As for the medium whose
vibrations should transmit light, Newton could conceive of an
aether, less dense than air but far more elastic, pervading all bodies
and expanded throughout the universe, transmitting heat by its
vibrations as well as light, 2 acting as the agent of reflection and

1 Newton's terminology is obscure: it is not quite clear whether by " bigness "
he means amplitude or wave-length.

1 The existence of invisible (infra-red) heat rays was first demonstrated by
Sir William Herschel (1800).

THE PRINCIPATE OF NEWTON 259

refraction. Conversely, in Query 29 Newton declares: 'Are not
the Rays of Light very small Bodies emitted from shining Sub-
stances? For such Bodies will pass through uniform Mediums in
right Lines without bending into the Shadow, which is the Nature
of Rays of Light.'

Colour might be accounted for by supposing that the smallest
corpuscles of light gave the sensation violet, and the largest, being
less refracted, the sensation red. From his study of the double
refraction in Icelandic spar (which Huygens, in his Traiti de la
Lumihe, had failed to explain completely in terms of the wave-
theory) Newton concluded that the " sides" of a ray of light
might have different properties, and he did not see how these
could be associated with wave-propagation. These two points
were, for him, decisive objections against the ideas of Hooke and
Huygens, yet he himself found it necessary to conceive of a
periodicity in the "Fits of Easy Reflection and Transmission"
which he introduced in Book II in order to deal with the pheno-
mena now ascribed to optical interference. 1 Newton's corpuscular
theory, therefore, did not render an aether unnecessary, nor did it
dispense entirely with the concept of aetherial vibrations. As he
was evidently not satisfied with its completeness, it was unfortu-
nate that some later physicists paid insufficient attention to
Newton's caution: 'Since I have not finish'd this part of my
Design, I shall conclude with proposing only some Queries, in
order to a farther search to be made by others.'

Not only does the Principia differ from the Opticks in form a
mathematical, as compared with an experimental, treatise but
its relationship to the contemporary scientific background is
different also. It presented no less of a puzzle to contemporaries
than the optical discoveries of fifteen years earlier, partly for the
same reason that Newton chose to propound even apparently
absurd theories if they alone suited the facts described, partly for
the additional reason that the propositions of the Principia seemed
to contravene the mechanistic philosophy which science had so

1 In each regularly successive "Fit of Easy Reflection'* the ray tended to be
reflected upon meeting a surface; in between in the " Fits of Easy Transmission "
to penetrate into it. Thus the behaviour of a ray encountering the two surfaces
of a thin medium (such as the air gap between two glass plates) depended
upon the dimensions of the intervals between the surfaces and of the intervals
between the "Fits."

2 6o THE SCIENTIFIC REVOLUTION

recently adopted with confidence. The theory of gravitation stated
in terms of action at a distance was regarded by Cartesians as
no better than a revival of the occult forces from which science
had been liberated by mechanical hypotheses. Nevertheless, the
Principia was far more in keeping with a certain scientific tradition
one overshadowed by the triumph of Cartesian science than
was the Opticks; its thesis was more clearly anticipated in earlier
notions, due to Gilbert, Kepler, Borelli and Hooke; its materials
had largely been prepared by other hands than those of Newton
himself.

Descartes had flatly denied the validity of attraction as a
scientific concept. Since all forces were mechanical in his view, a
body could move only because other bodies impacted upon it,
and so impelled it by pushing. Therefore he had described prob-
able ways in which gravitational, magnetic, or electric "attrac-
tions" might be caused by such impacts of the matiere subtile upon
solid bodies. His system implied that the various motions of the
planets around the sun were conditioned by the structure of
the solar system as a whole, and particularly by the properties
of the aetherial matter, rotating like a vortex, with which it was
filled. They were not determined by separate relations between
the individual celestial bodies; this perhaps explains why Kepler's
empirical laws of planetary motion were of little interest to him.
The earlier notions of attraction, however, had conceived rather
of each celestial body, regarded as a physical entity, exerting an
influence directly upon cognate matter. In Aristotle's theory of
gravity and levity the matter of the universe was drawn, or
attracted, to its natural place, the attraction being specific to
each kind of matter, since earth could not tend naturally to the
place of fire, nor vice versa. Thus the same kind of matter tended
to collect together in the same place. In the Copernican system,
this concept of attraction to specific spherical layers about the
centre of the universe no longer had meaning, but the cosmic order
could be preserved by transferring the attraction from the place
to the matter which had, in Aristotle's cosmology, occupied that
place. The basic principle that matter tends to coalesce with like
matter implied by Aristotle, could now emerge more clearly.
For Gilbert this principle, justified quite naively by theological
reasoning, enabled bodies to preserve their integrity. 'Cohesion
of parts, and aggregation of matter, exist in the Sun, in the Moon,

THE PRINCIPATE OF NEWTON 261

in the planets, in the fixed stars,' so that in all these bodies the
parts tend to unite with the whole 'with which they connect
themselves with the same appetence as terrestrial things, which we
call heavy, with the Earth.' 1 This means that gravitation is a
universal property of matter, but peculiar to each body; the same
gravity is not common to all, in Gilbert's view, because a piece of
lunar matter would always tend towards the moon, and never
adhere to the earth.

It might seem that after Galileo's contention that the matter of
earth, moon and planets the non-luminous heavenly bodies
was of the same kind, it would have been a straightforward step
to argue that all this earthy matter shared a common attraction,
like drawing like. But against such an argument the teleological
framework of the theory of attraction which was in no way
required to explain the known behaviour of lunar or solar matter,
apart from its consistency was doubly effective. In the first place,
if the matter of the moon, for example, were attracted towards
the earth, the theory would cease to explain the cohesion of the
parts of the moon. Secondly, a common gravitational attraction
would suggest that all the earthy matter in the universe would
collect in one mass and this was Aristotle's view, which Galileo
opposed. Thirdly, neither Galileo nor any of his contemporaries
knew of any function which such a common attraction could be
supposed to fulfil. The theory of specific attractions remained far
more plausible.

This theory had been used by Gilbert, and by Copernicus before
him, as an alternative to the Aristotelean causation of the motions
of heavy terrestrial bodies. It was less a new cosmological principle,
than a new physical principle applied to cosmology. As such it is
also used by Kepler:

A mathematical point, whether it be the centre of the universe or not,
cannot move heavy bodies either effectively or objectively so that
they approach itself. ... It is impossible, that the form of a stone,
moving its mass [corpus], should seek a mathematical point or the
centre of the world, except with respect to the body in which that
point resides. . . . Gravity is a mutual corporeal affection between
cognate bodies towards their union or conjunction (of which kind the
magnetic faculty is also), so that the Earth draws a stone much more
than the stone seeks the Earth. Supposing the Earth to be in the

1 On the Magnet, trans, by S. P. Thompson (London, 1900), pp. 219, 229.

262 THE SCIENTIFIC REVOLUTION

centre of the Universe, heavy bodies would not be borne to the
centre of the Universe as such, but to the centre of a cognate spherical
body, to wil the Earth. And thus wherever the Earth is assumed to be
carried by its animal faculty, heavy bodies will always tend towards it. 1

So far Kepler has said nothing very new. He has repeated that
the concept of attraction of like to like can replace the Aristotelean
concept of matter being attracted to specific places, and he has
limited his use of this concept to heavy bodies cognate with the
earth. But he has stated, for the first time, that the attraction
is mutual (the analogy between gravity and magnetism, so fruit-
fully begun by Gilbert, is now being extended), and this point he
amplified further:

If two stones were placed close together in any place in the Universe
outside the sphere of the virtue of a third cognate body, they would
like two magnetic bodies come together at an intermediate point,
each moving such a distance towards the other, as the mass of the
other is in proportion to its own.

Here an original conception of the magnitude of the motion due

to gravitational attraction was introduced ( --* = 2 ), in which it

W 2 0*1 /

was related to the ratio of the masses of the two bodies. Kepler,
therefore, began the investiture of the theory of attraction with a
definite dynamical form. Further, he postulated that the earth and
the moon were cognate matter, like the two stones:

If the Moon and the Earth were not retained, each in its orbit, by
their animal or other equivalent forces, the Earth would ascend
towards the Moon one fifty-fourth part of the distance between them,
and the Moon descend towards the Earth about fifty- three parts; and
they would there join together; assuming, however, that the substance
of each is of one and the same density. 2

Kepler then went on to demonstrate, from the ebbing and
flowing of the tides, that this attractive force in the moon does
actually extend to the earth, pulling the waters of the seas towards
itself; much more likely was it that the far greater attractive force
of the earth would reach to the moon, and greatly beyond it, so
that no kind of earthy matter could escape from it. 3

1 Astronomia Nova; Gesammelte Werke, vol. Ill, pp. 24-5.

2 Assuming also that the diameter of the earth is about 3! (v/5s) that of the
moon, which is a little too large.

3 Loc. cit., pp. 25-7.

THE PRINCIPATE OF NEWTON 263

Clearly no one invented the theory of gravitational attraction;
it grew through many diverse stages. And clearly also the genesis
of the theory of universal gravitation is found in Kepler. Newton's
hasty calculation of 1666, his later theory of the moon, and his
theory of the tides, are all embryonically sketched in the Astronomia
Nova. But the attraction was still specific, applicable only to heavy,
earthy matter; Kepler himself did not go so far as to suppose that
the sun and planets were also mutually attracting masses, or that
the dynamical balance he indicated as retaining the earth and
moon in their orbits with respect to each other also preserved the
stability of the planetary orbits with respect to the sun. He failed,
as Copernicus, Gilbert and Galileo failed, to see the full power of
gravitational attraction as a cosmological concept.

Nevertheless, Kepler's idea that the satellite revolving round a
central body is maintained in its path by two forces, one of which
is an attraction towards the central body, although applied only to
the earth-moon system, holds the key to all that followed and to
the Principia itself. Galileo, like Copernicus, had believed the
planetary revolutions to be "natural," i.e. inertial; the celestial
bodies were subject to no forces. Kepler, however, believed that the
motive force of the universe resided in the sun which, rotating
upon its own axis, 'emits from itself through the extent of the
Universe an immaterial image [species] of its body, analogous to
the immaterial image [species] of its light, which image is itself
rotated also like a most swift whirlpool and carries round with
itself the bodies of the planets.' 1 Each planet, moreover, was en-
dowed with its own "soul" which influenced its motions. 2 Such
notions confused the dynamical elements of the situation for
Kepler since the sun's force operated tangentially upon the
planet, he did not imagine that a centripetal force was necessary
to retain it in the orbit. In the singular case of the earth and moon,
it was necessary for him to suppose that the "animal or other
equivalent force" of the moon was sufficient to overcome the
attraction towards the earth which would have distorted its path.
This physical, attractive property of heavy matter could not as yet
be made the basis of the stability of the celestial system; rather it
was a disturbing feature which the cosmological properties of the
heavenly bodies had to overcome.

1 Loc. cit., p. 34.

2 Cf. Harmonices Mundi (1619), Gesammelte Werke, vol. VI, p. 264 et seq.

264 THE SCIENTIFIC REVOLUTION

With Descartes the position was altogether reversed. He knew
that bodies in free motion move in straight lines. He knew that his
planets, swirled like Kepler's in a solar vortex, would if uncon-
strained travel in straight lines outside its limits. He knew, there-
fore, that some centripetal force must bend these straight lines
into the closed curves of the orbits. Rejecting Kepler's mysterious
attraction, he supposed this force to be provided by the varying
density of the solar vortex, which resisted the planets' natural
tendency to recede towards its periphery.

After the publication of Descartes' Principia Philosophic ( 1 644)
which for the first time applied the law of inertia systematically to
the planetary motions, the elements of the problem of universal
gravitation were completely assembled. The essential step was to
replace Descartes' conception of the nature of the centripetal
force required to hold the universe together by the Keplerian idea
of attraction, with the sun taken as the central body. Kepler's
problem could now be approached from a completely fresh aspect:
knowing that the moon must be, as it were, chained to the earth
to prevent it flying off into space, might not this bond be that
"corporeal affection between cognate bodies towards their union"
described by Kepler? Three men, all about the year 1665, formu-
lated this question in similar terms, and attempted to answer it:
Alphonso Borelli, Robert Hooke and Isaac Newton.

Borelli, who was a member of the Accademia del Cimento, tried
to find in Kepler's ideas the basis for a complete mathematico-
mechanical system of the universe. 1 He regarded the light-rays
radiating from the sun as levers pressing upon the planets, re-
volving because the sun revolved, and able to exert a pressure
because they were themselves material emanations. He explained
that the least force would impart some motion to the greatest mass,
and that therefore (in the absence of resistance) the planets would
move with a speed proportionate to the force impressed. 2 This,
like Kepler, he supposed to become more feeble as the distance
from the sun was greater, so that the outer planets would move
more slowly than the inner. Instructed by Descartes, Borelli knew
that under such circumstances a centripetal force was necessary to

1 Theories Mediceorum Planetarum ex cattsis physicis deduct* (Florence, 1666).

2 As Prof. Koyr has pointed out, Borelli has unwittingly formulated the
Aristotelean doctrine. Acceleration, not velocity, is proportional to force
applied: hence Borelli's planets could never maintain a uniform speed.

THE PRINCIPATE OF NEWTON 265

maintain the planets in their orbits, but he carefully avoided speak-
ing of this as an attraction since the word was banned from the
phraseology of mechanism. Nor did he identify this force with
that which in the earth is called gravity. Instead, he postulated
that all satellites in the celestial machine had a natural tendency
or appetite to approach the central body about which they re-
volve thus the planets sought the sun an appetite constant at
all distances, and not at all affecting the central body itself. The
stability of the planet in its orbit was therefore conditioned by the
perfect balance of the centrifugal and centripetal forces to which
it was subject, and this he was able to illustrate experimentally;
but Borelli was further required to explain why these orbits are
elliptical, not circular. The answer is highly ingenious: Borelli
imagined that each planet was created outside its circular orbit.
In this position the excess of centripetal over centrifugal force
would urge the planet to its proper distance from the sun, but the
momentum acquired would carry it beyond, to a point inside the
circular orbit. Here the centrifugal would exceed the centripetal
force, and the planet would again be pressed outwards, and again
carried by momentum to its former station. l Then the cycle would
be repeated. Thus the ellipse was a result of a slow oscillation
about a stable position a circle round the central body com-
pared by Borelli to the oscillation of a pendulum, to and fro,
passing through a stable position at the perpendicular. This hypo-
thesis was in accord with the observed fact that the velocity of the
planet is greatest at its nearest approach to the sun.

Borelli's theory, an amalgamation of those of Kepler and
Descartes, in regarding the planets as impelled by a sort of vortex
centred upon the sun conceived of the universe as a driven, not
a free-spinning, machine. To it the law of inertia could not be
directly applied hence Borelli's confusion concerning force and
momentum. Both Hooke and Newton took two more important
steps: they assumed that the planetary motions were purely in-
ertial the universe was a great top and that there was a uni-
versal, mutual attraction between masses of matter. Newton,
moreover, remedying the mistakes in the principles of dynamics

1 Nearly two hundred years later, Clerk-Maxwell accounted for the stability
of the innumerable small satellites which compose Saturn's rings in a mathe-
matical analysis, the principle of which was dimly anticipated in this hypothesis
of Borelli.

266 THE SCIENTIFIC REVOLUTION

which permeate Borelli's treatise, effected a meticulous analysis
of the forces which the latter (and Hooke) had described so
loosely.

There is ample evidence that by 1 685 Robert Hooke had a very
complete picture of a mechanical system of the universe founded
on universal gravitation. In the early days of the Royal Society he
performed unsuccessful experiments to discover whether gravity
varies above and below the earth's surface. In Micrographia (1665)
he conjectured that the moon might have a 'gravitating prin-
ciple' like the earth. In a discourse read to the Royal Society in
1666 Hooke improved on Borelli with the supposition that a
'direct motion' might be inflected into a curve by 'an attractive
property of the body placed at the centre.' 1 Like earlier writers he
compared this centripetal attraction to the tension in the string
of a conical pendulum, which retains the bob in its circular path.
In 1678 he wrote: 'I suppose the gravitating power of the Sun in
the center of this part of the Heaven in which we are, hath an
attractive power upon all the planets, . . . and that those again
have a respect answerable.' 2 This is the first enunciation of the
true theory of universal gravitation of gravity as a universal
principle that binds all the bodies of the solar system together.
The same force whereby the heavenly bodies 'attract their own
parts, and keep them from flying from them,' also attracts 'all
the other celestial bodies within the sphere of this activity.' It is
this force which, in the sun, bends the rectilinear motions of the
planets into closed curves. And this force is 'the more powerful in
operating, by how much nearer the body wrought upon is' to the
attracting body. 3

These ideas, Hooke claimed, he had expounded as early as
1670. But it was not until 1679 that he hit upon a hypothesis to
describe the rate at which the gravitational attraction should de-
crease with distance. In that year he renewed his correspondence
with Newton, discussing an experiment to detect the earth's rota-
tion through the deviation of falling bodies. This in turn led to a
debate on the nature of the curve which a heavy body would
describe if it were supposed to be able to fall freely towards the
centre of the earth, during which (in a letter to Newton dated

1 R. T. Gunther: Early Science in Oxford, vol. VI (Oxford, 1930), p. 266.

2 Ibid., vol. VIII, p. 228.

3 Ibid., vol. VIII, pp. 27-8, 229-30, etc.

THE PRINGIPATE OF NEWTON 267

6 January 1 680) Hooke stated the proposition that the force of
gravity is inversely proportional to the square of the distance,
measured from the centre of the gravitating mass. 1 He was con-
vinced that this "inverse square law" of attraction, combined
with the ideas he had already sketched out, would be sufficient to
explain all the planetary motions.

Hooke's scientific intuition was certainly brilliant. Of all the
early Fellows of the Royal Society, in a generation richly endowed
with genius, his was the mind most spontaneously, and sanely,
imaginative; schemes for new experiments and observations oc-
curred to him so readily that each day was divided between a
multiplicity of investigations; physiology, microscopy, astronomy,
chemistry, mechanics, optics, were each in rapid succession sub-
jects for his insight and ingenuity. No topic could ever be broached
without Hooke rising to make a number of pertinent points and
to suggest fruitful methods of inquiry. With regard to celestial
mechanics, Hooke's conception was as far-reaching as Newton's;
but it was not prior and it was not proven. The publication of the
Principia, accompanied by Hooke's charge of plagiary against
Newton, inflamed the suspicion between the two men into out-
raged anger. Both suffered from a touchy pride; neither would
recognize the true merits of the other. In Newton's eyes, Hooke
grasped after other men's achievements, having merely patched
together some notions borrowed from Kepler, Borelli and Huy-
gens. To Hooke, Newton had merely turned into mathematical
symbols ideas that he had himself already expressed without at-
tracting notice or reward. He was ever unwilling to admit the
supreme advantage that Newton held over himself, of being
mathematician enough to demonstrate as a theory, confirmed by
observation, that which Hooke himself had only been able to
assert as a hypothesis. In fact the different status which attaches
to a scientific theory and a scientific hypothesis a difference which

1 Hooke thought that this same law would apply to the force of gravity
below the earth's surface. Newton later proved (Principia, Bk. I, Prop. LXXIII)
that within a sphere the centripetal force is inversely proportional to the dis-
tance from the centre, not to the square of the distance. Ismael Bouillau, in
Astronomia Philolaica (1645), had argued that the intensity of Kepler's "moving

virtue" resident in the sun would decrease, like that of light, as ^. Therefore,

he said, since the velocities of the planets are not in this proportion to their
distances from the sun, they could not be impelled by such a force emanating
from it.

268 THE SCIENTIFIC REVOLUTION

Newton emphasized more than once was something to which
Hooke proved himself insensitive by a number of episodes in his
career. As Newton pointed out, Hooke did not invent the theory
of attractive forces, as such; and after Huy gens' theorems on the
centrifugal acceleration of rotating masses had been published,
the inverse square law could easily be deduced. Granting the
highest merit to Hooke's scientific intuition, it is quite clear from
certain confusions inherent in the development of his hypothesis
between 1666 and 1685 that his mastery of the principles of
dynamics was never completely confident, and that his thought
was never safeguarded by the precision of mathematical analysis.
Newton complained, in a letter to Halley at the time when
Hooke was voicing his protests before the Royal Society, that the
latter wished to assign to him the status of a mathematical drudge
and claim for himself the sole invention of a new system of celestial
mechanics. The truth is far otherwise. By 1666 Newton was al-
ready able to calculate centrifugal accelerations. This calculation,
applied to Kepler's laws, gave him the inverse square law of
attraction. 1 If the earth's gravitational attraction was assumed to
act upon the moon, he computed that in accordance with this law,
at the distance of the moon from the earth this centripetal force
would be " pretty nearly" equal to the centrifugal force created
by the moon's own revolution about the earth. Gravity would be
precisely the chain required to bind the moon in its orbit. 2 But
such a calculation was not strictly appropriate: for a planet's
(and the moon's) orbit is not circular but elliptical, with the central
body (sun or earth) at one focus of the ellipse. Moreover, in calcu-
lating the distances and relative forces, Newton had proceeded as
though the earth and moon were points, that is, reckoned that if

a

the force of gravity at the surface of the earth was , then at the

1 In a circle of radius r, if T is the time taken by a body to complete one
revolution, the centripetal force required to hold it in its path is F -=3. But
according to Kepler's Third Law, in the solar system T 2 = k'r*. Substituting,
F = ^/-g whence, omitting the constants, F is proportional to -^.

2 Newton's calculation in 1666 did not give a perfect confirmation of the
inverse square law, because the value he took for the earth's radius (and hence
the distance of the moon from the earth) was too small. It used to be 'supposed
that this discrepancy induced him to lay the matter aside. The view given below
is now generally accepted.

THE PRINCIPATE OF NEWTON 269

g

moon it was ;~ y 2 . He had not proved that the external gravita-
tional attraction of a sphere could be computed as though its mass
were concentrated in a point at the centre. The difficulties in-
volved in perfecting the hypothesis upon which his first casual
trial was founded were mainly mathematical, and at this time
beyond Newton's skill. So great were they that Halley was aston-
ished to learn (in 1684) that Newton had overcome them; had
proved, in fact, that the path followed by a body, moving obliquely
in relation to a second which exerts a centripetal force upon it,
must correspond to one of the conic sections. 1

In 1666, therefore, Newton was not satisfied that the inverse
square law represented more than an approximation to the truth.
Impressed by the mathematical difficulties involved, he laid the
hypothesis aside. For about thirteen years (1666-79) there is not
the least evidence that he paid any attention to dynamics, uni-
versal gravitation or celestial mechanics. Optics, mathematics,
alchemy and perhaps already theology, filled his mind. So much,
at least, Newton owed to Hooke: that he was compelled to return
to his former hypothesis. Even when driven, by Hooke's unwel-
come letters, to review the mystery of gravity, he was guilty of
blunders and misapprehensions. Even when, pricked by Hooke's
corrections, he had solved the problem of the inverse square law
and the elliptical orbit, Newton once more set his success to cool
for a further five years. Only Halley's visit to Cambridge in 1684,
and the warmth of his admiration and offers of assistance, set the
Principia in train.

The book is often described as though its sole function was to
establish what has been called the Newtonian system of the uni-
verse. That it did so is, indeed, its main historical importance; the
Third Book and the System of the World, in which Newton set him-
self directly to this task, are likely to be read with far greater
interest than the earlier sections. But Newton's influence on subse-
quent science, in this work alone, penetrated to a far greater
depth. He defined mass and the laws of motion. He gave to science
formal concepts of space and time which needed no revision for

1 Newton established (Principia, Bk. Ill, Prop. XL) that the path of a comet
is a parabola, and that the orbit of a returning cornet, such as that examined
by Halley (ibid., Prop. XLI), is an extended ellipse of which the portion near
the sun is scarcely distinguishable from a parabola.

270 THE SCIENTIFIC REVOLUTION

two centuries. He expounded and exemplified a " method of
philosophizing" that is still regarded as a valid model. He virtually
created theoretical physics as a mathematical science in the form
which it preserved to the end of the last century. For Newton, the
mathematical principles in nature were not merely evidenced by
the elementary dynamics of Galileo, or even by his own majestic
computations relating to the planetary motions, but were to be
traced in the whole field of experimental physics and more
conjecturally in the phenomena of light, in the constitution of
matter and the operations of chemistry. Outside physics, Newton's
work was never finished it could not be finished and his ideas
remained half-formed. The Principia, however, is a treatise on
physics almost as much as it is a treatise on celestial mechanics;
and in some sections Newton made meticulous use of the quantita-
tive experimental method. 1 The theorems and experiments on the
vibrations of pendulums in resisting media, on the free fall of
bodies and the trajectory of projectiles in the same, are not perhaps
of great intrinsic interest, as certainly they were of no practical
importance, nor closely relevant to the motions of the planets; but
it is not impossible to understand why Newton concerned himself
with them. For, firstly, such problems were close to the heart of
seventeenth-century physics, in a tradition which Newton himself
brought to a climax. And secondly, they served to prove his point
that the principles of nature are mathematical; that with number
and measure science could reach beyond the uncontrolled imagina-
tion of a Descartes, or even the idealism of a Galileo. In Newton's
eyes, scientific comprehension was not limited to vague qualitative
theories on the one hand, or definite statements about a state of
affairs much simpler than that which is actually experienced on
the other; it could proceed, by due techniques, to definite ideas
about all that is physical, down to the properties of each constituent
corpuscle. To illustrate this conception of science is the purpose of
the Principia.

Otherwise, both logically and emotionally, the framework of
celestial mechanics would have been without foundation. Here
Newton and Descartes were more alike than the crude antithesis
of their cosmologies would allow. Descartes had proceeded, in the
Principles of Philosophy, from his clear ideas of what must be,

3 Thus, fresh experiments on the descent of heavy bodies in resisting media
were added by him to each of the later editions of 1713 and 1726.

THE PRINGIPATE OF NEWTON 271

through the laws of motion and the properties of moving bodies,
to his celestial mechanism. Newton likewise: developing his
mathematical method from the definitions and the laws of
motion, through the long analyses of the motions of bodies in many
different circumstances until he could discern in the heavenly
motions special cases of those principles of motion that he had
already elucidated. Newton perceived, as Descartes had done, as
Huygens did when he all but abandoned Descartes, that a theory
which attributed the most noble and enduring phenomena in
nature to the play of mechanical forces could not stand on a
handful of assumptions, two or three happy computations and the
vague, undemonstrative, mechanistic philosophy that had become
fashionable. 1 Like Descartes, but with an infinitely more subtle
logic, with all the rigour of mathematics and with cautious appeal
to observation and experiment, Newton displayed the whole
science of matter-in-motion before he turned to the solar system
specifically. An unfinished treatise, De Motu Corporum, preceded
the Principia; the study of a particle in motion must precede that
of a circling planet. And if Newton found it necessary to investi-
gate the solid of least resistance, or the flow of liquids, it was to
prove the universality of that science of moving particles that he
proposed to apply, not to a minute part, but to the whole of man's
physical environment. The Principia, in fact, does not expound a
particular scientific theory to account for the motions of the
heavens, it develops a theory of physical nature which embraces
these phenomena, and all phenomena of matter-in-motion, within
its compass.

As such it was, of course, a mechanistic theory. No other was,
or is, conceivable within the range of physics. Not that Newton
excluded God from the universe:

This most beautiful system of the sun, planets, and comets, could only
proceed from the counsel and dominion of an intelligent and power-
ful Being. ... He endures forever, and is everywhere present; and
by existing always and everywhere, he constitutes duration and
space. 2

1 In this, of couise, Newton powerfully revealed his immense superiority
over Hooke, who could never have constructed the laborious scaffolding upon
which Book III of the Principia is raised.

2 General Scholium, concluding the Principia. Gf. Florian Gajori: Sir Isaac
Newton* s Mathematical Principles of Natural Philosophy (Berkeley, 1946), pp. 544-6.

272 THE SCIENTIFIC REVOLUTION

God was for Newton the Final Cause of things, but, excellent and
laborious theologian as he was, he made no confusion between
physics and theology. 1 That Newton seemed, by the theory of
universal gravitation, to contravene the principles of mechanism,
was due to misapprehension. Though certain phrases in the Prin-
cipia might seem to indicate the contrary, he did not believe
that gravity was an innate property of matter, nor that two
masses could attract each other at a distance without having any
mechanical relationship. To Bentley Newton wrote:

It is inconceivable that inanimate brute matter should, without the
mediation of something else, which is not material, operate upon and
affect other matter without mutual contact. . . . That gravity
should be innate, inherent, and essential to matter, so that one body
may act upon another at a distance through a vacuum, without the
mediation of anything else, by and through which their action and
force may be conveyed from one to another, is to me so great an
absurdity that I believe no man who has in philosophical matters a
competent faculty of thinking, can ever fall into it. 2

He added to the second edition of the Principia a brief statement
that by attraction he meant only to describe the tendency of bodies
to approach each other, no matter what the cause. As to the prob-
able nature of this cause, he professed himself ignorant. 3 It was
sufficient to infer that the phenomenon existed and was universal;
like Galileo, Newton regarded the effect as established if it could
be described, though the cause were hidden. To suppose that par-
ticles or masses exert a gravitational attraction was not, therefore,
in Newton's language to postulate an occult quality in matter but
to describe a fact a fact that was to be demonstrated in the
laboratory by Henry Cavendish seventy years after Newton's
death. Nor did Newton believe that the celestial spaces across
which the sun's attraction holds the planets in their orbits were
necessarily empty of all matter.

His refusal to ascribe a cause or mechanism to universal gravi-
tation was indeed one of Newton's principal advantages in celes-

1 Newton, however, expressed a sentiment typical of the age in a letter to
Bentley (1692): 'When I wrote my treatise about our system, I had an eye on
such principles as might work with considering men for the belief of a Deity;
and nothing can rejoice me more than to find it useful for that purpose.' (Ibid.,

P. 66 9 ).

2 Quoted by Cajori, op. cit. 9 p. 634.

3 In a letter to Boyle, he outlined a theory of aetherial contraction which he
never troubled to develop thoroughly.

THE PRINCIPATE OF NEWTON 273

tial mechanics. He was free, as the Cartesians were not, simply to
state and analyse the observable facts, and the inferences neces-
sarily drawn from them. He did not seek to construct a model
which would be rendered clumsy and contradictory by the
very attempt to explain everything in nature by corpuscular
mechanisms.

Hypotheses [wrote Newton], whether metaphysical or physical,
whether of occult qualities or mechanical, have no place in experi-
mental philosophy. . . . l And to us it is enough that gravity does
really exist, and act according to laws which we have explained, and
abundantly serves to account for all the motions of the celestial
bodies, and of our sea. 2

The concluding paragraph of this General Scholium indicated a
possible solution of many "occult" mysteries, fully in the
seventeenth-century mechanical tradition. For,

We might add something concerning a most subtle spirit which per-
vades and lies hid in all gross bodies; by the force and action of which
spirit the particles of bodies attract one another at near distances, and
cohere, if contiguous; and electric bodies operate to greater dis-
tances . . .; and light is emitted, reflected, inflected, and heats
bodies; and all sensation is excited, and the members of animal bodies
move at the command of the will. . . .

Newton's imagination was not less generous than that of Descartes,
though less dogmatic. He was as fully convinced of the existence
of an (Bther^ the residuum of the major secrets of nature, as Descartes
or any nineteenth-century physicist. Further hints were to be given
years later in the Queries appended to the Opticks, but Newton did
not know how these things could be investigated, much less proved.
Nevertheless, his attitude (less plain certainly in the first edition
of the Principle than it has since become) was widely misunder-
stood. Newtonian empiricism was rapidly accepted by his own
countrymen: probably no scientist has received a more immediate,
or a warmer, acclaim from the intellectuals as well as the professed
scientists of his race. Abroad it was distrusted. Neither Huygens
nor Leibniz (who set the tone for many lesser men) could stomach

1 Newton, of course, did not mean that tentative hypotheses have no use in
an investigation; he framed many such himself. He meant that an unconfirmed
and undemonstrated hypothesis should not be taught as an adequate theory.

2 Gajori, op. cit., p. 547.

18

274 THE SCIENTIFIC REVOLUTION

the downright statement of Proposition VII, Book III. 1 Attempts
to reconcile the Cartesian mechanical theory of celestial vortices
with Newtonian mathematical laws were prolonged into the mid-
eighteenth century. Not until fifty years after the publication of
the Principia did Voltaire's proclamation of his admiration for the
profound English geniuses, Newton and Locke, begin to win ad-
herents. The essential truth, that Newton and Descartes shared
the same idea of nature, was thus long obscured; and Newton has
perhaps been too often praised for being other than he was. The
idol of perfection who was endowed by the nineteenth century
with every attribute of scientific insight and vigour, with abhor-
rence of hypothesis and mystery, with serene temper and con-
ventional religion, was not the genuine Newton. It is perhaps
paradoxical but not unjust that his greatest successor was to
arise not from the crowd of reverend English gentlemen who were
to claim Newton as their own, but in the person of the sceptical
French mathematician, the Marquis de Laplace, whose Mfoanique
Celeste (1799-1825) extended in time the laws that Newton had
traced in space.

1 'That there is a power of gravity pertaining to all bodies, proportional to
the several quantities of matter which they contain.*

CHAPTER X
DESCRIPTIVE BIOLOGY AND SYSTEMATICS

BEOLOGIGAL study, as it is practised today in laboratories and
field stations, is essentially a creation of the nineteenth
century. The work of Darwin on evolution, of Mendel on
genetics, of Schleiden and others on the cell theory, so transformed
the texture of the biologist's thought that it would be appropriate
to attribute to the period 1830-70, rather than to any earlier age,
the "biological revolution" which completed the modern scien-
tific outlook. The belief in the fixity of species was no less respect-
able than the belief in the fixity of the earth; the belief that the
Creator must have personally attended to the fabrication of every
kind of diatom and bramble was no less primitively animistic than
the belief that His angels governed the revolutions of the planetary
orbs. Exactly as the mechanistic philosophy of the seventeenth
century was accused of encouraging scepticism and irreligion, on
a greater scale (because the issue was more clear and more
decisive) the mechanistic biologists of the nineteenth met the full
force of ecclesiastical wrath. The liberty of the scientist to direct
his theories in accordance with the scientific evidence alone was
equally at stake. But there is this difference. Biology was certainly
"modern" in some respects if not all before the nineteenth
century. A great renaissance had already occurred, which itself
far surpassed all that had gone before. Materials had been heaped
up from which a great generalization such as evolution could be
drawn. Above all, the scientific method of biology was already in
existence that was not the creation of the nineteenth century.
The researches of Leeuwenhoek and Malpighi, the systematics of
Ray and Linnaeus, were preliminaries as essential to the syntheses
which introduced the truly modern outlook as the work of
Copernicus and Galileo was to that of Newton.

None of the ancient founders of biology was primarily in-
terested in collection, description and classification as ends in
themselves. Aristotle the zoologist and Theophrastus the botanist
were always philosophers their purpose was to investigate the

275

276 THE SCIENTIFIC REVOLUTION

functioning of living organisms; Dioscorides studied botany as the
servant of medicine. Partly, perhaps, because the range of species
examined was comparatively small neither Aristotle nor Theo-
phrastus knew more than about five hundred distinct kinds of
animals or plants the problem of cataloguing them did not
become of overriding importance, though much thought was given
to order and arrangement. Since the Greek empire extended into
India, exotic species were available, but they did not attract
great attention. 1 To the Greek mind, the attempt to answer the
questions that living nature posed was more important than the
compilation of information, and for this the materials close at
hand were sufficient. Over-leaping a great space of time, in the
last century collection and taxonomy have again become no more
than specialized branches of biology. The study of function, of
the processes of growth and differentiation, has assumed a more
fundamental importance. The experimental has replaced the
encyclopaedic method, so that a modern zoologist may find a
greater interest in the works of Aristotle than in those of any
natural historian of the pre-Darwinian age.

The intervening period has, indeed, very special characteristics.
For long there were no adequate successors to the Greek botanists
of the fourth century B.C. The Romans were competent writers on
agriculture, but such an author as Pliny added nothing beyond
the cult of marvels to the existing texts which he pillaged. The
philosophic spirit of the Greeks almost perished, and was only
revived in the botanical work of Albert the Great (De Vegetabilibus
et Plantis, c. 1250). Albert was an Aristotelean botanist at least,
his main authority was a translation of two books on plants then
attributed to Aristotle. 2 He was interested in the philosophy of
plant growth, in the variety of their structures and (as he believed)
in their constant mutations. Care in the morphological analysis
of plants for purposes of description and identification was com-
bined with renewed attention to the problem of classification, but
Albert was not greatly impressed by the importance of cata-
loguing. Such an emphasis was then unusual, for in his time
herbalism medical botany had already become a principal
interest. It is a strange paradox that while the learning of the

1 One important exception was the date-palm, which provided the only
example of sexuality in plants known before the late seventeenth century.

2 But now assigned to Nicholas of Damascus (first century B.C.).

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS 277

later middle ages turned so naturally to argument in metaphysics
and philosophy, and thence to logic, cosmology and physics, the
intellectual problems posed by the living state were so often
ignored. Only in its relations with medicine can medieval biology
be generally said to have had a serious intellectual content, to
have attempted to answer questions.

Herbalism looked to Dioscorides, rather than to Aristotle and
Theophrastus. Before the fall of Rome the tradition he founded
had already suffered debasement and the decline, both in matter
and in illustration, continued throughout the early middle ages.
In the thirteenth century, however, there were already skilful
herbalists with a good knowledge of Dioscorides and his com-
mentators, some familiarity with exotic drugs, and an interest in
description and identification. The herbal of one of them, Rufinus,
serves to show that he, at least, did not scruple to add remarks
of his own to the literary tradition, and that he was aware of
distinctions in kind unknown to the more famous compilers of
the sixteenth century. 1 Rufinus was clearly well acquainted with
drug plants and druggists, but he made no attempt to classify,
merely arranging his notes in alphabetical order. The greater part
of his text was made up of quotations from earlier pharmacological
authorities (Dioscorides, the Circa instans of about 1 1 50, the Tables
of Salerno, and others), but Rufinus' own additions were mostly
botanical, such as this description of Aaron's Beard:

Aaron's Beard has leaves which are thick in substance, nearly a span
broad and long, and it has two little beards to each leaf. The leaves
are divided down to the root. It has a tuberous root in the ground,
from which a cosmetic ointment is made, and it sometimes has
blotched leaves. It forms its flower in a capsule, contrived by a
marvellous artifice and having this yellowish capsule around it, in
the centre of which is a sort of finger, with two little "apples" below
it, wonderfully contrived. The plant which has blotched leaves is
masculine and that without blotches on the leaves is feminine. 2

His manuscript was apparently unillustrated, so that the identifi-
cation of uncommon plants from it would have been very doubtful.
The herbal flourished, to become enormously popular soon
after the invention of printing. But the herbalist's interest in the
plant was always in knowledge of means to an end. Some of his

1 Lynn Thorndike: The Herbal of Rufinus (Chicago, 1946).

ibid., P . 54.

278 THE SCIENTIFIC REVOLUTION

medicaments were minerals, or derived from animal sources, and
it was only because such a large proportion of medieval physic
was derived from vegetables, that the pharmacopoeia assumed a
preponderantly botanical form. Thus descriptive zoology was a
poor relation of herbalism, though animals were also described
as the immediate companions and servants of man, because they
offered useful moral lessons, and because some of them had an
exotic or symbolic fascination. Conceiving that the world was
created for the use and instruction of man in working out his
own salvation, the medieval mind naturally adopted a somewhat
functional approach to the living state. The task of the naturalist
was simply to describe living things, with their particular uses (or
wonders, or edifying properties) so that other men might use them
(or wonder at them, or be edified). Despite the occasional philo-
sophic questioning of an Albert, there was no powerful motive to
elevate him above a lexicographical mentality. And the naturalist
was less interested in collecting facts about creatures that might
form the material of a science, than in human reactions to this
and that, in the diseases against which a given plant was supposed
to be beneficial, in the moral to be drawn from the habits of the
ant-lion.

Thus the origins of natural history were essentially anthropo-
centric, in the Roman Pliny, in the early Christian compilers like
Isidore of Seville, in the thirteenth-century encyclopaedia of
Bartholomew the Englishman, in the late medieval herbalists.
Human interest in nature was limited to the production of a
catalogue raisonnt.

The early stages of the renaissance brought no important re-
orientation. Occasionally the representational art of a " Gothic"
stone mason or wood carver had enriched a cathedral with a
recognizable likeness of a living species. About the beginning of
the fifteenth century the graphic artist began to realize the
aesthetic possibilities of exact imitation of nature in the illumination
of manuscripts here were the roots of both the naturalistic art
of a Diirer, and biological illustration. By 1550 the technique of
life-like illustration had been mastered, with greatest distinction
in the herbals of Brunfels (1530) and Fuchs (1542). This technique
was ultimately as necessary to botany and zoology as. to human
anatomy, but it did not occasion any immediate enhancement of
the level of botanical knowledge, for the texts of both Brunfels'

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 279

and Fuchs' books were poor, and excelled in description by
unillustrated works, such as that of Valerius Cordus. Brunfels,
indeed, tried to find some more natural arrangement than that
of an alphabetical list, but the latter was by no means abandoned
as yet. The botanists of the sixteenth century, with the exception
of Cesalpino and Gesner, were still herbalists, and the herbal was
still an adjunct to the pharmacopoeia, enabling the apothecary to
identify such medicinal plants as Swallow-wort and Fennel, Sage
and Fumitory, whose names are perpetuated on the delightful
majolica drug-pots of the time.

Humanism had its effect upon biology, as upon all branches of
science, without challenging the main emphasis on collection and
classification. The authority of Dioscorides and Theophrastus was
reinforced rather than weakened; their texts were better under-
stood, but did not encourage originality in ideas. Mediterranean
botanists particularly took up the task of identifying more exactly
the species described by Dioscorides; some, like Mattiolo, Cordus
and Conrad Gesner, were content to put forward their own work
as expansions of his, with considerable display of philological
learning. Gradually it was learnt that Greek names had been
abused by application to species quite different from those known
to the Greeks themselves; and that, moreover, the name often
covered a whole group of similar plants, not a specific type.
Northern botanists, on the other hand, acquired knowledge of
plants not included in the traditional Mediterranean flora; Charles
de 1'Ecluse alone is reputed to have found two hundred new
species in Spain and Portugal (1576), and later he was equally
successful in Austria and Hungary. Cataloguing and description
were extended far beyond the range of the merely useful. Decora-
tive plants, like the daffodil and horse-chestnut this last one of
many importations into western Europe at this period were
noticed as well as the medicinal, along with many new species
reported by the explorers to the Far East and the Americas. The
common and uncommon plants of hedgerow, pasture and upland
were no longer neglected. A garden was now judged by the
multitude, rarity and beauty of the species represented in it, while
the Hortus Siccus became a repository of trophies exchanged among
collectors. For the men of the renaissance collected plants,
plumages and skins as they amassed coins, antique statuary and
manuscripts, since greater wealth and leisure permitted such

2 8o THE SCIENTIFIC REVOLUTION

costly and learned ostentations. The plants in some renaissance
gardens, like that of the Venetian patrician Michieli (c. 1565),
were commemorated in water-colour and written description.

Though the character of the product of this vastly increased
activity in botany, or herbalism, was not greatly changed in the
sixteenth century, the character of the new herbalist was certainly
modified. As he attached less importance to medicinal value, he
became more keenly interested in fine distinctions; whereas the
ancient and medieval herbalist had hardly been concerned with a
unit smaller than the genus, their successors began to discriminate
between different species within the genera, and even between
varieties of the same species. Again, the new naturalists were often
scholars and gentlemen, they had therefore greater opportunities
for botanizing over wide areas, even despatching emissaries for
this purpose; they could acquire a more extensive literary know-
ledge and employ the best draughtsmen. Doubtless such men felt
the aesthetic appeal of nature more keenly than the apothecary or
peasant. As Fuchs wrote:

There is no reason why I should expatiate on the pleasure and delight
of acquiring knowledge of plants, since there is no one who does not
know that there is nothing in this life more pleasant and delightful
than to wander over mountains, woods and fields garlanded and
adorned with most exquisite little flowers and plants of various sorts.
. . . But it increases that pleasure and delight not a little, if there be
added an acquaintance with the virtues and powers of these plants. 1

Fuchs' observation ends with a touch of that pedantry which has
always divided the scientist from the artist; the scientific tendency
is, after all, to dissect and destroy the thing of beauty, but there is
no reason to doubt that the intellectual inquisitiveness which leads
via microscope and herbarium to the unreadability of a Flora, may
have its aesthetic foundation. This also links naturally with the
urge to collect and preserve, the emphasis upon the rare and the
expensive, which are so typical of biology from the sixteenth to
the nineteenth century. Collector's mania has often been derided,
yet it may yield genuine scholarship, as in (for example) the study
of ceramics or bibliography. The botanist's character was more
complex. He could claim that his activities were useful to man,
and contributed to the worship of God. If Sir Joseph Banks'

1 De Historia Stirpiwn (Basel, 1542), Preface, sig. aav. Quoted by A. Arber:
Herbals (Cambridge, 1953), p. 67.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 281

attempts to transplant the breadfruit to the West Indies were
vain, naturalists had great success with tobacco, the potato, maize
and innumerable ornamental species. In nature they saw abund-
ant evidence of Design, and so created the tradition which led
through Ray's Wisdom of God to Paley's Natural Theology, or
Evidence of the Existence and Attributes of the Deity , collected from the
Appearances of Nature. There was thus a variety of arguments for
commending biology to the attention of a serious and devout
mind, of which medical utility was not the least important. Few
naturalists in this period would have given whole-hearted support
to the views of the Bohemian, Adam Zaluzian (1592):

It is customary to connect Medicine with Botany, yet scientific treat-
ment demands that we should consider each separately. For the fact
is that in every art, theory must be disconnected and separated from
practice, and the two must be dealt with singly and individually in
their proper order before they are united. And for that reason, in
order that Botany, which is (as it were) a special branch of Natural
Philosophy, may form a unit by itself before it can be brought into
connection with other sciences, it must be divided and unyoked
from Medicine. 1

The task of the descriptive biologist was also far more complex
than that of the cataloguer of human artifacts, indeed, it was this
complexity which enforced the development of systematics. Prob-
lems of nomenclature, identification and classification rather
suddenly became acute between 1550 and 1650, and constituted
one of the main theoretical topics in biology for nearly three
hundred years. Naturalists tried to follow a "natural" order of
groupings which meant that they were long deceived by superficial
characteristics. Aristotle had distinguished, in zoology, between
viviparous and oviparous creatures, between the cephalopodia and
other molluscs; Dioscorides had distributed plants among the four
rough groups of trees, shrubs, bushes and herbs. Lesser distinc-
tions, between eggs-with-shells and eggs-without-shells, between
deciduous and non-deciduous, flowering and non-flowering, were
also very ancient. In the main such distinctions were preserved as
the basis of arrangement until late in the seventeenth century.
Nomenclature was equally in need of reform, if standardization
was to be obtained, and the name to have a logical connection
with the system. Description was the very basis of a communion
1 Methodi Herbaria Libri Tres, quoted in Arber, op. cit., p. 144.

282 THE SCIENTIFIC REVOLUTION

of understanding in biology, for on it depended the hope of arriv-
ing at a single comprehensive Flora which would enable all men
to agree upon the identity of any given specimen. Here the classical
tradition was very frail, partly owing to the defects of its language
in referring to the parts of animals and flowers.

No consistent answers to the problems of taxonomy were pro-
duced before the eighteenth century; even today the concept
"species" cannot be exactly defined, and many systems of classifi-
cation have succeeded that of Linnaeus. Nevertheless, the great
compilers of the sixteenth century, in their attempts to make an
encyclopaedic survey of all living things, more than mastered
their Greek inheritance and demonstrated the fruits of exact ob-
servation. Their view of their undertaking was of course far from
strictly biological. Thus Conrad Gesner, in his enormous Historic
Animalium (published 1551-1621), besides naming and describing
the animal, discussed its natural functions, the quality of its soul,
its use to man in general and as food or medicine in particular, and
gave a'concordance of literary references to it. The Italian natural-
ist Ulissi Aldrovandi strove for even deeper omniscience when (for
example) writing of the Lion he noted at length its significance in
dreams, its appearance in symbolism and mythology, and its use
in hunting and tortures. But Aldrovandi was also one of the first
zoologists to give a skeletal representation of his subjects where
possible. Along with the spirit of sheer compilation there developed
a growing tendency to specialize, exemplified in Rondelet's book
on Fishes (1554), in Aldrovandi's treatise on the different breeds
of dog, in the Englishman Thomas Moufet's Theatre of Insects
(I634J. 1 All these works, and some portions of the vast encyclo-
paedias, were written with conspicuous attention to the kind of
detail that could only be obtained through systematic personal
observation. Most of the old fables debasing natural history the
birth of bees from the flesh of a dead calf, and of geese from
barnacles, the inability of the elephant to bend its legs, and the
tearfulness of crocodiles were at least doubted, though they
lingered long in popular books.

The classification of animals in accordance with Aristotle's
scheme presented no great difficulties. The Latin names gave
sufficient identification, superficial distinctions were marked. In the

1 This, written about forty years earlier, was largely the work of Thomas
Penny (c. 1530-88).

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS 283

group of oviparous quadrupeds, for instance, Gesner had only a
few divisions frogs, lizards, tortoises and he knew only three or
four different kinds in each. Plants were more recalcitrant. Alpha-
betical lists had their uses, and so had others in which the groups
consisted of plants having a similar habitat or function. When the
attempt was made to render identification easier by adopting
arrangements based on form and structure, more profound diffi-
culties were encountered. In general, it seemed desirable to make
the arrangement as natural as possible, by taking into considera-
tion the maximum number of characteristics, but it was difficult
to decide what the most important of these were. Reliance on
superficial features, like the possession of prickles, or habits like
climbing, was apt to prove very deceptive. The early systematists
consequently tended to make increasing use of a single character-
istic of the plant as a determinant de 1'Obel chose the leaf, and
Cesalpino the seed. One advantage of this method was that it led
to the more intensive study of particular parts of the plant, espe-
cially the flower, and to the improvement of descriptive termi-
nology. Such systems, of which Linnaeus' was the logical and
highly successful climax, were artificial, convenient indices to the
prodigality of nature; but they did promote conscious study of
the problems of taxonomy. Before 1550 there were hardly any
firm principles by which species were distinguished, while the
arrangement of the species was a matter for the discretion of
each author. By 1650 there was a great measure of agreement on
specific identities, and it was gradually becoming clear that
there was a difference between a search for a method, which would
make identification easy, and an endeavour to trace the natural
affinities between species and larger groupings.

Attention to systematics was partly enforced by the sheer multi-
plicity of species. Some six thousand distinct plants had already
been described by 1600, and the number trebled during the follow-
ing century. Since it was the pride of the good botanist to be able to
identify every plant presented to him, or if it were a new species to
indicate its relationship to known ones, there were strong reasons
for correlating identification and arrangement with one or more
morphological characteristics. Caspar Bauhin, in 1623, outlined
the natural groupings of botanical species more clearly than any
of his predecessors, and made more extensive use of the binomial
nomenclature in which one element of the name was shared by the

284 THE SCIENTIFIC REVOLUTION

genus, or group of closely related species. A little later Jung, at
Hamburg, greatly improved the technical description of the dis-
position and shape of leaves, and of the various parts of the flower.
A younger contemporary, the Englishman John Ray (1627-1705),
laid the foundations of modern descriptive and systematic biology,
in botany at least owing something to Jung's methods. Ray had
some experience of dissection, but he was not an experimenter, nor
a microscopist. Though his interests extended to the ecology, life-
history and physiology of his subjects thus he was much more
than a plain cataloguer he did not himself do much to advance
the newer branches of biology growing up in his time. On the
other hand, his philosophic and general scientific outlook was
wider than that of most succeeding naturalists; like many other
Fellows of the Royal Society, he was fascinated by technological
progress, accepted the broad picture of a mechanistic universe
under divine surveillance, and joined in the expulsion from biology
of myth and mystery.

Ray was perhaps the first biologist to write separate treatises on
the principles of taxonomy. 1 These were exemplified in his great
series of descriptive volumes, the Historia generalis plantamm (1686-
1704) and Historia insectorum (1710), with the Ornithologia (1676)
and Historia Piscium (1686) in which he collaborated with his
patron, Francis Willughby. Taken together for all these books
were actually written and published by Ray they represented
by far the most complete and best arranged survey of living nature
that had ever been attempted. Ray had exercised his keen faculty
for observation intensively over the whole of England, and ex-
tensively over much of western Europe; he was deeply learned in
the writings of ancient and modern naturalists; above all, he wel-
comed new ideas. From Grew he accepted as probable the sexual
reproduction of plants; from Redi and Malpighi the experimental
disproof of spontaneous generation; and he himself taught that
fossils were the true remains of extinct species, not mere "sports"
of nature nor God-implanted tests of man's faith in the truth of the
Genesis story. If the enumeration of species was his principal task
which still left him room for his Collection of English Proverbs,
Topographical Observations, and Wisdom of God Ray was very far
from supposing that classification was the end of biology..

In botanical systematics Ray favoured a "method" which was

1 Methodus plantarum nova (1682); Synopsis methodica animalium quadrupedum et
serpentini generis (1693); Methodus insectorum (1704).

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS

more natural than those of his contemporary Tournefort and his
successor Linnaeus. He admitted that the familiar triple distinc-
tion between trees, shrubs and herbs was popular rather than
scientific, though he continued to use it while also making the far
more fundamental distinction between mono- and dicotyledonous
plants. For finer discrimination he relied upon no single character-
istic but appealed to the forms of root, leaf, flower and fruit. The
necessity for a formal method of classification was fully apparent
to him it was particularly required by beginners in botany

3^

o tJ I Large

r! ?* ,~ ^

S3 fe

(Polypi, Crustacea)

Small
Jj ' (Insects)

'With Lungs

Without Lungs

^ (Fishes)

One ventricle

Heart

(Oviparous quadrupeds,
Serpents)

/Oviparous
(Birds)
Two ventricle
, Heart

Viviparous
\ [Mammals]

f Cetaceans

With hoofs etc.
(Ungulates)

With nails etc.
^(Unguiculates)
Fig. 10. Ray's Classification of Animals

but he did not expect that all living forms could be perfectly ac-
commodated within it. Taxonomists would always have difficulty
with 'species of doubtful classification linking one type with an-
other and having something in common with both.' 1 In zoological
classification Ray was perhaps even more successful, through
basing his groups upon decisive anatomical features. He was the
first taxonomist to make full use of the findings of comparative
anatomy, particularly among mammals 2 and with regard to such
characteristic features as feet and teeth, thereby discerning such
groups as the Ungulates, Rodents, Ruminants, etc. (Fig. 10). This
part of his work was freely adopted by Linnaeus.

1 Cf. the Preface to Methodus Plantarum, and C. E. Raven: John Ray t Naturalist
(Cambridge, 1950), Ch. viii.

2 This class was recognized by Ray, though not given this name.

286 THE SCIENTIFIC REVOLUTION

Meanwhile, the naturalist's range of observation was being
vastly extended by the microscope (Chapter 8). In the use of this
instrument the primary emphasis was still on description; at this
stage, attempts to construct elaborate theories upon the new evi-
dence were infrequent and misleading. There was opportunity for
the ramification of activity, and it was not neglected. The study
of plant anatomy, originally enforced by the need for classificatory
systems, could now proceed to the structure of tissues and repro-
ductive mechanisms; zoological anatomy, likewise, stimulated by
the fertility of the comparative method as shown by Harvey and
many before him, was extended to strange creatures like the "orang-
outang 55 (dissected by Dr Edward Tyson), 1 and, with the aid of the
microscope, to levels of detail inaccessible to the naked eye.

Most of this new work prolonged existing tendencies. Marcello
Malpighi (1628-94), for example, completed Harvey 5 s discovery
of the circulation of the blood by following its passage from the
arterial to the venous system through the capillary vessels, at the
same time observing its red corpuscles. He was also able to go
farther than Harvey and Fabricius in examining the microscopic
foetus of the chick within the first hours of incubation, from which
he was led to believe that growth was a process of enlargement or
unfolding only: the foetus was "pre-formed" in the unfertilized
egg. 2 As a pioneer of histology Malpighi entered on less familiar
ground, in his microscopic examinations of the liver, the kidney,
the cortex of the brain, and the tongue, whose " taste buds 5 ' he
discovered. In the study of insects where Aristotle had shown
wonderful insight the serious scientific curiosity in which Mal-
pighi was joined by Jan Swammerdam (1637-80) had already
been anticipated by Hooke in Micrographia, and by even earlier
virtuosi with their " flea-glasses." These two naturalists, however,
were the first to explore fully the internal anatomy of minute
creatures, demonstrating that their organs are as highly differenti-
ated as those of large animals. Malpighi's treatise on the silkworm
has been described as the earliest monograph on an invertebrate;
in it he indicated the function of the trachea first observed by him,
which distribute air about the insect's body, and of other tubes by

1 Cf. M. F. A. Montagu, Edward Tyson, M.D., F.R.S. 1650-1708 (Memoir
XX, Amer. Phil. Soc., Philadelphia, 1943). The creature was, in fact a
chimpanzee. Tyson also published monographs on the "porpess", rattlesnake,
opossum etc.

2 Joseph Needham: History of Embryology (Cambridge, 1934), pp. 144 etseq.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 287

which the products of metabolism are excreted. He did much
work on the anatomy of the larval stages of insects, and observed
their evolution to maturity, but here he was excelled by Swammer-
dam, who also denied that there was any true transformation, even
in the emergence of the butterfly from the caterpillar, or of the
frog from the tadpole processes which he studied with enormous
care. In sheer technical skill exemplified in the quality of his
drawings as well as in the fineness of his dissection under the lens
and his unique methods of injection Swammerdam foreshadowed
the greater manipulative resources of the mid-nineteenth century.
Leeuwenhoek is chiefly remarkable for his work at much higher
magnifications and the discovery of a new world inhabited by
Infusoria and Bacteria (p. 241), but the ubiquitous curiosity which
led him to examine hairs, nerves, the bile, parts of plants, crystals
indeed almost everything that could be brought before his
lenses induced him to make some observations comparable to
those of Malpighi and Swammerdam, among which those on the
compound insect eye and on ants were particularly novel. From
observations on aphids he discovered parthenogenesis in animals
reproduction by the female parent alone.

In the plant kingdom, the microscope could not reveal a new
order of magnitude within the living state, as it did in the animal;
on the other hand, a much clearer idea of the structure of plant
tissues emerged including the description of their minute com-
ponents, the cells than was yet obtained in zoology. The pre-
sumed anatomical and physiological analogies between animals
and plants were indeed powerful incentives to inquiry at this
time. Sometimes analogy was wholly misleading, as with the
theory (popular until disproved by repeated experiments) that
the sap in plants circulates like the blood in animals, but in other
aspects, as when the " breathing" of plants was compared with
that of animals by Malpighi and later by Stephen Hales (1679-
1761), it led towards a more correct understanding. Malpighi,
despite the excellence of his descriptions of the differing structures
found in wood, pith, leaf and flower under the microscope, and
of the germination of seedlings, thought too exclusively in terms
of the animal form. Thus he wrongly identified the function of the
spiral vessels that he observed in plant tissue with that of the
tracheae in insects, and erected upon this identification a broad
theory of the increasing specialization of the respiratory organs,

288 THE SCIENTIFIC REVOLUTION

reaching its climax in mammals. He also tried to find in plants
the reproductive organs familiar from vertebrate anatomy. The
Englishman, Nehemiah Grew (1641-1712), whose independent
work is closely parallel to that of Malpighi, and of equal quality,
was a more restrained observer, though he believed (as he quaintly
wrote) 'that a Plant is, as it were, an Animal in Quires, as an Animal
is a Plant, or rather several Plants, bound up into one volume ' a
remark which, however strange the metaphor, expresses profound
intuition.

Grew was well aware, not only that the aims of ordinary natural-
ists still fell far short of attainment, but that these aims by no
means amounted to a true "Knowledge of Nature." His Philosophical
History of Plants (iSjz) 1 sketched a new and far more ambitious
programme. Many of the problems he proposed remain unsolved:

First, by what means it is that a Plant, or any Part of it, comes to
Grow , a Seed to put forth a Root and Trunk. . . . How the Aliment
by which a Plant is fed, is duly prepared in its several Parts. . . . How
not only their Sizes, but also their Shapes are so exceeding various. . . .
Then to inquire, What should be the reason of their various Motions;
that the Root should descend; that its descent should sometimes be
perpendicular, sometimes more level: That the Trunk doth ascend, and
that the ascent thereof, as to the space of Time wherein it is made, is
of different measures. . . . Further, what may be the Causes as of
the Seasons of their Growth; so of the Periods of their Lives; some being
Annual, others Biennial, others Perennial . . . and lastly in what
manner the Seed is prepared, formed and fitted for Propagation.

Some of these questions Grew himself tried to elucidate, most
brilliantly deducing that plants reproduce sexually, the flowers
being hermaphrodite like snails, with the stamens acting as the
male organs. 2 Nor did he neglect the possibility of examining the
plant substance by combustion, calcination, distillation and other
experimental methods of chemistry, though these were as yet too
primitive to be of real service. In this way he showed that the
matter of the pithy or starchy part of the plant was quite distinct
from that of the woody or fibrous part. Like Ray and other
naturalists Grew saw no reason to reject mechanism as a working

1 Reprinted in The Anatomy of Plants (London, 1682).

2 Op. cit., pp. 171-3. Hermaphroditism is not, of course, universal among
plants, as Grew thought.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 289

hypothesis which he developed (for example) in his account of
plant nutrition; as he put it, with a familiar simile:

[We need not think] that there is any Contradiction, when Philosophy
teaches that to be done by Mature:, which Religion, and the Sacred
Scriptures, teach us to be done by God: no more, than to say, That
the Ballance of a Watch is moved by the next Wheel, is to deny that
Wheel, and the rest, to be moved by the Spring ; and that both the
Spring, and all the other Parts, are caused to move together by the
Maker of them. So God may be truly the Cause of This Effect, although
a Thousand other Causes should be supposed to intervene: For all
Nature is as one Great Engine, made by, and held in His Hand. 1

A general sketch of the horizon in biology about the year 1 680
would show virile activity, a steady expansion of the sphere of
interest, and the fruitful exploitation of new techniques. Ad-
mittedly Man was still the prime focus of attention, whether in
the Royal Society's endeavour to introduce a scientific spirit into
agriculture, or in the relics of the belief (still held by a plant-
anatomist like Grew) that all vegetables have "virtues," or in
the frequent backward glances of the zoologist at the human
body. Nevertheless, as the peripheries rapidly became more remote
they assumed, as it were, a territorial autonomy. The survival of
anthropocentricity in the feverish concentration of Swammerdam
was small. It is significant that naturalists no longer defended
their preoccupations as useful, but rather as contributions to
knowledge of the universe, of the organic part of the divinely
created machine. And, though description and cataloguing of
macroscopic flora and fauna remained their principal tasks,
natural history showed clear signs of entering into partnerships
in which the skills of the human anatomist and physiologist,
the chemist, and the physicist, should be placed at its service.
Gradually, through the seventeenth century, biology had returned
to the philosophic attitude of an Aristotle; now it seemed likely
that the borrowing of modern knowledge and techniques would
permit the ancients to be as greatly excelled in these sciences as
in physics and mechanics.

Briefly, there was promise a promise of growth in depth and
extent that was hardly fulfilled during the next century and a
half. That it was not fulfilled may be attributed partly to the

1 Op. tit., p. 80.

19

2 go THE SCIENTIFIC REVOLUTION

fallaciousness of the early hopes, for neither microscopic technique,
nor chemical experiment, were capable of changing the pattern
of activity so permanently as the work done during the two
decades 1660-80 would suggest. These crude tools were soon
blunted. The close connection between biology and medicine,
which had encouraged study of the former science in the seven-
teenth century, tended to hamper its later development, for as
medical studies were permeated by the influence of Galen's ideas
until the nineteenth century, it was impossible that animal and
plant studies should escape the limitations of those ideas. Unable,
as yet, to build freely upwards upon the half-finished foundations
of their predecessors, eighteenth-century naturalists might well
be discouraged by the splendour of their inheritance. Discourage-
ment was all the more harsh because this inheritance included
such a feeble element of hypothesis to serve as a scaffolding for
their own researches. Thereafter it is not surprising that they felt
strongly a positive attraction that was both old and new. Like the
sixteenth-century encyclopaedists, they were subjected to a vast
incursus of new species, fruit of a renewed urge towards explora-
tion that drove Linnaeus into the sub-arctic tundra, and Joseph
Banks to the Pacific and Australasia. Moreover, this invasion
synchronized, not with a sense of confusion before the profligacy
of nature, but with an increasingly dogmatic confidence in a
System, the system of Linnaeus. Quite suddenly, about the middle
of the century, classification became one of the easiest, instead of
one of the most difficult, biological exercises. Not for the first or
the last time in science there was a rush to gather the harvest,
while the unbroken fields were neglected.

Admittedly, there was no very abrupt transition. In the early
part of the century Leeuwenhoek was still active, and a little later
Reaumur, one of the most versatile experimentalists of any age,
began to publish his monumental Memoir es pour servir d Vhistoire des
Insectes (1737-48) which continued the work of Malpighi and
Swammerdam. Low-power microscopy was applied to aquatic
subjects by Trembley, who experimented upon the capability
for regeneration and asexual reproduction by budding that he
discovered in fresh- water " polyps" (Hydra and Plumatella) , x and
by Ellis (Natural History of the Corallines, 1755). Plant physiology

1 Mtmoires pour servir d Vhistoire d'un genre de polypes d'eau douce ( 1 744) ; cf.
J. R. Baker: Abraham Trembley of Geneva (London, 1952).

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS 291

was studied by Hales with the aid of quantitative physical methods
largely derived from Boyle (Vegetable Staticks, 1727). He measured
the upward pressure of the sap in the roots of plants, the quantity
of water absorbed by the root and transpired by the leaves, and
the rate of growth in different structures. He proved that some
atmospheric substance entered into the composition of plants.
Such experiments he tried to elucidate mechanically by others on
the capillary attraction of water in fine tubes and porous sub-
stances; somewhat similar ones were extended to the circulation
of the blood in his Htemostaticks. Further important contributions
to physiology were made by the contemporary chemist-physicians
G. E. Stahl, Friedrich Hoffman and Hermann Bocrhaave, who
also continued a seventeenth-century tradition.

The physiological processes involved in reproduction and the
formation of the embryo, in particular, remained a matter for
heated controversy, on much the same lines as in the seventeenth
century. In J. T. Ncedham spontaneous generation had a new
champion, who found microscopic animalculae in boiled broth
that was (as he thought) effectively sealed from the air (1748). He
was answered in more precise experiments by Spallanzani (1767),
but this question was not regarded as decisively settled up to the
time of Pasteur. The great debate between Ovists and Animal-
culists was more widespread, and even less fruitful. Harvey had
believed in epigenesis, that is, that the growth of the embryo
proceeded both by the gradual differentiation of its parts, and by
their increase in size: 'there is no part of the foetus actually in
[the egg], yet all the parts of it are in [the egg] potentially.' The
effect of microscopy, soon after Harvey's death, was to give
immediate advantage to the alternative theory of preformation,
according to which the embryo merely swelled from being an
invisible speck which was from the first completely differentiated;
as Henry Power said: ' So admirable is every organ of this machine
of ours formed, that every part within us is intirely made, when the
whole organ seems too little to have any parts at all.' Preformation
was developed especially by Malpighi and Swammerdam. Since
the embryo, among oviparous creatures, develops in the maternal
egg, and microscopists believed that the first signs of its future
form could be detected as soon as the egg appeared, it was natur-
ally assumed by them that the embryo, or potential embryo, was
solely derived from the female. This view conveniently opposed

292 THE SCIENTIFIC REVOLUTION

the unfashionable Aristotelean conception that the male, supplying
the active "form," was the prime agent in generation, and
the female responsible merely for the passive "substance" of the
offspring. Aristotle seemed to be further confounded by the
discovery of the mammalian ovum attributed to De Graaf (1672).
This supposed discovery was premature De Graaf saw the
follicles since known by his name, and the true ovum was first
described by von Baer a century and a half later. However, it
brought about an essentially correct change of thought, to the
view that both viviparous and oviparous reproduction begin with
the fertilization of an egg formed in the female. According to
the Ovists, the ovum contained the embryo not potentially but
actually, and in the version of their theory known as emboitement
they supposed that this held within its own organs the ova of the
next generation, and so on ad infinitum like a series of Chinese
boxes: in the ovaries of Eve were confined the future forms of all
the human race.

The discovery of spermatozoa opened up a contrasting but
parallel theory. Leeuwenhoek, in one of his rare flights of hypo-
thesis, suggested that these "little animals" were the living
embryos, which were enabled to grow by transplantation into the
egg: c If your Harvey and our De Graaf had seen the hundredth
part they would have stated, as I did, that it is exclusively the
male semen that forms the foetus, and that all that the woman
may contribute only serves to receive the semen and feed it.' 1 He
supported this doctrine by reference to well-known cases where
the offspring was strongly marked with the characteristics of the
male parent. Hartsoeker (1694) and Plantades (1699) the last
perhaps as a deliberate fraud published illustrations of a
"homunculus" enclosed in the head of a spermatozoon. Emboite-
ment was also taken up by the Animalculists in the eighteenth
century. Rival interpretations of observations that were commonly
very imperfect and carelessly recorded continued for over a
hundred years. Some regarded the spermatozoa as products of
corruption, like the eel-worms in vinegar, for it was only in 1824
that they were proved essential to fertilization by Dumas and
Provost; at about the same time the experiments of Geoffroy
Saint-Hilaire on the production of monsters proved that the

1 Letter to Nehemiah Grew, 18 March 1678. Collected Letters, vol. II,
(Amsterdam, 1941), p. 335.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 293

appearance of the embryo is not preformed or predestined. At an
earlier date the scientist-mystic Swedenborg favoured epigenesis
(c. 1740), and more powerful support came from the researches
of Caspar Wolff at St. Petersburg (1768), who pointed out that,
as in plants the rudiments of flowers develop from undifferentiated
tissues and are at first undistinguishable from those of leaves, so in
animals no miniature foetus could be found in the earliest phase
of development, after which the nervous system, the blood-vessels,
and the alimentary canal were observed to arise in successive
stages. Generally speaking, however, the reaction against pre-
formation (and the consequent expiry of the Ovist-Animalculist
controversy) did not occur until the close of the eighteenth century,
although, as F. J. Cole has said, the admirable iconography of
Malpighi carried its own refutation of its author's doctrines. 1

In most other branches of biology the eighteenth century
appears equally unproductive of truly creative investigation. In
its more medical aspects, such as human and comparative
anatomy, and human physiology, the successes of the seventeenth
century were extended, particularly during the last two decades.
Lavoisier, for example, was able as a result of his new theory of
combustion to throw fresh light on animal respiration. But the
greatest biological achievement of the period, that which won the
greatest fame and attracted the greatest number of pupils, was
certainly that of Carl Linnaeus (1707-78). His mastery of the
order of nature 'God,' as he complacently acknowledged, 'had
suffered him to peep into His secret cabinet ' touched the imagi-
nation of a generation already turning towards a romantic
naturalism, which was soon to cherish Gilbert White and Thomas
Bewick, to prefer landscapes to portraiture, and to talk contentedly
of the noble savage. Linnaeus was the prophet of Wordsworth.
His arrogance, like Samuel Johnson's, enslaved admiration, while
the confidence with which he wrote as though personally present
at the Creation was the more acceptable (in that, in all respects,
it reassured the somewhat conventional religious conscience of the
age) because it counteracted the scientific agnosticism of Voltaire
and the French pkilosophes. Most of the major advances of science
have, in one way or another, imperilled the comfortable security
of the popular understanding. One great merit of Linnaeus' in-
tellect was that, save in his great gift for classification, it was
1 F. J. Cole: Early Theories of Sexual Generation (Oxford, 1930), p. 147.

294 THE SCIENTIFIC REVOLUTION

remarkably undistinguished; he had neither the wish nor the
power to e* pater les bourgeois.

That does not detract from the importance of his work. Linnaeus
was a sincere amateur of nature in all her moods; a competent
teacher of many subjects in biology and medicine, able to inspire
affection and devotion in his students; a voluminous and lucid
writer. Like Newton, he possessed a strong, though not wholly
attractive, character. Like Newton too, he saw the essentials of a
problem and solved it. And he was only slightly less dominant
than Newton in forcing future naturalists to follow the path that
he had cleared.

The Linnean systems of classification embraced the animal, vege-
table and mineral kingdoms, and even diseases. Of these the
second was by far the most complex, and the most influential. It
was derived by applying to the immense descriptive materials
amassed by Ray, Tournefort and others of his predecessors the
principle of plant sexuality firmly demonstrated by the experiments
of Camerarius (1694). Thus plants were distributed into twenty-
four Classes according to the number, proportions or situations of
the stamens (male organs), and each Class further subdivided in
accordance with the number of styles (female organs) . The first
three Classes in this system were Monandria (i stamen), Diandria
(2 stamens), and Triandria; the Class Polyadelphia had "stamens
united by their filaments into three or more sets." In each Class
plants with one style were assigned to an Order named Mono-
gynia, those with two to the Order Digynia, those with three to
the Order Trigynia, etc. Each Order, easily determinable by in-
spection of the flower, contained a number of genera, which
groups Linnaeus regarded as primary and as "naturally" distinct.
Each genus had a brief description of the features common to all
the species included in it, mainly derived again from the method
of fructification. In further division into species the shape of the
leaves and other characteristics became important. For example,
Genus 696 in Linnaeus' System of Mature is found in the Class Hex-
andria, Order Monogynia; it is called Berberis, and is distinguished
by "Calyx 6-leaved, petals 6, with two glands at the base of each,
style o, berry superior, 2-seeded." In this genus Linnaeus reported
five species, one European, one Cretan, one Siberian, and two
from Tierra del Fuego.

The main principles of this classification apparently became

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 295

clear to Linnaeus at an early age, and were worked out with the
aid of the experience gained in the course of his journey through
Lapland ( 1 732) and during later European travel. The first version
of the System of Nature (1735) was written in Holland when he was
acting as botanical curator to Boerhaave. The illustrations of the
principles were extended vastly in the subsequent editions which
speedily issued from the press. (The tenth, of 1758, is now the
standard work of reference.) The utility of the work depended
very much upon the rigidly methodical, and extremely succinct,
descriptions, which in turn were made possible by the use of a
technical terminology that was largely of Linnaeus' own creation.
He also paid great attention to nomenclature:

As I turn ovei the laborious works of the authorities, I observe them
busied all day long with discovering plants, describing them, draw-
ing them, bringing them under genera and classes: I find, however,
among them few philosophers, and hardly any who have attempted
to develop nomenclature, one of the two foundations of Botany,
though that a name should remain unshaken is quite as essential as
attention to genera. 1

The rules which Linnaeus drew up for coping with this problem
anticipated in part those now accepted by international agree-
ment, and within a few years his binomial system was universally
accepted among naturalists.

The Linnean Order was determined by a purely mechanical
procedure. To it might be assigned thousands of different plants.
How were the further distinctions to be defined, and the lines
drawn between mere differences of variety, those of species, and
those of genus? Even post-Linnean taxonomy has not succeeded
in drawing such lines firmly, and in practice Linnaeus made much
use of earlier experience. The concept of species is indeed some-
thing that can easily be grasped intuitively Aristotle had it in
perfect clarity for in very primitive languages the kinds of ani-
mals and plants are named even though the general concept
"plant" or "animal" is lacking. In surveying kinds of creatures,
it is not difficult to see why dog, wolf and hyena are more like each
other than any member of another group containing lion, tiger
and panther. The difficulty arises as the analysis of what consti-
tutes an effective likeness or unlikeness has to be made finer and

1 Critica Botanica, translated by Sir Arthur Hort, Ray Society (London, 1938) ;
Preface.

296 THE SCIENTIFIC REVOLUTION

finer: should the wolf (which is interfertile with the dog) be placed
in the same genus with the pekinese? Linnaeus realized that though
the species is the fundamental unit of taxonomy, the assignment
of the generic boundaries is the classifier's most tricky task. Here
he could offer no rigid rules, though he stated certain negative
propositions, and therefore his success was empirical rather than
theoretical. His system could be made to work, but because generic
groupings depended upon one man's notion of significant simili-
tude, it was far from infallible.

Although unable to define the characteristics of a species and a
genus precisely, Linnaeus did associate ideas with each of these
concepts that were received as dogmatic truths up to the time of
Darwin. Some had long been current without winning universal
credence. The most important of them was the fixity of species,
which Ray had not admitted. In Linnaeus' view each species
represented the descendants of an original entity, or pair of enti-
ties, individually created at the beginning of the world. Its flora
and fauna had always been exactly as they are now, and hence
the concept of species was justified (if not, in practice, defined) by
common descent from a unique created form, just as humanity
was defined by common descent from Adam. Equally, the disap-
pearance of species was ruled out, despite the evidence of fossils,
which were thus denied an organic origin. 1

Until late in life Linnaeus regarded the production of fertile,
stable hybrids by crossings between members of the same genus as
impossible; intergeneric hybrids were unthinkable. Shortly before
1 760 new evidence led Linnaeus to believe that new species could
arise have arisen through differentiation by crossing. Perhaps
after all only the ancestors of the Orders were created but he
never perfected this thought, of which he seemed ashamed, and
though he withdrew from subsequent editions of the System of
Nature confident statements that new species never occur, the
recantation came too late. It is strange that the chief legacy of
Linnean biology, the main scientific argument against Darwin, was
a doctrine in which the mature Linnaeus had himself lost faith. 2

1 Linnaeus was more orthodox than Steno, Hooke, Ray and others who
admitted that living species represented only by fossilized shells, teeth or bone
had disappeared from the world, incompatible as this seemed with divine
Providence, and the care taken to preserve all the land-anima'ls at the time of
the Flood.

2 Gf. Knut Hagberg: Carl Linrueus (London, 1952), Chapter XII.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 297

It is important to recollect that there was already, before the
end of the century, significant opposition to the doctrine of the
immutability of species. Evolutionary ideas were first applied to
the formation of the earth's crust, not its peopling with creatures.
Descartes and Leibniz, Burnet and Whiston, had each before 1 700
devised an hypothesis to account for the separating out of rock and
water from an incandescent mass or primitive chaos, and traced
the depression of ocean-beds, the elevation of mountain ranges, to
the action throughout long periods of purely mechanical forces,
though the time-scale imagined was absurdly short. The first two
of these ignored the story of the Flood completely. Fossils, if ac-
cepted as organic remains, enforced the conclusion that species
had either changed, or disappeared. The great French naturalist,
Georges Cuvier (1769-1832), who founded the science of palaeon-
tology, favoured the second hypothesis. Successive catastrophes
of which the Biblical Flood was the most recent had swept the
earth of life; successive creations had re-peopled it with new
species. His influence, more than any other, reinforced that of
Linnaeus in deriding evolutionary ideas, and in creating the in-
tolerant assurance in immutability which faced Darwin. But his
compatriot Buffon (1707-88), a man of less pretentious scientific
authority, whose main effort was directed towards descriptive
biology in the forty-four volumes of his Histoire Naturelle (once im-
mensely popular, now a dead weight in booksellers' basements)
chose the alternative explanation. For Buffon, as for Aristotle and
Ray, the living process became more complex by infinitesimal
gradations: 'Le polype d'eau douce sera, si Ton veut, le dernier
des animaux et la premiere des plantes.' The power to reproduce
in kind, and to grow, he regarded as the prime characteristic of
the living state. This power resided in "organic molecules," the
basic units of both plants and animals; death was the dispersion
of these molecules, nourishment their assimilation into the body
of the creature. Denying preformation in all its aspects, Buffon
asserted that the segregation of the " organic molecules" in the
sexual organs was the cause of reproduction, just as, in a different
way, it caused the generation of parasites. The organic molecules
had been the same since the beginning of the world; but, as he
stressed in his fipoques de la Nature, the world itself had altered,
evolved. In the Fifth Epoch elephants had roamed the far north;
the earth was hotter in its youth, and of greater vitality. Animals

298 THE SCIENTIFIC REVOLUTION

were larger, witness the ammonites big as cartwheels, the huge
tusks found in Siberia, perhaps even man was then a giant. In
general, Buffon imagined that the change in nature was towards
degeneration, but he was acute enough to see that where human
purposefulness had intervened, species had been changed for the
better. Bread-wheat, for example, was not a gift of nature, for it is
unknown in the wild state; it is evidently a herb brought to per-
fection by man's care and industry. ' Our best fruits and nuts ' he
wrote, ' which are so different from those formerly cultivated, that
they have no resemblance save in the name, must likewise be re-
ferred to a very modern date.' By selective breeding, man has in
a manner created secondary species which he can multiply at
pleasure.' Although, in such passages, Buffon seems to tread upon
the heels of Darwin, and although the fixity of species (together
with the taxonomical nicety attached to that doctrine) was alien
to his mind, he made no great play with the idea of evolution. It
was not, for him, an explanatory concept. He did not make it his
task to account for the origin of specific differences.

Thus, in a variety of ways, the elements of modern biology grew
out of the older natural history. Their growth was necessarily
spasmodic since it was not autogenous, the stages of the trans-
formation of the naturalist into the biologist being fixed by the
availability of techniques and ideas borrowed from physics, chem-
istry, medicine and philosophy. In the sixteenth century natural
history became a respectable branch of study; in the eighteenth it
was moulded into a formal discipline by Linnaeus; but the special
quality of the seventeenth century, which made biologists of men
like Harvey, Descartes, Hooke, Redi and Leeuwenhoek, who were
not naturalists, was the rich opportunity for opening up new sub-
jects, largely with the aid of imported methods. That the physical
science, and general intellectual climate, of the eighteenth century
had less in comparison to offer to the biologist was the chief reason
for the failure of these new subjects to continue their startling
initial progress.

The distinction between natural history and biology is not, of
course, recent. Aristotle was a naturalist in the History of Animals,
a biologist in the Generation of Animals. In the scientific renaissance,
the writings of such an embryologist as Fabricius clearly fall into
a different category from those of Gesner. But the distinction is

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 299

one which the events of the nineteenth century finally made plain.
Through this perspective, a man who studies the courtship of
birds is certainly a naturalist; another who examines the differ-
ences between bird-blood and mammalian blood who may not
know a teal from a tern is as certainly a biologist. The naturalist
takes the whole rural scene for his province, and is primarily
interested in creatures as individuals; the biologist is predomi-
nantly concerned to answer specific questions, and seeks general
truths. The biological sciences are descriptive indeed, in the same
sense, however, that the chemical sciences are descriptive for
they use concepts like "genes," "evolution," "photosynthesis"
which are as much the product of scientific inference as
"atom" or "polymerization." Natural history, on the other hand,
"describes" in the commonplace sense of the word; its concepts
like "mating," "hunting," "feeding young" are those of ordinary
thought, rarely the product of scientific inference. The naturalist
is indeed a trained observer, but his observations differ from those
of a gamekeeper only in degree, not in kind; his sole esoteric
qualification is familiarity with systematic nomenclature. 1

Natural history, as here differentiated from biology, seems at
the present time to be of small and shrinking scientific significance.
The naturalist has inevitably become dependent upon the deeper
insight of the biologist so that (for example) questions of classifi-
cation, after being his main concern since the sixteenth century,
have been radically modified during the last hundred years by
biological research into evolution and embryology. The introduc-
tion of new and more rigorous techniques, making large use of
the experimental method, has carved from the naturalist's former
province such subjects as ecology and animal psychology. In any
case, the observations of a Gilbert White are no more repeatable
than those of a Marcel Proust, and partly for the same reason that
their enduring interest resides in individual qualities of imagina-
tion and literary skill applied to a particular social setting. The
writing of natural history may continue, like that of the novel, ever
different and ever the same, but the evolution from it of scientific
biology could only happen once (or, more accurately, in successive

1 These distinctions are, it is recognized, subject to innumerable qualifica-
tions. In practice, many biologists share the naturalist's attitude in part, and
many naturalists the biologist's; more exact experimental methods are being
applied to field-work, etc.

300 THE SCIENTIFIC REVOLUTION

unique stages) just as the science of psychology could only emerge
once from the physician's interest in mental disorders.

The emergence of biology was certainly the leading contribution
of the scientific revolution to the study of living things. A totally
new kind of knowledge was thereby made possible, supplementary
to that already obtained through the renaissance of natural
history in the sixteenth century. Necessarily the first steps in this
emergence were mainly descriptive, in studies of comparative
morphology, minute anatomy and physiology, and the like. The
description of an animal or plant which permits its identification
may, however, be very different from a description of the same
creature in relation to an appropriate group of scientific in-
ferences. The structure of the hoof and leg of the horse may be so
depicted, or portrayed in words, that the member may be easily
distinguished from that of a dog; but to describe the same leg of
the horse in terms of its evolution by extension of the middle digit
of the foot and reduction of the side-digits is to embark upon a
very different procedure. Or, to take an example from mineralogy
(since this was a part of natural history until recent times) when
metallic ores have been classified and labelled under such names
as malachite, chalcocite or chalcopyrite, a new kind of knowledge
is brought in by assigning to them their appropriate chemical
formulae. Though these formulae are merely descriptive of the
composition of the minerals, they enable comparisons to be made
which are otherwise hidden.

A mineralist who considers gypseous alabasters, plaster stone, lamel-
lated gypsums, . . . and a great many other bodies as proper to be
distinguished from one another, and who is able to ascribe any
particular body to its proper species from considering its external
appearance, is possessed of a particular kind and degree of know-
ledge: He who besides being acquainted with the external appear-
ances, is able to prove that all these different bodies are composed of
a calcareous earth, united to the vitriolic acid; and thus makes several
species of things coalesce together, and unite, as it were, under one
general conception, hath a knowledge of these bodies different in
kind and superior in degree. 1

In the former example, appeal was made to the concept of
evolution, in the latter to the concepts of inorganic chemistry.

1 Richard Watson: Chemical Essays, vol. V (London, 1787), p. 127. Cf.
L. J. M. CoJeby in Annals of Science, vol. IX (1953), p. 106.

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 301

But the naturalist's description is sui generis, and all its complexity
is no deeper than that of an unfamiliar vocabulary.

At the close of the eighteenth century many of the procedures
followed by the biologist in the course of his still mainly descriptive
work as one may see from the investigations of Cuvier, of Haller,
of Lavoisier, of John Hunter already anticipated those of the
twentieth century. They were at least as "modern," by the same
comparison, as those of the contemporary physicist and chemist.
The great change has taken place in the intellectual framework
within which such procedures are ordered. Biology had, indeed,
successfully constructed an unco-ordinated group of scientific
inferences, but it was still devoid of basic guiding principles: or
rather, those which it possessed were derived from extra-scientific
sources. Comparable in this state to mechanics before the seven-
teenth century, the extent and the accuracy of the observational
material collected together was by 1800 far greater. The science
had followed a rather haphazard Baconian course, for although
information had been compiled piecemeal with great diligence,
the elucidation from it of keys to the understanding of living
nature had hardly begun. The "laws of nature" were as yet
purely inorganic: all the great theoretical principles of biology
have won their dominion during the last century. This being so,
it may be recognized that the chief difficulties confronting
biologists during the critical period 1750-1850 that in which
the influence of the natural-historian Linnaeus was at its height
were those of conceptualization; as, again, had been the case in
mechanics long before. The possibilities for significant theoretical
thinking open to men who accepted the futilities of emboitement or
the doctrine of successive catastrophes were as limited as those
available to the Aristotelean opponents of Galileo.

The similarity ceases, however, when the intrinsic difficulty of
establishing the "laws" of biology is compared with that of
clarifying the "laws" of mechanics. More mental effort is required
to grasp the necessity for the concept of evolution than to see the
plausibility of that of inertia; more important, it is possible to
justify the former only by elaborate discussion of varied and
obscure evidence. Darwin's Origin of Species has a very different
character from Galileo's Discourses on Two New Sciences. Darwin
devoted more than twenty years to the filling of note-books with
materials bearing on his problem, materials which were in part

302 THE SCIENTIFIC REVOLUTION

made accessible to him by a long tradition of descriptive natural
history, and which owed much to the taxonomical precision of
his authorities. He was himself an expert taxonomist. 1 Similarly,
the elements of the cell-theory were pieced together as the result
of an even greater mass of cumulative observation, extending to
the seventeenth century. The principles of biology could not
spring from the analysis of common and simple observations, as
did those of mechanics; and although it may truly be said that
much current research owes little directly to the tradition of
classificatory refinement stretching through and beyond Linnaeus,
its origin lies in descriptive work to which that refinement was
essential. A novelist does not need to be a lexicographer, but
dictionaries are an essential foundation of good literature.
Although biology has emerged from the natural history stage, its
methods are not, and perhaps can never be, identical with those
of physics. However great its development within laboratory walls,
it must always have room for those techniques of description and
discrimination with which the naturalists of the sixteenth century
first strove to create a science.

1 One reason for undertaking his monograph on the Cirrepedia (1851) was
to prove to himself (and the world) that he was no mere philosophical biologist;
though he afterwards doubted * whether the work was worth the consumption
of so much time.'

CHAPTER XI
THE ORIGINS OF CHEMISTRY

CHEMISTRY, as an integrated science with its own concepts,
its own techniques, and its own area of applicability, is a
product of the scientific revolution. The ancients, and their
medieval successors, had no such distinct science, though they
had much scattered empirical knowledge of this type, and some
theoretical ideas that would now be described as of a chemical
nature. Alchemy was not a primitive or pre-scientific chemistry,
for it was both less (in the restricted range of its pretensions) and
more (in its mystical affiliations) than a natural science. Chem-
istry, like biology, grew from a number of distinct roots, and
not by the expansion of a single tradition, as did mechanics and
astronomy. Hence the attempt to classify the sources of chemical
knowledge and theory in the early modern period becomes
complex, and shows that these had little relation to the sub-
divisions which now prevail. Researches of chemical significance
occurred in mineralogy, in physiology, in physics, in pharma-
cology, and most obviously in the development of technology.
Likewise, the concepts used by writers on chemistry before the
time of Lavoisier were often common property among natural
philosophers, rather than exclusive to their own science. Such is
the case with the four-element theory of matter, and with the
corpuscularian " mechanical" hypothesis; both were physical, or
rather cosmological, in origin. Chemistry, again like biology,
shows that a science gains stature as it acquires its own specialized
concepts as instruments of thought. Stage by stage, from the theory
of the three principles in the sixteenth century, through that of
phlogiston to the Lavoisierian notion of the chemical elements
and their combinations, the science developed coherence and
independence.

Hence the idea that there is a particularly chemical way of
studying matter and its properties, whether inorganic or organic
matter, was almost totally absent before the late sixteenth century,
and even then gained ground but slowly. Early speculations about

303

304 THE SCIENTIFIC REVOLUTION

the nature or composition of matter, and about the processes
involved when one kind of stuff is turned into another kind of
stuff, were a part of physics, as little empirical as the rest of physical
theory. They were scarcely at all connected with the practical
knowledge of certain groups of craftsmen. In a similar manner
it was far from obvious that a distinct science was required to
explain how the bread that man eats is transmuted into flesh and
bone. A pre-scientific physiologist might speak of " concoction"
in the stomach, but the term, though frequently used by chemists,
had no specific meaning. It was an empty word that described
nothing and explained nothing. When, however, certain experi-
menters adopted the belief that all metals are variously com-
pounded of sulphur and mercury using the names sulphur and
mercury in a particular sense distinct from that of ordinary
language it does become possible to speak of a chemical attitude
to substance. Robert Boyle frequently applied the word "chymist"
in this way, as describing those who thought and worked in
accordance with the three-principle theory. Otherwise the
chemist was only distinguished from other men by the nature of
his methods: 'What is accomplished by fire/ wrote Paracelsus,
c is alchemy whether in the furnace or in the kitchen stove.' 1
The chemist was indeed primarily a pyrotechnician, who knew (or
tried to discover) how to obtain certain results by long and gentle,
or short and fierce, heating. To the end of the seventeenth century
chemical analysis was practically confined to destructive distilla-
tion by fire, in which the substance to be analysed was forced to
yield its waters, oils, sublimates, salts and caput morluum. In this
sense the metal-refiner, the soap boiler and the distiller were
chemists; the practices of more learned men in the early modern
period were hardly less haphazardly empirical than theirs, and
owed little more to the guiding influence of a distinctive theory.
And, as chemical ideas were but slowly differentiated from those
generally current in natural philosophy, so chemical techniques
were very gradually differentiated from those of the kitchen and
workshop. Even in the time of Lavoisier they still bore strong
marks of their craft origin.

Two possible approaches to the early history of chemistry
are, therefore, bound to prove misleading, and to conceal the

1 Alchemy to Paracelsus meant something much wider than the search for
the secret of the transmutation of base metals into gold.

THE ORIGINS OF CHEMISTRY 305

significance of the development of the science during the period of
the scientific revolution. It is futile to attempt to trace the progres-
sive evolution from primitive beginnings into a modern form of
a texture of chemical theory, because the idea that it is useful to
apply a group of characteristically chemical concepts to the study
of nature is itself modern. It is equally futile to derive chemistry
from the elaboration of certain techniques of investigation, firstly
because it is doubtful whether these enabled useful empirical
facts to be discovered before a late date, and secondly because the
intellectual background to the refinement of technique is far more
significant than the refinement itself. If modern chemistry is not,
as mechanics is, the result of the progressive emendation of an
autogenous conceptual structure, it is also not that of purely
deductive reasoning applied to "natural history" information
collected about the properties of minerals, acids, alkalis, etc.
though this view seems to contain more truth than the former. On
the other hand, two analogous questions may usefully be asked.
What attempts were made to account for changes in the properties
of bodies effected by various manipulations (mainly with the aid
of heat) in the light of existing scientific theory? How successfully
were techniques adapted or invented with the double object of
advancing technology and understanding? By asking questions of
this form it is possible, without plunging into confusion, to
recognize the indubitable facts that chemistry was always an
eminently practical science, as well as a branch of natural
philosophy, and that it lacked (before Lavoisier) a coherent
conceptual scheme.

To state the problems in such terms is not to deny that theory
and practice were interdependent, or that individual chemists like
Boyle might both add to factual knowledge, and seek for an ex-
planation of chemical phenomena in current scientific thought.
It does, however, admit that these two strands in the history of
chemistry are logically distinct. This is very clear in the late
medieval period. Then, natural philosophers were engaged in try-
ing to fit the known facts of chemical change into the pattern of
Aristotelean ideas concerning the nature and properties of matter,
exactly as, more assiduously, they tried to arrange the facts of
physics and astronomy according to the same pattern. Meanwhile,
the pattern itself preserved its character, and no essentially new
ideas were brought out. By contrast, empirical knowledge of the

20

3o6 THE SCIENTIFIC REVOLUTION

phenomena of chemistry increased rapidly during the same period,
owing progressively less to a remote Hellenistic ancestry. In glass-
working, in the smelting and refining of metals, in dyeing and
leather-dressing, in military pyrotechnics, in the distillation of
alcohol and other " waters," in the glazing of pottery and the
preparation of pigments generally, in the manufacture of medica-
ments of all kinds briefly, in every aspect of chemical technology
the European world of about 1500 enjoyed a consistent superiority
over the Graeco-Roman. In the millennium between the fall of
Rome and that of Constantinople alcohol and the mineral acids
were discovered, saltpetre was distinguished from soda (this made
gunpowder possible), many new minerals were recognized,
named, and their usefulness exploited, the known compounds of
metals increased in number, chemical apparatus assumed a defi-
nite form, the control of furnaces was improved, and operations
like reduction and oxidation were mastered (though their nature,
of course, remained unknown) . Some of this knowledge emanated
from a Graeco-Egyptian tradition, centred on Alexandria; im-
portant elements were derived from India and China, but prac-
tically nothing came from the academic scientific line of the
ancient world, stemming from Plato and Aristotle through Pliny.
The whole was synthesized and further advanced by the Islamic
peoples, who were excellent chemical craftsmen, and further con-
siderable progress was made in the Latin West from the twelfth
century onwards. As some of the important sources, such as the
writings of Geber and the Book of Fires of Marcus Graecus, are
now accredited to Latin compilers who made use (to a degree
which cannot be exactly estimated) of unknown originals, the de-
tailed ascription of inventions in the chemical arts to Byzantium,
Islam, or Latin Europe is often impossible. But it is quite certain
that they are post-classical.

Little reflection of this growing empirical knowledge is to be
found in the writings of medieval natural philosophers, with the
rare exception of Roger Bacon. Only such discoveries as were
possibly effected, or alternatively adopted, by the alchemists (like
the preparation of mineral acids and the solution of metals in
them) were of interest. More was done by physicians, with regard
to pharmacologically useful discoveries. The third class of writing
which gives an insight into medieval chemical technology consists
of recipe books of many types, among them the different versions

THE ORIGINS OF CHEMISTRY 307

of the Mappa clavicula, the Note on various crafts of the monk Theo-
philus (c. 1200), the Book of Fires already mentioned, and the Book
on colour making of Peter of St. Omer (c. 1300). This class becomes
much fuller from the fourteenth century. While, therefore, texts
in this group may be drawn upon to form a picture of the level of
factual knowledge concerning the preparation and properties of
substances attained by the close of the middle ages, it is almost
useless to look to them for the beginnings of a chemical attitude.

The literature of alchemy is copious, and many have searched
in it for the beginnings of chemistry. There the grain of real know-
ledge is concealed in a vast deal of esoteric chaff. The view that
alchemy represents the pre-history of chemistry (as developing
chemical techniques, and factual knowledge of substances) is, after
all, primarily based on the fact that such information is frequently
set out, in the surviving texts, in an alchemical context. But there
is no means of knowing that, because a discovery or an observation
is first reported by an alchemist, it was made as a result of his
inquisitive experimentation. The most remarkable feature of all
alchemical writings is that their authors prove themselves utterly
incapable of distinguishing true from false, a genuine observation
(according to our modern knowledge) from the product of their
own extravagant imaginations. It seems unnecessary to give them
credit for making important truths known, when they were so
obviously incapable of discrimination. It is certain that many
practices and observations of alchemy were older than alchemy
itself, just as observational astronomy preceded astrology. It is also
certain that in the medieval period much knowledge was gained
outside the alchemical context which was restricted, almost ex-
clusively, to metallic compounds. Taken together, these facts
suggest that were the early history of practical, industrial chem-
istry more fully revealed, the inventiveness attributed to the
alchemical dream would be found exaggerated. Some of the dis-
coveries attributed to it may well have come from a differently
directed experimentation; some alchemists were also physicians.

The theoretical contribution of alchemy to science was very
small. Its own pretensions forbade the application of the usual
notions of natural philosophy to the phenomena studied, and
despite the interest of some philosophers in the art, there were
always others who derided it. The theory of transmutation held
by the later alchemists was originated by Jabir ibn Hayyan and

308 THE SCIENTIFIC REVOLUTION

al-Razi. It was made known to Europe in the twelfth century.
They believed that all metals are composed of " philosophic"
sulphur and "philosophic" mercury, which could be obtained by
art from the base metals, and recompounded to form the precious
metals: 1

Therefore if clean, fixed, red, and clear Sulphur fall upon the pure
Substance of Argentvive (being itself not excelling, but of a small Quan-
tity, and excelled) of it is created pure Gold. But if the Sulphur be clean,
fixed, white and clear, which falls upon the Substance of Argentvive,
pure silver is made . . . yet this hath a Purity short of the Purity of
Gold, and a more gross Inspissation than Gold hath. 2

It is enough to say that this theory was never developed (save in
mystical embroidery), that it was never attached to any sound
body of empirical knowledge, and that its persistence was the
greatest obstacle to the development of a rational chemistry.

In any case, the pursuit of alchemical chimaeras had long ceased
to bring any useful information to light by the beginning of the
sixteenth century. The significant event of this time was the
emergence, from the obscure and laconic notes of recipe-books, of
literate descriptions of the operations of chemical industry, espe-
cially those connected with metallurgy. These books have been
discussed already (pp. 221-3). Here at last was metallurgical
chemistry (and much more) free from the extravagances of al-
chemy. Here was a clear discrimination between fact and fiction
with regard to the " transmutations " effected by chemical art.
Theoretical speculation was almost entirely absent from these
accounts, Agricola alone being notable for an attempt to explain
his observations in terms of Aristotelean science, without, however,
improving its texture. Thus was founded a serviceable and lasting
tradition, which after a recession lasting through a couple of
generations (those most subject to the influence of Paracelsus) was
again revived by the scientific societies. From that time the
academic study of industrial chemistry was never neglected.
Eighteenth-century chemists like Black and Macquer were closely
associated with it. Lavoisier did an enormous amount of work as a
government consultant, reforming the administration and chem-

1 These principles were ultimately compounded of the Aristotelean ele-
ments, but could be procured, as it were, as intermediate states.

2 Argentvive = mercury. Works of Geber, Englished by Richard Russell i6"/8,
Ed. by E. J. Holmyard (London, 1928), p. 132.

THE ORIGINS OF CHEMISTRY 309

istry of the French explosives industry. And it may safely be said
that the rapid extension of chemical research in the nineteenth
century and later would have been impossible but for its close
connection with manufacture. Much earlier the remarks of the
Fellows of the Royal Society, especially Robert Boyle, on the
necessity of close attention to trade methods give a hint of a source
from which much was learnt not least, in the way of suggesting
the type of problems which might most usefully be attacked. For
on this, it is obvious, modern chemistry largely depended for its
early success. The only problems which the early chemist could
hope to solve in a rational way were the simple ones dealing with
the oxidation of metals, the calcination of limestone, quantitative
analysis of simple inorganic compounds which were in fact posed
by the basic chemical industries. However stimulating the fascin-
ating questions suggested by more elaborate chemical changes
might be, including those raised by the known connection be-
tween chemistry and medicine, answers to them remained far
over the horizon until such time as organic chemistry slowly
increased its scope through the mastery of inorganic reactions.

Though the endeavour to render physiology a branch of chem-
istry inevitably failed in the sixteenth and seventeenth centuries,
nevertheless it did on the one hand promote the development of
a distinctively chemical attitude to physiological and other prob-
lems, arid on the other led to extensive exploration of chemical
compounds with the object of using them as drugs. Inorganic
medicaments were not new. Salt has always been collected as a
necessity for life; antimony sulphide, copper salts, sodium carbon-
ate, ochres, alum, and other minerals are prescribed for various
purposes in the Papyrus Ebers (sixteenth century B.C.). 1 Possibly less,
and certainly not greater, faith was attached to them in late
medieval Europe. These were, however, natural substances, not
the factitious products of art, few of which had yet been identified
with naturally-occurring minerals.

Roger Bacon had taught that medicine should make use of
remedies provided by chemistry, but it was not until the sixteenth
century that his idea was fully developed, by Theophrastus
Bombastus von Hohenheim (1493-1541), called Paracelsus, the
founder of iatrochemistry (medical chemistry). His was not in
any sense a modern mind. He believed in the philosopher's stone.
1 H. E. Sigerist: History of Medicine, vol. I (Oxford, 1951), p. 343.

310 THE SCIENTIFIC REVOLUTION

He believed in the alchemical theory of transmutation, and in
others yet more wonderful:

If the living bird be burned to dust and ashes in a sealed cucurbite
with the third degree of fire, and then, still shut up, be putrified with
the highest degree of putrefaction in a venter equinus so as to become
a mucilaginous phlegm, then that phlegm can again be brought to
maturity, and so, renovated and restored, can become a living
bird. . . .!

He had in full measure the faculty for self-deception characteristic
of the Hermetic tradition. For him, the physician and chemist
were one, a magus whose operations influenced the natural and
supernatural worlds together. In the words of Lynn Thorndike:

for Paracelsus there is no such thing as natural law, and consequently
no such thing as natural science. Even the force of the stars may be
side-tracked, thwarted or qualified by the interference of a demon.
Even the most hopeless disease may yield to a timely incantation or
magic rite. Everywhere there is mystery, animism, invisible forces. 2

But he was an iconoclast. He poured scorn upon the revered
writings of Galen and other authorities. For their dietary rules and
herbal preparations he wished to substitute new drugs purified by
the action of fire. 'The work of bringing things to their perfection
is called alchemy, and he is an alchemist who brings what nature
grows for the use of man to its destined end.' Vulcan was to be his
apothecary. In his medical practice he made much use of chemical
preparations of herbs (to extract their virtue), laudanum, alcohol,
mercury and metallic compounds, obtained by techniques familiar
to alchemists. In theory, he added salt to the other alchemical
principles, sulphur and mercury; otherwise his theoretical notions
were fully as chaotic as those of other alchemists.

No great reformation was to be expected from Paracelsus' in-
coherent, obscure, megalomanic writings. Yet the iatrochemical
school flourished; the greater part of what was done up to Boyle's
time may be attributed to it, and during two generations chemists
were to a greater or less degree Paracelsians, known by their
attachment to the three principles. Indeed Paracelsus' theses with

1 A. E. Waiter Hermetical and Alchemical Writings of Paracelsus (London, 1894),
vol. I, p. 121.

2 History of Magic and Experimental Science, vol. V (New York, 1941), p. 628.

THE ORIGINS OF CHEMISTRY 311

regard to medicine, that useful drugs could be made in the labora-
tory, and that there was room for bolder experiment in the treat-
ment of disease, were obviously correct when purged of the
fantasies and occultism with which, in him, they were always
enmeshed. No one could doubt the efficacy of Glauber's sal mirabile
(sodium sulphate), and long before Paracelsus' time the adminis-
tration of mercury had been proved a specific against the common
and dangerous disease, syphilis. 1 The ambitions of the iatrochem-
ists were to reveal the chemical nature of physiological processes,
by discovering the secret laws by which the combinations and
recombinations of matter are governed, and to enlarge the list
of compounds known to be effective against disease. These were
rational objects, though the manner in which they were pursued
was haphazard. Paracelsus had done little in chemistry himself. His
successors devoted themselves more fully to mastering the tech-
niques which would yield hitherto unknown substances. They did
not hesitate to draw, where they could, upon the experience of
industrial chemistry.

These men were the "chy mists" or "spagyrists" known to
Boyle and his contemporary philosophical chemists. They were
men of learning and wrote Latin. Their view was narrow, being
limited by the doctrine of the three principles, and they were
often subject to the delusions of alchemy, but their books were
meant to be understood. They created no secret language.
Instead they began to describe, as plainly as their knowledge and
terminology allowed, how the operations of chemistry are per-
formed, from what materials and by what methods a large number
of compounds are prepared, and for what purposes they might be
employed. They began to compare the method used in one case
with that used in another, to detect analogies between different
compounds, and to try to explain what happened when a chemical
reaction occurred by means of concepts which they invented or
adapted. Here was the beginning both of a " natural history" of
chemistry, and of a chemical theory.

Andreas Libavius (d. 1616), the first important iatrochemist

1 Salivation was condemned by many non-iatrochemical physicians,
because death was so often caused by mercurial poisoning. Medical faculties
forbade the use of iatrochemical methods for well over a century, Sir Theodore
de Mayerne, James I's physician, being expelled from Paris on this account.
They were gradually admitted to official pharmacopoeias during the seven-
teenth century.

312 THE SCIENTIFIC REVOLUTION

after Paracelsus, refused to number himself among the latter's
followers. From his Alchemia (1597) he claimed, justifiably, to
have omitted the magical and superstitious elements introduced
by Paracelsus, and to have purified the art of his figments and
phantasms. * Unhappy would chemistry be, if it had been founded
by Paracelsus. . . . Filthy are the Paracelsian lies and blasphemies.'
Nevertheless, he still believed in transmutation. The Alchemia was
Libavius' most important work, though he admitted that it was
largely compiled from other writers. 1 It is a methodical account
of the chemical knowledge and laboratory technique of his time.
He described many antimonial and arsenical compounds, 2 sul-
phurous acid, the stannic chloride (SnCl 4 ) known as "Libavius'
fuming liquor," the extraction of many oils, waters and essences,
and the analysis of mineral waters. In the second edition there
is a long discussion, with wood-cuts, of the design of a chemical
laboratory. From such a work as this it was but a step to the
treatment of chemistry simply as an auxiliary of medicine. This
is the attitude of Jean Beguin in his Tirocinium Chymicum (1610)
who thus defined his subject: 'Chymistry is the Art of dissolving
natural bodies, and of coagulating the same when dissolved, and
of reducing them into salubrious, safe, and grateful medicaments.' 3
The Tyrocinium is a very straightforward recipe book, forerunner
of many others of the same kind.

The greatest of the iatrochemists, Johann Baptista van Helmont
(1577 or 1580-1644) was a figure in some ways only less flam-
boyant than Paracelsus, for he also gave his imagination free
licence. His criticism of academic medicine was more reasoned
than Paracelsus', but not less severe. 'The art of healing,' he
thought, " was a mere imposture, brought in by the Greeks. . . . To
this day the schools do scarcely acknowledge any other remedies
than blood-letting and their stock of laxatives; their whole
endeavour is with bleeding, evacuations, baths, cauteries, sweats,
so that they presume to cure all ills of the flesh by weakening the

1 There are two editions, Alchemia Andrea Libavii Med. D. Poet. Physici
Rotemburg, etc. (Frankfort, 1597), p. 424; and the large folio with wood-cuts
Alchymia Andrea Libavii, recognita, emendata, et aucta etc., (Frankfort, 1606),
pp. 196 -f 402 -f 192.

2 This, of course, was before the Triumphal Chariot of Antimony of the pseudo-
Basil Valentine.

3 Tyrocinium Chymicum, or Chymical Essqyes Acquired from t(ie Fountaine of
Nature and Manuall Experience [trans, by Richard Russell] (London, 1669), p. i.
This primer was deservedly popular.

THE ORIGINS OF CHEMISTRY 313

body and its strength, and by corrupting the blood.' 1 Despairing
of such methods, van Helmont turned to chemistry because
insight into nature generally, and the workings of the human body
in particular, could only be gained through a sound knowledge
of substance. To this end he developed a totally novel theory by
which he proved himself far more than a mere chemist like
Libavius. In the first thirty chapters of the Ortus Medicirue he
sketched out a new natural philosophy, often obscure and
muddled, and more than tinged with a naive credulity, which
was as much directed against Aristotle as against Galen. His
speculations ranged far beyond the bounds of chemistry and
medicine, to meteorology and the causes of earthquakes. The
most important of them was his contention that there are only
two elements, Air and Water. Fire he did not regard as a body,
and therefore it could not be an element. All solid bodies, includ-
ing the earths, were generated from water by the action of seeds
or ferments: The first beginnings of bodies, and of corporeal
causes, are two and no more. They are surely the element Water,
from which bodies are fashioned, and the ferment by which they
are fashioned.' 2 These divinely created ferments were the specific
organizers of water, the prima materiel, into minerals as well as
living things; they were immaterial, though the seeds to which
they gave rise were not. Van Helmont referred in support of this
doctrine to the success of chemists in reducing solid bodies to
an " unsavoury water" (e.g. by solution in acids, followed by
neutralization); to the fact that fishes are nourished solely on
water (!); and to his famous experiment on the growth of a
willow tree in a tub of earth. Although nothing but water was
added, the tree gained 164 Ib. weight in five years without any
diminution of the earth in which it was planted; water had
clearly been transmuted into solid matter by the action of the
"seed" in the tree. 3 Like Boyle later, van Helmont attacked the
three principles of orthodox chemists on the ground that some
bodies could not be resolved into them. He accepted the existence
of vacua in solid matter: for this explained how metals could be

1 Ortus Medicina, Col. I, 6; III, 7. This collection of all van Helmont's
works was published by his son at Amsterdam in 1648. An English translation
by John Chandler appeared in 1662.

2 Ortus Medicirue (Lyons, 1667), p. 23.

3 Ibid., p. 68. The experiment had been suggested by Nicholas of Cusa in the
fifteenth century.

314 THE SCIENTIFIC REVOLUTION

more dense than water. Air, however, could not be turned into
water, even by great compression, and was therefore a distinct
element.

False thinking on these matters was, in van Helmont's view, the
main cause of error in science down to his time. He also attached
great importance to two new conceptions, for which he coined
new names. One was "Bias" a sort of intrinsic motion in the
stars and planets (which thereby affected the earth beneath), in
the air, and in man. The other was "Gas," which name had
a significance quite other than that now attached to it. Van
Helmont's gas was simply a form of water, and he used the idea
to confirm further his theory that water was the prima materia.
Any matter, such as water vapour, carried into the extreme upper
air, was turned into gas (i.e. was finely divided, since 'gas is far
more subtle than vapour, steams, or distilled oils, although much
denser than air') by the sharp cold and the "death" of the
ferments. Then this gas might itself condense into vapour and fall
as rain: at any rate, it was the chief cause of meteorological
phenomena. Again, when substances burnt, the greater part of
them disappeared as gas, which was also water, or 'water
disguised by the ferments of solid bodies.' The point of van
Helmont's observation, that there is only i Ib. of ash obtained
from 62 of charcoal, the rest disappearing as spiritus Sylvester (wild
spirit), seems to be that the charcoal itself is gas, i.e. water. 1
He knew that if the escape of the spirit was prevented, by en-
closing the charcoal in a sealed vessel, combustion would not
occur. This led him into his celebrated definition: 'This spirit,
hitherto unknown, which can neither be retained in vessels nor
reduced to a visible body (unless the seed is first extinguished) I
call by the new name Gas.'* Thus van Helmont's element-theory
might be symbolized

water + seed (ferment) > substance
and with his concept of gas this became

water > vapour * gas * water,
and (water + seed) > substance * gas * water

1 He had already "proved" that ash could be turned into water.

2 Cf. Ortus Medicine " Progymnasma meteori," "Gas aquae," "Complexio-
nurn atque mistionum elementalium figmentum."

THE ORIGINS OF CHEMISTRY 315

In other words, the concept of gas was simply a complexity added
to the doctrine which van Helmont most wanted to drive home,
that is: water is all. Its main function was to explain the otherwise
rather awkward fact that the products of combustion do not
normally include much water-vapour. Just as he had to deny
corporeal status to flame and fire (which could not be supposed to
come from, or turn into, water) so van Helmont had to invent
gas as a form of water.

He noticed that gas might be evolved from a combination of
substances, or a substance acted upon by a ferment, though not
if the substance was taken by itself. Thus he found that saltpetre
alone yielded no gas, but that gunpowder does hence the violence
of the explosion. Grapes yielded a gas when bruised and fermented.
He also applied the name gas to the red fumes given off when
nitric acid reacts with silver, to the product of the reaction between
sulphuric acid and salt of tartar, to the furncs given off by burning
sulphur, to flatus, to the poisonous substance which collects in
mines and extinguishes candles, etc. While unable to recognize
and classify these different gases systematically, he was of course
able to make qualitative distinctions between nitric oxide, sulphur
dioxide, carbon dioxide, mixtures of hydrogen and methane, and
this particular attention to " fumes" (which must have been very
often observed in the past) was perhaps van Helmont's best
service to chemistry. But there is no evidence that he ever ad-
vanced beyond the notion that gases were substantially water,
modified by the characteristic of immaterial ferments: indeed, he
does not seem to speak of "gases" at all, as a plurality.

It has often been said, and rightly, that the long failure to
understand the role of the common gases was a grave obstacle
to the development of chemistry. It seems, however, that van
Helmont, despite the praise frequently meted out to him as the
first student of gases, really did little to lessen this obstacle. The
modern notion of gas involves two propositions, the second being
logically unnecessary, but required by experience: (i) There is a
state of matter in which the particles are separated and free to
move, rendering the matter tenuous and elastic; (2) Some forms
of matter are normally encountered only in this state. Now the
first of these propositions, though it was little developed theoretic-
ally before the nineteenth century (having been disregarded, for
the most part, by the practical chemists who really worked out

316 THE SCIENTIFIC REVOLUTION

something of the importance of gaseous elements in chemical
combinations) would not have seemed at all unfamiliar to
seventeenth-century physicists, to whom the particulate nature
and elasticity of "airs" were commonplaces. Their notions of
"factitious airs" and "elastic fluids" clearly foreshadowed the
modern physical idea of a gas. But they had no corresponding
chemical conceptions. The pivotal discovery, the apprehension that
made Lavoisier's chemistry possible, was the enunciation of the
second proposition in a chemical setting. It was the fact that some
participants in chemical reactions both elementary and com-
pound could normally be isolated in the gaseous state only,
though capable of entering into solid and liquid combinations,
which was of strategic significance.

Therefore van Helmont's view of gas as a state of matter
intermediate in fineness between a vapour and the clement air,
and as the fume, smoke or spirit evolved from a chemical process,
was of very little profit in itself. While his ideas helped to encourage
interest in these curious products, there was little real merit in
the attachment of a special name to something so vaguely con-
ceived, and so deeply involved in an unacceptable doctrine of
watery transmutations. Chemists especially the English con-
tinued to speak of "airs" and "elastic fluids" with good reason;
they chose rather to believe that gases were modified air than (with
van Helmont) that they were modified water, and air an inert
element. It cannot be said that they preferred the less plausible
of the two hypotheses. To have converted the Helmontian view
"gas is a state of water" into the statement "gas is a form of
material substances, distinct from air, which participates in
chemical reactions" was impossible. If van Helmont was right
(as we now know) in suggesting that gas is not air, it was far more
obvious to contemporaries that he was wrong in maintaining that
gas was a phase in water > substance > water transmutations.
Chemists like Boyle could make nothing of his Gas and Bias.
They could not see that of these two whimsical notions, the former
was far more worthy, since to them the single-element doctrine in
which van Helmont's gas is involved was incomprehensible. Even
to hint that the subsequent neglect of van Helmont's work on gas
retarded the development of chemistry is to misunderstand the
content of his thought, and to convey a thoroughly misleading
impression.

THE ORIGINS OF CHEMISTRY 317

About the middle of the seventeenth century the position in
chemical theory (to use what is still an anachronism) was that the
Aristotelean doctrine, now moribund and opposed to the broad
trend of the scientific revolution, was still respectable; practising
chemists, as a class, stood by their three principles and the general
tenets of iatrochemistry; van Helmont's single-element theory
aroused much interest, but won few adherents. Meanwhile, a
fourth approach to the problems of chemical combination, based
on the mechanical, particulate view of matter was taking shape,
and was soon to be developed elaborately by Robert Boyle.
Factual knowledge of chemical reactions and processes had also
ramified considerably since the time of Libavius. Van Helmont
himself, for all his natur-philosophische outlook, was a skilled prac-
tical chemist, who reported a good number of new preparations.
He taught that matter was indestructible, illustrating this belief by
the recovery of the original weight of a metal from the compounds
in which it was apparently disguised. 1 It is said that he made much
use of the balance: his famous tree-experiment shows how deceptive
quantitative methods may be when applied within an inadequate
conceptual scheme. A younger iatrochemist (who also pursued
the philosopher's stone) was Johann Rudolph Glauber (1604-70).
He described for the first time the preparation of spirit of
salt (HC1), sodium sulphate, and perhaps chlorine. Glauber had a
sound insight into certain types of chemical reaction, such as double
decomposition; for example, he explained the formation of " butter
of antimony" with sublimation of cinnabar from stibnite heated
with corrosive sublimate by saying that the spirit in the latter,
leaving the mercury, preferred to attach itself to the antimony in
the stibnite; the mercury then united with the sulphur in the
stibnite to form cinnabar. 2 From this example it is also clear that
Glauber employed the concept of chemical affinity he understood
that one unit in a reaction might attract 'another more than a
third.

1 ' Since nothing is made from nothing, the weight [of one body] is made
of the equal weight of another body, in which there is a transmutation of
matter, as well as of the whole essence' (Prog. Meteori, 18). Van Helmont's
argument seems to be, that the same weight of prima materia (water) is repre-
sented by equal weights of any substance, irrespective of their densities.

2 i.e., Sb 2 S 3 + 3HgCl 2 = 2SbCl 3 -f sHgS. Double decomposition in this
same reaction was indicated rather less clearly by Beguin in the 1615 edition
of his Tyrocinium Chymicum. Cf. T. S. Patterson in Annals of Science, vol. II
(London, 1937), p. 278.

3 i8 THE SCIENTIFIC REVOLUTION

In 1675 there was printed for the first time a new textbook on
chemistry by a practical man, Nicholas Lemery (1645-1715),
which remained popular for upwards of half a century. The title
of the Cours de Chymie contenant la maniere de faire les operations qui
sont en usage dans la Medecine sufficiently indicates its purpose. It
was a straightforward recipe-book, dealing first with the metals,
then with salts, sulphur and other minerals, and finally with
preparations obtained from vegetables and animals. Lemery was
not given to theorization, but he taught that there were, in addi-
tion to the three active principles mercury (spirit), sulphur (oil)
and salt, two passive principles, water and earth. He also accepted
the theory due to Otto Tachenius that salt acid -f- alkali, and
occasionally followed the particulatc ideas of Descartes. The Cours
de Chymie was the most successful of many similar practical books
published at about the same time: an English example is George
Wilson's Compleat Course of Chymistry (? London, 1699). By the end
of the seventeenth century the best accounts of experimental
chemistry were those written with medical applications in mind,
and though the old, esoteric iatrochemistry deriving from Para-
celsus had perished, future progress was to owe much to physicians
and apothecaries, among them Boerhaave, Cullen, Scheele and
Black. It is of significance also that the teaching of chemistry in
universities, beginning c. 1 700, everywhere placed it as an auxili-
ary to medicine. Even at the close of the eighteenth century most
of Black's pupils at Edinburgh were medical students. 1 From the
time of Boyle to that of Priestley and Cavendish the role of the
"amateurs" in chemistry was relatively insignificant, and the
reason is not far to seek. This was a period of rapid practical
development in the subject, but of minor theoretical expansion.

It is therefore appropriate now to turn to this last of the great
philosophical chemists, Robert Boyle, who is one of the most
enigmatic figures of the scientific revolution. There can be no
doubt that he was one of its leading personalities, nor that he made
wide, and incisive, use of the new ideas maturing in his time.
Whether he was himself capable of any major creative act in
scientific thought is more arguable. Possibly his originality (but
not his perseverance) as an experimenter has also been exagger-
ated; it is difficult to estimate accurately, since Boyle's works are

1 Cf. the interesting paper by Dr. James Kendall in Proc. Roy. Soc. Edin.,
Section A ? vol, LXIII (Edinburgh, 1952), p. 346 et seq.

THE ORIGINS OF CHEMISTRY 319

perhaps the first to be filled with descriptions of experimental
research. These books, on which his fame was established, are
hugely prolix and sometimes tedious, containing masses of ob-
servations haphazardly selected and arranged, through which the
reader has to pick his way in search of the point of the discussion,
often to find that Boyle has been unable to make up his own mind.
Yet they are always redeemed by the sense of a sharp and con-
tinuous purpose, a far-reaching breadth of learning, and a humility
in face of the facts of nature that forbade dogmatism.

The task Boyle set himself was to examine philosophically the
natural phenomena made known by chemical art; to determine
the underlying nature of the material transformations of which
a cumulative description had been built up since the time of
Libavius, and of the processes by which they were brought about.
He undertook to prove to philosophers that chemistry could be
more than a collection of recipes, and to the "chy mists'* that in
revealing nature's secrets they would have a more noble aim than
the concoction of medicines. Not that Boyle despised the applica-
tion of chemistry to medicine. He regularly dosed himself and his
friends, and welcomed any new compound that promised thera-
peutic value, but he was aware that science as a whole is greater
than the cure of disease. Boyle wrote no textbook of chemistry,
like Lemery's, rather he usually assumed such a level of knowledge
in his readers; nor was he greatly interested in the piling up of
more and more empirical knowledge for its own sake. Almost
always he wrote with a definite problem in mind, some aspect of
his ambition to restore natural philosophy as a unified whole, in
which chemical knowledge should play its due part. He sought to
build a bridge between chemistry and physics, the two sciences
concerned with the properties of matter, which ought to start
from common ground and be explicable one in terms of the other.
In this respect Boyle had much in common with van Helmont,
whom he greatly admired (while admitting his frequent inability
to comprehend him); but whereas van Helmont had criticized
natural philosophers for their ignorance of ideas to which he him-
self had been brought by his own quasi-Paracelsian development,
Boyle proceeded quite differently. Essentially a physicist looking
at chemistry, Boyle sought to demonstrate that the facts and pro-
cesses of chemistry were explicable in terms of the corpuscularian,
mechanical hypothesis of matter which he had adopted.

320 THE SCIENTIFIC REVOLUTION

In the first of his major works to be printed, which is also the
most widely read, this is certainly not very clear. The purpose of
the Sceptical Chymist (1661), as its title suggests, is negative, not
positive. It was to clear the ground of the three theoretical atti-
tudes to chemistry which were then in vogue. Boyle disposed
rapidly of the four Aristotelean elements, for they were no longer
plausible entities (at least to the progressive experimental
scientist). 1 His main attack was upon the three principles of the
orthodox chemists, his real target. In this connection there was
nothing novel in his own definition of a chemical element, nor in
his insistence on the importance of discovering what the ultimate
constituents of compound bodies are. 2 He argued that none of the
chemists' principles could be extracted from metals like gold or
mercury; that their criterion of analysis by fire was in any case
faulty, since it could not divide glass into its known constituents,
sand and alkali. He pointed out (like van Helmont) that the
natures of bodies are not changed by entering into combinations,
since the same bodies could sometimes be recovered separately
in their original state. He emphasized acutely the illogicalities
and contradictions in which the ideas commonly entertained by
chemists were involved. This criticism was warrantable, but in the
Sceptical Chymist Boyle equally proved that he could create nothing
to take the place of that which he would destroy. No more than
any other contemporary did he believe that ordinary substances
gold, mercury, sulphur were elements, though they resisted
analysis. He used van Helmont's tree-experiment (which he re-
peated) to show that vegetable matter could be formed from water
alone, without the participation of earth and fire, or salt and
sulphur, but he did not believe that all things were made of water.
In the end Boyle failed not only to draw up his own list of chemical
elements, but even to decide definitely whether such simple
substances do exist at all.

1 However, they were by no means dead. The four Aristotelean elements
were still to recur in the eighteenth century, whether in Chambers^ Dictionary
or in P. J. Macquer's Dictionnaire de Chymie, where it is said (s.v. Umens)
* on doit regarder en chymie le feu, Pair, Peau et la terre, comme des corps
simples.'

2 Cf. The definition of van Helmont (Prog. Meteori, 7): 'An element would
cease to be a simple body, if it were divisible into anything prior, or more
simple. But nothing among corporeal things is granted to be prior to, or more
simple than, an element.' Boyle did not claim any originality for himself,
rather admitting that his definition was a common one.

THE ORIGINS OF CHEMISTRY 321

There was, indeed, sufficient reason in his corpuscular physics
why he should have been doubtful, why he should have thought
that anything might be transmuted into anything else, by nature
if not by art. 1 Some of the evidence is set forth in the Sceptical
Chymist: Boyle believed, with most of his generation, that metals
and minerals like saltpetre "grew" in the earth. These substances
were not themselves elements; neither were they formed from
pre-existing elements, for such elements could not be traced in the
earth where the growth occurred. 'From thence' wrote Boyle
'we may deduce that earth, by a metalline plastick principle
latent in it ["seed"], may be in process of time changed into a
metal' a common enough opinion. 2 From a survey of pheno-
mena of this kind he came to the conclusion that transmutations
in the chemical sense were possible by means of this "plastic
power" in the earth, as also by the "seminal virtue" in seeds (for
the salts etc. in wood were certainly not present as such in the
water with which the tree was nourished). However puzzling this
might be from the chemist's point of view, it was not at all inex-
plicable to the physicist in Boyle, for his physical theory of matter
taught him that all substances are made up of the same funda-
mental particles. 3 Since, therefore, substances differ from one
another only in the 'various textures resulting from the bigness,
shape, motion and contrivance of their small parts, it will not be
irrational to conceive that one and the same parcel of the universal
matter may, by various alterations and contextures, be brought
to deserve the name, sometimes of a sulphureous, and sometimes
of a terrene or aqueous body.' 4

The theory of matter which Boyle favoured led him to believe
(as he acknowledged in the early pages of the Sceptical Chymist)
that in its basic and primitive form matter existed as 'little

1 One transformation in which Boyle was naturally very interested was that
of base metals into gold. Like Newton he seems never to have been altogether
confident that this transmutation, though theoretically attainable, was actually
practicable.

2 Works (London, 1772), vol. I, p. 564. Boyle cited Cesalpino and Agricola
for the statement that metals reappear in previously worked-out veins. For
Agricola's belief that metals are generated from the Aristotelean elements
earth and water, cf. De re metallica (New York, 1950), p. 51, note.

3 A modern analogy would be the proposition that the chemical element is
an unsound and illogical concept, since all are composed of the same sub-atomic
particles.

4 Works (London, 1772), vol. I, p. 494.

322 THE SCIENTIFIC REVOLUTION

particles, of several sizes and shapes, variously moved. 5 These
were further organized into 'minute masses or clusters/ being
the 'primary concretions' of matter, some of which were in
practice indivisible. Hence the clusters that compose gold, being
inviolable by the ordinary chemist's art, could always be recovered
from any compound of the metal. But a mass of such corpuscles
was not an element, for as Boyle stated, the particles of two sets of
corpuscles might so regroup themselves that 'from the coalition
there may emerge a new body, as really one, as either of the
corpuscles was before they were mingled.' 1 Thus vinegar acting
upon lead formed the "sugar" of lead (lead acetate) but by no
means could the acid spirit of vinegar be recovered from the new
compound; Boyle thought its corpuscles were destroyed. The
indivisible corpuscles of glass were formed by a "coalition" of
those of sand and ashes; so that resistance to chemical analysis by
fire or acids was not a test of elementariness: for such indestructible
corpuscles could as well be found in the bodies due to art, as in
those due to nature. The same experience that taught Boyle that
glass was not to be numbered among the elements, prevented him
from knowing whether gold was one or not: he thought it was
probably not.

It is plain that Boyle's corpuscularian philosophy, in many ways
so fertile, prevented him from taking any step towards the modern
conception of the chemical element (an achievement usually
credited to him). In fact it led in the opposite direction, for so
long as Boyle, the physical chemist, concentrated on explanations
of chemical reactions in terms of corpuscles and particles, he would
be the less likely to believe that if elements existed at all, their
existence was very significant to his new outlook. Lavoisier deter-
mined that if a body resisted chemical analysis it should be
accepted, pragmatically, as an element. Boyle could not have
done this, because he thought in corpuscular terms. No body made
up of corpuscles could be simple, homogeneous or elementary in
the strict sense, because the corpuscles themselves were com-
pounded of a variety of particles. The pragmatic test of resistance
to analysis proved only that some concretions of these particles
into corpuscles were more coherent than others, whether brought
about by nature (gold) or by art (glass). But coherence and
elementariness could not be equivalent, since Boyle knew that
1 Works (London, 1772), vol. I, pp. 474-5, 506-7.

THE ORIGINS OF CHEMISTRY 323

some corpuscles whose coherence resisted analysis were factitious,
i.e. non-elementary.

The impasse was complete, and Boyle could not avoid it. Nor
was it really important for him to do so: the truth that chemical
changes occur by modifications of corpuscular structure, and by
re-shuffling of the particles within corpuscles, was far more sig-
nificant to him than a dubious search for primary elements, whose
existence he was quite content to regard as hypothetical. In this
he may be said to have anticipated the attitude of a modern
physical chemist who (of course within a far more rich and
exact conceptual framework) thinks in terms of molecules, atoms,
ions and kinetic theory, without paying much attention to the
elementariness of hydrogen or carbon.

That Boyle's chemical theory was predominantly shaped by his
corpuscularian physics is apparent from many works beside the
Sceptical Chymist. He was no dogmatist, he was no follower of
systems, he believed that hypotheses should be framed to fit the
facts, but it was quite clear to him that complete scepticism and
abhorrence of all theory were antithetical to true philosophy. 1
Indeed, his ambition to bring chemistry into natural philosophy
would have been meaningless had he not had a theory of natural
philosophy, essentially a theory of matter, to hand for the purpose:

I hoped I might at least do no unseasonable piece of service to the
corpuscular philosophers, by illustrating some of their notions with
sensible experiments, and manifesting, that the things by me treated
of may be at least plausibly explicated without having recourse to
inexplicable forms, real qualities, the four peripatetick elements, or
so much as the three chymical principles. 2

Thus for Boyle solution always represented the intcrspersion of
the corpuscles of the solvent among those of the dissolved body,
heat consisted of material particles, and "air" of all kinds mainly
of elastic corpuscles of a particular type, among which the
mingling of other corpuscles gave each "air" its own character.
He constantly attributed the properties of acids, oils, salts, etc.
to the nature of their component corpuscles. In fact the theory was
brought into play whenever Boyle commented on a chemical
experiment. Instances are particularly numerous in the Origin of
Forms and Qualities, where (as examples chosen at random) he

1 Cf. Ibid., p. 591.

2 Certain Physiological Essays (1661), Works, vol. I, p. 356.

324 THE SCIENTIFIC REVOLUTION

spoke of 'the body of silver, by the convenient interposition of
some saline particles [being] reduced into crystals ' of Luna cornea
(silver chloride); or, of another experiment, 'considered that the
nitrous corpuscles [of nitric acid], lodging themselves in the little
spaces deserted by the saline corpuscles of the sea-salt, that passed
over into the receiver, had afforded this alkali 5 ; 1 or again declared
that

the more noble corpuscles which qualify gold to look yellow, [and
to resist nitric acid] . . . may either have their texture destroyed
by a very piercing menstruum, or, by a greater congruity with its
corpuscles, than [with] those of the remaining part of the gold, may
stick closer to the former and ... be extricated. 2

Corpuscularian ideas were especially developed by English
scientists in relation to the allied reactions of combustion and
calcination. Both were anciently regarded as separations: the
ash or calx (oxide) remaining was an earthy residue left after the
more volatile parts of the combustible or metal had been driven
off by fire. It was well known, however, that the calx (oxide)
exceeded the original metal in weight: whence Jean Rey was led
to believe (in 1630) that though the calx was lighter than the
metal in nature, it became heavier by the attachment to it of air
which had become thickened in the furnace. Boyle later thought
that the increased weight came from fire-particles penetrating
the walls of the crucible and impregnating the calx. This explana-
tion was widely accepted until it was decisively confuted by
Lavoisier. With regard to combustion it was well known to Boyle
and others that bodies would not burn without air, unless (like
gunpowder) they contained some nitrous material. A familiar
experiment (originally described by van Helmont) showed that
when a candle was burnt in a closed vessel over water, the air
within diminished and the water rose up inside. From these and
other observations Robert Hooke sketched a theory in Micrographia
according to which combustible bodies were dissolved by a certain
substance present in the atmosphere, this solution (like others)
evolving great heat, and thus flames, which Hooke took to be
' nothing else but a mixture of Air, and volatil sulphureous parts
of dissoluble or combustible bodies, which are acting upon each

1 i.e., KC1 + HNO 3 = KNO 3 + HC1.

2 Origin of Forms and Qualities, Section VII. Boyle is obviously far from
thinking that gold might consist of a single kind of corpuscle.

THE ORIGINS OF CHEMISTRY 325

other.' This aerial substance he identified with 'that which is
fixt in Salt-peter* This same theory was elaborated in much greater
detail by the physician John Mayow in 1674, who also set it
uncompromisingly in the corpuscularian framework. In his view
the atmosphere consisted of a mass of air-corpuscles with which
were mingled others that he called " nitro-aerial particles,"
because they were fixed in nitre and nitric acid. These nitro-aerial
particles were highly elastic, and responsible for the hardness of
quenched steel. They also corroded metals exposed to the air.
The same particles, reacting violently with the sulphureous
corpuscles of combustible bodies, produced heat and flame, as
Hooke had said; therefore combustion could not occur without
them. Air in which combustion had taken place was (in some
way which Mayow did not explain) deprived of its nitro-aerial
particles, thereby decreasing in elasticity and causing the water
to rise in van Helmont's experiment. Similarly air breathed by
animals lost its nitro-aerial particles, so that the expired air was
less elastic (i.e. occupied a smaller volume) than that inspired;
the same particles caused the blood to ferment and provoked
animal-heat. They caused fermentation generally; they formed
the fiery body of the sun, and the flash of lightning; in short, the
nitro-aerial particle became in the hands of Mayow a deus ex
machina for explaining many totally unrelated phenomena. He
had no idea that these particles made an "air," or that the
atmosphere was a mixture of "airs" of which that was one. The
notion (first put about by Thomas Beddoes, Davy's patron) that
Mayow had closely anticipated the oxygen-theory of Lavoisier
cannot support serious examination: his was a typical corpuscul-
arian philosophy.

During the next hundred years studies on combustion and
calcination were to prove vital to the progress of chemical theory,
while the accumulation of empirical fact was proceeding in a way
which rendered the dubiety of theory almost irrelevant. The
attempt to explain chemical reactions in terms of the mechanistic
theory of matter, begun by Descartes and continued by Boyle,
Mayow and others, was abandoned in the early years of the
eighteenth century. Its claims were too wide, its achievements too
lacking in definition. Not that chemists doubted the particulate
structure of matter, but since nothing was known about the size,
hardness, shape, etc. of corpuscles, statements in which these

326 THE SCIENTIFIC REVOLUTION

properties of the fundamental constituents of matter were involved
were recognized as meaningless. This downfall of Boyle's hopes
the cause of the subsequent neglect of the theoretical import in
his writings was accelerated by the ascendancy of Newtonian
mechanics. The laws which governed the stars must be applicable
also to the smallest particles of matter, and the laws of chemical
affinity be subject to the supreme law of gravitational attraction.
The elements of this theory, already sketched by Newton in the
Queries to his Opticks (I7O4), 1 were soon after worked out more
completely by Kcill and Freind. The later empirical study of
affinity (e.g. by Geoffrey, who published tables of affinity in 1718)
was certainly encouraged thereby, but after the middle of the
century (when attraction had long been abandoned by practical
chemists) it became clear that the property of attraction in
corpuscles was as intangible as their other properties: nothing
could be said about it, other than that it existed. And so the am-
bition to render chemistry a branch of physics was, for the time,
frustrated. Dalton's atomic theory was conceived entirely in a
chemical context, and it was under the aegis of chemistry that the
second penetration of atomism into modern scientific thought was
to take place.

If to many chemists of the early eighteenth century it seemed
hopeless to base their theories directly on the properties of atoms
or corpuscles, they were not the less convinced of the existence of
elements or principles of an ultimately corpuscular nature. The
principles adopted by the German chemist G. E. Stahl (1660
1734) from the writings of J. J. Becher (whose Physica Subtenant
of 1669 Stahl republishcd in 1703) were accepted by most of his
colleagues, especially those in Germany and England, until near
the close of the century. Stahl's principles were water and three
kinds of earth: air was not chemically active. The three earths
corresponded to the three principles of the iatrochemists, but
Stahl preferred to call the second (sulphur) phlogiston. The
followers of Stahl made much use of affinity in explaining reactions
(meaning, in this case, the tendency of like to react with like) 2

1 Newton's investigations into chemistry were almost completely unknown
in detail at this time, as indeed they still are.

2 Thus Junker on the formation of corrosive sublimate (Helene Metzger,
Newton, Stahl, Boerhaave et la Doctrine Chimique (Paris, 1930), p. $42): * Common
salt consists of an acid and an alkaline base. Vitriolic acid, being more powerful,
seizes the base and drives out the acid from the salt. This acid would escape

THE ORIGINS OF CHEMISTRY 327

and of a novel theory of salts (as earth + water). The theory of
phlogiston was far from being the whole of their chemical doctrine,
though it was the dominant feature of that doctrine because it
permitted the co-ordination of many previously isolated facts. 1
Phlogiston was the substance emitted during combustion and the
calcination of metals, the "food of fire" or "inflammable prin-
ciple." The complete, or almost complete, combustion of charcoal,
sulphur, phosphorus, etc. demonstrated that these bodies were
very rich in phlogiston: while the formation of sulphuric acid,
phosphoric acid, etc. from the solution of the fumes produced by
combustion demonstrated that the substances themselves actually
consisted of nothing but the acid joined to phlogiston (i.e. sulphur
minus phlogiston > sulphuric acid: therefore sulphuric acid +
phlogiston = sulphur) . When a metal was heated, the phlogiston
driven off left a calx behind (therefore calx -f phlogiston= metal).
Conversely, by heating the calx with charcoal, phlogiston was
exchanged and the metal restored. Many reactions became
comprehensible when interpreted in terms of an exchange of
phlogiston, so that often where a modern chemist sees a gain or
loss of oxygen, Stahl saw an inverse loss or gain of phlogiston.

Oxygen has weight: and a modern chemist would insist that
phlogiston ought to have negative weight, a suggestion actually
mooted when Stahlian chemistry was already moribund. The
matter was not serious at first. Boyle himself had explained the
increased weight of a calx in a way that nowhere conflicted with
the idea of phlogiston. Until such time as gases were collected,
and the gain or loss of weight due to the participation of a gaseous
element in a reaction could be correctly estimated by means of
the balance, it was impossible to achieve a balance of masses in a
chemical equation. Chemical mathematics, before 1775, was such
that there was no palpable absurdity in the conception of
phlogiston as a material fluid: as Watson said,

You do not surely expect that chemistry should be able to present you
with a handful of phlogiston, separated from an inflammable body;
you may just as reasonably demand a handful of magnetism, gravity,

freely, but meeting with another substance (mercury) with which it has some
analogy (though not so great as with its own base), it forms a saline substance
with it. This substance (corrosive sublimate) is volatile because both mercury
and the acid from salt are volatile: they have an identity of "mercurial
principle".'

1 This is particularly emphasized by Mme. Metzger, op. cit.

328 THE SCIENTIFIC REVOLUTION

or electricity. . . . There are powers in nature which cannot otherwise
become the objects of sense, than by the effects they produce; and of
this kind is phlogiston. 1

The purely logical objection which has often been raised against
the phlogiston theory is therefore of small value. Eighteenth-
century scientists readily admitted the existence of weightless,
impalpable fluids such as electricity and caloric. Caloric was
indeed phlogiston revived, stripped of its chemical attributes to
become Lavoisier's "pure matter of heat." 2 Nor did Stahl's
influence check the progress of chemistry as an empirical science;
rather his views provided a useful provisional scheme for the
explanation of many experiments. As such many chemists accepted
them, without sacrificing their liberty to interpret experiments in
the light of the evidence alone. Lavoisier himself was at first far
more keenly aware of the need to scrutinize experimental data,
than of any implausibility inherent in the phlogistic doctrine
itself. The practical chemists were always far more interested in
particular problems than in universal theories; some, like Boer-
haave, were never followers of Stahl. Hence it seems unnecessary
to suppose that the fortunes of chemistry were inextricably bound
up with those of the phlogiston theory, whose scope was largely
restricted to the phenomena of combustion and calcination; but
it is certain that the age of phlogiston witnessed great progress in
chemical experimentation, though the hypothesis has so often been
characterized as futile and retrogressive. In the phlogiston period
the chemistry of gases was begun by Black, Cavendish, Scheele
and Priestley; the vain attempt to base chemical theories on
organic and inorganic reactions conjointly was abandoned; there
were striking improvements in the analysis of inorganic com-
pounds. Considerable development in the application of chemistry
to manufacture also took place. By contrast, few comparable
discoveries can be linked with the corpuscular chemistry of Boyle
and Mayow.

Irrespective of its ultimate redundancy, phlogiston was un-
doubtedly a useful concept until about 1 765, when the systematic

1 Richard Watson: Chemical Essays > vol. I (London, 1782), p. 167.

2 Compare Watson on phlogiston: * Chemists are of opinion that fire enters
into the composition of all vegetables and animals, and most minerals; and
in that condensed, compacted, fixed state, it has been denominated the
phlogiston.' (Op. cit. 9 p. 165.)

THE ORIGINS OF CHEMISTRY 329

study of gases was begun by Henry Cavendish (1731-1810). It
enabled a consistent interpretation to be given to experiments on
combustion, and many others involving oxidation and reduction. 1
Chemists gained a valuable insight into a number of reactions in
phlogistic terms, and so learnt to treat natural substances
sulphur, carbon, salts, alkalis, acids, metals, earths, and so forth
as the really active participants in their processes. Lavoisier's
chemical revolution was based on a level of factual knowledge,
and a pragmatism with regard to chemical combination, un-
equalled at any earlier time. The fact that it often happened that
Lavoisier could simply invert the phlogistic doctrine is evidence
of the service which the phlogistonists had performed. Only with
the discovery of the common gases when hydrogen was taken to
be pure phlogiston, nitrogen to be phlogisticated air, oxygen to
be dephlogisticated air, etc. did phlogiston become a serious
impediment to the interpretation of experimental work; only then
did the question of its usefulness as a hypothesis become really
significant.

The technique of collecting gases over water was invented by
Stephen Hales before 1720; Joseph Priestley (1733-1804) substi-
tuted mercury when working on water-soluble gases. Hales
examined "airs" produced in a variety of chemical processes,
particularly in order to discover the quantity evolved from a given
weight of materials, but he drew no new qualitative distinctions
between them. From his experiments he concluded that "air"
was capable of being fixed in substances as a solid. The first
chemist to label such a "fixed air" decisively, at the same time
discovering its function in a number of reactions, was Joseph Black
(1728-99). The linkage is important, for many "airs" had been

1 It is not difficult to find examples of reasoning in phlogistic terms which
led to satisfactory experimental procedures. Thus Scheele (1779) wished to
establish the ratio by volume of "pure air" (oxygen) to "foul air" (nitrogen)
in the atmosphere. He argued: 'When this pure air meets phlogiston uncom-
bined, it unites with it, leaves the foul air, and disappears, if I may say so,
before our eyes. If, therefore, a given quantity of atmospheric air be included
in a vessel, and meet there with some loosely adhering phlogiston, it will at
once appear, from the quantity of foul air remaining, how much pure air was
contained in it before.' He therefore took a small amount of iron filings, mixed
with sulphur and a little water, which he knew to be a preparation very rich
in phlogiston, and used it to effect the "disappearance" of the "pure air" in
a known volume of common air. Scheele's mixture does in fact take up oxygen
very readily. The result he obtained (9 : 24) was not good, but his procedure
was perfectly correct. (Cf. Chemical Essays (London, 1901), pp. 190-4.)

330 THE SCIENTIFIC REVOLUTION

roughly identified in the past (e.g. as inflammable, or extinguish-
ing flame), but none had been clearly described as being distinct
in species from common air, nor had any function been ascribed
to them as participants in chemical processes. The most striking
part of Black's work (Experiments upon Magnesia alba, etc., 1 756)
was his proof that quicklime was lime deprived of "fixed air": the
quantitative relation was completely established. Black found that
a mild alkali became caustic through loss of its "fixed air," and
that "fixed air" was emitted with effervescence when lime was
dissolved in acids. He made constant use of the concept of affinity
in explaining his experiments: thus, discovering that when quick-
lime was added to a mild alkali, the original weight of lime 1 was
precipitated and the alkali rendered caustic, he said that "fixed
air" had been exchanged because of its greater affinity for quick-
lime than for the alkali. He carefully pointed out that though
both water and the atmosphere contained "fixed air," it was not
identical with "common air." Later he discovered it in exhaled
breath, and in common air passed over burning charcoal: the
precipitation of lime from lime-water proved to be a specific test.
The whole essay was a neat model of scientific method: at one
stage in his work Black drew up a list of predictions, each of which
he was able to verify by experiment, thus proving that "fixed air"
played the part he had assigned to it.

In all this there was no mention of phlogiston. Though Black
was very far from rejecting the phlogiston theory in its entirety
until long after this time, he was convinced that his experi-
ments could be explained without phlogiston, and he resisted all
attempts to argue that phlogiston was involved in them. Black
had not, in 1756, actually collected his "fixed air," for the tech-
nique of imprisoning fugitive "elastic fluids" in vessels was still
almost unknown to chemists. It was described by Cavendish in
his paper On factitious airs (1766), and thereafter widely used. He
distinguished between Black's "fixed air" and another (hydrogen)
deriving (as he thought) from metals, which he found to be lighter
than common air. At about the same time the German apothecary
Carl Wilhelm Scheele (1742-86) separated the two major con-
stituents of the atmosphere "Feuerluft" (oxygen) and "verdor-
bene Luft" (nitrogen): he also prepared oxygen in various ways
in the laboratory, as did Joseph Priestley, quite independently, in
1 Calcined by Black to make the quicklime.

THE ORIGINS OF CHEMISTRY 331

1774. Most of the characteristic qualities of these and other gases
were noted.

Such were the strategic few, among a great number of other
major discoveries made by chemists who thought without reserva-
tions in the framework of which phlogiston was an essential part.
Two of the pioneers of gas chemistry, Priestley and Cavendish,
were never reconciled to Lavoisier's doctrines. Their refusal was
no doubt due to rigidity of mind, but it points also to the fact that
the phlogistic theory had imposed no barrier upon the activities
of these skilful experimenters. It also emphasizes Lavoisier's own
originality in devising new interpretations of their experiments.
While the adherents of phlogiston were by no means agreed in
the details of their exposition Priestley, for example, thinking
of oxygen as dephlogisticated air, and Cavendish preferring to
treat the gas as dephlogisticated water a situation by no means
unusual on the frontier of research, these hesitations did not
inhibit inquiry; on the contrary, it is quite clear that Scheele,
Priestley and Cavendish were each at times induced to make
certain fertile experiments by reasoning in the phlogistic manner.

The situation in which the further progress of a branch of
science is directly dependent upon an adequate matching of
theoretical concepts and experimental facts is by no means
uncommon. This was certainly the case when Galileo and Newton,
respectively, revised the concepts of mechanics, and again with
physics in the nineteenth century. But though such a matching of
fact and theory is always useful it is far from being invariably
essential. Did such a situation exist in chemistry at the end of the
eighteenth century? The evidence would seem to suggest that it
did not. The empirical attitude of the great experimenters was in
reality far more important than their theorization: it is therefore
the less likely that any plausible modification of the doctrines
prevailing through the first three-quarters of the eighteenth
century would have had much influence on the course of events.
No one would deny that Lavoisier was the first chemical theorist
of genius. No one would deny that his interpretation of the
phenomena was far superior to that of the phlogiston theory: it
was one upon which the ultimate advancement of chemical
knowledge depended. Yet it is also perfectly clear that the
inventive empiricism of his contemporaries was just as necessary
for this as his own logical, interpretative intellect, and that,

332 THE SCIENTIFIC REVOLUTION

moreover, the rapid progress of chemistry in the nineteenth
century owed a great deal to developments, such as electro-
chemistry and the atomic theory, to both of which Lavoisier's own
insight into the nature of chemical reactions contributed nothing.
Antoine Laurent Lavoisier (1743-94) was, like Newton, less
the author of new experiments than the first to realize their full
significance. Experimentation for its own sake, which delighted
Priestley, had little appeal for him. In his laboratory work he
proved himself a skilful analyst, and an able exponent of the
quantitative methods of Black and Cavendish, but not greatly
imaginative in the way that Cavendish (or, later, Faraday) was a
supremely imaginative experimenter. None of his most famous
experiments was new: the element of originality in them was
limited to Lavoisier's insistence upon paying heed to the teachings
of the balance:

We may lay it down as an incontestable axiom, that, in all the opera-
tions of art and nature, nothing is created; an equal quantity of
matter exists both before and after the experiment; the quality and
quantity of the elements remain precisely the same; and nothing
takes place beyond changes and modifications in the combination of
these elements. 1

His first investigation was into the composition of the water in
various localities about Paris. In his second he refuted the ancient
fallacy that water was converted into earth by long heating and
evaporation: he found that the " earth" obtained was dissolved
glass. Thirdly, he discovered that air was " fixed" in phosphorus
pentoxide and sulphur dioxide (made by burning phosphorus and
sulphur), bringing about an increase of weight. He predicted that
the same would be found true of all combustibles, and that the
increased weight of metallic calces was due to a similar fixation of
air. This last prediction he confirmed (1772), by reducing lead
oxide to lead with charcoal: a large quantity of air was evolved.

Lavoisier had set out to produce facts, and by quantitative
methods he had succeeded. Some of them were not exactly new,
though they had formerly been less precisely stated, but he per-
ceived that there was enough to make the phenomena of combustion

1 Elements of Chemistry (trans, by Robert Kerr), (Edinburgh, 1790), p. 130.
But Lavoisier was in no sense the first chemist to subject notions of chemical
composition to quantitative tests. There are many earlier examples of this
procedure.

THE ORIGINS OF CHEMISTRY 333

and calcination worthy of detailed examination. All his future
success followed from his apprehension of this significance. He
embarked upon ' an immense series of experiments ' intended to
reveal the properties of the different "airs" involved in chemical
reactions, which seemed ' destined to bring about a revolution in
physics and chemistry. 5 In fact, however, Lavoisier's qualitative
study of gases did not advance very far between February 1773
(when he wrote the note just quoted) and October 1774, though
he did satisfy himself that the "air" given off in the reduction of
lead oxide with charcoal was Black's fixed air, and that Boyle's
explanation of the origin of the increased weight of metallic calces
was false. 1 At this stage he was still uncertain whether the "air"
combining with metals to form their calces was Black's fixed air,
or common air, or something occurring in the atmosphere. He
had, apparently, missed the importance of Black's own observa-
tion that burning charcoal was a source of his fixed air. He could
hardly have claimed, at this point, to have done more than
indicate a series of reactions in which some kind of air was
involved, parallel to those already described, more completely,
by Black.

In October 1774 Lavoisier was informed by Priestley himself of
the evolution of an "air" (oxygen) from the red calx of mercury
(mercuric oxide) when reduced by itself to the metal with the aid
of a strong heat. 2 Some months later Priestley had established that
this " dephlogisticated air" (as he now called it) was respirable as
well as capable of supporting combustion. Soon after Lavoisier
was able to report new experiments to the Academic des Sciences:
the calx of mercury reduced with charcoal gave fixed air, reduced
alone it gave off Priestley's new air. Therefore it was, said
Lavoisier, common air in a highly active state which combined
with metals to form their calces. Evidently he did not yet regard
it as a particular constituent of the atmosphere, a view which he
adopted in the course of the next two years, when he realized that
one fraction of the air was inert during combustion and calcina-
tion. This he called mofette. The atmosphere, therefore, contained
two "elastic fluids," as Scheele had discovered some time before.

1 In this he had been anticipated by the Italian chemist, Beccaria. The
equivalence of the increased weight of the calx with the weight of the air
admitted when the retort was opened was not as exact as Lavoisier wished.

8 Lavoisier's own claim to the discovery of oxygen is generally rejected.

334 THE SCIENTIFIC REVOLUTION

By August 1778 Lavoisier could announce that "eminently
respirable air" (the "dephlogisticated air" of Priestley) combin-
ing with a metal, formed a calx, and that the same air combining
with charcoal gave Black's fixed air (carbon dioxide). The prob-
lem of calcination was thus solved, and other discoveries followed
rapidly. Lavoisier found that sulphur and phosphorus, in burning,
also combined with "eminently respirable air" only, and that it
was this combination that yielded acids by solution in water. He
found the same air in nitric acid, and was led to conclude that it
was present in all acids. In respiration, the mofette part was exhaled
unchanged, but the respirable part was exhaled as the fixed air
which Black had found in the breath. From experiments carried
out in collaboration between 1 782 and 1 784 Laplace and Lavoisier
judged that respiration was a process of slow combustion, for the
amount of heat produced by an animal in breathing out a certain
volume of fixed air, was almost equal to the amount produced in
burning enough charcoal to give the same volume.

In his memoirs before 1778 Lavoisier had not eschewed the
word "phlogiston" completely, though he was uncertain of its
role in his experiments, if it existed at all. By 1778 the elements of
his new theory of oxidation were quite firm, and in it phlogiston
had no part for he had proved that the phlogiston-concept was
the inverse of the truth. The processes of oxidation (combustion,
calcination) were not analyses but syntheses, in which phlogiston
was as redundant as it was in Black's fixed-air reactions. Once
the pattern of the substitution of the oxygen-concept for the
phlogiston-concept became clear, it could be extended to whole
groups of reactions, over almost the whole area of chemistry, by
the development of suitable analogies. Indeed it was possible to be
deceived by such analogies. 1 Proceeding in this way, it became
ever more plausible to propose the exclusion of phlogiston from

1 e.g. in Lavoisier's account of the relation of "oxygenated muriatic acid"
(chlorine) to "muriatic acid*' (hydrochloric). Lavoisier was convinced that
the latter was a compound of an unknown base with oxygen (as were all acids,
in his view), and the former a compound of the same base with a higher
proportion of oxygen (by analogy with sulphurous, sulphuric acids, etc.).
Therefore he postulated aXO + . . . O 2 -> 2XO 2 + ... for 4.HC1 -f- . . . O a
-> C1 2 -f- 2H 2 O + . . . His name for it was simply the inverse of "dephlogisti-
cated marine acid gas" (Scheele) and really considerably less appropriate,
since if hydrogen = phlogiston (Cavendish), HG1 H -> Gl. (Cf. Elements of
Chemistry, pp. 69-73, 2 33~5)* Davy discovered the true composition of HG1,
and established that chlorine is an element.

THE ORIGINS OF CHEMISTRY 335

the doctrine of chemistry altogether. In 1783 Lavoisier was
impelled to make a direct attack upon the phlogiston theory,
which he seems to have disliked even before he had any very solid
grounds for doing so. In this comparison of his own theory with
that of the phlogistonists, he insisted upon their inconsistencies
and duplications of hypothesis much as Galileo had analysed the
weaknesses of his opponents long before. Phlogiston was not
merely superfluous; it had come to mean quite different things in
different contexts, and had become a mere drudge in chemical
theory.

From this time the number of adherents to Lavoisier's views
increased steadily, first in France, and then abroad. One serious
difficulty remained. Lavoisier had not been able to discover the
product of burning " inflammable air" (hydrogen) with common
air, or with "respirable air" (oxygen). Nor could he account for
the evolution of hydrogen when metals were dissolved in weak
acids, and its non-appearance when the calces of metals were so
dissolved. All this could easily be explained in terms of phlogiston.
Once again enlightenment came from the English experimenters.
In 1 782 Cavendish continued experiments begun by Priestley and
others in which an electric spark was passed through mixtures of
hydrogen and common air. The work was done with wonderful
neatness, and he was able to identify the condensate inside his
glass vessel as common water, the gases disappearing in a ratio of
2:1 by volume. By June 1783 these experiments were known to
Lavoisier, who, paying Cavendish scant tribute, hastily repeated
them. Initial scepticism was replaced by a rapid reinterpretation
in terms of his theory: water was the oxide of hydrogen, and
hydrogen was evolved by the action of metals from the water
present in the weak acids.

The last act in the "chemical revolution" was the establish-
ment of a new terminology. The existing names of compounds
were either misleadingly descriptive ("butter of antimony"), or
redolent of the displaced theory ("dephlogisticated air") and
even older notions ("spirit of salt"), or based on common words
like "salt" and "earth." In 1787 Lavoisier and three of his
French adherents devised a new nomenclature, still substantially
preserved, in which the names were intended to identify the
nature of the substances. Thus hydrogen (water-former) replaced
"inflammable air" and oxygen (acid-former) "eminently respirable

336 THE SCIENTIFIC REVOLUTION

air." Mofette became azote (inert) or to non-French chemists
nitrogen (nitre-forming). Compounds of an element with oxygen
were all oxides, with sulphur sulphides, etc. This aim to establish
regular patterns of nomenclature has been consistently followed.
At the same time Lavoisier abandoned the attempt to seek (in
chemistry) any reality more fundamental than that revealed by
ordinary analysis. Substances which resisted analysis were, to him,
elements; for example the common gases, metals, sulphur, carbon,
lime, and a number of earths and other "radicals" some of which
were soon analysed into other constituent elements. Lavoisier
already used the word " radical" in the sense of a unit in chemical
reactions, and an element was simply an indestructible radical.
All this was fully explained in the first textbook of the new
chemistry, the Traiti Elementaire de Chimie of 1 789.

Its publication draws a convenient line of demarcation. Yet it
is important to recognize how little, as well as how much, was
really new in it. The theory, and the arrangement based upon the
theory of chemical combination, was all Lavoisier's. The inorganic
experiments and substances described had almost all been known
for twenty years, and the majority for much longer. Lavoisier and
his friends, however, had created the organic section (dealing
with the composition of alcohol and sugar, etc.) almost unaided.
If the table of elements was new, it derived (by a simple modifica-
tion) from the older chemists' practical habit of treating phos-
phorus, sulphur, metals, etc. as virtually compounds of element
+ phlogiston. Lavoisier still spoke of earths and alkalis much as
they had done, and knew little more about them. On the mystery
of chemical affinity he said nothing, on the plea that it was unsatis-
factory to discuss it in an elementary treatise. Perhaps it is most
surprising, in the beginnings of modern chemistry, to discover
Light and Heat listed as elements. 'Light,' wrote Lavoisier,
* appears to have a great affinity with oxygen , . . and contributes
along with caloric to change it into the state of gas.' It also com-
bined with the parts of vegetables to produce their green pigment. 1
Lavoisier also regarded light as a modified caloric, or vice versa;
this caloric, the invisible, weightless matter of heat was essential
to his view of matter. Caloric was interspersed between the
particles of bodies: in small measure in the solid, to a great extent
in the liquid, and most of all in the gaseous state when (so to

1 Elements of Chemistry (trans, by Robert Kerr), (Edinburgh, 1790), p. 183.

THE ORIGINS OF CHEMISTRY 337

speak) the particles of matter floated freely in the fluid. Oxygen
gas was really oxygen matter plus caloric, which was liberated as
free heat when the oxygen became "fixed" in combination with
a combustible. Caloric also caused the physical expansion of
heated bodies, by pushing their particles farther apart. Here are
undoubted vestiges of corpuscular mechanism in Lavoisier's
thought, when he handled (in a method which would have been
familiar to Boyle, but unacceptable to him) the problem of the
origin of heat and flame, which had so much puzzled Boyle
himself. Here, on the boundary of physics and chemistry, the
ideas of the seventeenth-century physico-chemical corpuscularians
still survived.

What Lavoisier did is clear enough: how was he able to do it?
Disregarding the noisy disputes of theorists and rival interpreta-
tions of this or that experiment, factors can be discerned beneath
the surface, not always conspicuous to the great theorist himself,
leading towards the chemical revolution. Some are fairly obvious:
for example, increased reliance on quantitative procedures. What
was important here was not the mere tabulation of weights and
measures, still less the making of a serious mistake like Boyle's
(p. 324) for numerous exposures of the error failed to make plain
its momentous importance but rather use of measure for con-
structive purposes, to arouse or to answer questions. "Let us
regard the facts without prejudice" said Lavoisier; but a table of
facts concerning quantitative reactions is not, and can never be, a
chemical theory. He might rather have said "Let us be astonished
when we contrast the facts with the expectations created by our
theory." This was the spirit of Galileo's, of Newton's, of Black's
researches. Rigorous quantitative methods were only useful in
proportion as they brought about a sharper juxtaposition of fact
and theory, of the flint and steel to which Lavoisier supplied the
tinder.

In the second place, the work of the great theorist co-ordinated
that of the great experimenters in more senses than one. They
supplied him with the pieces whose interlocking provided a perfect
picture, and they also built the framework of chemical knowledge
within which alone his theory could carry conviction. If Lavoisier's
prime experiments were rarely of his own invention, they were
the more telling in that they were familiar, in the same way that
Galileo's reasoning was the more forceful because it was focussed

22

338 THE SCIENTIFIC REVOLUTION

on commonplace experiences. As a third example, it may be
observed that Lavoisier extended to its logical conclusion a
practical, pragmatic way of thinking about the matter in a
chemist's retort which went back at least to the mid-seventeenth
century. Earlier chemists had thought of a salt as a metal-stuff
and an acid-stuff in combination, had carried out analyses in
terms of the sulphur-content, metal-content, alkali-content and
so forth of the original material, and having come to see chemical
reactions as a process of subtraction and addition, they had
invented the theory of affinity to account for it. To this chemist's
attitude to matter and its transformations ignoring the question
of the ultimate physical reality of what took place Lavoisier
brought rigour and precision, but it can hardly be said that he
created it. Perhaps in this was the core of the chemical revolution,
that it severed chemistry from physics, albeit temporarily. Boyle
had been frustrated because he tried to explain chemical pheno-
mena rigidly in terms of a physical theory, consciously denying
himself the use of any other concepts; Lavoisier succeeded most
where he was the pragmatic chemist, least when (in his theory of
caloric) he in turn sought to bind physics and chemistry prema-
turely in one. Despite electro-chemistry and other developments
of the first half of the nineteenth century, this hiatus continued,
lasting throughout the formative period of modern chemistry.
Only in the third stage of chemical atomism, with the acceptance
of Avogadro's hypothesis after 1869 and the publication of the
periodic table did the reconciliation of chemistry and physics,
foreseen by Boyle, and partially abandoned by Lavoisier, become
an attainable objective.

CHAPTER XII

EXPERIMENTAL PHYSICS IN THE
EIGHTEENTH CENTURY

THE dual character of eighteenth-century science has already
been remarked upon. On the one hand, those threads which
the historian of science has carefully followed through the
preceding hundred years tend to become dry and brittle; the ex-
citement had passed and there remained but its sequelae, a rather
timid experimentation and a cool, logical extension of what were
now commonplace ideas. The mood changed too. The rebellious
spirit of a Galileo was no longer necessary, for the works of Aris-
totle had passed out of serious science into the care of classical
scholars, and the scientific revolutionaries were now respectable
citizens of the republic of learning. As the scientific movement
became more comme ilfaut, so it acquired an element of dullness:
no one can be very interested in the sort of chemical experiments
that Dr. Johnson performed to soothe his mind, in the lessons on
mechanics that were arranged for the royal children, or in the
scientific pot-boilers of John Wesley. As science became fashion-
able, patronage demanded that a major discovery be presented as
a humble tribute rather than as a challenge to established philo-
sophy. But these idiosyncrasies of a society which left Priestley
to the mercy of the Birmingham rabble and made Banks President
of the Royal Society, and in which the Ladies* Diary was filled with
mathematical conundrums, are not after all of the first importance.
Nor was the England of Hume and Gibbon or the France of
Voltaire and Diderot immune to the challenge of intellect; and it
is obvious from what has gone before that in its science the
eighteenth century was by no means an age of mere continuations,
for the creative drive was not so much weakened as altered in
direction.

On the other hand, therefore, new threads of rich interest
strengthened the texture of science in the eighteenth century.
Strategic advances were not made along the broadest paths, but

339

340 THE SCIENTIFIC REVOLUTION

where the giants of the seventeenth century had been least suc-
cessful. This is strikingly apparent in physics. The natural heirs
of Newton were among the French school of mathematicians
D'Alembert, Clairaut, Lagrange, Laplace. The fundamental con-
cepts of mechanics were defined more neatly and exactly by them,
while at the same time they moulded the mathematical structure
of the science into a beautifully complete and harmonious series of
equations. They achieved an elegance and precision in compari-
son with which the work of the seventeenth century seems involved
and fumbling: even Newton's Principia, beside the Mtcanique
Celeste of Laplace, reveals a clumsy mathematical treatment. And
Laplace, unlike Newton, saw no reason to bring God into his
hypotheses. But the refinements of the French mathematicians
in no way modified the essential principles of mechanics, which
were already fixed, although their more penetrating analysis en-
abled some new problems to be solved, and some old errors to be
corrected. The many new and useful ideas that they put forward
must therefore be ascribed to the second order of discovery, as
being derivative rather than fundamental. At the same time, at a
lower level, experimentation in mechanics, pneumatics, hydraulics
and optics the organized departments of physical science was
taken up extensively. In Leiden Musschenbroek, in London the
Hawksbees, were already creating before 1710 a tradition of
demonstrative teaching. It is perhaps invidious to call their lec-
tures semi-popular, for the experiments they devised were often
far more ingenious and conclusive than those suggested by the
pioneer physicists. Such a work as Desagulier's Course of Experi-
mental Philosophy (1734 etc.) was a valuable manual of laboratory
practice and a sound introduction to physics without mathematics.
Concurrently there was a steady improvement in the design of
familiar instruments, such as the barometer, thermometer, hygro-
meter, air-pump, balance and so on; with these multitudes of
observations were performed, without, however, eliciting any
major discovery. The situation in physics was clearly, so far as its
more highly organized departments were concerned, very different
from that in astronomy (for example), where Bradley's discovery
of the aberration of light was the direct result of refinement in
angular measure. Yet even so, problems of values arise, and it
cannot be taken for granted that the less dramatic work of the
eighteenth century had the less significance. It could be argued,

PHYSICS IN THE EIGHTEENTH CENTURY 341

for instance, that the graduated scales of Fahrenheit and Reaumur
alone made thermometry effective in science, with important
results in both physics and chemistry.

It is indeed very easy to undervalue second-order discoveries
in a period of consolidation. Creative ability of the first order is
extremely rare, and though its works must figure largely in any
short account of the development of science, it would be absurd to
suppose that it could flourish apart from the context created by
men with smaller endowments. Between the peaks of scientific
achievement there is a time when activities are re-phased, when
perspectives alter, when with an enlarged range of facts the major
problems gradually modify their shape. Without this Newton
could not have succeeded Galileo, nor Darwin Linnaeus. More-
over, it very rarely happens that the statement or the demon-
stration of a first-order discovery are so perfect that they win
complete conviction, or that its potentialities are fully exploited.
The task of welding the fabric of science together, of preserving
the logic and homogeneity which originality in its highest
degree often seems to imperil, usually falls to the derivative
investigator, and it is by this consolidation, as well as by its most
splendid feats of conceptualization and experiment, that science
grows.

Two aspects of such consolidation are well illustrated in the
experimental physics of the eighteenth century. The expedition
to the head of the Gulf of Bothnia led by Maupertius and Clairaut
in 1736-7 was a bold undertaking for the time. Forests tangled
with fallen trees had to be penetrated, rapids navigated, and
quadrants handled when the mercury had sunk far below zero, by
these gentlemen fresh from the salons of Paris. Their purpose was
to measure the length of a degree of latitude, in order to compare
their result with that already obtained in France by Picard. Upon
this comparison rested the verification of an important theory. For
if the degree proved to be longer in northern than in southern
latitudes, then the earth was flattened in the polar regions, as
Newton had reasoned from dynamical considerations. This proved
to be the case, and the ratio of the polar to the equatorial diameter
of the earth was found to be 177/178. Some years later a similar
ratio was worked out from the results of another geodetic expedi-
tion to Peru (1735-43). The critics of the Newtonian theory of the
earth's shape, including the astronomer Jacques Cassini, were

342 THE SCIENTIFIC REVOLUTION

thus decisively confuted. 1 Newton's theory, however, gave the
ratio of flattening as 229/230. A much better agreement was
obtained in Clairaut's own reinvestigation of the theory (1743),
which yielded a formula relating the earth's ellipticity to the
gravitational attraction at any latitude. 2 By these means, not only
was the application of the principles of mechanics to the great
mass of the earth itself validated, but the actual method of apply-
ing them was improved to give a better coherence between theory
and experiment. At the same time, new light was thrown on the
pendulum experiments made in different parts of the globe. The
impregnability of Newton's theory of attraction was further in-
creased, at a time when it had still to win the confidence of many
continental scientists.

The course of these events was predictable. It was certain that
if there was a controversy over the shape of the earth, it would be
settled by making measurements that was the established spirit
of the scientific revolution. It was also certain that if theory and
measurement did not wholly coincide attempts would be made to
re-examine the theory in search of some neglected factor. Exactly
this happened and the theory was improved. In contrast, other
second-order discoveries in eighteenth-century physics, though
continuations of what had gone before, were altogether unpre-
dictable. Perhaps the most striking of them was made by the
London optician, John Dollond, in 1759. Newton had supposed
that when a beam of light passed through a prism, the dispersion
of the colours in the spectrum cast was in an invariable proportion
to the degree of refraction, and quite independent of the material
of the prism. Consequently he had held that chromatic aberration
(caused by the failure of lenses to bring all colours to the same
focus, owing to dispersion) was incapable of correction. The
German mathematician Euler, thinking of the human eye as a
perfect lens-system made up of several media, suggested that a
triplet "lens" formed by enclosing water between the interior
concave surfaces of two juxtaposed glass lenses would likewise be
free from aberration. He was able to work out (1747) the required
curvatures, but attempts to put his idea into practice failed.

1 Cf. Pierre Brunet: La vie et Vcetwre de Clairaut, in Revue d'Histoire des Sciences ,
vol. IV (Paris, 1951), pp. 105-32.

2 The theory was also revised a little earlier by the Scottish mathematician
Maclaurin using methods much less comprehensive than those of Clairaut.

PHYSICS IN THE EIGHTEENTH CENTURY 343

Following Euler's suggestion, Dollond experimented on the rela-
tive dispersion and refractive power of water and glass, and later
of the two kinds of glass, crown and flint. 1 He found that in a
"doublet," consisting of a convex lens of flint-glass and a concave
lens of crown-glass, the curvatures could be so adjusted that the
dispersions were nearly equal and opposite, while the greater re-
fraction of the flint-glass enabled the combination to behave as a
convex lens. An almost achromatic object-glass for telescopes was
possible: astronomers, who had been increasingly turning to the
reflecting telescope, were once more able to make use of the more
reliable refractor. Attempts were made almost at once to apply
Dollond's discovery to the manufacture of achromatic objectives
for microscopes, a task of which the solution occupied more than
fifty years. Perhaps most important of all, Newton's authority in
optics was seriously checked, almost for the first time. His confi-
dent belief, unfounded on experiment, was exposed as an error.

The principal innovations in eighteenth-century physics were,
however, in totally new directions, showing that the conceptual
fertility and experimental ingenuity so marked in the preceding
hundred years were far from exhausted. Indeed, the two major
lines of advance were intrinsically far more difficult than those
hitherto followed. The seventeenth century had failed, for ex-
ample, both to place the science of heat on an exact quantitative
foundation, and to make the conceptual distinctions which were
essential to a true understanding of the phenomena. For these
the vague notions of corpuscularian philosophers that heat was
* nothing else but a very brisk and vehement agitation of the parts
of a body' (Hooke) were a very unsatisfactory substitute. Even
Boyle had not been able altogether to renounce the idea of "fire
particles," or to distinguish firmly between combustion and other
manifestations of heat. Eighteenth-century physicists found it more
useful to think of heat as a fluid (called caloric in the new chemi-
cal nomenclature), which flowed from hot bodies to cold; an
hypothesis which (like that of phlogiston) proved to be radically
mistaken but which served well at a certain stage.

In particular, this view of heat was extraordinarily appropriate

since most of the eighteenth-century experiments on heat were

concerned with thermal capacity and calorimetry. Measurements

of temperature by means of thermometers (though without regard

1 Flint-glass contains a large proportion of lead, crown none.

344 THE SCIENTIFIC REVOLUTION

to any widely accepted scale) had become fairly commonplace
after 1660, but for a long time no distinction was made between
the temperature of a body, and the amount or quantity of heat
present in it. This was natural enough, for it was believed that
equal weights of all substances had the same thermal capacity
that is, if equal weights of water and iron were placed in the same
oven, they would both be raised to the same temperature in a
given time. Fahrenheit seems to have been the first to note a con-
trary observation. Comparing the heating and cooling effects of
equal volumes of water and mercury, he found that the latter was
not thirteen times as effective as the former, as the density-ratio
would suggest, but only 60 per cent, as effective! From this Black
judged (about 1760) that the amounts of heat required to raise
two different bodies through the same number of degrees of tem-
perature were in a very different proportion from that of their
densities (assuming the volumes to be equal). Black went on to
compare the amount of heat required to raise i Ib. of water
through t with that required to raise i Ib. of any other substance
through 7~, which could easily be done by mixing the two to-
gether at different temperatures so that they attained a common
temperature. From this experiment the relative heat-capacities
(or specific heats) of various substances could be ascertained,
taking that of water as a standard. 1 It was easy to imagine that
different substances had different capabilities for absorbing the
matter of heat (caloric), the association of the familiar notions
fluid and capacity proving as fruitful in the science of heat as it did
later in the science of electricity.

Black's other discovery concerning the capacity of bodies for
acquiring heat was even more surprising. The plausible notion
that when a solid (such as ice, or a metal) was brought to its
melting point as shown by a thermometer, only a small amount of
further heat was required to liquefy it had not been challenged.
Similarly it was thought that a minute loss of heat was enough to
cause water at 32 F. to congeal : no discontinuity between the
solid and liquid states, in relation to heat lost or absorbed, was
imagined. Black, however, observed that after a spell of cold

1 e.g. mixing i Ib. of water at f, and i Ib. of mercury at T (T > /), the
resulting common temperature being x, the quantity of heat sufficient to
raise the mercury through (T x) has raised the water through (x f):
whence the ratio of the thermal capacities of water and mercury is as ( T #)
to (x - /).

PHYSICS IN THE EIGHTEENTH CENTURY 345

weather masses of ice and snow would last for weeks without
melting; were it not so 'torrents and inundations would be incom-
parably more irresistible and dreadful. They would tear up and
sweep away everything, and that so suddenly that mankind should
have great difficulty to escape their ravages.' A piece of melting
ice, he reasoned, must still be capable of absorbing a great quantity
of heat, although the water running from it was at freezing-point.
In other words, the ice was capable of taking up heat, without a
corresponding increase in temperature being apparent; the only
effect of this extra heat was the liquefying of the ice. It was latent,
because it seemed to be c absorbed or concealed within the water,
so as not to be discoverable by the application of the thermometer.'
Black then proceeded to measure experimentally the amount of
latent heat taken up by ice on its conversion into water, and by
water on its conversion into steam. Thus he attained the concep-
tion of a definite quantity of the " matter of heat" insensible to
the thermometer being involved in any change of physical state;
this "quantum" of heat was not a mere agent dissolving ice into
water, but was a physical constituent of water differentiating it
from ice, or alternatively, from steam.

Later, Laplace and Lavoisier were able to perfect Black's ex-
periments with the ice-calorimeter which they invented. 1 They
pointed out that such quantitative determinations could be
carried out without theoretical preconceptions, but, like Black,
they favoured the material theory, as is very evident in Lavoisier's
Traite Mementaire de Chimie. Like Black, they concluded that any
sample of matter (in a given physical state, at a given temperature)
consists of substance and heat, the absolute degree of heat being
incapable of registration on a thermometer, and residing in all
bodies even at the lowest attainable temperatures. Their experi-
ments went much further than Black's in studying the evolution
or loss of heat in chemical operations, whence it appeared that
the theory of chemistry would need to account not merely for
matter-reactions (syntheses, analyses, exchanges and so forth) but
for the heat-reactions with which these are integrally associated.
In modern terms, they had realized that questions of energy are
involved in chemical processes; as the concept energy was unknown
to them, however, they naturally tended to make the heat-reaction

1 In this instrument, the quantity of heat lost by a body in falling to o C.
was measured by the weight of water melted from a surrounding jacket of ice.

346 THE SCIENTIFIC REVOLUTION

cognate to the matter-reaction, by treating heat itself as a material
entity, and measurements of "quantities of heat" as measurement
of something, which would be conceived (at least in imagination) as
existing apart from the matter whose quantity of heat was
measured. The very obvious formulation

ice + heat -> water; water + heat -> steam

emphasized the dichotomy between the matter (water-corpuscles)
identical in ice, water and steam, and the absorbed quantity of
something measurable making the distinction between its three
states. Attempts, throughout the eighteenth century, to measure
the mass of heat by weighing heated and cooled bodies, which had
a negative result, did not disturb those who held that heat was a
weightless fluid. 1 Only in 1798 was attention called to the fact
that bodies can evolve an indefinite amount of heat through fric-
tion by Benjamin Thompson's (Count Rumford) experiments. On
the material theory the quantity of heat contained in a body at
a given temperature was limited absolutely, but in spite of this
difficulty, the kinetic view of heat (as it was less applicable, at this
stage, to any other phenomena than those of friction) failed to
displace the material theory for another half-century.

This fact is itself enough to provoke reflection among those who
hold that quantitative experiments are infallible instruments of
scientific progress. When the theory of heat was entirely qualita-
tive, not to say speculative, in the seventeenth century, a more
"correct" kinetic view prevailed. The material theory which so
successfully resisted, in the decade 1840-50, the attrition of Mayer
and Joule was decisively established by the quantitative experi-
ments of Black, Laplace, Lavoisier and others. The "correct"
kinetic view was in fact decisively obstructed by its failure to yield
neat and easily comprehensible quantitative results, and for this
reason it could not, perhaps, ever have been established save (as
it eventually was) under the cloak of a generalized concept of
energy.

In many of its aspects eighteenth-century physics represents
the pre-history of this concept. Mechanical energy, as vis viva, and
the power to do work, was very attentively considered. The first

1 It is very strange that the illogicality of the concept of matter without
weight (which has been held by some to have inspired Lavoisier's attack on
phlogiston) was one which he himself embraced in his own theory of caloric.

PHYSICS IN THE EIGHTEENTH CENTURY 347

steps towards the study of chemical energy were taken by Laplace
and Lavoisier. The very complex role of heat in physical and
chemical changes was at least partially disclosed, and in a purely
practical way the connection between heat energy and mechanical
energy was of great interest to engineers, ever extending the utility
and efficiency of the steam-engine as a prime mover. The major
invention of this period Watt's introduction of the separate con-
denser is said to have been inspired by Black's discovery of latent
heat, and certainly Watt carried on his own investigations into the
physics of heat. 1 It was clearly his purpose to squeeze the maxi-
mum mechanical value from the "quantity of heat" contained in
steam and so cut down the coal bills of those who bought his
engine but the theoretical implications, in terms of a "perfectly
efficient" engine, were only worked out by Sadi Carnot about
1824. Heat energy in the form of invisible radiation was also
known, and the likeness in properties between this form of heat
and light was recognized. Experiments to find out whether light
itself has energy for if a beam of light consisted of a stream of
corpuscles travelling at a very high speed, their impact upon an
opaque surface should be detectable, even though very minute
yielded some positive effects, but these were most probably due to
other causes. Perhaps most important of all was the elucidation
of a new form of energy, electricity. Certainly this was the most
striking, the most original, and the most progressive branch of
eighteenth-century physics. The spectacle of the erect hair, the
nasal sparks, of an electrified youth hung in silk cords from the
ceiling excited the rather coarse humour of the age; the mystery
of lightning drawn off down an iron rod and confined, like a jinn,
in a Leyden bottle, was witness to the strange power of nature and
man's intellectual mastery of it; while, at a more serious and
prosaic level, a new corpus of experimental and theoretical know-
ledge was taking shape, of incalculable importance for the future.
No one could have foreseen, in Franklin's day, the extent to which

1 It was not at all necessary, however, for Watt's purpose that the main
cause of the wastefulness of contemporary steam-engines (the chilling of the
cylinder and piston by the injection of cold water to produce a vacuum) should
have been so scientifically diagnosed. An intuitive realization of the folly of
alternately heating and cooling the same masses of metal without any produc-
tive purpose would have been amply sufficient. So that, whatever advice Watt
may have received from Black, it can hardly be said that the separate condenser
was an immediate fruit of the physics of heat.

348 THE SCIENTIFIC REVOLUTION

physics was to become the science of electricity, yet already by
1800 almost every experimental physicist was to some degree an
electrician.

All this grew from very humble origins. Gilbert had shown that
the attractive property of rubbed amber was quite widespread in
nature, and had coined such terms as "electric" (from Greek
elektron = amber), and "charged body." Soon afterwards the
mutual repulsion of similarly charged fragments of light materials
was noticed for the first time. But the first hints of more remark-
able effects followed upon the introduction of the first electrical
machines, and thus anticipated the course of the later history of
electricity: every important step was brought about by some new
instrument or device. For electrical phenomena are not made
manifest in nature; the few that occur (such as lightning) could
never conceivably have been interpreted correctly in the light of
reason. They were entirely hidden from artisans and other prac-
tical men skilled in nature's ways, no tools or instruments of
science or art could be easily adopted to an inquiry into electricity,
and the human body is very limited in its reactions to electrical
stimuli from outside. There could, therefore, be no progress in
electrical science without means of creating charges, currents etc.,
and means of revealing their various properties. Theoretical
rationalization was bound to be, in the very early stages, of rela-
tively little importance, and in any case subject to extremely rapid
fluctuations.

The first electrical machine was a globe of sulphur or glass,
mounted on an axle and rotated by a handle, which was rubbed
against the hand until highly electrified. The glow, visible in the
dark, produced by discharge between the globe and the hand was
first noted by Otto von Guericke, who also succeeded in trans-
mitting the electrical effect along a linen thread. Another curious
phenomenon observed at about the same time was for long unre-
lated to electricity. This was the luminosity in the vacuum of a
barometer when the mercury was shaken. Only in 1745 was it
shown that under these conditions the glass tube became electrified,
though Hawksbee, about 1710, had caused a similar glow to
appear upon an electrical machine worked in vacuo, and inside an
exhausted vessel rubbed externally. Hawksbee allowed a chain
to hang against the globe of his electrical machine, so that the
charge would be taken to a large "prime conductor," but the next

PHYSICS IN THE EIGHTEENTH CENTURY 349

improvement the use of a soft rubber instead of the operator's
hand was only introduced a little before the middle of the
century.

The study of conduction was taken further by Stephen Gray
(1732), who found that charges could be transmitted along, or
induced into, very long lines of thread when these were suitably
supported. He was thus led to make the fundamental distinction
between insulators and conductors, for silk filaments did not permit
his charges to leak away, while equally fine copper wires did.
Hair, resin and glass proved like silk non-conducting. A French-
man, Charles Dufay, had the ingenuity to mount a variety of
substances upon insulating supports in order to demonstrate that
all including the metals could be electrified by friction when
isolated from the earth; he saw that Gray's distinction between
insulators and conductors was really more primary than the
established one between electrics and non-electrics, to which it
had seemed analogous. Dufay, moreover, discovered that a frag-
ment of gold leaf, charged with an electrified glass rod, was not
repelled (as he expected) by a piece of electrified amber, but
strongly attracted to it. The lesson, from magnetism, was obvious
enough; the two charges, the one "vitreous" and the other
"resinous," were of opposite sign. In the neutral state all bodies
contained equal quantities of both electricities; the action of fric-
tion was to remove a part of one or the other, leaving behind
a superfluity of the second.

Any substance could be charged on a suitable stand. A number
of experimenters tried to electrify water in insulating glass vessels:
they discovered, to their distress, that if with one hand grasping
the jar full of liquid, with the other hand they tried to take away
the wire leading into it from the electrical machine, they ex-
perienced a frightful shock. They had, in fact, formed a condenser
and discharged it through their bodies: it was an easy step to
make the "Leyden jar" more convenient by lining it within and
without with metal foil and to learn to handle it with greater
caution. With the aid of powerful frictional machines, and the
large charge built up in a Leyden jar, it was possible by 1750 to
produce very striking sparks, and discharges heavy enough to kill
small animals or to be transmitted through long circuits of wire
or water. Attempts were even made to estimate the velocity of
the motion of a charge by the interval between two sparks across

350 THE SCIENTIFIC REVOLUTION

gaps separated by a long circuit: but of course without success.
The heating effect of electricity (e.g. in melting fine conductors) was
easily perceived as were some of the effects associated with dis-
charge through a vacuum. Upon electrical theory the effect of the
discovery of the condenser was profound. The dualistic hypothesis
of Dufay was clearly susceptible of simplification: it was unneces-
sary to suppose that there were two kinds of electricity (com-
parable to the two poles of a magnet) for " oppositeness " could be
taken, as in mathematics, as a difference in quantity rather than
a difference in quality. On such a view, with a normal charge a
body would be neutral, with an excess of electricity positively
charged, and with a defect of electricity negatively charged. This
view could be applied with particular success to the novel
phenomena revealed by the condenser.

The man who so applied and developed the unitary theory of
electricity was Benjamin Franklin (1706-90), retired printer of
Philadelphia, popular philosopher, later hero of the American
revolution and elder statesman of the young republic. With his
plain common sense and distrust of subtlety, Franklin combined
an active scientific imagination sharpened, perhaps, by his almost
complete ignorance (during the creative stages of his work) of
European theories. In his opinion, which strongly reflected the
corpuscularian ideas of the age, electricity was a fluid, consisting
of particles mutually repelling each other, but strongly attractive
to other matter, which distributed itself uniformly as an "atmo-
sphere" about a body or connected system of bodies. Electrification
was a process whereby an excess of this fluid was collected upon a
particular body, such as a glass rod, by friction or other means, so
that it became positively charged; or removed from it so that it
became negatively charged. Franklin believed (mistakenly) that a
discharge was simply a transfer, often in the form of a unidirec-
tional spark, from a body more highly charged with the fluid to
one less charged; and the repulsion between two positively charged
cork balls was readily attributed by him to the repulsion between
the excess of electric particles. When Franklin became aware that
negatively charged bodies also repel each other, he encountered a
difficulty which his theory could not overcome. He fully realized
the importance of the deduction, from his fluid theory, that within
a closed system the quantity of electricity must be conserved: a
person, placed on an insulating stand, could collect a positive

PHYSICS IN THE EIGHTEENTH CENTURY 351

charge upon a glass rod by rubbing it, but only by electrifying his
own body negatively to an equal degree, that is, by forcing
electricity from his body into the tube. By inverse reasoning from
the same principle Franklin explained the action of the condenser,
for every addition of electricity to one of its surfaces produced a
corresponding loss (to earth) from the other, as shown by the fact
that the Leyden jar could not be charged unless one plate was
earthed. The total quantity of electricity in the jar was always
constant, only its distribution being modified by electrification
since a connection between the plates (under any conditions)
ensured a return to the neutral state. Franklin regarded the
condenser as fully charged when all the electric " atmosphere"
had been driven off the earthed plate, for then no more could be
added to the positive plate, since this would have increased the
total quantity present.

This theory, and the experiments intended to confirm it, of
which many were already familiar to European electricians, were
warmly welcomed, as indeed were all contributions to science
from the New World at this time. But at first Franklin's letters did
not carry conviction, nor did they have any very dramatic effect.
Strangely, it was a less creditable, but more showy, suggestion
that brought about his lionization. Many electricians had noted
the similarity between the electric spark and lightning and be-
tween the accompanying crackle and thunder, speculating on the
possible identity of the two effects; there was therefore nothing
very new in Franklin's similar speculation. He, however, had
noticed particularly the powerful action of pointed conductors in
"drawing off" a charge silently and conjectured that if thunder-
clouds were, as he supposed, positively charged, the fact could be
revealed by drawing electricity away to a high, pointed conductor.
Having described the experiment, he failed to execute himself
(for a variety of reasons, among which lack of courage was
certainly not one). It was first successfully performed in France,
soon after the translation of Franklin's early letters was made.
The well-known "Kite experiment" at Philadelphia was carried
out, with a like result, before news of the French attempts and
of his own sudden fame as the tamer of lightning had reached
Franklin in America. Richmann, at St. Petersburg, was the first
"martyr" to the pursuit of this new branch of electrical
science.

352 THE SCIENTIFIC REVOLUTION

Until the moment of Franklin's intervention (1746-55) elec-
tricians had been wholly preoccupied with qualitative effects.
Most of the material published had dealt with the description of
phenomena, which the experimenters had sought to explain in the
light of ad hoc hypotheses, each of them jejune in varying degrees
and inadequate to explain all the facts. Franklin himself had not
sensibly modified this state of affairs, for though his single-fluid
theory was more comprehensive than any other, it was not com-
pletely so, nor did it really rise above the phenomenalistic level of
his work. The revisions he introduced himself were sufficiently
serious for it to be classified (logically) as no more than a pro-
visional working hypothesis. The investigation of new effects
continued to be of some importance as, for example, in the study
of induction, of the role of the dielectric in condensers, and of
pyro-electric phenomena but a more rigorous inquiry into the
quantitative aspects of electrical phenomena grew up alongside it
during the second half of the century. In accordance with the
general principle already mentioned (p. 237), the electrician's
apparatus, which had formerly been limited to the revelation of
the qualities of electricity, now began to be adopted to measure
quantities. An interesting instance of this is the elaboration, from
the pith-balls and gold-foils formerly employed to test for the
existence of charges, of the torsion-balance of Coulomb (c. 1 784)
and the electrometer of Bennet (1787). Hitherto, though the
achievement of solid additions to knowledge and the ingenuity of
theorization must be duly recognized, experiment and thinking
in electricity had been amateurish, for the former had often
partaken of the nature of a parlour game, and the latter had
included much extravagance. The rapid success of Franklin,
starting almost from zero, is an indication as well of the super-
ficiality of the subject, as of his own ability. Now, however,
electrical science began to acquire a more serious status as a
branch of physics.

Among the first to deny themselves the pleasure of declaring
what electricity is, was Joseph Priestley. His precisely regulated
experiments on conduction contain the seeds of later ideas of
electrical resistance; like ^Epinus a little earlier, he found that
the distinction between conductors and insulators was far from
absolute. Priestley used the length of a spark-gap, across which a
discharge would jump instead of traversing a long circuit, as a

PHYSICS IN THE EIGHTEENTH CENTURY 353

measure of the circuit's resistance. He repeated Franklin's experi-
ment to show that there is no charge inside an electrified hollow
vessel of metal, and deduced from it (by analogy with a familiar
theorem on gravitational attraction) the opinion that c the attrac-
tion of electricity is subject to the same laws with that of gravita-
tion ' that is to say, it varied proportionately to the inverse square
of the distance. This was perhaps the first proposition about
electricity that could be formulated mathematically, and more-
over a prediction to which experimental verification could be
applied. This was done by Robison two years later (in 1769), by
Cavendish, and by the French engineer Coulomb. Cavendish
designed an ingenious apparatus by which one metal sphere could
be enclosed within another, with or without electrical contact
between the two, finding that the charge applied was invariably
confined to the outer sphere. He ascertained that the electric
force must vary as the square of the distance within limits of
db ! per cent. Many other quantitative experiments (partially
anticipating the later work of Michael Faraday) were performed
by him about 1771-3, which with typical unconcern he kept
entirely to himself. He was the first electrician to adopt a standard
of capacity (a metal-covered sphere, 12 i inches in diameter), with
which he compared the capacities of other bodies, stating these
as "inches of electricity," that is as the diameters of spheres of
equal capacity, and to realize that the charge upon a conductor
is proportional to both its capacity and the " degree of electrifica-
tion" applied. By "degree of electrification " Cavendish under-
stood the extent to which the "electric fluid" was compressed
into a body, so that he approached very near to the later concept
of electrical potential. He also knew that the capacity of a con-
denser varies with the material of the dielectric, and made several
measurements of what Faraday was afterwards to name specific
inductive capacity. He measured the conductivity of a variety of
solutions in glass tubes, discovering that this was independent of
the size of the discharge passed through them. Considering that
he made use of crude pith-ball electrometers, and relied upon his
own senses to compare the violence of electric shocks, the numeri-
cal results he obtained were astonishingly good. All this work,
unfortunately, had no effect upon the subsequent progress of
electrostatics, as it was totally unknown. The inverse square law of
electric force was first demonstrated in print by Coulomb (1785),

23

354 THE SCIENTIFIC REVOLUTION

in experiments one of which was similar to that of Cavendish,
while others made use of Coulomb's torsion-balance for the direct
measurement of forces. These experiments in turn served as the
foundation for Poisson's mathematical study of electrostatic forces
in the early nineteenth century.

The interval was marked by no important discoveries. This was
undoubtedly due in very large part to the sudden fascination of a
new set of phenomenalistic effects, wholly unsuspected, in which
electricity appeared in another of its Protean forms. Hitherto the
manifestations of electricity had been limited to two groups: (a)
shocks and sparks, (b) repulsions and attractions. To the first
group belonged, besides the laboratory effects, those of lightning
and the torpedo or electric fish. No serious physiological study had
been made of the first group of effects it was merely known that
a shock produced violent muscular contractions, and followed a
more or less direct path through the body though the adminis-
tration of shocks was (like most other things) regarded as having
a medical value. Hence experimentation in electricity had been
practically confined to the exploitation of the attraction-repulsion
effect in a variety of different ways. This in turn had its influence
on theory. In the first place electricity was literally regarded as an
effluvium, a particulate atmosphere surrounding the charged body.
How, Newton had asked, can an electrified body 'emit an ex-
halation so rare and subtle, and yet so potent, as by its emission
to cause no sensible diminution of the weight of the electrick
body . . .P' 1 Then again, the Abbe Nollet (1700-70) had sup-
posed repulsion and attraction to be the work of outflowing and
inflowing streams of the electric fluid. Later in the century, the
analogy between electrical and gravitational attraction becoming
more obvious, the electric effluvium seemed as absurd as the gravi-
tational effluvium of pre-Newtonian physicists, and "action at a
distance" was accepted. Thus the theory of electricity passed
through various phases of mechanical explanation, much as the
theory of gravity had done in the seventeenth century, owing to
the focussing of attention upon its mechanical manifestations.
Just as the weightless fluid caloric was capable of mechanically
expanding bodies, so the weightless electric fluid was capable of
putting them in motion even of causing continuous rotation in
a light wheel. Mechanical analogies really justified the concept of

1 Opticks, Query 22.

PHYSICS IN THE EIGHTEENTH CENTURY 355

electricity as a fluid, whose particles were capable of action at a
distance, for electricity could flow along conductors, filling bodies
to their "capacity," and yet be impeded by "impermeable" sub-
stances. Borrowings from the languages and ideas of hydraulics
are indeed obvious; Cavendish's concept of electrical "pressure"
showed how fertile they could be.

It is the nature of a fluid, even an elastic fluid, to flow, and the
study of "electrostatics" had actually embraced some investiga-
tion into the flow of electricity along conductors. But the effects
produced by the flow of charge (under the prevailing conditions of
experiment) were not striking as compared with the mechanically
obvious effects of a static charge. The motion of electricity, re-
vealed by a spark or a shock, was in any case a transient event,
restoring the apparatus to a condition of electrical neutrality, so
that the phenomenon of electricity had always appeared to be
discontinuous, indeed so much so as to be almost adventitious.
Charges were immediately annihilated by conduction to earth,
and no perfectly insulating material was known. They were
formed only by the chance electrification of a cloud, or by the
discontinuous action of friction, which suggested that they were
mechanically produced. The appearance of all the known effects
depended upon the discontinuity in the movement of electricity,
leading to the accumulation of large static charges.

The discovery of new manifestations of electricity was thus of
absorbing interest for a variety of reasons. These were not the
result of mechanical action, nor were they themselves mechanical
in nature. They were continuous, and they required no effort. In
the prevailing theory some segregating action was necessary to
bring about the conditions of electrification the fluid had to be
impelled from one body to another, leaving the former unnaturally
empty and making the latter unnaturally full so creating an un-
balanced state which nature herself sought to adjust at the first
opportunity. The new effects predicated no such positive action;
it was not necessary, in order to produce them, to build up
mechanically an artificial "degree of electrification."

The differences between the new phenomena and the old were
sufficient, at first, to obscure the connection between them. About
1780, in the laboratory of the Italian anatomist Luigi Galvani
(1737-98) at Bologna, an assistant happened to notice that when
he touched with his scalpel the crural nerve of a frog's leg which

356 THE SCIENTIFIC REVOLUTION

he was dissecting the muscles were violently contracted. It was
remarked that this occurred while a spark was being drawn from
an electrical machine placed on the same table. Galvani repeated
the strange experiment, under the same conditions and with a like
result. He introduced many variants, all of which proved that the
experiment failed unless the operator was in electrical connection
with the nerve, and the frog's leg effectively earthed. From this
Galvani suspected that some sort of electrical circuit was involved
for muscular contractions were known to occur when discharges
were sent through dead animals even though the frog was not
directly linked to the electrical machine. Many experiments were
performed at this stage to gain conviction that the stimulus was
really electrical. The next major step was a successful demonstra-
tion that lightning flashes acted upon the limb in an identical
fashion when similar electrical connections were made to it. In the
course of these atmospheric experiments Galvani observed that
frogs hung from an iron lattice in his garden by brass hooks pene-
trating into the spinal marrow gave occasional convulsions. Once,
happening to press one of the hooks firmly against the iron, he saw
immediate contractions. At first he thought that these were due to
the escape to earth of some atmospheric electricity accumulated
in the frog. To test this suspicion he re-created the same condi-
tions indoors, placing the frog on an iron plate and pressing the
brass hook firmly against it. Still the convulsions occurred ( 1 786) .
Other combinations of metals, or even a circuit through his own
body, or a homogeneous wire, with which he made a " conducting
arc" between nerve and muscle, had the same effect, but not in-
sulators. Again Galvani satisfied himself by elaborate experiments
that the decisive circumstance was the existence of a path along
which electricity could flow.

Had he been a more enthusiastic electrician, Galvani might
have inquired more fully into the curious situation in which a
spark from an electrical machine or Leyden jar could influence
a frog's leg insulated from it. Instead, after his discovery that the
spark was unnecessary provided that a direct connection was made
between nerve and muscle, he abandoned that subject. At this
point two other lines of inquiry suggested themselves. He could
examine more carefully the nature of the electrical circuit, and
this he did in some detail, finding that some metals were less
effective than others in the conducting arc, that liquids could be

PHYSICS IN THE EIGHTEENTH CENTURY 357

used, and that a single conductor was less effective than one made
up from two metals. But he did not attach great importance to the
bimetallic circuit, because convulsions were obtained with a single
conductor. He was therefore led to concentrate upon the second
line of inquiry, convinced as he was that Leyden jars, machines,
thunderstorms and other familiar sources of electricity could be
excluded from his explanation of the phenomena, and that the
conducting arc was simply an ordinary conductor of electricity.
The physiology of the frog's reactions now drew his attention,
since it appeared that the mere electrical connection of nerve and
muscle was capable of causing the same contractions as the appli-
cation of an electrical stimulus to these parts. In the former case
the electricity moving along the conductor must have been sup-
plied by the frog itself. To hypothesize further still, was not the
stimulus given by a nerve to a muscle always electrical, for (as he
said) ' the hidden nature of animal spirits, searched for in vain
until now, appears at last as scarcely obscure' it was electricity!
Prepared in the brain, and distributed by the nerves, this "animal
electricity" on entering the muscles caused their particles to at-
tract each other more strongly, and the fibres correspondingly to
contract. In the muscles also electricity was stored, as in a Leyden
jar, so that from a communication between them and a nerve
ensued the convulsions witnessed in his last series of experiments.
Thus Galvani brought his electrical discoveries to a close by
riding off on a physiological hobby-horse, abandoning physics in
order to debate how his new knowledge of animal electricity
might be applied to the cure of disease. Many other scientists
eagerly followed his example.

An alternative and less dramatic interpretation would have
made the frog's leg merely a sensitive detector of an electric
current through the circuit linking nerve and muscle, as in Gal-
vani's first experiments, the stimulus for the convulsions being
always supplied by an external source of electricity. On this view,
little compatible at first sight with his later discoveries, Galvani
had not discovered a new example of animal electricity (already
familiar in electric fish) ; he had invented a new electrical instru-
ment, and a new source of electricity in motion the bimetallic
conductor of his last experiments. This was the interpretation of
Galvani's work put forward by Alessandro Volta (1745-1827) of
Pavia in 1792, about a year after the first account of them was

358 THE SCIENTIFIC REVOLUTION

published. At first Volta had given credence to Galvani's own
explanation, hailing his discoveries as no less epoch-making than
those of Franklin. Gradually, however, Volta uncovered facts
which compelled him to differ from Galvani. The most delicate
electrometer revealed no electricity in animal tissues; to cause the
muscles to contract, it was only necessary to apply an electrical
stimulus to the nerves, and not to the muscles themselves; and to
create this stimulus a bimetallic junction was essential. 1 Finally,
in a letter destined for the Royal Society, Volta asserted that the
frog's leg as prepared by Galvani was nothing other than a deli-
cate electrometer, and that most of the phenomena attributed to
animal electricity were ' really the effects of a very feeble artificial
electricity, which is generated in a way that is beyond doubt by the
simple application of two different metals. 5

By this time [wrote Volta in November 1 792] I am persuaded that
the electric fluid is never excited and moved by the proper action
of the organs, or by any vital force, or extended to be brought from
one part of the animal to another, but that it is determined and con-
strained by virtue of an impulse which it receives in the place where
the metals join. 2

He had invented a new theory of contact electricity, and was
compelled, in its defence, to criticize the physiological views of
the wretched Galvani, who died in despair after some years of
futile controversy. Meanwhile Volta continued his experiments.
He found that the metals whose contact caused a flow of electric
fluid could be arranged in a definite order, that other conductors
such as carbon had the same effect, and that any moist conductor,
such as water, served to bridge the different metals as well as
animal tissues. By 1795 he had propounded the "law" that when-
ever two dissimilar metallic conductors were in contact with each
other and a moist conductor, a flow of electricity took place. In
1 796 he demonstrated that the mere contact of different metals
produced equal and opposite charges upon them, made visible
by the electroscope. This was the first proof of the identity of
galvanic and frictional electricity, of which Volta had always been
convinced. The charges, which appeared to be indefinitely pro-
curable, were positive or negative according to the order of the

1 Volta ascribed the effects obtained by Galvani with a single conducting
element to lack of homogeneity and other differences in the metal.

2 Opere (Firenze, 1816), vol. II, pt. i, pp. 165-6.

PHYSICS IN THE EIGHTEENTH CENTURY 359

metals used in the series which he had discovered earlier. 1 The
intensity of the effects produced was still minute, and Volta real-
ized that it could not be increased by multiplying the number of
bimetallic junctions so much was obvious from the distribution
of charges. The case was different when two or more pairs of metal
plates in contact were joined together, not directly or by use of a
third metal conductor, but by one of the moist conductors such
as salt water, either placed in cups into which the metal plates
were dipped, or soaked into cardboard discs inserted between each
bimetallic pair. In this arrangement (described by Volta in 1800)
the intensity of the effects produced was proportional to the number
of the pairs of plates, so that Volta could charge condensers,
produce sparks, and give severe shocks. This " artificial electrical
organ" (which Volta compared to the natural electrical organs of
certain fish), electromotor, or pile, as it was afterwards called, was
as he said like a feebly charged Leyden jar of immense capacity,
for it would yield electricity continuously. The continuity of the
flow of electricity from terminal to terminal of the pile was par-
ticularly emphasized by Volta in his descriptive letter to the Royal
Society; as there was no instrument suitable for the detection of
continuous currents, he had to quote his physiological sensations
in proof of their existence. The situation was paradoxical, but none
the less real.

It seems clear that Volta, who was little interested in the
chemical effects associated with the passage of an electric current,
completely misunderstood the functioning of the single cells in
his pile. He regarded the "electric force" as originating from the
contact of two different metals, not from the reaction of these
with the moist electrolyte between them. In modern theory the
voltaic cell consists (for example) of copper, electrolyte and zinc;
but to Volta himself the copper-zinc junction was the "cell,"
the source of electricity, and the electrolyte served merely to
connect these together without neutralizing the charges collected
on the metals. He was still thinking, essentially, in electrostatic
terms:

The action exciting and moving the electric fluid is not due, as is
falsely believed, to the contact of the humid substance with the metal;
or at any rate it is only due to that in a very small degree, which may

i.e. -f Zn, Pb, Sn, Fe, Cu, Ag, Au, C . These experiments were only made
possible by Volta 's improvement of the electroscope in earlier years.

360 THE SCIENTIFIC REVOLUTION

be neglected in comparison with that due to the contact of two
different metals, as all my experiments prove. In consequence the
active element in my electromotive apparatus, in piles, or in cups, or
in any other form that may be constructed in accordance with the
same principles, is the mere metallic junction of two different metals,
certainly not a humid substance applied to a metal, or included be-
tween two different metals, as the majority of physicists have claimed.
The humid layers in this apparatus serve only to connect the metallic
junctions disposed in such a way as to impel the electric fluid in one
direction, and to make this connection so that there shall be no
action in a contrary direction. 1

This theory did not long survive. As Nicholson pointed out in
1802, an electric current could be drawn from cells consisting
of one metal and two electrolytes, and by this time already the
work on the new form of electricity was assuming a markedly
chemical character. Fabroni, in 1 796, had observed the oxidation
of one of a pair of plates of different metals joined together and
immersed in water. Ritter had perceived that the order of the
metals in Volta's series was a chemical order that of their
exchange in solutions of their salts. Very soon after Volta's letter
of 1800 reached London, Nicholson and Carlisle, experimenting
with the first of his piles to be constructed in England, had, by
following up a chance observation, electrolysed water into oxygen
and hydrogen. Solutions of metallic salts were rapidly decomposed
by the same means. Even in the mid-eighteenth century chemical
changes had been effected by electrostatic discharges, so that a
way of proving yet more firmly the identity of frictional and gal-
vanic electricity offered itself. It was certain that electrical forces
could bring about a chemical change; was the converse also true?
Humphry Davy asserted this boldly. In 1800 he pointed out that
the voltaic pile could act only when the electrolyte was capable
of oxidizing one of the metal elements, and that the intensity of
its effect was directly related to the readiness of the electrolyte to
react with the metal. Six years later, in a Bakerian lecture, Davy
said:

In the present state of our knowledge, it would be useless to attempt
to speculate on the remote cause of the electrical energy, or the
reason why different bodies, after being brought into contact, should
be found differently electrified; its relation to chemical affinity is,

1 Opere, vol. II, pt. ii, p. 158; (written in 1801).

PHYSICS IN THE EIGHTEENTH CENTURY 361

however, sufficiently evident. May it not be identical with it, and an
essential property of matter?

For on Davy's view, in accord with his experiments on contact
electricity, in the simplest types of electrochemical activity an

alkali which receives electricity from the metal would necessarily, on
being separated from it, appear positive; whilst [an] acid under similar
circumstances would be negative; and these bodies having respect-
ively with regard to the metals, that which may be called a positive
and a negative electrical energy, in their repellent and attractive
functions seem to be governed by laws the same as the common laws
of electrical attraction and repulsion. 1

Thus Davy held that the concept of affinity, upon the basis of
which the phenomena of chemical combination were explicable,
was itself to be explained in terms of electrical forces or "energies."
His prediction that electrolysis would prove to be a most valuable
tool of chemical analysis was well borne out in the following year
when, by this method, he isolated potassium from potash and
sodium from common salt.

In the same lecture of 1 806 Davy presented his electrochemical
theory of the voltaic pile. He thought that, owing to the opposite
"electrical energies" of the metals used, decomposition of the
electrolyte occurred by the breaking down of its natural affinity,
as in a solution of salt (for example) c the oxygene and the acid
are attracted by the zinc [plate], and the hydrogene and the
alkali by the copper [plate].' The production of electricity, when
the plates were joined in a circuit, was continuous because the
chemical action, that is the solution of zinc in the electrolyte and
the evolution of hydrogen from the copper plate, was continuous:
'the process of electro motion continues, as long as the chemical
changes are capable of being carried on.' Davy also believed that
owing to the tension created by the electrically opposed metals,
the whole of the electrolyte was in a state of continual decompo-
sition and recomposition. There were obvious defects in this
account, but it had the great merit of integrating in one hypo-
thesis the facts of contact electricity, discovered by Volta, and the
facts of chemical change associated with the flow of electric
current through compound bodies. Evidently Davy realized that
the action of electrolysis and of the voltaic pile are essentially the

1 Philosophical Transactions, 1807, pp. 33, 39.

362 THE SCIENTIFIC REVOLUTION

same, though the one requires an electric current to be applied,
and the other yields a current. At the same time he recognized
that electricity could be produced without chemical change, and
chemical changes occur with which no electrical effects were
associated; therefore chemical changes could not be 'the primary
causes of the phenomena of GALVANISM.'

The scope of electrochemical theory was extended and defined
by the Swedish chemist J. J. Berzelius, whose first memoir ap-
peared in 1803. To pursue it farther would be to exceed the limits
of this volume. What may be noticed is the significance of the
sudden emergence of this young branch of science, electricity, as
a bridge between physics and chemistry. A situation in which
certain phenomena had been studied for their physiological
significance, then reinterpreted by a physicist, and finally taken
up by chemists, was absolutely unprecedented in science. The
still-mysterious unity of nature was once more vindicated. For
twenty years the chemical manifestations of electricity dominated
research almost as completely as its mechanical manifestations
had in the eighteenth century; it was not until about 1820, with
the work of Oersted and Faraday, that the mechanical effects of
current electricity (provided by the voltaic battery) attracted
attention. Similarly, and inevitably, the mathematical theory of
electric current was many years younger than that of electric
charges, since in each case the mathematical theory was developed
from the quantitative measurement of mechanical effects. All
this was the fruit of the one crucial invention of the voltaic pile,
the battery as it was soon to be called, to which Volta was led
systematically from the first chance observations of Galvani. The
chemical effects of transient electrostatic discharges had aroused
little interest, whereas those of current electricity were spectacular.
They raised the question of the relationship between the thing
"electricity" or "electric fluid" and ordinary ponderable matter
in a new and challenging form. Not only did electricity appear
(in Davy's words) as c an essential property of matter' this, after
all, in a different context, was the conclusion already drawn by
Franklin and Dufay it was rather that electricity was an active
and determinant concomitant of matter without which, according
to Davy and Berzelius, the chemical behaviour of the elementary
forms of matter would be inconceivable. It was a logical conse-
quence of the electrochemical theory that electricity was very far

PHYSICS IN THE EIGHTEENTH CENTURY 363

from being a kind of discontinuous abnormality, of concern only
to the curious electrician who took pains to disturb bodies from
their normal condition of comfortable neutrality. Electricity was
not an adventitious atmosphere, or other circumstance, like
humidity, which could be left out of account except for very
special circumstances. From being casual, the rapid progress of
ten years rendered it causal, having a function deeply involved
in the differentiation of the various species of matter. Within a
few more years the physicist was constrained to follow the chemist
in making necessary adjustments so that he too could own in
what sense electricity was "an essential property of matter,"
thus commencing his long ascent to the truth that the concepts
" electricity" and " matter" are not complementary, but actually
inseparable. In short, through the electricians' research, the link
between the mathematical conception of matter, begun by
Newton, and the empirical (or at least pragmatic) conception of
matter proper to chemistry, was at last indicated although it is
even yet far from being completely established.

CONCLUSION

MUCH more has been learnt about Nature, from the struc-
ture of matter to the physiology of man, in the last century
and a half than in all preceding time. Of this there can be
no doubt. But the scientific revolution ends when this vastly de-
tailed exploration began, for it was that which made such investi-
gation possible. At this point, in the early nineteenth century, a
scientific paper on almost any topic is intelligible as a direct pre-
cursor to research which still continues. With infinitely feebler
tools, but with the same insistence upon accuracy in observation,
the same confidence in quantitative experimentation, the same
enmeshing of theory, hypothesis and factual reporting which
philosophers then and now found so resistant to logical analysis,
men were tackling their problems as scientists today are tackling
far more complex ones.

It has become almost a truism to assert that the development
of natural science is the most pregnant feature of Western civiliza-
tion. With technology and this is hardly any longer an independ-
ent characteristic it is the one product of the West that has had a
decisive, probably permanent, impact upon other contemporary
civilizations. Compared with modern science, capitalism, the
nation-state, art and literature, Christianity and democracy, seem
regional idiosyncrasies, whose past is full of vicissitudes and whose
future is full of dark uncertainty. Each of these features of Western
civilization has made its contribution to the genesis of science, to
which perhaps their combination was essential, but one may
imagine that science can flourish after one or all of these has lost
its historic individuality. Indeed, that is already happening.
Modern science was the offspring of a form of society which has
lasted some four hundred years, playing a dominant role in world
history; that form of society is now in dissolution, but it seems un-
likely that science will necessarily disappear with it. For this, more
than any other feature of Western society, has been the cause of the
changes that we witness, and this also will be the most powerful
influence on the moulding of a future society.

If this much or even a fraction of it be granted, it seems

364

CONCLUSION 365

unfortunate that we understand the genesis of modern science as
little as we do. The modern study of Nature alone has had a de-
termining effect upon the course of civilization, on history in its
political, economic and intellectual totality. The science of Egypt
and Babylonia, China and India, Greece and Islam and medieval
Christendom had no such effect. The recovery of it by historians
contributes little in a positive way to the understanding of the rise
and decay of these societies, though such work does illuminate the
origins and peculiarities of modern science. Among the challenges
to which these societies responded successfully, or failed to meet,
the ubiquitous challenge of Nature was certainly one; but the
organized, conscious, rational response to it that we call science
was of minor importance. Because of this, because some of these
earlier strivings with Nature are continuously connected, and
because all of them share certain common characters distinguish-
ing them from modern science, they may be grouped together as
intermediate between yet more primitive attempts to explain and
master the mysteries of man's environment, and modern science.
We know that modern science emerged from this intermediate
stage, from which no other society than the recent western Euro-
pean was capable of escaping, and it is this emergence that we do
not adequately comprehend.

Many questions have been cursorily handled in this book be-
cause satisfactory discussion would require a different and much
more extensive treatment. Perhaps it is not possible yet. Little is
known about the immediate pre-history of the scientific revolu-
tion, which seems to demand a fundamental revision of the con-
cept of the Renaissance: the relationship (for example) between
Oresme and Leonardo, between Leonardo and Galileo, as men
each thinking about Nature in a different way, is still obscure.
Equally so are the relations of art, technology and science at this
critical period, though it is easy to frame hypotheses, and conse-
quently the whole problem of the connection between the changes
in society and the concurrent changes in science is involved in
doubt, to all but the dogmatic Marxist. Above all, the crucial
question of the scientific revolution is seen through a veil which
philosophers have hardly begun to raise. Why do men commit
themselves to one kind of proposition about Nature rather than
another? Why do they (in the absence of factual guidance) find
one type of statement more plausible than an alternative? Why

366 THE SCIENTIFIC REVOLUTION

prefer discourses about corpuscular streams, to talk of spirits, when
there is no evidence for either? Why believe (or not believe) in the
existence of the vacuum? Such questions are less relevant to the
understanding of recent science (though perhaps not wholly
negligible), but to the understandings of its origins they are vital.
Men's thoughts and actions were modified in ways that we simply
cannot ascribe to the results of observation and experiment; by
such standards, for example, the whole history of Cartesian science
is utterly incomprehensible.

Why do men reject one kind of science in favour of another?
Why in modern Europe alone did they move from the intermediate
to the modern stage? The answer cannot be simple, or single. It
requires psychological and philosophical insight, as well as a com-
mand of the historical facts, to which we have as yet scarcely at-
tained, for the operation, the incidence, and the impact of the
creative intellect are almost unknown. We cannot rely only upon
appeal to experiment, observation, measurement, or any other
over-simplification of the complex processes of science, to present
us with a solution to this problem. Still less hopeful is the economic
interpretation of the history of science, which seeks to tell us why
men sought for control over natural forces, but cannot explain
how they were able to acquire it. The economic motive may have
made their attitude to Nature less disinterested, but cannot alone
have changed its character. So, too, we recognize that precision
in measurement has been of great importance, that experiment
is the touchstone of hypothesis, that to the percipient observer the
unexpected is always a fertile challenge. Yet many of the most
dramatic challenges in the history of science have issued not from
the unexpected, not from the spectrum that was oblong instead of
round, not from the frog's leg that jerked instead of remaining
still, but from the orthodox, the expected, the familiar pattern of
experience and thought. What predisposed men to struggle for the
moving earth, atomism, evolution, and so disturb the calm quies-
cence of their time when no awkward barrage of fact enforced
their turbulence? For, contrary to the straightforward inductive
view of science, it has often happened that men have looked for
facts to demonstrate a theory, as Galileo, Boyle and Newton did,
without science being any the worse for that. Perhaps the finest
minds are capable of stretching far beyond the immediate war-
ranty of facts.

CONCLUSION 367

If we admit so much, we may admit more. If modern science is
not merely an elaborate digest of pointer-readings, then it is the
more obvious that the scientific revolution involved more than
the discovery of ways of making such readings and digesting them
into a coherent synthesis. In the growth of modern science creative
imagination, preferences, assumptions and preconceptions, ideas
of the relations of God and Nature, arbitrary postulates, all played
their parts. Here then is the crux; that we cannot write the full
history of science save by reflecting the operations of original
thought, which we do not understand; and that we cannot exclude
from science, which is rational, the influence of factors which are
irrational.

APPENDIX A
BOTANICAL ILLUSTRATION 1

CERTAINLY naturalistic representations, both botanical and zoological,
may be attributed to the medieval period but only to its beginning
and end. Such are to be found in the Greek Codex Vindobonensis (fifth
century) or in the Latin herbal of Pseudo-Apuleius (seventh century) ; in
both, however, there is already evidence of degeneration from the best
Hellenistic models. They occur again in the works of miniaturists and
other artists from the end of the fourteenth century onwards. Between
these periods formalism and symbolism flourished and 'it is safe to
assert that at the beginning of the thirteenth century scientific botanical
illustration reached its nadir in the west' (Blunt). The herbal was then
a mere uncritical catalogue, illustrated by figures which are purely
conventional and heavily stylized. Botanical knowledge revived under
the influence of the translators, as in the De Plantis of Albert the Great
(c. 1200-80), the Herbal of Rufinus (c. 1290) and the Buck der Natur
of Conrad von Megenburg (1309-74), all of which show occasional
evidence of first-hand observation. Some originality is also shown in
utilitarian writings of the thirteenth century and later dealing with
hunting, falconry and agriculture. But the revival of naturalistic illus-
tration was wholly the work of the artist, during the first stages of the
Renaissance. Some of the best early representations of plants come
from the brushes of Botticelli or the brothers van Eyck, as later from
Durer and Leonardo. Manuscripts equally prove that it was the artist,
not the man of learning, who returned to the natural model. Some ex-
cellent figures, like those of Cybo of Hy&res, are purely decorative and
have no relation to the text they adorn. The almost contemporary
Burgundian school of illuminators and Italian artists developed in the
first years of the fifteenth century great technical and artistic skill in
the representation of plants, producing such masterpieces as the herbal
of Benedetto Rinio, prepared by Andrea Amadio, now preserved at
Venice. The earliest printed herbals, however, still maintained the old
stylized convention, seen for example in the English Crete Herball (1526).
Only with the work of Brunfels (Herbarum viva icones, 1530-36, illus-
trated by Hans Weiditz) and of Fuchs (Historia stirpium, 1542, illustrated
by Albrecht Meyer) was naturalistic interpretation transferred to the
wood-cut block.

1 Gf. Charles Singer: From Magic to Science (London, 1928); and "The herbal
in antiquity and its transmission to later ages," J. Hellenic Studies, vol. XLVII,
1-52; Wilfrid Blunt: The Art of Botanical Illustration (London, 1950).

369 24

THE SCIENTIFIC REVOLUTION

APPENDIX B

COMPARISON OF THE PTOLEMAIC AND
COPERNICAN SYSTEMS

THE geometrical equivalence of the geostatic and heliostatic methods
of representing the apparent motions of the celestial bodies, adopted by
Ptolemy and Copernicus respectively, is not often clearly emphasized

though it is vital to any discussion of
the nature of the change in astro-
nomical thought effected by Coper-
nicus. In a simplified form it may be
easily demonstrated.

Upper Planets (Fig. 11). On the
Copernican hypothesis, O is the
place of the sun, B that of the earth
which has revolved through any
angle COB, and D that of a planet
which in the same time has revolved
through the angle COD. The appar-
ent position of the planet is on the

T- TT line BD. Transposing this into Ptole-

FIG. n. The Upper Planets. . A ^v i i i A

rr maic terms, O is the fixed earth, A

the sun, and D the centre of the planet's epicycle. If F is the place of
the planet in the epicycle, then DF:DO = BO:DO. Moreover, AOB
is a straight line, and ZFDO = /.COB /.COD = ,/ BOD. These

relations follow from the form of the
constants used by Ptolemy and Co-
pernicus respectively (p. 15). Thus
the apparent position of the planet
is given as before, since the line FO
is parallel to BD, and the triangles
AFO, BDO, are identical.

Lower Planets (Fig. 12). Here the
situation is slightly different. The
Copernican representation is similar
to that given above, with the sun at
O, earth at B, planet at D, and the
position given by the line BD. On
the Ptolemaic representation the
central earth is at O, the sun at A,
and the centre of the planet's epicycle is located on the radius AO.
Values for the radii of the deferent and epicycle may be chosen so that
D'FrD'O = DO:BO, provided that D'F + D'O<AO = BO. As be-

FIG. 12. The Lower Planets.

APPENDIX B 371

fore, these relations follow from the form of the constants adopted by
Ptolemy and Copernicus. For the same reason the velocity of rotation of
F about D' is such that Z.OD'F = /.GOD - /.COB = /.BOD. Thus
it follows (as with the upper planets) that FO and BD are parallel, and
that the maximum elongation of the planet from the sun is the same on
either hypothesis.

It may be noted that since any geometrical complexity added to one
representation may be duplicated by a corresponding one in the other,
the apparent positions of the planets are always the same on either
hypothesis. In the case of the inferior planets, Venus and Mercury,
however, the triangles OD'F, BOD, are similar but not identical.
These planets cannot appear on the Ptolemaic hypothesis, as they do on
the Copernican, on the remote side of the sun from the earth. On the
latter hypothesis, but not on the former, Venus should appear in quad-
rature with the sun at maximum elongation. This fact was observed
by Galileo with the telescope. A simple adjustment to the Ptolemaic
system (proposed long before) made it identical with the Gopernican in
this respect by centring the epicycles of Venus and Mercury upon the
sun, i.e. drawing them about A.

APPENDIX G
SCIENTIFIC BOOKS BEFORE 1500

WITHOUT compiling any very elaborate statistics, it is apparent from
the work of A. C. Klebs ("Incunabula Scientifica et Medica," Osiris,
vol. IV, 1938) that the printed literature of science at the beginning of
the sixteenth century was in the main dominated by its established
traditions. Klebs lists more than 3,000 editions of 1,044 titles by about
650 authors. Among these occur 95 editions (and collections) of works
attributed to Aristotle, 18 editions of the Natural History of Pliny the
Elder, 7 of Ptolemy's Cosmographia (but none of the Almagest), and 5 of
Lucretius. Of ancient medical writers, Dioscorides (De materia medico)
was printed twice, and Galen (complete so far as known) once. But
separate works of both Hippocrates and Galen were included in num-
erous collections of medical authorities. Celsus (De medicina) was printed
four times. Collections of classical writers on military affairs, agricul-
ture and astronomy were popular enough to justify more than one
edition. Euclid was printed twice only.

Translations from the Arabic were often printed. They include
Avicenna's Canon of Medicine (14 editions) and the works of other great
Islamic physicians: al-Razi (15 editions besides titles in collections),
Mesue (19 editions) and Serapion (4 editions). Averroes* commentaries

372 THE SCIENTIFIC REVOLUTION

on Aristotle were well known in print, but not Arabic astronomical
writings.

Works deriving from the Latin West before 1400 form a very numer-
ous group. The long-used Etymologic of Isidore of Seville was printed 8
times. An early product of the renaissance of learning in Europe, the
Quastiones Naturales of Adelard of Bath, merited 2 editions. Works by,
or attributed to, Albert the Great were immensely popular, especially
the Secreta mulierum and the Liber aggregations, amounting to 150 edi-
tions. Thomas Aquinas appeared in 17 editions and numerous collec-
tions, Albert of Saxony in eleven. Two more sought-after books were
the Sphere of Sacrobosco (3 1 editions) and the Physiognomia of Michael
Scot (21 editions). Less well known medieval treatises, like those of
Oresme (3), Thomas Bradwardine (3) or Walter Burley (5) all found
publishers. The most widely read English author was undoubtedly
Bartholomew (De proprietatibus rerum) with 1 2 editions in Latin, 8 in
French, and others in English, Spanish and Flemish. Some medical
writers of the middle ages were still in demand for study, to judge from
the 31 editions of Arnald of Villanova, the 13 of Guy de Ghauliac, and
the 9 of Mondino. The most popular of all medical treatises was still the
Regimen sanitatis of Salerno (41 editions). With these the 35 editions of
printed herbals before 1500 may be linked.

The proportion of scientific books printed in the vernacular languages
was small, but it was a microcosm of the whole. The German language
was perhaps the best endowed in this way, and next French; in Italy,
probably, the university tradition was too strong to render such ver-
nacular printing profitable, and the literate class in fifteenth-century
England did not at first demand many serious books. Many were of an
ephemeral nature prognostications and predictions, almanacks, and
popular treatises on the maintenance of health. This last group in-
cludes the Livre pour garder la sante (1481), and the German Regimen
sanitatis zu Deutsch (1472). Gaxton printed The Gouvernayle of helthe in
1489. A book even more full of marvels than Bartholomew's, and
equally widely available, was Mandeville's Itinerarius (in English,
French, German, Italian and Flemish). Herbals were soon made
accessible to the vernacular reader (German and French 1486, English
1525), as were treatises on anatomy deriving from Mondino (German,
Hieronymus Brunschwig, 1497; Italian and Spanish, Johannes de
Ketham, 1493 and 1494). The Chirurgia of Guy de Chauliac was repre-
sented in three languages before 1 500. There were also some vernacular
books on reckoning.

Here, then, is evidence drawn from two dissimilar sources enforcing
the same conclusion. On the one hand, the great ItaKan printing-
houses, supplying a highly literate and academic market, found it
profitable to publish many of the "classics" of medieval science, often

APPENDIX C 373

in several editions; on the other hand, vernacular printing shows the
same intellectual content scaled down and vulgarized. There was no
sudden craving for originality, no epidemic of criticism. This is also
apparent from Mr. H. S. Bennett's study of early English publications
dealing with science and medicine (English Books and Readers, 1475-
1557, Ch. vi). The first surgical texts in English were based on Johannes
de Vigo and Guy de Chauliac; the first anatomy text (by Thomas
Vicary, 1548) on Mondino. Gaxton's Myrrour of the World (1481) 'is a
typical example of the encyclopaedia beloved of the Middle Ages, and
here made available to the ordinary reader with no attempt to bring
it up to date. 5 Yet it was reprinted in 1490 and 1529. Such works, Mr.
Bennett writes: 'contributed little or nothing that was new. Their
compilers were content to reproduce knowledge that had been current
for centuries, and the stationers traded in these wares confident that
their customers would not be put off by their old-fashioned con-
tents.' (But were the customers conscious that the contents were old-
fashioned?) Gaxton made no greater effort to revise the geographical or
historical knowledge which he imparted in his books, much of it taken
directly from the thirteenth and fourteenth centuries. In short, so far
as the respective tastes of printers, students and the general public may
be ascertained, they were conservative; those texts which had been
most in demand before the invention of printing were the very ones
that became most widely disseminated after it. Printing, therefore, had
comparatively little immediate effect on the literature of science in the
way of substituting novelties for traditions, though it did condemn to
darker oblivion those texts which were already half-forgotten by the
mid-fifteenth century, and, by reason of this, it reveals the strength of
the conservative forces extant in the early stages of the renaissance.

BIBLIOGRAPHICAL NOTES

STUDIES on the history of science are already so numerous that it is only possible
in these notes to give some indications of indebtedness, and of some possible
lines of exploration. I restrict myself here mainly to the English and French
languages, though these are (obviously) far from containing everything of
importance.

General: The journals his and Osiris, Annals of Science, Archives Internationales
d*histoire des Sciences (continuing Archeion), and Revue d'histoire des Sciences, are
indispensable. The bibliographies in Isis analyse work in the history of science
during the last forty years; cf. also G. Sarton, A Guide to the History of Science
(Waltham, Mass., 1952), and the handlist published by the Historical Associa-
tion (Helps for Students of History, No. 52). The period covered by this volume is
treated in all the general histories of science (Singer, Dampier, Wightman,
Mason etc.) and especially by Professor H. Butterfield, The Origins of Modern
Science (London, 1949), an< ^ H. T. Pledge, Science since 1500 (London, 1939).
A. Wolf, History of Science, Technology and Philosophy in the Sixteenth, Seventeenth and
Eighteenth Centuries gives many valuable scientific details but is very deficient in
interpretation.

CHAPTER I

For reference and bibliography, G. Sarton, Introduction to the History of Science
(Baltimore, 1927-48, 5 vols.) and Lynn Thorndike, History of Magic and
Experimental Science (New York, 1923-41) are essential. There is no fully adequate
short history for the medieval period. For Islam, cf. H. J. J. Winter, Eastern
Science (London, 1952), A. Mieli, La Science Arabe (Leiden, 1938). Some of the
older books, e.g. G. Singer, From Magic to Science (London, 1928) are still useful.
A. C. Crombie, From Augustine to Galileo (London, 1952) and Robert Grosseteste
and the Origins of Experimental Science (Oxford, 1953), takes a favourable view
of the medieval contribution to the scientific revolution, with much biblio-
graphical information. C. H. Haskins, The Renaissance of the Twelfth Century
(Cambridge, Mass., 1928), and Studies in the History of Medieval Science (Cam-
bridge, Mass., 1924) ; J. Huizinga, The Waning of the Middle Ages (London, 1924) ;
H. Rashdali, Universities of Europe in the Middle Ages (ed. Oxford, 1936), are
useful for background. Editions of texts are being published in quantity, e.g.
E. A. Moody and M. Clagett, The Medieval Science of Weights (Madison, 1952);
L. Thorndike, The Sphere of Sacrosbosco (Chicago, 1949), and The Herbal of
Rufinus (Chicago, 1946).

CHAPTER II

(a) There are general histories of medicine by F. H. Garrison (Philadelphia,
1929) and A. Castiglioni (New York, 1947) the latter has the more synthetic
treatment. A valuable survey is C. Singer, The Evolution of Anatomy (London
1926^ J. B. de C. M. Saunders and C.D. CVMMey, Andreas Vesalius (New York,

375

376 THE SCIENTIFIC REVOLUTION

1950) give the anatomical illustrations with short notes. Cf. also C. Singer,
Vesalius on the Human Brain (London, 1952) the only translation of a fair
portion of De Fabnca; H. Gushing, A Bio-bibliography of Andreas Vesalius (New
York, 1943); S. W. Lambert et al. 9 Three Vesalian Essays (New York, 1952);
Saunders and O'Malley, and Singer, in Studies and Essays . . . offered to George
Sarton (New York, 1946), articles in the Bull. Hist. Med., vol. XIV, 1943;
J. P. McMurrich, Leonardo da Vinci the Anatomist (London, 1930), Vittorio Putti,
Berengario da Carpi (Bologna, 1937); G. Keyncs, The Apologie and Treatise of
Arnbroise Pare 1 (London, 1951); Sir G. Sherrington, The Endeavour of Jean Fernel
(Cambridge, 1946).

(b) The edition of Ptolemy which I have found most accessible is that of the
Abbe Halma (with French translation, Paris, 1813-16), and for Copernicus the
original printing of 1543. Secondary works are: A. Armitage, Copernicus, the
Founder of Modern Astronomy (London, 1938), H. Dingle in The Scientific Adventure
(London, 1952), J. L. E. Drcyer, History of Planetary Systems from Thales to Kepler
(Cambridge, 1906), F. R. Johnson, Astronomical Thought in Renaissance England
(Baltimore, 1937), E. Rosen, Three Copernican Treatises (New York, 1939), D. W.
Singer, Giordano Bruno, his Life and Thought (London, 1950), D. Stimson, The
Gradual Acceptance of the Copernican Theory (New York, 1917).

(c) Metallurgy and industrial chemistry are dealt with in G. Agricola, De re
metallica (trans. H. C. and L. H. Hoover, New York, 1950); C. S. Smith and
M. Gnudi, The Pirotechnia of Vannoccio Biringuccio (New York, 1943), C. S.
Smith and A. Sisco, Treatise on Ores and Assaying of Lazarus Packer (Chicago,
1951). On history of pharmacology, E. Kremers and G. Urdang, History of
Pharmacy (Philadelphia, 1940).

CHAPTER III

There is no wholly satisfactory English work on Galileo. J. J. Fahie, Galileo, his
Life and Works (London, 1903) is uncritical and out of date. F. Sherwood Taylor,
Galileo and the Freedom of Thought (London, 1938) is better but limited. In trans-
lation there are Dialogues concerning Two New Sciences (H. Crew and A. de Salvio,
New York, 1914, 1952), Dialogues on the Two Chief Systems of the World (T. Salus-
bury, London, 1667; S. Drake, California, 1953). Pierre Duhem's classic Etudes
sur Leonard de Vinci (Paris, 1906-13) and Origines de la Statique (Paris, 1905-6)
are invaluable. Cf. also L. Cooper, Aristotle, Galileo, and the Leaning Tower of
Pisa (Ithaca, 1935), Rene Descartes, Oeuvres (ed. Ch. Adam and P. Tannery
(Paris, 1897-1913), R. Dugas, Histoire de la Mlcanique (Neuchatel, 1950), G.
Galilei, Opere, ed. A. Favaro (Firenze, 1890-1909), A. Koyr, Etudes GaliUennes
(Paris, 1939; Actualit^s Scientifiques et Industrielles Nos. 852-4 most impor-
tant), E. Mach, Science of Mechanics (Chicago, 1907), A. Maier, Die Vorlaufer
Galileis in 14. Jahrhundert (Rome, 1949) and Die Impetustheorie (Rome, 1951),
R. Marcolongo, "Lo sviluppo della meccanico sino ai discepoli di Galileo* * in
Atti d. R. Ace. dei Lincei (Physical Series) vol. XIII (Rome, 1920), A. Mieli, "II
Tricentario dei 'Discorsi e Dimostrazioni Matematiche' di Galileo Galilei"
in Archeion, vol. XXI (Rome, 1938) critical of Duhem etc., N. 'Oresme, "Le
Livre du Ciel et du Monde" in Medieval Studies, vols. III-V (1941-3), G.
Sarton, "Simon Stevin of Bruges" in his. vol. XXI (1934).

BIBLIOGRAPHICAL NOTES 377

CHAPTER IV

In addition to works already mentioned, A. Armitage, "The Deviation of
Falling Bodies," Ann. Sci., vol. V (1947), I. Boulliau, Astronomia Philolaica
(Paris, 1645), J. L. E. Dreyer, Tycho Brake (Edinburgh, i8go),Johann Kepler,
Gesammelte Werke (Munich, 1938-), S. I. Mintz, "Galileo, Hobbes, and the
Circle of Perfection," Isis, vol. 43 (1952), D. Shapley, "Pre-Huygenian Observa-
tions of Saturn's Rings," Isis y vol. 40 (1949).

CHAPTER V

The best study is H. P. Bayon, "William Harvey, Physician and Biologist," Ann.
Sci., vols. Ill, IV (1938-9). General books are F. J. Cole, Early Theories of Sexual
Generation (Oxford, i93o),J. Needham, History of Embryology (Cambridge, 1934),

E. Nordenskiold, History of Biology (New York, 1946), C. Singer, History of
Biology (New York, 1950). Cf. also H. Brown, "John Denis and Transfusion of
Blood, Paris, 1667-8," Isis, vol. 39 (1938), L. D. Cohen, "Descartes and More
on the Beast-Machine," Ann. Sci., vol. I (1936), C. Dobell, Antony van Leeuwen-
hoek and his "Little Animals" (London, 1932), G. Kcynes, "The History of Blood
Transfusion," Science News, vol. Ill (1947), A. van Leeuwenhoek, Collected
Letters (Amsterdam, i939~),W. Pagel, "William Harvey and the Purpose of the
Circulation," Isis, vol. 42 (1951), C. E. Raven, John Ray (Cambridge, 1950),

F. Redi, Opere (Napoli, 1778, Milano, 1809-1 1), J. Trueta, "Michael Servetus
and the Discovery of the lesser Circulation," Tale Jo. ofBiol. and Med., vol. XXI
(1948), R. Willis, Works of William Harvey (London, 1847).

CHAPTER VI

There is to my knowledge no complete history of scientific method. Useful
contemporary studies are R. B. Braithwaite, Scientific Explanation (Cambridge,
1953), M. R. Cohen and E. Nagel, Introduction to Logic and Scientific Method
(London, 1934), S. Toulmin, Philosophy of Science (London, 1953). Cf. also F. H.
Anderson, Philosophy of Francis Bacon (Chicago, 1948), A. G. A. Balz, Cartesian
Studies (New York, 1951), E. A. Burt, Metaphysical Foundations of Modern Physical
Science (London, 1925), A. C. Crombie and H. Dingle, op. cil. for Chs. I and
II, A. Gewirtz, "Experience and the non-mathematical in Descartes," Jo.
Hist. Ideas, vol. II, 1941, E. Gilson, La Philosophie an Moyen Age (Paris, 1944),
J. H. Randall, "The Development of the Scientific Method in the School of
Padua," Jo. Hist. Ideas, vol. I (1940), B. Russell, History of Western Philosophy
(London, 1946).

CHAPTER VII

(a) An excellent survey is M. Oinstein, The Rdle of Scientific Societies in the ijth
Century (Chicago, 1938). Cf. also J. Bertrand, UAcadtmie des Sciences et les
Acadtmiciens de 1666 a 7795 (Paris, 1869), T. Birch, History of the Royal Society
(London, 1756), H. Brown, Scientific Organization in ijth Century France (Balti-
more, 1934), A. Favaro, "Documenti per la Storia dell Accademia dei Lincei,"
Bullettino di Bibliogrqfia e di Storia delle Science, vol. XX (Rome, 1887), A. J.
George, "The Genesis of the Academic des Sciences," Ann. Sci., vol. Ill (1938),
F. R. Johnson, "Gresham College: Precursor of the Royal Society," Jo. Hist.
Ideas, vol. I (1940), R. F. Jones, Ancients and Moderns (St. Louis, 1936), R.

37 8 THE SCIENTIFIC REVOLUTION

Lenoble, Mersenne ou la Naissance du Mtcanisme (Paris, 1943), Sir H. Lyons, The
Royal Society (London, 1944), Notes and Records of the Royal Society, passim,
(b) A very important essay, with full references, is M. Boas, "The Establishment
of the Mechanical Philosophy," Isis, vol. X, 1952. Also, H. Brown, "The Utili-
tarian Motive in the Age of Descartes," Ann. Set., vol. I (1936), R. K. Merton,
"Science, Technology and Society in iyth Century England," Osiris, vol. IV
(1938), G. Milhaud, Descartes Savant (Paris, 1921), J. F. Scott, The Scientific
Work of Rene' Descartes (London, 1952), P. Mouy, La Developpement de la Physique
CarUsienne (Paris, 1934), J. R. Partington, "Origins of the Atomic Theory,"
Ann. Set., vol. IV (1939).

CHAPTER VIII

M. Cantor, Vorlesungen tiber Geschichte der Mathematik (Leipzig, 1880-1908), is
still essential for reference. J. E. Montucla, Histoire des Mathematiques (Paris,
1 799- 1 802) is well worth reading on the seventeenth century. Cf. also D. E. Smith,
History of Mathematics (New York, 1923), and more popular accounts by E. T.
Bell, A. Hooper and others. M. Daumas, Les Instruments Scientifiques aux if et
i8 e Siecles is excellent. The only good history of a single instrument is R. S.
Clay and T. H. Court, History of the Microscope (London, 1932). Further, I. B.
Cohen, "Roemer and Fahrenheit," Isis, vol. 39 (1948), J. W. Olmsted, "The
Application of Telescopes to Astronomical Instruments," Isis, vol. 40 (1949),
L. D. Patterson, "The Royal Society's Standard Thermometer," Isis, vol. 44
0953)5 F- Sherwood Taylor, "The Origins of the Thermometer,'Mwz. Sci.,
vol. V (1947).

CHAPTER IX

The best recent biography of Newton is that of L.T. More (London, 1934), which
does not wholly supplant Sir D. Brewster's Memoir (Edinburgh, 1855). Other
sources: E. N. da C. Andrade, "Robert Hooke," Proc. Royal Society A, vol. 201
(1950), A. Armitage, " 'BorrelFs hypothesis' and the Rise of Celestial Mechan-
ics," Ann. Set., vol. VI (1948-50), A. C. Bell, Christian Huygens and the Develop-
ment of Science in the Seventeenth Century (London, 1947), W. J. Greenstreet (ed.),
Isaac Newton, Memorial Volume (London, 1927), R. T. Gunther, Early Science in
Oxford, vols. VI-VIII, X, XIII (Oxford, 1930-8), W. G. Hiscock, David
Gregory, Isaac Newton and their Circle (Oxford, 1937), History of Science Society,
Isaac Newton (London, 1928), A. Koyre, "La Mecanique Celeste de J. A.
Borelli," Rev. d'Hist. des Sciences, vol. V (Paris, 1952) and "An Unpublished
Letter of Robert Hooke to Isaac Newton," Isis, vol. 43 (1952), T. S. Kuhn,
"Newton's *3ist Query* and the Degradation of Gold," Isis, vol. 42 (1951),
E. F. MacPike, Correspondence and Papers of Edmond Halley (London, 1937),
L. D. Patterson, "Hooke's Gravitation Theory and its Influence on Newton,"
Isis, vol. 40 (1949), Royal Society Newton Tercentenary Celebrations (Cambridge,
1947), E. W. Strong, "Newton and God," Jo. Hist. Ideas, vol. XIII (1952),
H. W. Turnbull, James Gregory Tercentenary Volume (London, 1939), A. H.
White, Memoirs of Sir Isaac Newton's Life by William Stukeley (London, 1936).
The best editions are those of the Principia by F. Cajori (Berkeley, 1946) and of
the Opticks (London, 1931). The Oeuvres Completes of Christiaan Huygens (La
Haye, 1888-1950) are invaluable for reference.

BIBLIOGR/APHICAL NOTES 379

CHAPTER X

To the books listed for Gh. V may be added: A. Arber, Herbals (Cambridge,
1950), P. G. Fothergill, Historical Aspects of Organic Evolution (London, 1952,
with full bibliography), Knut Hagberg, Carl Linrusus (London, 1952), W. P.
Jones, "The Vogue of Natural History in England, 1750-70,' 'Ann. Sci., vol. II,
1937, C. E. Raven, English Naturalists from Neckam to Ray (Cambridge, 1947),
and Natural Religion and Christian Theology (Cambridge, 1953), C. Singer, "The
Dawn of Microscopical Discovery," Jo. Roy. Microscopical Soc. (1915).

CHAPTER XI

There is no modern history of chemistry on the large scale. J. R. Partington,
Short History of Chemistry (London, 1948) is an excellent introduction. Cf. also,
on industrial chemistry, A. and N. Clow, The Chemical Revolution (London, 1952) ;
L. J. M. Coleby, The Chemical Studies of P. J. Macquer (London, 1938), P. George
"The Scientific Movement and the Development of Chemistry in England,"
Ann. Set., vol. VIII (1952),^ S. Kuhn, "Robert Boyle and Structural Chem-
istry in the I7th Century," Isis, vol. 43 (1952), D. McKie, Antoine Lavoisier
(London, 1935), and Essays of Jean Rey (London, 1951), and "Black's Chemical
Lectures," Ann. Sci., vol. I (1936), H. Metzger, Les Doctrines Chimiques en France
du dibul du if a la Jin du i8 e Siecle (Paris, 1923) and Newton, Stahl, Boerhaave et la
Doctrine Chimique (Paris, 1930), L. T. More, Life and Works of Robert Boyle
(London, 1944), J. R. Partington, "Joan Baptista van Helmont," Ann. Sci.,
vol. I (1936), and with D. McKie, "Historical Studies in the Phlogiston
Theory," -4wi. Sci., vols. II-IV( 1937-9), T. S. Patterson, "Jean Beguin and his
Tyrocinium Chemicum," Ann. Sci., vol. II (1937), and "John Mayow in Con-
temporary Setting," Isis 9 vol. 15 (1931), J. M. Stillman, The Story of Early
Chemistry (New York, 1924)^. H. White, History of the Phlogiston Theory (London,
1932).

CHAPTER XII

P. Brunet, L 9 Introduction des Theories de Newton en France au 18' Siecle (Paris, 1931),
I. B. Cohen, Benjamin Franklin's Experiments (Cambridge, Mass., 1941 with
useful historical introduction), E. S. Cornell, "The Radiant Heat Spectrum,"
Ann. Sci. 9 vol. Ill (1938), D. Fleming, "Latent Heat and the Invention of the
Watt Engine," Isis, vol. 43 (1952), L. Galvani, Opere edite e inedite (Bologna,
1841), D. McKie and N. H. de V. Heathcote, The Discovery of Specific and Latent
Heats (London, 1935), J. C. Maxwell, Electrical Researches of Henry Cavendish
(Cambridge, 1879), Philosophical Magazine, Natural Philosophy through the i8th
Century (Commemoration Number, 1948), A. Volta, Collezione del Opere (Firenze,
1816), W. Cameron Walker, "The Detection and Measurement of Electric,
Charges in the i8th Century," Ann. Sci.,vol. I (1936), Sir E. Whittaker, History
of Theories of Aether and Electricity, vol. I (Cambridge, 1951).

INDEX

ACADEMIES :

Accademia dei Lincei, 188
Accademia del Cimento, 151, 189-

191, 193, 264

Acad6mie Franchise, 188, 196
Academic Royale des Sciences, 98,

100, 1 86, 191, 195-8, 201, 202, 205,

215, 333

Berlin, 201-2

Royal Society, 31, 99, 152-4, 182, 186,
189, 192-5, 198, 200, 215, 216, 241,
246, 249, 250, 266-8, 284, 289, 309,

338, 358-9

Aepinus, F. U. T. (1724- 1802), physicist,
352

Agricola [Georg Bauer] (1490-1555), 70,
73, 163, 221-3, 308, 321 n.

al-Battani (d. 929), astronomer, 61, 63

Albert of Saxony (i3i6?-9o), philo-
sopher, 56, 81-2, 83, 85

Albert the Great (c. 1200-80), philo-
sopher, 28, 31, 134, 276, 278, 369

Alchemy, 26, 69, 223-4, 244, 249, 307-8

Aldrovandi, Ulissi (1522-1605), natural-
ist, 156

Alfonsine Tables, 16

Alhazen (c. 965-1040), physicist, 21-2,

251

al-Razi (d. 923-4), physician, 39, 308

Anatomy, ancient and medieval, 3740
and art, 41-4
comparative, 145-6, 286
renaissance, 41-51, 135-6, 142-4, 148

Animalculists, 291-3

Animism, 12, 21, 310

Apollonius of Perga (b. c. 262 B.C.),
mathematician, 126

Aquinas, Thomas (12257-74), philo-
sopher, 5

Archimedes (287-212 B.C.), mathe-
matician, 9, 10, 21, 76, 124, 158, 171,

235
Aristotle (384-322 B.C.), philosopher, 5,

74, 186-7,217, 339
as biologist, 10, 28, 37-8, 71, 129, 133,
134, 154, 156, 158, 275-7, 281-2,
286, 289, 295, 297-8

38

as physicist, 12, 19, 21, 23-6, 35, 53,
56, 66 ff., 76, 78, 92, 97, 100, 103,
106, 109 ff., 114, 117, 165, 172,206-
207, 210, 260-1, 306, 313
scientific method of, 160-3, J 68-9, 185
Arzachel (c. 1029-87), astronomer, 61
Astrolabe, 4, n, 14, 17, 235
Astronomy, Copernican, 3, 51-68, 108,
119, 192, 194, 261, 370-1 ; and re-
ligion, IO2-6
Galilean, 107-16
Kepler's Laws, 117, 121-6, 248, 260,

268

Newton and, 248

Ptolemaic, 3, 11-18, 52-65; con-
stants of, 15 n.

Atomism, see Philosophy, mechanical
Averroes (b. 1126), philosopher, 138
Avicenna (979- IO 37) physician, 4, 39,

71, 138, 140

Avogadro, Amadeo (1776-1856), physi-
cist, 338

BACON, FRANCIS (1561-1626), philo-
sopher, 7, 31, 34, 75 n., 135, 182,

189, 192-4, 197, 201-2, 2O7, 211,
213, 219, 235, 243

on scientific method, 161, 164-9,

173-4, 1 80, 183-5
Bacon, Roger (1214-94), philosopher,

6, 22, 31, 34, 163, 306, 309
Baer, K. E. von (1792-1876), biologist,

292
Baker, Henry (i 69$- 17 74), microscopist,

241

Ballistics, 78, 93, 190, 230
Banks, Sir Joseph (1743-1820), natural-
ist, 191, 280, 290, 339
Barrow, Isaac (1630-77), mathematician,

231, 247, 249
Bartholomew the Englishman (/. c.

1220-40), 30, 72, 278
Basil Valentine, pseudonym, 69, 224
Bauhin, Caspar (1560-1624), botanist,

131, 283
Bausch, Lorentz, 201

I 25

INDEX

Bayle, Pierre (1647-96), writer, 204

Beccaria, G. B., 333

Becher, J. J. (1635-82), philosopher, 326

Beddoes, Thomas (1760-1808), physi-
cian, 325

Beeckman, Isaac (1588-1637), philo-
sopher, 89-92, 93, 96, 100, 207

Beguin, Jean (c. 1550-1620), chemist,
312, 317 n.

Benedetti, Giovanbattista (1530-90),
mathematician, 78, 87

Bennet, Abraham (i75~99)> 35 2

Bentley, Richard (1662-1742), philo-
sopher, 272

Berengario da Carpi (1470-1550), ana-
tomist, 38, 41, 44, 45, 138

Berkeley, George (1685-1735), philo-
sopher, 185

Berzelius, J. J. (1779-1848), chemist, 362

Bewick, Thomas (1753-1828), engraver,

293
Biological Illustration, 29-30, 41 ff,, 48,

71, 277, 278-9, 369
Biological Sciences :

blood transfusion, 153-4

Cartesian ideas on, 14851

circulation of the blood, 141-8

evolution, 284, 296-8

medieval ideas, 27-31

microscopy, 240-2, 286-7, 290 flf.

physiology, 135-41, 152-3, 287-9, 291

renaissance of, 130-4, 275-84

taxonomy, 276, 281-6, 290, 294-6
Biringuccio, Vanoccio (Jl. c. 1540),

metallurgist, 70, 221-2
Black, Joseph (1728-99), chemist, 82 n.,

224, 308, 318, 328, 329-30, 332-4,

337 ; on heat, 344-7
Boccaccio, Giovan (1315-75), 8
Bode, J. E. (1747-1826), astronomer, 126
Boerhaave, Herman (1668-1738), chem-
ist, 291, 295, 318, 328
Bonamico, 78

Bonnet, Charles ( 1 720-93), naturalist, 241
Borelli, Alfonso (1608-79), 77, 150, 247,
260

and theory of gravitation, 264-6, 267
Boswell, Sir William (d. 1649), diplomat,

192

Boyle, Robert (1627-91), philosopher,
23 n., 25, 105, 143, 151, 172, 182,
191-6, 208, 216, 219, 220, 223, 225-
226, 238, 291, 343, 365

and chemistry, 304-5, 309, 311, 313,

316-28, 333, 337, 338
and mechanical philosophy, 211-13,

214

and Newton, 244, 247, 272 n.
Boyle's Law, 227
Bradley, James (1692-1762), astronomer,

340

Brahe, Tycho, see Tycho

Briggs, Henry (1556-1630), mathe-
matician, 229

Brouncker, William, Viscount (1620?-
1684), P.R.S., 193 n., 194

Brunfels, Otto (1489-1534), herbalist,
131, 278-9, 369

Bruno, Giordano (1548-1600), philo-
sopher, 55, 74, 77, 103-5

Brunschwig, Hieronymus (c. 1450-1512),
223

Buffon (George Louis Leclerc, Comte de,
1707-88), 297-8

Buridan, Jean (c. 1295-1358), philo-
sopher, 6, 20-21, 56

Burnet, Thomas (1635-1714), divine,
297

CAIUS, JOHN (1510-73), physician, 38

Calendar, 3, 16, 53

Caloric, 328, 343-6

Camerarius, Rudolph Jacob (1665
1721), botanist, 157, 294

Canano, Giovanbattista, of Ferrara
(1515-79), anatomist, 41, 46

Cardano, Jerome (150176), philosopher,
20, 78, 156, 163, 226

Carlisle, Sir Anthony (1768-1840), sur-
geon, 360

Carnot, Sadi (1796-1832), engineer, 347

Cassini, Jacques (1677-1756), astrono-
mer, 341

Cassini, Jean (1625-1712), astronomer,
197-8

Cavalieri, Bonaventura (1598-1647),
mathematician, 226, 227, 231

Cavendish, Sir Charles (1591-1654),
mathematician, 192

Cavendish, Henry (1731-1810), on
chemistry, 318, 328-32, 334 n., 335
on physics, 272, 353-5

Celsus (fi. c. A.D. 14-27), physician, 41

Cesalpino, Andreas (1519-1603), botan-
ist, 131, 279, 283, 321 n.

INDEX

383

Cesi, Frederigo, Duke of Aquasparta, 188
Charles II, K. of England (1660-85),

194

Chaucer, Geoffrey (1340?-! 400), 4
Chemistry, 24-6, 131, 212, 244, 249,

303-3 8

electrochemistry, 360-3
iatrochemistry, 309-13, 317-18
industrial, 70, 201, 220-4, 304, 306-7

Christian IV, K. of Denmark (1588-
1648), 118

Clairaut, Alexis Claude (1713-65),
mathematician, 340, 341-2

Clement VII, Pope (1523-34), 54

Colbert, Jean Baptiste (1619-83), 195,

197

Collingwood, R. G., 9
Colombo, Realdo (1516-59), anatomist,

46, 48, 142

Combustion, 324-5, 327, 330, 332-6
Comenius,J. A. (1592-1671), 194 n.
Copernicus, Nicholas (1473-1543), as-
tronomer, 6, 1 6, 35, 74, 102, 108-9,
114-17, 120 ff., 163-4, 174*234,261,
263, 275

compared with Vesalius, 36-7

system of, 51-68
Cordus, Valerius (1515-44), botanist,

13^279
Coulomb, Charles Augustin (1736-

1806), engineer, 352-4
Cullcn, William (1710-90), physician,

318
Cuvier, Georges (1769-1832), naturalist,

297, 30i

D'ALEMBERT (Jean le Rond, 1717-83),
mathematician, 340

Dalton, John (1766-1844), chemist, 215,
326

Dante Alighieri (1265-1321), 72

Darwin, Charles (1809-82), biologist,
256, 275, 296-8, 301, 341

Davy, Sir Humphry (1778-1829), chem-
ist, 325, 360-2

Dee, John (1527-1608), mathematician,

55> 72
De Graaf, Regnier (1641-73), biologist,

292

De Groot, 100
De 1'ficluse, Charles (1524/5-1609),

botanist, 279

De rObel, Matthias (1538-1616), natu-
ralist, 283

Democritus (c. 460-370 B.C.), 97, 103,
207

Desaguliers, John Theophilus (1683
1744), physicist, 340

Desargues, Gerard (1593-1662), mathe-
matician, 191

Descartes, Ren6 (1596-1650), 83 n., 89
92, 93~4, 99. ioo, 105-6, 113, 127,
191, 196, 198-200, 205, 215, 236,
258,274,297,318,325
and biology, 129, 138, 298
ideas of matter and motion, 95, 207-

213

and mathematics, 227, 228, 230
mechanics of, 96-8
and Newton, 99, 244, 247, 270-1
and optics, 251, 252 ., 254
physiological ideas of, 148-52, 157
on scientific method, 164, 177-84
and theory of gravitation, 260, 264-5

De Thou, J. A. (1553-^ 17)1 *95

Diderot, Denis (1712-84), philosopher,

339

Digges, Thomas (d. 1595), mathemati-
cian, 104

Dioscorides (Jl. c. A.D. 50), herbalist, 10,
217, 276, 277, 279, 281

Doliond, John (1706-61), optician, 242,

342-3

Dorninico Soto (1494-1570), theologian,
83-5, 88, 91-2

Drebbel, Cornelius (1572-1634), 192

Drury, John, 1 93 n.

Dryander, Johann (c. 1500-60), physi-
cian, 41, 46

Dufay, Charles (1698-1739), electrician
349-50, 362

Dumas, J. B. A. (1800-84), chemist, 292

Dupuy, 195

Dttrer, Albrecht (1471-1528), 278

Dymock, Cressy, 193 n.

ELEMENTS, 313-15, 320-3

Aristotelean, 1 7 ff., 23-6, 60, 208

Elizabeth I, Qu. of England (1558-
1603), 72

Ellis, John (17107-76), naturalist, 241,
290

Ent, Sir George (1604-89), physician,

193

384

INDEX

Epicurus (340-270 B.C.), 97, 187, 207

Ercker, Lazarus (?~I593), metallurgist,
221-2

Estienne, Charles (1504-64), anatomist,
41,44,46, 139

Euclid (fl. c. 300 B.C.), 10, 171

Eugene, Prince of Savoy (1663-1736),
202

Euler, Leonhard (1707-83), mathe-
matician, 342-3

Eustachio, Bartolomeo (1520-74), ana-
tomist, 46

Evelyn, John (1620-1706), virtuoso,
i93/*- i94>200

Experimental method, 6, 32-3, 45, 86,
99* 129-35, 145-6, 173-6, 181-3, 185,
189-91, 199, 216, 223-4, 233, 255-
257, 270, 273-4

FABRICIUS (FABRIZIO), HIERONYMUS, of
Aquapendente (1537-1619), physician,
139, 286, 298
Fabricius, Johann (fl. c. 1605-15),

astronomer, 108

Fabroni, Giovanni (1752-1822), 360
Fahrenheit, Gabriel Daniel (1686-1736),

physicist, 238, 341, 344
Fallopio, Gabriele (1523-62), anatomist,

46,48

Faraday, Michael (1791-1867), physi-
cist, 185, 332, 353, 362
Ferdinand II, Duke of Florence, 190
Fermat, Pierre ( 1 60 1 -65) , mathematician,

94, 191, 230, 231, 252 n.
Fernel, Jean (1497-1558), physician, 46,

135-6, 138

Field, John (i 5257-87), astronomer, 55
Mamsteed, John (1646-1719), astrono-
mer royal, 120, 198-9, 238
Foster, Samuel (c. 1600-52), astronomer,

193
Franklin, Benjamin (1706-90), 347,

35<>-3> 358> 362
Frederick I, Elector of Brandenburg and

K. of Prussia (1688, 1700-13), 201
Frederick II, Emperor (1194-1250), 28
Freind, John (1675-1728), physician,

326
Fresnel, Augustin (1788-1827), engineer,

245

Fuchs, Leonard (1501-66), herbalist,
131* 278-9, 280, 369

GALEN (A.D. 129-99), physician, 9, 10,

36> 37-5', 7i, 74, '29, i3i-6> 138, 141*
152, 217, 310, 313

Galileo Galilei (1564-1642), 18, 35, 45,
48, 56-7. 59, 65, 68, 98-100, 105,
106, 127, 135, 147-8, 158, 167, 182,
188-90, 194-5, '99, 207,211,217,
219, 225-6, 230, 233-5, 238, 275,

30i, 33', 335, 337, 365-6
on astronomy, 107-17, 120 n., 121
and Descartes, 92-101
importance of, 74-7
on mechanics, 78-92
and Newton, 247 n., 261, 263, 270,

272

scientific method of, 164, 168-78,
180-1, 183-4

Galvani, Luigi (1737-98), anatomist,
355-8* 362

Gassendi, Pierre (1592-1655), philo-
sopher, 156, 157, 191, 196, 207-8, 215

Geber, pseudonym, 69, 306

Gemma Frisius (1508-55), astronomer,

54-5

Generation, 25, 27-8, 284, 290-3, 297
spontaneous, 28, 154-7, 284, 291

Geoffroy, Etienne Francois (1672-1731),
chemist, 326

Gerard of Cremona (c. 1114-87), trans-
lator, 4, 39

Gesner, Conrad (1516-65), naturalist,
279, 282-3, 298

Gibbon, Edward (1737-94), historian,

339

Giese, Tiedeman, 55
Gilbert, William (1540-1603), physician,
72, 86, 89, 93, 96, 185, 188, 192, 211,

235, 348

and gravitation, 260-2, 263
Glauber, Rudolph (1604-70), chemist,

133* 3"* 317
Glisson, Francis (1597-1677), physician,

193
Goddard, Jonathan ( 1 6 1 7-75) , physician,

193
Graunt, John (1620-74), statistician, 225

Gravitation, theory of, 66, 79, 86, 99,

126-8, 206, 248, 259-74, 342
action at a distance, 96, 99, 127, 260,

265, 272

Gray, Stephen (d. 1736), electrician, 349
Gregory, James (1638-75), mathemati-
cian, 239

INDEX

385

Grcsham, Sir Thomas (i5i9?~79), mer-
chant, 187 n.

Gresham College, 187 n., 192, 205

Grew, Nehemiah (1641-1712), botanist,
157, 240, 284, 288-9

Grimaldi, Francesco Maria (1613-63),

254

Grosseteste, Robert (d. 1253), bishop of
Lincoln, 5-6, 22

Guericke, Otto von (1602-86), 348

Guido da Vigevano (c. 12801350),
physician, 7

Giinther, Johann (1487-1574), anatom-
ist, 44, 45, 138, 140

Guy de Chauliac (d. 1368), surgeon, 71

HAAK, THEODORE (1605-90), translator,

'93

Hales, Stephen (1679-1761), physio-
logist, 287, 291, 329

Haller, Albrecht von (170877), physio-
logist, 301

Halley, Edmond (1656-1742), astrono-
mer, 120, 199, 246, 249, 268, 269

Harriot, Thomas (1560-1621), mathe-
matician, 192, 230

Harrison, John (1693-1776), horologist,
242

Hartlib, Samuel (d. 1670?), 193, 194 n.

Hartsoeker, Nicholas ( 1 656-1 725) , micro-
scopist, 292

Harvey, William (1578-1657), physician,
10,37,46,51, H9, 15^2, 158, 185,
192, 235, 239, 286, 298
on generation, 154-7, 291, 292
on the circulation, 1 34-48
predecessors of, 139-43

Hawksbee, Francis (d. 1713?), electrician,

340, 348

Heisenberg, Werner, 114
Helmont, Johann Baptista van (1577 or

1580-1648), philosopher, 312-17, 319,

320; 324
Henri de Mondeville (fl. c. 1280-1325),

surgeon, 40
Heraclides of Pontus (c. 388-310 B.C.),

astronomer, 65 n.
Herbals, 29, 71, 131, 276-82
Hero of Alexandria (ist cent. A.D.),

mechanician, 10, 207
Herschel, Sir William (1738-1822),

astronomer, 242, 258 n.

Hevelius, Johann (1611-87), astronomer,
120, 236, 240

Hipparchus (fl. c. 161-127 B.C.), as-
tronomer, 15, 61, 118

Hippocrates (c. 460-380 B.C.), physician,

io,37

Hobbes, Thomas (1588-1679), philo-
sopher, 104, 192

Hoffman, Friedrich (1660-1742), chem-
ist, 291

Hooke, Robert (1635-1703), physicist,
119 n., 152, 194, 199, 211, 219, 240,
246, 286, 296 ., 298, 324-5, 343
on gravitation, 260, 264-9, 271 n.
on optics, 251-5

Horrocks, Jeremiah (1617-41), as-
tronomer, 192

Humanistic scholarship, 1-2, 8-10, 53,
188, 229, 279, 371-3

Hume, David (1711-76), philosopher,

339

Hunter, John (1728-93), anatomist, 301
Hus, John (c. 1370-1415), 2
Huygcns, Christiaan (1629-95), physi-
cist, 98-9, 181-2, 190, 194 n., 195-7,
203, 232-3, 271

and gravitation, 267-8, 273

and Newton, 250 n.

and optics, 252 ., 255, 259
Huygens, Constantyn, 250 n.

IBN AL-NAFIS AL-QURASHI (c. 1208-88),

physician, 140

Instrument-making and Instruments, 69,
119-20, 234 ff.

air-pump, 2367

balance, 224, 235

barometer, 190, 238

electrical, 348-9, 352-3, 359

hygrometer, 190

microscope, 235-6, 239-41

telescope, 107, 235, 239-40, 242, 248

thermometer, 190, 238
Inventions, I, 6-7, 22, 99
Isidore, Bp. of Seville (c. 560-636), 278
Islamic Science, 3, 4, u, 17, 21-2, 39,

53, 5 6 > 61, 69 n., 118, 138, 140, 163 n.,

220, 229, 230, 306-8

JABIR IBN HAYYA"N (fl. c. 775), physician,
307

386

INDEX

James I, K. of England (1603-25), 192
James II, K. of England (1685-8), 249
John of Holywood (Sacrobosco) (c.

1200-50), 12
John Stephen of Calcar (b. 1499 ; d.

1546-50), artist, 48

Johnson, Samuel (1709-84), 293, 339
Johnson, Thomas (d. 1644), botanist, 156
Jordanus Nemorarius (?/. c. 1 180-1237),

mechanician, 6

Joule, James Prescott (1818-89), physi-
cist, 256, 346
Journals, scientific, 203-4
Jung, Joachim (1587-1657), botanist, 284
Junker, Gottlob Johann (1680-1759),
physician, 326 n.

KEILL, JOHN (1671-1721), mathemati-
cian, 326

Kepler, Johann (1571-1630), astrono-
mer, 48, 68, 1 06, 108-9, *7'> l8 5>
192 n., 226, 231, 243, 247, 260
astronomical discoveries of, 1 16-28
and gravitation, 261-5, 267

LAGRANGE, JOSEPH Louis (1736-1813),

mathematician, 340
Laplace, Pierre Simon Marquis de ( 1 749-

1827), mathematician, 274, 334, 340,

345-7

Lavoisier, Antoine Laurent (1743-94),
chemist, 24, 224, 256, 293, 301

and chemistry, 303, 305, 308, 316, 322,
324-5, 328, 329, 331, 332-8

and physics, 345-7
Laws of Nature, 171-3

Acceleration, 80, 92-4, 1 1 3

Inertia, 86-7, 89, 92-3, 96
Leeuwenhoek, Antoni van (1632-1723),

microscopist, 131, 203, 236, 241-2,

275, 286, 290, 292, 298
Leibniz, Gottfried Wilhelm (1646-1716),
201-2, 204,216, 273, 297

and mathematics, 227, 231-2, 250 n.
Lemery, Nicholas (16451715), chemist,

3-8

Leonardo da Vinci (1452-1519), 9, 10,
20, 29, 41-2, 46, 78-9, 82, 91, 138, 163,

365

Libavius, Andreas (i54O?-i6i6), iatro-
chemist, 311-13, 317

Linnaeus, Carl (1707-78), naturalist,

131, 275, 282, 283, 285, 290, 293-6,

298, 341
Locke, John (1632-1704), philosopher,

250, 274
Logarithms, 229
Longomontanus, Christian (1562-1647),

astronomer, 123
Louis XIV, fC. of France (1660-1715),

195-6
Lower, Richard (1631-91), physician,

152-4

Lucretius (c. 98-55 B.C.), poet, 9, 103,
206-7

Lull, Raymond (1232-1315/16), philo-
sopher, 224

Lusitanus, Amatus (1511-68), anatomist,

139
Luther, Martin (1483- 1546), reformer, 55

MAGH, ERNST (1838-1916), physicist, 86
Machiavelli, Niccolo (1469-1527), 9
Maclaurin, Colin (1698-1746), mathe-
matician, 342
Macquer, Pierre Joseph (1718-84),

chemist, 308

Macrobius (fl. c. 400), commentator, 4
Malpighi, Marcello (1628-94), biologist,
146, 156-7, 240, 242, 275, 286-8,
290-1 ; 293

Marco Polo (c. 1250-1323), i
Marcus Graecus (prob. pseudonym, c.

1300), 306

Margarita Philosophica^ 1 1 ff., 20, 22-3, 26
Martianus Capella (fl. c. 470), Roman

writer, 65
Massa, Niccolo (d. 1569), anatomist, 41

.44,46

vxMathematics, 9, n, 69, 97, 100, 126,
170-1, 178, 1 80, 192, 218, 224-34, 2 48

Mattiolo, Pietro Andrea (1500-77),
herbalist, 279

Maupertuis, P. L. Moreau de (1698-
1759), mathematician, 341

Maxwell, James Clerk (1831-79), physi-
cist, 265 n.

Mayer, Robert (1814-87), physician, 346

Mayerne, Sir Theodore Turquet de
(1573-1655), physician, 311 n.

Mayow, John (1645-79), physician, 325,
328

Mazarin, Jules Cardinal ( 1 602-6 1 ) , 1 96

INDEX

387

Medicine, 3-4, u, 37-51, 70-1, 73,

130-4, 200, 277-81, 310 ff.
Mendel, Gregor (1822-84), botanist,

130, 275

Merrett, Christopher (1614-95), physi-
cian, 193
Mersenne, Marin (1588-1648), 94, 113,

191, 195, 196, 199
Michelangelo (1475-1564), 41
Michieli, 280

Milton, John (1608-74), 193 n., 197 n.
Mondino dei Luzzi (c. 1275-1326),

anatomist, 40, 45
Montmor, Habert de, virtuoso, 194 .,

196, 200
Moray, Sir Robert (d. 1673), virtuoso,

193 n., 194

More, Henry (1614-87), theologian, 247
Moufet, Thomas (1533-1604), physician,

156, 282
Musschenbroek, Pieter van (1692-1761),

physicist, 340

NAPIER, JOHN (1550-1617), mathe-
matician, 192, 228-9
Natural History (see also Biology), 10, 25,
27-31, 71, 130, 198, 274 ff., 298-302
Navigation, 3, 6, 192, 219, 235
Neckham, Alexander (1157-1217), philo-
sopher, 31
Needham, John Turberville (1713-81),

291

Needham, Joseph, 77 n.

Newton, Sir Isaac (1642-1727), 21, 88,

94, 102, 105, 116, 171-3, 177, 182,

198-9, 205, 216, 223, 226, 234, 275,

294, 321, 326, 331-2, 337, 340-1,

354, 3^3, 365
and Descartes, 99, 2 1 1
and gravitation, 263-70
life etc., 244-50
alid mathematics, 229, 231-3
mechanical philosophy of, 213-15,

270-4

and optics, 239, 250-1, 254-9, 342-3
Nicholas of Cusa (1401-64), philosopher,

ii, 59, 104, 313

Nicholas of Damascus (c. 64-1 B.C.), 276 n.
Nicholson, William (1753-1815), 360
Nollet, ;4M/Jean-Antoine (i 700-70), 354
Novara, Domenico Maria da (1454-

1504), astronomer, 54

OBSERVATION, accuracy of, 17, 43, 49,
52-3, 1 15, 1 18-19, 167, 199, 217, 223-4,

353
Oersted, Hans Christian (1777-1851),

physicist, 362
Oldenburg, Henry (i6i5?~77), publicist,

191, 193 > 194 > 1 9$> 203, 249
Omar Khayyam (c. 1040-1124), mathe-
matician, 230

Oresme, Nicole (c. 1323-82), philosopher,
6, 20-i, 24, 53, 78, 85, 87, 103, 365
on diurnal rotation, 5660
variation of qualities, 80-3, 88 rc., 89,

230
Osiander, Andreas (1498-1552), divine,

55
Ovists, 291-3

PALEY, WILLIAM ( 1 743-1 805) , theologian,
281

Paracelsus (Theophrastus Bombastus von
Hohenheim (c. 1493-1541), 70, 73-4,
132-3, 224, 304, 308-12, 218

Pare, Ambroise (1510-90), surgeon, 71,

133
Pascal, Blaise (1623-62), mathematician,

100, 101, 190-1, 195, 227
Pasteur, Louis (1822-95), bacteriologist,

154, 256, 291

Paul III, Pope (1534-49), 55
Peiresc, Fabri de (1580-1637), virtuoso,

191
Pell, John (161185), mathematician,

193
Penny, Thomas (c. 1530-88), botanist,

282 n.

Peter of St. Orner (c. 1350-1400), 307
Peter the Stranger (fl. c. 1270), physicist,

6

Petrarch, Francesco (1304-74), poet, 8
Petty, Sir William (1623-87), political

economist, 193 n., 194 n. y 225-6
Peurbach, Georg (1423-61), astronomer,

ii,53

Philosophy, mechanical, 9-10, 21, 97,
101, 148-51, 157, *59, 205-16, 248,
254, 259-60, 271, 274, 289
and chemistry, 319-26
Philosophy of science, Baconian, 164-8,

301

Cartesian, 177-84
Galilean, 168-77

388

INDEX

Philosophy of science, in Greece, 1 59-63

Newtonian, 255-8, 270-4
Phlogiston, 326-36
Physical sciences :
Acoustics, 23, 226
Dynamics, Aristotelean, 18 ff., 52-3,

57, 66-8

Galilean, 78-92, 110-14, 11 7
Impetus theory, 1921, 56, 7887
Electricity, 206 ; static, 347~55 J

current, 355-63
Heat, 23-4, 169-70, 190, 206, 328,

343-7
Optics, 21-3, 180, 209-10, 214, 235-6,

239, 245, 248, 250-9, 342-3
Magnetism, 206, 210
Mechanics, Newtonian, 245, 248,

262-74, 34^-2
Statics, 21, loo-ioi
Picard, Jean (1620-83), astronomer, 198,

341

Plantades, 292

Plato (429-348 B.C.), 4, 20, 24, 162, 306
Plattes, Gabriel (fl. c. 1640), agronomist,

193".
Pliny the Elder (A.D. 23-79), 4 7 J > 2I 7>

276, 298, 306
Poisson, Sime'on Denis (1781-1840),

physicist, 354

Pole, Reginald, Cardinal (1500-58), 41
Pope, Alexander (1688-1744), poet, 250
Porta, Giovanbaptista (c. 1550-1615),

1 88

Power, Henry (1623-68), physician, 291
Prevost, J. L., 292

Priestley, Joseph (1733-1804), on chem-
istry, 328 ff.

on physics, 339, 352-3
Proust, Marcel (1871-1922), writer, 299
Ptolemy (fl. A.D. 127-51), astronomer, 12,

15-17, 21, 52 ff., 61, 63 ff., 107, 109,

117, 162

Pythagoras (?58o-?5OO B.C.), mathe-
matician, 63

RANELAGH, Countess of, 193 n.
Raphael Sanzio (1483-1520), artist, 41
Ray, John (1627-1705), naturalist, 131,

I57> 197 n., 275, 281, 284-5, 288, 294,

296, 297
R6aumur, Re"ne Antoine Ferchault de

(1683-1757), 241,290, 341

Recorde, Robert (i5io?-58), mathe-
matician, 55

Redi, Francesco (1626-98), physician,
130, 156-8,284,298

Regiomontanus (Johann Miiller, 1436-
1476), astronomer, n, 53

Reinhold , Erasmus (151153)) astrono-
mer, 54-5, 58

Reisch, Gregor (d. 1525), see Margarita
Philosophica

Renaissance, 6-10, 29-30

Renaudot, Th6ophraste (1583-1653),
journalist, 195

Rey, Jean (b. c. 1582, d. after 1645),
physician, 324

Rheticus (Georg Joachim, 1514-76),
astronomer, 54, 58, 63

Riccioli, Giovanbattista (1598-1671),
astronomer, 94

Richelieu, A. J. du Plessis, Due de (1585-
1642), 1 88, 195, 196

Richmann, Georg Wilhelm (1711-53),
physicist, 351

Ritter, J. W. (1776-1810), physicist, 360

Roberval, Giles-Personne de (1602-75),
mathematician, 94, 191

Robison, John (1739-1805), physicist,

353

Roemer, Ole (1644-1710), astronomer,
1 20, 197-8

Rohault, Jacques (1620-73), teacher,
208-10

Rondelet, Guillaume (1507-66), natural-
ist, 73, 282

Rudolph II, Emperor (1576-1612), 118,
123

Rufinus (c. 1350-1400), herbalist, 277,
369

SAGROBOSGO, see John of Holywood

Saint-Hilaire, Geoffroy (1722-1844), bio-
logist, 292

Sanctorius (1561-1636), physician, 129

Sarpi, Paolo, 85

Scheele, Carl Wilhelm (1742-86), chem-
ist, 318, 328, 329 n., 330-1, 333, 334 n.

Scheiner, Christopher (1575-1650), as-
tronomer, 1 08

Schleiden, M, J. (1804-81), biologist, 275

Schoenberg, Nicholas, 55

Science and Technology, 6-7, 818-24,
236, 347

INDEX

389

Serveto, Michael (1509-53), theologian,
46, 105 n., 140-2

Shakespeare, William (1564-1616), 72

Slusius (Sluze, R. F. W. Baron de, 1622-
1685), mathematician, 247

Sorbiere, Samuel (1615-70), physician,
196-7

Spallanzani, Lazzaro (1729-99), bio-
logist, 154, 291

Sprat, Thomas (1635-1713), divine, 189

Stahl, Georg Ernst (1660-1734), chemist,
291, 326-8

Stelluti, Francesco (1577-1653), natural-
ist, 1 88, 240

Steno (Stensen, Niels, 1638-86), anatom-
ist, 296 n.

Stevin, Simon (1548-1620), engineer,
100-1, 227, 229

Stukeley, William (1687-1765), anti-
quary, 248

Sturm, Christopher (1635-1703), mathe-
matician, 20 1

Swammerdam, Jan (1637-80), anatom-
ist, 157, 240, 286-7, 289, 290-1

S wedenborg, Emmanuel ( 1 689- 1772),
philosopher, 292

Sylvius (Jacques Dubois, 1478-1555),
physician, 46

TAGHENIUS, OTTO (fl. c. 1660), chemist,
318

Tartaglia, Niccolo (1500-57), mathe-
matician, 20, 78-9, 227

Telesio, Bernard ( 1 508-88) , philosopher,
163

Thabit ibn Qurra (c. 830-901), astrono-
mer, 53, 6 1

Thales (c. 640-546 B.C.), philosopher, 23

Theophilus the Monk (? fl. c. 1200), 307

Theophrastus (380-287 B.C.), herbalist,
10,28,217,275-7,279

Thevenot, Melchise"dec (1620-92), 197

Thompson, Benjamin (Count Rumford ;
1753-1814), 346

Timocharis of Alexandria (/. c. 300 B.C.),
astronomer, 61

Tompion, Thomas (1639-1713), horo-
logist, 219

Torricelli, Evangelista (1608-47), physi-
cist, 189, 190, 227 n., 230, 238

Tournefort, Joseph Pitton de (1656-
1708), naturalist, 131, 285, 294

Transmission of learning, i, 4, 6-7
Trembley, Abraham (1700-^84), micro-

scopist, 241, 290

Tycho Brahe (1546-1601), astronomer,
52, 94, 1 08, 112, 123-4, 191 >
192/1., 198,217,243

work of, 1 1 82 1
Tychonic System, 65-6
Tyson, Edward (1650-1708), physician,

286

ULUGH BEIGH (1393-1449), son of Timur

Lang, 1 1 8
Universities, 2-3, 11, 40, 42, 131

Bologna, 3, 40, 54

Cambridge, 143, 182, 187, 246, 247,
249> 250, 269

Cracow, 54

Louvain, 44

Montpellier, 40

Oxford, 182, 187, 190

Padua, 3, 36, 44, 47-8, 76, 139, 142-3

Paris, 3, 5, 20, 44, 48, 81, 142, 182

Pisa, 76-7, 109

Salerno, 39

Wittenberg, 54

VAL VERDE DE AMUSGO, JUAN (fl. c. 1 540
1560), anatomist, 142

Vesalius, Andreas (1514-64), anatomist,
9> 35-5 1 * 70, 7i> 74> 140-1, 163, 217,
235

compared with Copernicus, 36-7
on the heart, 139

Viete, Francois (15401603), mathe-
matician, 228

Viviani, Vincenzo (1621-1703), mathe-
matician, 76 n., 189

Volta, Alessandro (1745-1827), physi-
cist, 357-60, 362

Voltaire, Fran$ois Marie Arouet de
(1694-1778), 274, 293, 339

WALLIS, JOHN (1616-1703), mathe-
matician, 193, 247
Watson, Richard (1737-1816), divine,

327
Watt, James (1736-1819), engineer,

347
Wesley, John (1703-91), 339

390

INDEX

Whiston, William (1667-1752), divine, Wolff, Caspar ( 1 738-94) , biologist, 293

297

Wordsworth, William (1770-1850), 293

White, Gilbert (1720-93), naturalist, Wren, Christopher (1632-1723), archi-

293, 2 99 tect, 153, 194

Wilkins, John (1614-72), divine, 103, Wyclif, John (d. 1384), 2

193, 194
William of Moerbeke (c. 1215-86),

translator, 39
William of Ockham (c. 1295-1349),

philosopher, 56, 163
Willughby, Francis (1635-72), naturalist,

284

YOUNG, THOMAS (1773-1829), physicist,
245

ZALUZIAN, Adam Zaluzanski of (c. 1500

Wilson, George (163 1-171 1 ), chemist, 318 1610?), botanist, 281