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Plate I 







(formerly WHET HAM) 

Sc.D., F.R.S. 

Fellow and sometime Senior Tutor of Trinity College > Cambridge 
Fellow of Winchester College 



First edition, March 1944 
Reprinted, August 1944 



Preface page ix 

Chapter I. THE ORIGINS i 

Prehistory The Dawn of History Egypt Babylonia China and India Crete 
and Mycenae. ** **< 


Greek Religion The Ionian Philosophers The Atomists The Pythagoreans 
Greek Medicine Socrates and Plato- -Aristotle The Hellenistic Period 
Deductive Geometry Archimedes, Aristarchus and Hippaichus The School of 
Alexandria Alchemy The Roman Age. 


The End of Ancient Learning The Fathers of the Church The Dark Ages- 
The Arabian School The Revival in Europe The Thirteenth Century and 


The Causes Leonardo da Vinci The Reformation Copernicus and Astronomy 
Chemistry and Medicine Anatomy, Physiology and Botany Magnetism and 
Electricity Philosophy Witchcraft. 


Galileo Boyle, Huygens and others Scientific Academies Newton and Gravi- 
tation Mass and Weight Optics and Light Newton and Philosophy Newton 
in London. 


Philosophy Mathematics and Astronomy Chemistry Physiology, Zoology and 
Botany Geography and Geology Machinery. 


The Scientific Age Heat and Energy Thermodynamics The Wave Theory of 
Light Spectrum Analysis Electric Currents Electro-magnetism The Atomic 
Theory Organic Chemistry Chemical Action Solution Colloids. 


Biology and its Effects Physiology Bacteriology The Carbon and Nitrogen 
Cycles Geography and Geology Evolution and Natural Selection Anthro- 
pology Nineteenth-Century Science and Philosophy Psychology. 



Genetics Geology and Oceanography Biochemistry, Physiology and Psychology 
Viruses and Immunity Anthropology. 


The Physical Revolution Cathode Rays and Electrons Radio-activity X-rays 
and Atomic Numbers Positive Rays and Isotopes The Structure of the Atom 
The Transmutation of Elements Electro-magnetic Waves Relativity. 


The Solar System The Stars and Nebulae -The Structure of Stars Stellar 
Evolution The Beginning and End of the Universe Conclusion. 

A Note on Bibliography 1 74 

Index 176 


I. Isaac Newton Frontispiece 

II. Archimedes facing p. 28 

III. Leonardo da Vinci 29 

IV. Galileo 62 
V. Galileo's original telescope 63 

VI. Charles Robert Darwin 122 

VII. Lord Rutherford of Nelson 123 

VIII. Tracks of a particles in oxygen 148 

IX. The Spiral Nebula in Canes Venatici 149 

Plate I is from a photograph by Ramsey and Muspratt; Plate II is from Cox, 
Mechanics; Plate III, Anderson photograph, supplied by Mansell; Plate IV, photo- 
graph supplied by Rischgitz; Plate V is from Dampier, Cambridge Readings in Science; 
Plates VI and VII by permission of Elliott and Fry; Plate VIII is from Rutherford, 
The Newer Alchemy; Plate IX is from Jeans, The Universe Around Us. 


1. Palaeolithic flint tool page 2 

2. Cave drawing of a mammoth 4 

3. Bronze palstave of late middle bronze age, found at 
Hilfield, Dorset 6 

4. Early Egyptian pottery 9 

5. An Egyptian queen driving in her chariot 10 

6. The Theorem of Pythagoras 19 

7. Drawing of a dissection of development of Sepia by 
Aristotle 23 

8. Diagram of the Universe by Copernicus 51 

9. Diagram of declination of iron magnet 57 

10. Co-ordinate geometry by Rene* Descartes 59 

1 1 . Curve of error 96 

12. Asymmetric carbon atom 107 

13. Curve of error in biology 124 

14. Thomson's apparatus for cathode rays 144 

Figs, i and 2 are from Burkitt: TTie Old Stone Age; fig. 4, from Abydos, by Petrie, 
by permission of the Egypt Exploration Society; fig. 5, from The Rock Tombs of El 
Amarwy by Davies, by permission of the Egypt Exploration Society; fig. 7, from 
Aristotle's Historia Animaliwn (Oxford); fig. 8, from Dampier & Whetham: 
Cambridge Readings in the Literature qf Science; fig. 9, from De Magnete by William 
Gilbert; figs. 1 1-14, from Dampier: History of Science. 


The speed with which three editions of my larger book A History of 
Science and its Relations with Philosophy and Religion have been called 
for shows that many men are interested in the subjects with which it 
deals. Some, however, have found the philosophic part difficult to 
read, and have asked for a straightforward story of the growth of 
science reduced to its simplest terms. 

It is impossible to ignore altogether the connexion of science with 
other activities, but description can, if we will, be confined to the more 
direct impacts. The Greek Atomists, besides speculating on the 
structure of matter, developed therefrom a mechanical theory of life. 
Conversely, the philosophy of Plato, even as modified by Aristotle, 
/toq much stress on innate ideas and logical deduction to make a 

durable background for the beginnings of inductive experimental 
science. To Newton and his immediate followers the Heavens declared 
the Glory of God, but Newton's work produced a very different 
effect on the minds of Voltaire and other eighteenth-century sceptics. 
Darwin's revival of the old theory of evolution on the new basis of 
natural selection not only suggested an alternative origin for man- 
kind, but spread evolutionary doctrine far beyond the limits of 
biology. The recent revolution in physics has shaken the evidence for 
philosophic determinism which the older synthesis seemed to require. 
Such broad effects must be noticed, but the more technical aspects 
of philosophy may be passed by. 

In writing this 'Shorter History', I have had two objects: firstly, to 
help the general reader, who wishes to know how science, which now 
affects his life so profoundly, reached its present predominance, and 
secondly, to meet the needs of schools. Those older schoolboys whose 
chief subjects are scientific should look at them also from a humanist 
standpoint, and realize their setting in other modes of thought, while 
those studying literature need some knowledge of science before they 
can be said to be well educated. For both groups, I believe that the 
history of science, the story of man's attempts to understand the 


mysterious world in which he finds himself, makes the best way of 
approach to common ground. Moreover, an opinion is growing that 
early specialization is dangerous, an opinion which leads to a desire 
to give even scholarship candidates a well-balanced education. I hope 
that this little book may be useful to schoolmasters who share my 
views, and lead many readers to study its longer prototype. 

I wish to thank those who have allowed me to use their illustrations, 
and the Cambridge University Press for making publication possible 
in war-time. I must also thank my sister, Miss Dampier, for helping 
in the tedious work of preparing the index. 

W. G. D. D. 

December 1943 

I have taken the opportunity of the reprinting of this book to 
make a few verbal changes in the text. A more general point, sug- 
gested by one of my reviewers, may perhaps be made here. A history 
of science must inevitably be chiefly an account of those experiments 
which succeed, and of the theories which, for a time at any rate, 
survive. Thus it gives a false impression of an unbroken series of 
triumphs. We must not forget that, in the background, are many 
attempts that fail, for each one that is inscribed on the roll of fame. 

W. C. D. D. 
July 1944 



Prehistory. What is Science? The word comes from the Latin 
sci re, to learn, to know, and thus should cover the whole of learning 
or knowledge. But by English custom it is used in a narrower sense 
to denote an ordered knowledge of nature, excluding such humanistic 
studies as language, economics and political history. 

Science has two streams corresponding to two sources, the first 
a gradual invention of tools and implements whereby men earn their 
living more safely and easily, and the second the beliefs they form to 
explain the wonderful universe around them. The first may perhaps 
better be called technology, for its problems are too difficult for early 
theory, .and only in later stages does it become applied science; the 
second, which in historic times grew into a pure search for knowledge, 
is the main subject of this book. 

If we seek for the beginning of science and the matrix in which it 
arose, we must trace the jrecords of early man as given us by geologists 
and anthropologists, who study respectively the structure and history 
of the earth and the physical and social characters of mankind. 

It is probable that the crust of the earth solidified some thousand 
million years ago, 1-6 thousand million, or 1*6 x io 9 years, is a recent 
estimate. Geologists recognize six great periods which followed that 
event: (i) Archaean, the age of igneous rocks formed from molten] 
matter; (2) Primary or Palaeozoic, when life first appeared; 
(3) Secondary or Mesozoic; (4) Tertiary; (5) Quaternary; (6) Recent. 
The age of these periods relative to each other is shown by the 
position of their deposits in the earth's strata, but no certain estimate 
can be made of their absolute age in years. 

One school of anthropologists holds that traces of man's handiwork 
are first seen in tertiary deposits, and the most recent evidence is 
heM to support this view. The earliest signs of man, perhaps some- 
where between one and ten million years ago, a minute fraction 
of the earth's life, are flints or other hard stones roughly chipped 



into tools or weapons. They are found lying on the surface of the 
earth, in river beds^ in excavations made by engineers or dug 
deliberately to find them, and in caves one of the most primitive 
types of dwelling. The oldest stone tools, named eoliths, are difficult to 
distinguish from natural products, flints chippecf 
accidentally by the action of water or movements 
in the earth, but the next group or palaeoliths 
are clearly artificial and of human origin (Fig. i). 

Ignoring the doubtful eoliths, we can divide 
the stone age into two parts. Palaeolithic man 
only chipped his implements; he hunted wild 
animals, but did not tame them or cultivate the 
soil. Neolithic man belonged to a different and 
higher race, which seems to have invaded Western 
Europe, bringing with it domestic animals, some 
skill in agriculture and in the forming of pottery 
and of golished implements in flint or hard ig- 
neous stone, in bone, horn or ivory. In some parts 
of the world Neolithic man found out how to 
smelt copper and harden it with tin, thus passing 
from the stone to the bronze age, and incidentally making the first 
discovery in metallurgy. Later on, bronze gave place to iron, prob- 
ably because of its greater advantage in weapons of war. 

Returning to a consideration of the stone age, we see that the 
variety and finish of the tools used increase as we examine the 
higher, and therefore later, deposits. Weapons dropped in war or the 
chase give us only casual finds, but occasionally we come upon the 
floor or hearth of a prehistoric dwelling, and add more largely to our 
collection. Signs of fire, such as burnt flints, show another agent in 
the hands of man, while the remains of plants and animals indicate 
by their nature the climate of the time, whether warm, temperate 
or glacial. 

At an early stage in the story, man took to living in caves, a shelter 
from the weather ready to his hand, and a museum kept for ^is, 
containing not only dropped tools and weapons, but also, beginning 
in Palaeolithic times, pictures drawn on the walls by the inhabitants, 

FIG. i. Palaeolithic 
flint tool 


pictures from which we can gain some knowledge of the life lived 
by men thousands or millions of years ago, and even an insight into 
their thoughts and beliefs. 

Lower Palaeolithic civilizations, dating from the beginning of the 
quaternary era, and ending as the last ice age approached, must have 
covered an immense stretch of time, during which there seems to 
have been a steady improvement in culture, at all events in the lands 
which are now England and France. 

Middle Palaeolithic times are associated with what is known as 
Mousterian civilization, so named from the place where it was first 
discovered Moustier near Les Eyzies. The race which made it, 
known as Neanderthal man, again from its place of discovery, was 
of a low type, generally held not to be in the direct line of human 
evolution. The cold of Mousterian times drove man more extensively 
to caves and rock shelters as homes, and so preserved many of his 
tools, jvvhich show that he had learnt to fashion them from flakes 
chipped off flints, unlike the majority of Lower Palaeolithic tools, 
which were made from the cores left when flakes were chipped away. 

Upper Palaeolithic or Neo-anthropic man appeared in France 
after the worst of the last ice age was over, though a continuing 
mixture of reindeer with stag in the bones and pictures shows that 
the climate was still cold. The Upper Palaeolithic race was far higher 
in the scale of humanity than any earlier one, and began to make 
household objects; there was a definite bone industry and the flaking 
of flint was greatly improved. We can see such things as eyed needles 
and double-barbed harpoons carved in bone, and found in Mag- 
dalenian, Upper Palaeolithic, deposits. These and other tools and 
weapons show a marked advance on earlier implements. 

Of somewhat the same age are the oldest pictures on the walls of 
caves. Outlines of men and animals horses, buffaloes and extinct 
mammoths appear. Then, as some indication of beliefs, we have 
drawings thought to represent devils and sorcerers. 

To gain a more definite idea of these beliefs, we may compare them 
with those of early historical times, as described by Greek and Latin 
authors, and those still found among primitive people in various 
parts of our modern world. A huge amount of such evidence has 



been collected by Sir James Frazer in his great book The Golden 
Boughy primarily to explain the rites of Diana Nemorensis, Diana of 
the Wood, carried on, even in classical days, in the Grove of Nemi 
in the Alban Hills near Rome, and obviously surviving from earlier, 
more barbarous, ages. In the Grove of Nemi lived a priest-king who 
reigned there until a man, stronger or more cunning than he, slew 
him and held the kingship in his stead. 

FIG. 2. Cave drawing of a mammoth 

In order to explain this tragic custom, Frazer ranges over the 
world and over long stretches of time. He deals in turn with magic, 
magical control of nature, nature spirits and gods, human gods, gods 
of vegetation and fertility, the corn-mother, human sacrifices for the 
crops, magicians as kings, the periodic killing of kings, especially 
when crops fail or other catastrophes happen, and the arts as an 
approach to primitive science. Some anthropologists regard magic 
as leading directly to religion on one side and to science on the other, 
but Frazer thinks that magic, religion and science form a sequence 
in that order. Another anthropologist, Rivers, holds that magic and 
primitive religion arise together from the vague sense of awe and 
mystery with which the savage looks at the world. 


Magic assumes that there are rules in nature, rules which, by the 
right acts, can be used by man to control nature. Thus magic is a 
spurious system of natural law. Imitative magic rests on the belief 
that like always produces like. When frogs croak, it rains. The savage 
feels he can do that too; so, in a drought, he dresses as a frog and 
croaks to bring the wished-for rain. Countless similar instances of 
imitation might be given. Contagious magic believes that things 
once in contact have a permanent sympathetic connexion. The 
possession of a piece of another man's clothing, and still more of a 
part of his body his hair or his nails puts him in your power; 
if you burn his hair, he too will shrivel up. 

Now these examples take the magician no farther; by coincidence 
his action may sometimes be followed by the appropriate happening, 
but more often it fails. Suppose, however, that, by accident, the 
magician hits on a real relation of cause and effect for illustration 
he rubs together two bits of wood and produces the miracle of fire. 
By that experiment he has learnt a true fact which he can repeat at 
will, and he has, for that one relation, become a man of science. But 
in magic, if he fails too often to produce his effect, he may be forsaken 
or even killed by his disappointed followers, who may perhaps cease to 
believe in the control of nature by men and turn to propitiate imagined 
and incalculable spirits of the wild, gods or demons, in order to 
obtain what they want ; thereby they pass to some form of primitive 
religion. Meanwhile, far out on the other wing, the discovery of fire, 
the taming of animals, the growing of crops, the gradual improvement 
in tools, and the development of many other simple arts, lead, by 
a less romantic but surer road, to another origin of science. Whatever 
may be the relation between magic, religion and science and that 
relation may differ in various times and places there is certainly a 
real and intimate connexion between them. Science did not germinate 
and grow on an open and healthy prairie of ignorance, but in a 
noisome jungle of magic and superstition, which again and again 
choked the seedlings of knowledge. 

Neolithic man again shows an advance. Structures such as Stone- 
henge, where a pointer stone marks the position of the rising sun at the 
solstice, serve not only religious uses but astronomical functions also. 


Prehistoric burials often give interesting information. They are 
found till the end of Neolithic times, cremation only appearing 
commonly in the bronze age, and then mostly in Central Europe 
where forests supplied fuel. Well-finished stone implements were 
often placed in the tombs, showing us the state of contemporary art, 
and sometimes suggesting a belief that such things would be useful 
to the dead when they passed over to another world a belief then 
in survival. 

FIG. 3. Bronze palstave of late middle bronze age, found at Hilfield, Dorset 

We must not assign to primitive people, whether prehistoric, 
ancient or modern, too rationalist an outlook. When a savage dreams 
of his dead father, he does not reason about it, but accepts the dream 
as real, and his father as, in some sort, alive not perhaps as much 
alive as his mother still in this world, but quite clearly surviving his 
death, though perhaps in an attenuated form as a spirit or ghost. 
There is no distinction in kind between natural and supernatural, 
only a vague difference in degree. 

With the coming of the bronze age, we pass to a higher culture, 
made possible by the use of metal. We find axes, daggers and their 
derivatives spears and swords, and household goods such as lamps. 
Man has definitely passed from the use of stone as his sole material, 


and when bronze is replaced by iron, we approach and soon enter 
periods when true history can be pieced together by written records 
on stone, clay, parchment or papyrus. 

The Dawn of History, Settled life, with primitive agriculture 
and industrial arts, seems first to have begun in the basins of great 
rivers the Nile, the Euphrates with the Tigris, and the Indus, while 
analogy would suggest that the early civilization of China too began 
near its rivers. In contact here and there with these river folk were 
nomads, pastoral people, wandering with their flocks and herds over 
grass-clad steppes or deserts with occasional oases. Nomad society 
was, and is, essentially patriarchal, the social unit being the family, 
perhaps with slaves, and the government the rule of the father. In 
normal times, the units kept separate from each other, each in search 
of food for their beasts. In the Old Testament we have an early and 
vivid account of the life of nomad people. 

And Lot also, which went with Abram, had flocks, and herds, and 
tents. And the land was not able to bear them, that they might dwell 
together. . . . And Abram said unto Lot ... Is not the whole land before 
thee? separate thyself, I pray thee, from me: if thou wilt take the left 
hand, then I will go to the right; or if thou depart to the right hand, 
then I will go to the left. 1 

With these isolationist views and customs, neither civilization nor 
science was possible. Co-operation between the family groups only 
arose for some definite purpose a hunt of dangerous wild beasts, 
or war with other tribes. But sometimes, owing to a prolonged 
drought, or even perhaps to a permanent change in climate, the 
grass failed, the steppes or oases in the deserts became uninhabitable, 
and the nomad folk overflowed as an irresistible horde, flooding the 
lands of the settled peoples as barbarous conquerors. We can trace 
several such outrushes of Semites from Arabia, of Assyrians from the 
borders of Persia and of dwellers in the open grass-clad steppes of 
Asia and Europe. 

Now it is clear that we need not look among nomads for much 
advance in the arts, still less for the beginnings of applied science. 

1 Genesis xiii. 5-9. 


But the Old Testament, preserved as the sacred books of the Jews, 
not only gives in its earlier chapters an account of nomads, but later 
on deals with the legends of the settled kingdoms in the Near and 
Middle East Egypt, Syria, Babylonia and Assyria a good intro- 
duction to the more recent knowledge obtained by the discovery of 
the buildings, sculptures and tablets, and by the excavations of such 
relics as royal tombs. This later knowledge is of course fragmentary, 
depending upon the double chance of the survival of ancient records, 
and of their discovery and correct interpretation by present-day 

Since the late stone age, the sea-coasts and islands of the Aegean 
have been chiefly occupied by the Mediterranean race, short in 
stature with long-shaped head and dark in colouring; to them is due 
what prehistoric advance in civilization occurred. Farther inland, 
especially among the mountains, the chief inhabitants were and are 
of the so-called Alpine race, a stocky people of medium height and 
colouring, and broad, round-shaped skulls, who pushed into Europe 
from the east. Thirdly, spreading out from the shores of the Baltic, 
we find a race which may be called Nordic, tall, fair-haired and, like 
the Mediterranean people, with long-shaped heads. 

Egypt. Egypt is divided into two very different parts the Delta, 
where the Nile seeks the sea through mud flats of great fertility, and 
the valley of Upper Egypt, spreading for a few miles broad in the 
rift through which the river makes -its way between the sands of the 
western desert and the rocky hills of the eastern shore. 

On both sides of the Nile rift, and at many points along its length, 
Palaeolithic implements are found, showing that human occupation 
began in early geological times. Then came Neolithic man, with his 
better tools and the great discovery of the potter's art. When soft 
clay is worked into a designed form and fixed in that form by fire, 
a new thing has been created. Here is something more than adapta- 
tion, as in flint weapons or stone bowls, something which means true, 
invention and a long step towards civilization. 

The history of Egypt begins with the first dynasty of kings, 
somewhere about 3000 years before Christ. Earlier times are repre- 


seated by legends such as that of the divine Horus, Sun of the Day, 
and his followers. The hieroglyphic script, in which many Egyptian 
records are written, was first deciphered from the Rosetta stone, 
discovered by Boussard in 1799 near Rosetta, 
east of Alexandria. On it is set out a decree 
of Ptolemy V Epiphanes, in hieroglyphics, de- 
motic script 1 and Greek. Thus those hiero- 
glyphics were interpreted by Champollion and 
Young, and a beginning made in the study of 
Egyptian documents, both on incised stone and 
on paper made from papyrus which, in the dry 
climate of Egypt, does not perish. 

The first clearly historical king was Menes 
(3188-3141 B.C.), who became sovereign of all 
Egypt and founded the city of Memphis. Even 
under bis, the first, dynasty, records were kept 
of the chief events of each year, such as the 
height of the Nile flood. Documents become 
plentiful in the time of the fourth dynasty, and 
the pyramids, orientated astronomically, were 
built from the fourth to the twelfth dynasty, 
but the best achievements in practical arts begin 
to appear under the eighteenth dynasty, some- FlG ' * Early Egyptian 
where about 1500 to 1350 B.C. 

The Egyptians imagined a divine intervention to explain the origin 
of every craft, art or science; especially were they referred to Thoth, 
a moon god who measured time in days and years, and established in 
the temples 'watchers of the night' to record astronomical events. 

In arithmetic a decimal system was employed as early as the first 
dynasty. It had no sign for zero (a much later Indian invention) 
and no positional notation, also no separate signs for numbers 
between i and 10, so that the unit had to be repeated to the number 
required. Fractions also were dealt with by units, so that our T 7 ^ was 
written as J J implying addition. These unit fractions persisted long 
after mixed fractions became general. 
1 A shortened form of hieroglyphics. 



FIG. 5. An Egyptian queen driving in her chariot 

The official calendar contained 365 days in the year, though the 
Egyptians seem to have known that the solar year was nearer 365 J, 
The former year thus worked back through the seasons, completing 
a cycle in about 1500 years, a period which appears to have been 


taken to mark an era of time. Five days were held to celebrate the 
birthdays of five chief gods, and were not counted in the temples, 
which kept a year of 360 days. This calendar of course diverged 
even more rapidly from the true year. By the time of the Romans, 
the many calendars in use brought confusion, but Julius Caesar, with 
the technical advice of Sosigenes, accepted and established as the 
Julian calendar a year of 365 days 365 with an additional day 
every fourth year. This, being a little too much, was corrected by 
Pope Gregory XIII in 1582, and in England in 1752, by dropping 
out one leap year in three centuries out of four. 

The periodic submersion of the ground by the Nile, with the 
consequent loss of boundary-marks, led to the art of land measure- 
ment by surveyors or 'rope stretchers', an art which later, in the 
hands of the Greeks, became the science of deductive geometry. 

The stars were grouped in constellations, which were identified 
with deities, and so represented on ceilings and coffin lids. The 
Universe was imagined as a rectangular box, with Egypt at the 
middle of its base. The sky was supported by four mountain peaks, 
and the stars were lamps hung from the sky by cables. Round the 
land ran a river, on which travelled a boat bearing the sun. 

The Egyptians had a considerable amount of medical knowledge, 
and several known papyri contain notes or treatises on medicine 
mingled with magic. The first physician whose name has survived is 
I-am-hotep, ' he who cometh in peace ' ; after death he became a god 
of medicine. The custom of embalming the dead led naturally to 
anatomy and so to surgery, illustrated in carvings as early as 2500 B.C. 
The number of diseases treated rationally gradually increased, but 
mental disorders continued to be referred to exorcists, who, with 
amulet and charm, professed to drive out the evil spirits. 

Ancient Egypt made great advances in technical arts. The stu- 
pendous building work of the pyramids is still a wonder, and the 
ruins of temples at Karnak and Philae show high artistic merit. 
Set squares, levels and plumb lines are among the tools found. The 
beam balance was used for weighing, and many weights have been 
discovered, but it seems that different standards were used in different 


parts of the country. A weaving loom is pictured as early as the 
twelfth century B.C., so that spinning must also have been practised. 
A ship under full sail is pictured in a tomb of the fourth dynasty; 
also wheeled chariots drawn by horses (see p. 10). 

To sum up the science of ancient Egypt was the handmaid of 
practical arts, housekeeping, industry, architecture, medicine, but 
in that role it achieved considerable success. Egypt had much 
influence on other lands, especially on Crete in the Minoan ages and 
afterwards on Greece, where its practical science was sublimated 
into a pure search for knowledge. 

Gambyses, son of Gyrus the Persian, conquered and crushed 
ancient Egypt. The thirtieth dynasty, 400 B.C., was the last native 
line, and another barbarian, Ochus, completed the ruin. When 
Alexander entered the country, he was hailed as a deliverer; he 
founded Alexandria, which later on succeeded Athens as the intel- 
lectual centre of the world. In 30 B.C., after the reign of the great 
Cleopatra, Egypt became a Roman province. 

Babylonia. Babylonia is the country of the rivers Tigris and 
Euphrates, and Babylon was for long the huge capital city, of which 
only ruins remain. Other cities were numerous, one of the oldest 
being Ur of the Chaldees, from which Abraham set forth on his 

The country consisted of two parts, the upper, a land of steppe 
and desert, and the lower, formed by the silt and mud of the rivers, 
the fertility of which made the wealth of the people. On the west 
was Arabia, and on the east Assyria, on the foothills of the Persian 

The first name of the country was Sumer, and its earliest inhabitants 
in historical times were called Sumerians. These people >vere after- 
wards mixed with Semites invading from Arabia, and Assyrians from 
the hills. The land is subject to violent storms and floods, the memory 
of one such being preserved in the legend of Noah and the deluge. 
Like this wild nature with its dangers, the Babylonian gods were 
mostly inimical to man. 

The Babylonian Universe was, like the Egyptian, a box, the Earth 


being its floor. In the centre were snow mountains in which was the 
source of the Euphrates. Round the Earth was a moat of water, and 
beyond it celestial mountains supporting the dome of the sky. More 
useful than such speculations was astronomical observation, which 
can be traced back to about 2000 B.C. by records found on clay 
tablets. By the sixth century, the relative positions of the Sun and 
Moon were calculated in advance and eclipses predicted. 

On the basis of such definite knowledge, a fantastic scheme of 
astrology was built up, in the belief that the stars controlled human 
affairs. Ghaldaean astrologers were specially famous, while sorcerers 
and exorcists acted as physicians. 

Wheat and barley seem to have been indigenous, and were cul- 
tivated for food at an early date. This made a calendar necessary; 
the day as a unit of time is forced on man, and attempts to measure 
the number of months in the cycle of the seasons were made at a 
date said to be about 4000 B.C. The day was divided into hours, 
minutes and seconds, and a vertical rod or gnomon set up as a sun- 
dial. Seven days were named after the Sun, the Moon and the five 
known planets, and thus the week became another unit of time. 

But perhaps the most striking scientific achievement was the 
recognition of the need for fixed units of measurement, and the issue 
on royal authority about 2500 B.C. of standards of length, weight and 
capacity. The unit of length for instance was the finger, about f inch; 
the cubit contained 30 fingers, the surveyor's cord 120 cubits and 
the league 180 cords or 6*65 miles. 

The Sumerians too had some skill in mathematics and engineering. 
They had multiplication tables and lists of squares and cubes. 
Decimal and duodecimal systems were used, special importance 
being assigned to the number 60 as a combination of the two, as seen 
in the measures of minutes and hours. Simple figures and formulae 
for land surveying led to the beginning of geometry. Maps of fields, 
towns, and even of the then known world, were drawn. But all were 
mixed with magical conceptions, which later passed westward. 
European thought was dominated for centuries by Babylonian ideas 
of the virtues of special numbers and the prediction of the future by 
geometrical diagrams. 


China and India. The civilization of China approaches in age 
that of Egypt or Babylonia, but China was isolated, and had no 
early contact with those countries. There are legends ranging back 
to some such time as 2700 B.C., but historical records only appear about 
2000. Fine pottery and bronze vessels are found in the age of the 
Shang dynasty, 1750 to 1 125, and iron weapons were first used about 
500 B.C., later than in Europe. By 100 B.C. trade had been established 
with Persia and other countries. Culture reached a high level under 
the Chou dynasty (say noo to 250), with practical arts like agri- 
culture and the irrigation of land. 

The earliest religion, Taoism, was inextricably mixed with magic. 
Confucius in the sixth century before Christ introduced a purer faith, 
and established an Academy, where the literary classes were separated 
from the priestly. The teaching of Buddha reached China in A.D. 64. 
In later times China has the credit of an independent invention of 
paper, and the discovery of the magnet with its use in the compass. 

Indian Culture seems to have begun in the valley of the Indus, 
in the third millennium before Christ. The original dark-skinned 
people were mixed in the north of India by an incursion of Aryan 
invaders, who impressed their language and civilization on the 
former inhabitants. A decimal notation was already in use, and, in 
the third century, the scheme of numerals we employ to-day was 
invented; though it reached us through the Arabs, and is known 
erroneously as Arabic. In ethical philosophy, Buddha (560 to 
480 B.C.) is pre-eminent, and schools of medicine with famous 
physicians had been established in his time. 

A primitive atomic theory was formulated or borrowed from the 
Greeks, and, a century or so before Christ, the idea of discontinuity 
was extended to time. Everything exists but for a moment, and in 
the next moment is replaced by a facsimile; a body is but a series of 
instantaneous existences time is atomic. 

Crete and Mycenae. The early civilization of the Eastern Medi- 
terranean is best known to us by the researches begun by Sir 
Arthur Evans at Cnossus in Crete, the birthplace and chief home 


of what is now called Minoan Culture, from Minos, the legendary 
king of Crete. Its beginnings, Early Minoan, seem to be contem- 
porary with dynasties I to VI in Egypt; Middle Minoan with 
dynasty XII, while Late Minoan corresponds to dynasty XVIII, and 
can be dated 1600 to 1400 B.C. There seems to have been constant 
intercourse in trade and otherwise between the two countries. 

The Cretan script is like, but not identical with, that of Egypt; 
its early pictorial characters had come to have phonetic meanings 
when we first find them; they are still undeciphered, but we have 
much information from other sources. There are remains of skilfully 
engineered roads crossing the mountain passes; applied science in 
the palace mechanical, hydraulic and sanitary; mural decoration 
with pictures showing costumes (some worthy of modern Paris), 
weapons and armour, and light chariots drawn by horses. 

The Palace at Cnossus was destroyed by civil disturbance or 
foreign enemies about 1400 B.C. It is worth noting that, at some- 
what the same time, Egypt was attacked by sea-borne raiders, who 
resemble in many ways the Achaean invaders of Greece. 

But we can look to the mainland for another site of Eastern 
Mediterranean culture. Rich relics of a civilization similar to that 
of Crete have been found at and near Mycenae. But about 1400 the 
Aegean lands were in turmoil and Mycenae like Cnossus went down. 

The earliest of Greek traditions speaks of the coming of the 
Achaeans, apparently brown-haired tall men from the grass-lands 
lying to the north, immediately perhaps from the valley of the 
Danube, bringing with them horses and iron weapons to conquer 
the bronze of the Minoans, and the custom of burning instead of 
burying the dead. It is thought by some that here we see the first 
incursion of the Nordic race tall, fair, and with long-shaped 
skulls filtering through the pastures and steppes of Europe from 
their original home by the shores of the Baltic. However that may 
be, they were followed about noo by the Dorians, also probably 
from the nearer north, who overran the Peloponnese. By this mixture 
of peoples a nation was created ; Minoan civilization gave place to 
Greek, and we enter the full light of history. 


Greek Religion. As Xenophanes recognized as long ago as the 
sixth century before Christ, whether or no God made man in His 
own image, it is certain that man makes gods in his. J"he gods of. 
Greek mythology first appear in the writings of Homer and Hesiod, 
and, from the character and actions of these picturesque and for the 
most part friendly beings, we get some idea of the men who made 
them and brought them to Greece. The men differ in customs and 
beliefs from the Minoans and Myceneans, and it is probable that they 
were the Achaeans, who came down from somewhere in the north. 

But ritual is more fundamental than mythology, and the study of 
Greek ritual during recent years has shown that, beneath the belief 
or scepticism with which the Olympians were regarded, lay an older 
magic, with traditional rites for the promotion of fertility by the 
celebration of the annual cycle of life and death, and the propitiation 
of unfriendly ghosts, gods or demons. Some such survivals were 
doubtless widespread, and, prolonged into classical times, probably 
made the substance of the Eleusinian and Orphic mysteries. Against 
this dark and dangerous background arose the Olympic mythology 
on the one hand and early philosophy and science on the other. 

In classical times the need of a creed higher than the Olympian 
was felt, and Aeschylus, Sophocles and Plato finally evolved from 
the pleasant but crude polytheism the idea of a single, supreme and 
righteous Zeus. But the decay of Olympus led to a revival of old 
and the invasion of new magic cults among the people, while some 
philosophers were' looking to a vision of the uniformity of nature 
under divine and universal law. 

The Ionian Philosophers. The first European school of thought 
to assume that the Universe is natural and explicable by rational 
inquiry was that of the Ionian nature-philosophers of Asia Minor. 
One of the earliest known to us is Thales of Mifctus (c. 580 B.C.), 
merchant, statesman, engineer, mathematician and astronomer. 
Thales is said to have visited Egypt, and, from the empirical rules 


for land-surveying there in vogue, to have originated the science of 
deductive geometry. He pictured the Earth as a flat disc, floating 
on water, instead of resting on a limitless solid bottom, and pro- 
pounded the idea of a cycle from air, earth and water through the 
bodies of plants and animals to air, earth and water again. 

Anaximander (ob. 545) recognized that the heavens revolve round 
the pole star, and inferred that the visible dome of the sky is half a 
complete sphere, with the Earth at its centre, the Sun passing under- 
ground at night. Worlds arise from the primordial stuff of chaos by 
natural causes, such as are still at work. The first animals came from 
sea slime, and men from the bellies of fish. .Primary matter is .etcraaL 
buFall things made from it are doomed to destruction. 
~~Some men, such as Empedocles of Sicily, held that there were 
four elements, earth, water, air and still more tenuous fire. By 
combinations of the four, the various types of matter were made. 
Empedocles proved the corporeal nature of air by showing that water 
can only enter a vessel as air escapes. 

The Ionian philosophy was brought to Athens by Anaxagoras of 
Smyrna about 460 B.C. Anaxagoras added to itsjachf"i^1 H*nt Ky 
the belief that the heaynl^ 
Earth ;_the Sun being MjMyT^^og^Helios but a burning stone. 

The lonians also made advances in practical arts, inventing or 
importing the potter's wheel, the level, the lafthe, the set square and 
the style or gnomon, used as a" sundial to tell the time and to deter- 
mine when the Sun's altitude at noon was greatest. 

The Atomists. The intellectual heirs of the lonians were the 
Atomists Leucippus, who founded a school at Abdera in Thrace 
some time in the fifth century, and Democritus, born there in 460 B.C. 
Their views are known to us by references in later authors such as 
Aristotle, by the work of Epicurus (341 to 270), who brought the 
atomic theory to Athens, and by the poem of the Roman Lucretius 
two centuries later. 

The Atomists taught that everythin^happens_ 
necessity. They carried lartner the Ionian attempt to explain matter 
in terms of simpler elements. Their atoms are identical in substance 


but many in size and shape; 'strong in solid singleness 5 , they have 
existed and will exist for ever. Thus differences in the properties of 
bodies are due to differences in size, shape and movement of atoms. 
The appearances as seen by the senses have no reality : ' according to 
convention there is a sweet and a bitter, a hot and a cold, and 
according to convention there is colour. In truth there are atoms 
and ajzoidL* 

Literary men sometimes claim for the Greeks anticipations of 
modern science. But the modern atomic theory which Dalton 
sponsored in the early years of the nineteenth century was based on 
the definite facts of chemical combination in equivalent weights, and 
was soon verified experimentally by predictions obtained by its aid, 
as were the later developments of the theory due to J. J. Thomson, 
Aston, Rutherford, Moseley and Bohr. In the absence of such clear 
experimental evidence, the atomic theory of Democritus and Lucretius 
is little more than a lucky guess. If many different hypotheses are put 
forward, one of them may well chance to be somewhere near more 
modern views. The atoms of the Greeks had no firm basis, and_were 
upset by the equally baseless criticism of Aristotle. The Greek atomic 
theory was more philosopnyiEiS T science 

TTeverffieless tKe men of Ionia and the Atomists were closer to a 
scientific attitude of mind than were some other schools in ancient 
times. They, at all events, tried to explain the world on rational lines. 
They failed; but they had the credit of what, in another connexion, 
is now called 'a near miss'. 

The Pythagoreans. As a contrast to the rational and materialist 
philosophy of the lonians and Atomists, we find systems of thought 
formulated, perhaps direct from Orphism, by those of more mystical 
minds. One of the earliest and greatest of such men was Pythagoras, 
who was born at Samos, but moved to Southern Italy about the 
year 530 B.C. In spite of his mysticism, he was a mathematician and 
an experimenter, and, on the latter account, was accused by Hera- 
clitus of practising 'evil arts'. 

The Pythagoreans were the first to emphasize the abstract idea of 
number," Irrespective of the actual bodfes counted 1 .' "In practice this 

AJ\L> HUME 19 

made arithmetic possible, and in philosophy it led to the belief that 
number lay at the base of the real world, though it was difficult 
to reconcile with another Pythagorean discovery the existence of 
incommeasurable quantities. The idea of the importance of number 
was strengthened when experiments with sound showed that the 
lengths of strings which gave a note, its fifth and its octave were in 
the simple ratios of 6 : 4 : 3. The distance of the planets from the 
earth must conform to a musical progression, and ring forth 'the 
music of the spheres'. Since 10=14-24-34-4, ten was the perfect 
number, and the moving luminaries of the heavens must be ten also; 
as only nine could be seen, there must be somewhere an invisible 
'counter-earth'. Aristotle rightly blamed this juggling with facts. 

But the Pythagoreans recognized the Earth as a sphere, and saw 
that the apparent rotation of the heavens could best be explained by 
a revolving Earth, though they thought that, balanced by the counter- 
earth, it swung round, not the Sun, but a fixed point in space thus 
tliey did not fully anticipate Aristarchus and Copernicus as is some- 
times said. 

Pythagoras and his followers carried farther the science of deductive 
geometry indeed the forty-seventh 
proposition of the first book of Euclid 
is known as the Theorem of Pythagoras. 
Though the equivalent 'rule of the 
cord ' for laying out a right angle may 
have been long known in Egypt, it is 
probable that Pythagoras was the first 
to prove by deduction from axioms that 
the square on the hypotenuse of a right- 
angled triangle is equal to the sum of 
the squares on the other two sides. 

The mystic view was also seen in 
Heraclitus (c. 502), poet arid ghilu=~ 
iopHer, to whom thejjrimary element Fio. 6. The Theorem of 

was a soul-stuff of which the world is Pythagoras 

mage, though all things "arieln a state of flux irdvra p'et. Again, 
Alcmaeon the physician regarded man the microcosm as a miniature 


of the Universe or macrocosm; his body reflects the structure of the 
world, and his soul is a harmony of number. These fanciful ideas 
reappear both in classical times and in the Middle Ages. 

But the Pythagorean doctrines were opposed by other contem- 
porary philosophers. Zeno of Elea thought he had discredited the 
theory of numbers and also multiplicity by a series of paradoxes, 
Achilles pursuing a tortoise reaches the spot whence the tortoise 
started ; but the tortoise has now moved on to a further place ; when 
Achilles gets there it has again moved ; Achilles can never catch the 
tortoise. The paradoxes rest on misconceptions about the nature oj 
infinitesimals, of time, and of space, only to be cleared up in the 
nineteenth century with the recognition of different kinds of infinity. 

Greek Medicine. It is probable that Greek medicine owed much 
to Egypt. There were two schools those of^Cos and Gnidos, the 
former placing most trust in vis medicatrix naturae. In our own day 
it has been said that, while the difference between a good doctor and 
a bad one is immense, the difference between a good doctor and 
none at all is very small. Perhaps Cos had made the same discovery. 
CrilSos, having more (or less) faith, searched for a specific remedy 
foTeach disease. 

* 'Greek medicine reached its zenith in Hippocrates (460-375), called 
'the "Father of Medicine', with a theory and practice of the art in 
advance of the ideas of any period till modern times. Observation 
and experiment appeared, with conclusions based on" inductive 
reasoning, while many diseases were accurately described and fairly 
appropriate treatment indicated. 

Socrates and Plato. A considerable advance in knowledge was 
due to the historians, who described the nature of countries as well 
as their histories. The greatest were Hecateus (540-475), Herodotus 
(484-425) and Thucydides (460-400). The latter gave an eye- 
witness's account of the Peloponnesian war and described the plague 
at Athens and the solar eclipse of the year 431. 

A reaction from atomism held that since sensation certainly exists, 
while its messages about reality are doubtful, sensation itself is the 
only reality. And so we come to Socrates (470-399), whose work we 


know chiefly from the writings of Xenophon and Plato. Socrates 
was primarily an educationalist, using the dialectic method of ques- 
tion and answer to eliminate opinions he thought false and suggest 
those he thought true, exposing with inimitable humour ignorance, 
stupidity and pretentiousness wherever he found them. He rejected 
mechanical determinism and indeed all the conflicting theories of 
the physicists, and held that their search for a knowledge of reality 
was a futile attempt to transcend the limits of human intelligence. 
He regarded the mind as the only subject worthy of study; the true 
gelf was notjhe bodypbut the "souT^^lmyard IIIeT^TTiusjji_a^sejisc 
he led a religious reactionTHioljigFpopular clamour charged him with 
newfangled atheism, but Aristotle' credits Socrates with two scientific 
achievementsuniversal definitions and inductive reasoning^ ~" 

Socrates' disciple JFlato (428-348; deduced theories of nature from 
human needs and desires, and showed the influence of the Pytha- 
gorean mystical doctrines of form and number. His astronomy was 
crude, though he regarded the stars as floating free in space, moved 
by their own divine souls. He initiated the idea of cycles, to represent 
the apparent path of the Sun round the Earth an idea afterwards 
developed in detail by Hipparchus and Ptolemy. 

Plato's cosmos was a living organism with body, soul and reason, 
Alcmaeon's macroscopic analogy of man the microcosm. On such 
ideas Plato's science was, for the most part, fantastic. Moreover, he 
despised experiment as a base mechanic art or blamed it as impious, 
though he prized highly the deductive subjects such as mathematics. 
But he invented negative numbers, and treated the line as flowing 
from a point the basic idea of Newton's method of fluxions. 

Thus Plato was led to his famous theory of * intelligible forms ' 
the doctrine that ideas or 'forms' alone possess full reality, the 
doctrine that, in later ages, became known as * realism'. When the 
mind begins to frame and reason about classes and definitions, it 
finds itself dealing not with individuals but with these hypothetical 
types or forms. Natural objects arc in a constant state of change, it is 
only the- typej&._prjforms that are constant and JJicretorfLreal^ There 
is a clear analogy between the ideas or forms of Plato and the 
abstractions we now find inherently necessary for science, abstractions 


which enter into our formulation of scientific concepts and our 
reasoning about their relations. Plato was very near some kinds of 
modern philosophy, but his idealism was not calculated to help 
experimental science at that stage of the world's history. 

Aristotle. Aristotle (384-322), born at Stagira in Chalcidice, 
was a son of the physician to Philip, king of Macedon, and was himself 
the tutor of Alexander the Great. He was the most notable collector 
and systematizer of knowledge in the ancient world, and, till the 
Renaissance in modern Europe, no one approached him in scientific 
learning. The early Middle Ages had only incomplete compendiums 
of his writings, and their attitude of mind was chiefly Platonic; but 
in the thirteenth century Aristotle's full works were recovered, and 
finally made the basis of the philosophy of Scholasticism by Saint 
Thomas Aquinas, a philosophy which was only replaced, after four 
hundred years of dominance, by the science of Galileo and Newton. 
Hence comes Aristotle's supreme importance in the history of thought. 

Aristotle was at his best as a naturalist. Biology till lately was 
merely an observational science, giving little opportunity for the 
speculative theories so dear and so dangerous to the Greeks. Aristotle 
mentions five hundred animals, some with diagrams gained by 
dissection. He described the development of the embryo chicken, 
detected the formation of the heart, and watched it beat while yet 
in the egg. In classification he saw that it was well to use as many 
distinguishing qualities as possible to bring together animals nearly 

Even in physiology Aristotle made advances, insisting on the need 
for dissection. He considered the structure and function of lungs and 
gills, and, having little knowledge of chemistry to help him, con- 
cluded that the object of respiration was to cool the blood by contact 
with air a false idea, but perhaps the best possible at the time. The 
brain too was to Aristotle a cooling organ, the seat of the intelligence 
being in the heart, though Alcmaeon and Hippocrates had already 
placed it in the brain. 

Aristotle rejected the atomic theory. Democritus taught that in a 
vacuum heavier atoms would fall faster than light ones ; Aristotle, with 


an equal absence of evidence, argued that in a vacuum all must fall 
equally fast, but, as this conclusion is inconceivable, there can never 
be a vacuum, and the theory of atoms, which requires it, _is fajse. 
If all things are made of a common material^ all would be heavy, 
and nothing tend to rise in seeking its 'natural place'. No^oneTill 
Archimedes understood what we now call density or specific gravity 
the weight per unit volume on which, compared with that of the 

FIG. 7. Drawing of a dissection of development of Sepia by Aristotle 

surrounding medium, rise or fall depends. Unlike the objective 
physics of Democritus, who sought to explain nature by material 
atoms, the concepts of Aristotle were attempts to express man's 
perceptions of the world in terms natural to his mind in those days, 
categories such as substance, essence, matter, form, quantity, quality, 
concepts acceptable to the Greeks and Mediaevalists, but to us vague 
and unsatisfying. Aristotle acr.eptpd the spherical fnrip nf thp Rarrii^ 
but still regarded it as the centre of the Universe. 

Aristotle was a disciple of Plato, but, being himself chiefly engaged 
in the study of individual animals and other bodies, he did not follow 
Plato into extreme idealistic 'realism'. He held in a modified form 


what afterwards came to be called 'nominalism', which gives reality 
to individuals, though Aristotle allowed some reality also to 'forms' 
or universals. Thus Aristotle was a philosopher as well as a naturalist. 
Moreover, he created formal logic with its syllogisms and show of 
complete proofs. It was a great achievement, and could be applied 
well to deductive subjects like mathematics, especially geometry, as 
we shall see later. But syllogistic logic has little to do with experi- 
mental science, where inductive discovery and not deduction from 
accepted premises is the first object sought; deduction only cornes in 
when, a hypothesis having been framed, we wish to predict con- 
sequences fit for experimental examination. Aristotle's influence did 
much to turn Greek and mediaeval science into a hopeless search for 
absolutely certain premises, and a premature use of deductive 
methods. Some think that here we have one of the chief reasons why 
little advance was made in science for two thousand years. Never- 
theless, Aristotle regarded theories as temporary expedients ; it was 
in later ages that his views were made into a fixed and rigid scheme. 

The Hellenistic Period. With Alexander of Macedon we enter 
a new epoch. As he marched to the East, he took with him Greek 
learning, and in turn brought Babylonia and Egypt into closer touch 
with Europe, while his staff, in the first co-operative researches, 
collected facts about geography and natural history. Gradually the 
nations were linked together, the upper classes by Greek culture, and 
the rest by a universal Greek dialect, y KOIV^, the common speech, 
understood 'from Marseilles to India, from the Caspian to the 
Cataracts'. Commerce became international and thought free. 

The general philosophic systems of Athens gave place to more 
modern methods, definite and limited problems were specified and 
attacked singly, and real progress in natural knowjedge was made. 
The change somewhat resembles the overthrow ofmediaeval scho- 
lasticism by the clear-cut science of Galileo and Newton. Though other 
places were involved, the centre of this new learning was Alexandria, 
the Egyptian city founded in 332 B.C. by Alexander the Great. 

The Greek element was predominant, but Babylonian astronomy 
became available in Greek translations, bringing with it the fallacies 


of Chaldean astrology. The fantastic idea of the relation between the 
cosmos as macrocosm and man as microcosm strengthened the bcjief 
1n thcfcontrol of 4 man by the planets in their courses r apd in a ^^pHlpss 

ind them which rules stars and gods and men. To meet this 
terrible Babylonian creed, men sought any means of escape from 
Fate. They looked firstly to the heavens themselves, where apparently 
incalculable bodies like comets offered some hope of freedom ; secondly 
to magic, which promised control of nature, the papyri of the time 
being full of recipes for charms and spells. But, absurd as it seems, 
we must not forget that, in some parts of England and Wales, a belief 
in magic, charms and spells lies a very little way beneath the surface 
even to-day. 

At the same time the Mystery Religions also spread from the East. 
These religions, based on prehistoric rites of initiation and com- 
munion, sought salvation by personal union with a Saviour God, 
known under many names, who had died and risen again. With the 
breakdown of the Olympians and the local deities, in the second 
century before Christ, and onwards till the rise of Christianity, men's 
deepening religious sense was mostly met by the Mystery Religions. 

Astrology, magic and religion make their appeal to the many, 
philosophy and science to the few. The most important Hellenistic 
philosophy was Stoicism, taught in Athens about 315 B.C. by Zeno 
of Citium. JLt spread both east and west, till it became the chiej 
philosophy of Rome. Its theology was a form of pantheism with a 
high and stern concept*oT morality. 

The Stoic had little to do with science, which is more concerned 
with the revival of atomism by Epicurus of Samos (342-270), whose 
writings preserved its tenets till Lucretius recorded them two cen- 
turies later. Epicurus led a reaction against the idealist philosophy 
of Plato, holding that all is corporeal and .death is the end of life. 
Gods exist, bift tney are products of nature and not its creators and 
are * careless of maixjdnd '. Butjm^J^free^uyecJ.neither to capricious 
gods nor to blind remorseless fate. The only test of reality is man's 
sensation. To Epicurus as to Democritus, all things are made of 
atoms and void7~afio! our world "is but one of many, formed by the 

chanc^coT^unctions oT Stoms J^mHAite^ space ^aii^ endless time. 


Thus Epicurus built a system of cheerful if shallow optimism on the 
atomic theory and a primitive sensationalism. 

Deductive Geometry. Perhaps the most successful and charac- 
teristic product of the Greek mind was deductive geometry. Started 
by Thales about 580 B.C. on Egyptian land-surveying, it was developed 
by Pythagoras, approved by Plato* and Aristotle, and the existing 
knowledge collected and systematized by Euclid of Alexandria about 
300 B.C. in such a complete way that his work was the standard 
text-book of geometry in my own youth. From a few axioms regarded 
as self-evident, a series of propositions was deduced by logical prin- 
ciples, the model of a deductive science. 

But nowadays we look at deductive geometry in one of two possible 
ways, both different from that of Euclid. Firstly, it can be taken as 
the intermediate, deductive step in a science observational and 
experimental. The axioms and postulates are really hypotheses as to 
the nature of space, reached by induction from the observed pheno- 
mena; the observer deduces what he can from his hypotheses, and 
this process forms the science of deductive geometry. But to complete 
the whole it is necessary to see whether or no the consequences agree 
with observation or experiment, all on the general lines of an 
inductive, experimental science. Till quite lately, astronomy verified 
Euclid; it required Einstein's alternative hypothesjs about space^and 
the power ofjoodern telescopes, to^ showjjiat Euclideanspace, 
though in accordanccjyitl^jacts to a high ' 


nbTthe whole "truth ; it breaks down when tested to the utmost limrt. 
can Took at the problem In another way . Observation 

suggests space of a certain kind, and from this the mind defines an 
ideal space which is exactly what actual space seems to be. We can 
then, with no reference to nature, develop the logical consequences 
Df the definition without asking if they correspond with observation. 
[f, for instance, space is defined as an extension of three dimensions, 
one set of consequences those of Euclid follows. If we start afresh 
and define what corresponds to space as having n dimensions, other 
results follow. It is a pretty exercise in pure mathematics, but it has 
nothing necessarily to do with nature or experimental science. 


But of course both these methods are essentially modern; the 
Greeks accepted thesimplc belief that space is what it seems to bcj 
arid the axioms of Euclid's geometry self-evident facts. But never- 
theless Greek geometry was a great achievement, a step in mathe- 
matical science which never had to be retraced. 

Archimedes, Aristarchus and Hipparchus. And now we come to 

one of the greatest names in Greek science perhaps the greatest 
Archimedes of Syracuse (287-212), who laid the foundations of 
mechanics and hydrostatics (see Plate II, facing p. 28). Certainly he 
is the Greek with the most modern scientific outlook. The origins of 
these sciences are to be found in the practical arts, and this primitive 
knowledge Archimedes put into form by a combination of experiment 
and the deductive methods learned in geometry: hypotheses are set 
forth, their consequences deduced and then compared with the 
results of observation and experiment. 

The use of the lever is illustrated in the sculptures of Assyria and 
Egypt two thousand years before Archimedes, but, with the Greek 
love of deduction, Archimedes deduced the law of the lever from 
axioms which he rcg^rdf^ as *Hf-evidftnt ' (i) that equal weights 
placedat equal distances from the point of support balance^ and 
(2) that with equal weights at unequal distances the one_at_thc 
greater disfarice jcscends . Implicitly the law of the lever, and its 
equivalent the principle of the centre of gravity, are contained in 
thp^jry|mir^j2nt jt is well t.n have the r.nnnfixyonjpjgna^^ 
Nowadays we treat the law of the lever as a matter of experiment, 
and deduce other mechanical results from this basis: it is just a 
question of where to begin. 

The idea of density which, unknown to Aristotle, caused him to go 
so far astray, became clear to Archimedes. The story is that King 
Hiero, having_giyen gold to arti&er2LtQJliake|iim a crown, suspected 
them of 'alloying it with silver and asked Archimedes to test his 
suspicion. Archimedes, thinking over the problem in his bath, 
noticed that his body displaced an equal volume of water, and saw 
in a flash that for equal weights the lighter silver alloy would displace 
a larger volume of water than the heavier gold. Exclaiming * 


cvpvjKa ', Archimedes is said to have leapt from his bath, presumably 
to test the crown and then tell Hiero of his discovery. When a body 
floats in a liquid, its weight is equal to the weightjof IjquKf displaced 
aiid^ when it isTmnierseaj ite%ejpinsTimrnished by that ampunt. 
This is called 'the principle of Archimedes'. 

But Archimedes' chief intercsf lay in geometry, and he thought 
more of his geometrical discoveries than of the practical results 
compound pulleys, hydraulic screws, burning mirrors for which he 
was famous among the people; he thought them the recreations of 
a geometer at play. The modernity of his outlook caused his works 
to be eagerly sought for at the Renaissance, especially by Leonardo 
da Vinci. His writings were nearly lost to the world; at one time the 
only survival was one manuscript of the ninth or tenth century A.D. 
which disappeared. But three copies had been made, and from them 
the text was recovered. Archimedes was killed at the storming of 
Syracuse in the year 212. His tomb was found and restored in 75 B.C. 
by Cicero, then Quaestor in Sicily. 

Meanwhile an older contemporary of Archimedes, Aristarchus of 
Samos (310-230), had made a great advance in astronomy in his 
still existing work On the Sizes and Distances of the Sun and Moon. By 
applying some capable geometry to eclipses of the Moon and to its 
appearances when half full, Aristarchus concluded that the ratio of 
the diameter of the Sun to that of the Earth must be greater than 
19:3 and less than 43 : 6, that is about 7:1. This figure is of cdurse 
much too small, but nevertheless the method is sound, and the result 
that the Sun is larger than the Earth was in itself a revolutionary 
achievement. But both Archimedes and Plutarch say that Aristarchus 
went much farther, and advanced the theory that the fixed stars and 
the Sun remain unmoved, while the Earth revolves round the Sun 
in a circular orbit. Sir Thomas Heath calls Aristarchus ' the Ancient 

But Aristarchus was too much in advance of his age, though, 
according to Plutarch, Seleucus the Babylonian held the heliocentric 
view in the second century B.C. and sought new evidence to support 
it. For the rest, the belief in the solid Earth beneath man's feet as the 

Plate II 


Plate III 

LEONARDO DA VINCI. Self Portrait at Turin 


centre of the Universe was too strong even for philosophers and 

Hipparchus was born at Nicaea, and worked at Rhodes and then 
at Alexandria from 160 to 127 B.C. He used the older Greek and 
Babylonian records, invented many astronomical instruments and 
made accurate observations therewith, dividing his circles into 360 
degrees in the Babylonian manner. He discovered the precession of 
the equinoxes, measured this slow motion and the distance of the 
Moon, and got them nearly right. He was a competent mathe- 
matician, and invented both plane and spherical trigonometry. 

His cosmogony was wrong in its fundamental assumption, but the 
idea that the Sun, Moon and planets were carried round the Earth 
in crystal spheres or cycles, while on these were superposed smaller 
orbits or epicycles, though complicated, could be made to represent 
the facts, and, expounded by Ptolemy of Alexandria about A.D. 127 
to 151, held the field till the sixteenth century. And, as long as the 
Earth was the centre, the follies of astrology almost inevitably arose 
again and again. Plato had heard of astrology, but it was first really 
brought to Athens from Babylon by Berossus about 280 B.C., and 
recurred from time to time through the ages. One would have 
thought that it would have been effectively put down by Copernicus, 
Galileo and Newton, but, I am told, a belief in astrology is still 
prevalent among the uneducated in all classes. 

The School of Alexandria. One of Alexander's generals, Ptolemy 
(not to be confused with the astronomer), founded in Alexandria a 
Greek dynasty which lasted till the death of Cleopatra in 30 B.C. The 
reign of the first Ptolemy (323-285) was made illustrious by Euclid 
the geometer and Herophilus the anatomist and physician. 

About the middle of the third century before Christ the famous 
Museum was founded at Alexandria. It had departments of litera- 
ture, mathematics, astronomy and medicine, which were research 
institutes as well as educational schools. They all used the greatest 
library of ancient times, containing some 400,000 volumes or rolls, 
and reckoned one of the wonders of the world. But one section of 


the library was destroyed by the Christian Bishop Theophilus about 
A.D. 390, as a stronghold of pagan learning, and the rest, whether 
accidentally or wilfully, by the Muhammedans in 640 one of (he 
greatest losses which the human mind has suffered. The library must 
have contained copies of the works of countless authors now for ever 
gone, some of their very names perhaps perished. 

In medicine the leading Alexandrians were Herophilus, Erasistratus 
and Eudemus. Herophilus, living in the reign of Ptolemy I, was the 
earliest great human anatomist, and the most famous physician since 
Hippocrates. He described the brain, nerves and eye, the internal 
organs, arteries and veins, and proved that the site of intelligence is 
the brain and not the heart as taught by Aristotle. Erasistratus, 
a younger contemporary of Herophilus, also practised human dis- 
section and made experiments on animals, treating physiology for 
the first time as a separate subject. He held the atomic theory and 
its accompanying philosophy in opposition to medical mysticism. 

Meanwhile there had been increases in geographical knowledge, 
beginning in the fourth century before Christ. Hanno, passing the 
Pillars of Hercules at the western exit from the Mediterranean, sailed 
down the west coast of Africa ; Pytheas voyaged round Britain ; and 
Alexander marched to India. It came to be generally accepted that 
the Earth was a sphere, and some idea of its size was formed. The 
variation with latitude in the length of day and night led Ecphantus 
to the idea of the revolution of the Earth on its axis, though it was 
still placed at the centre of space. 

The first great physical geographer was Eratosthenes^Librarian of 
th Museum at Alexandria. By measuring the distance apart and 
the latitudes of two places on the same meridian, he calculated the 
circumference of the Earth as 24,000 miles, a result surprisingly close 
to the modern estimate of 24,800. He conjectured that the Western 
Ocean might be divided by a New World, though later Poseidonius, 
underestimating the Earth's size, proclaimed that an explorer sailing 
west for 70,000 stades (7000 or 8000 miles) would come to India. This 
it was that inspired Columbus. Ptolemy too was a geographer as 
well as an astronomer, and made maps of the then known world 


Apollonius the mathematician carried geometry into the study of 
various curves, and Hero the mechanician invented contrivances 
such as the siphon, a thermoscope and a primitive steam-engine. 

Alchemy. In early times industries arose to supply imitations of 
jewels and other things too expensive for the people, for instance, 
cheap alloys which looked like silver and gold. Matter itself, Plato 
and other philosophers believed, was unimportant, but its qualities 
were real. The mordant salts used in dyeing will etch metals, and, 
if a small quantity of gold has been added, usually to an alloy of tin, 
lead, copper and iron, whitened by the addition of mercury, arsenic 
or antimony, etching may leave a golden surface; the gold, they 
believed, acting as a ferment, changed the whole into the nobler 
metal. Such facts and such ideas were linked with others, and 
particularly with astrology. The Sun generates his image, gold, in 
the body of the Earth, the Moon represents silver, the planet Venus 
copper, Mercury quicksilver, Mars iron, Jupiter tin and Saturn the 
heavy and dull metal lead. The gods had been moved from Olympus 
to the sky, but there, as Sun, Moon and planets, they continued to 
control the destinies of man, and help him to obtain the noble metals 
his soul longs for. Qualities clearly can be changed, and qualities 
are the essence of things indeed philosophically are the things. On 
such an underlying basis of practice and beliefs, the alchemists, allied 
with the astrologers, were started and encouraged in their vain quest 
for an elixir of life to cure all ills, and a philosopher's stone Jo trans 
mute base metals into gold. Their search failed, but, in its course, the 
astrologers hel^^^a^gnamy^_aiiithe alchemists made discoveries 
on which was founded the science of chemistry. Astrology came 
originally from Babylon, jnit alchemy, igjjjdjlits first clear appearance 
in Alexandria during the first century of the Christian era, and lasted 
there for three hundred years. The Alexandrian alchemist was neither 
a fool nor a charlatan, but an experimenter, acting in accordance 
with tE^cs t philosophy of his a^ it was the philosophywhich was 
lerovgcTamong the Arabs andln Europe, 

the prevalent philosophy and terminology both had altered, and the 
new alchemists, not understanding the Alexandrians, tried to change 


the substances themselves, and not merely their qualities. They 
usually hid their failures in a flood of mystical verbiage. 

The Roman Age. The Romans had great efficiency as lawyers, 
soldiers, and administrators, but little creative intellectual power; 
the art, science and medicine of Rome were borrowed from the 
Greeks. The Romans onlyj^r^d, for sr^gnrgjasj* help in practical life. 
They ignored the essential basis, knowledge sought for its own sake, 
and in a few generations pure science, and following it applied 
science, ceased to advance. 

The chief Roman philosophy was Stoicism, founded by Zeno of 
Gitium, brought to Rome by Diogenes the Babylonian, and best 
known in the writings of Seneca and of the Emperor Marcus Aurelius. 
Stoicism acquired a tincture of Platonism from Poseidonius, more 
famous as a traveller and geographer, who explained the tides by 
the joint action of the Sun and Moon. 

The atomism of the Greeks was expounded by Lucretius (98-55 B.C.) 
in hfcr-poem de.Rerum Nafura. The poerff aims at the overthrow of 
superstition by ^he acceptance of the atomic and mechanical philo- 
sophy, causation controlling all things, from the invisible vapour of 
water to the mighty skies, the flaming walls of the world -flammantia 
moenia mundi. 

Among the writers of compendiums were Pomponius Mela a 
geographer, and Cicero the statesman (106-43 B.C.), who wrote 
de Natura Deorum, which contains some information about the scientfefc 
knowledge of the time. Both Virgil and Varro wrote on agriculture, 
and 100 years later the elder Pliny (A.D. 23-79) produced in his,. 
Naturalis Historia a much more complete encyclopaedia of the whole 
science of his period geography, man and his qualities, animals, 
plants and trees, together with agriculture, fruit-growing, forestry, 
wine-making, the nature and use of metals, and many of the fine 
arts. He described the lion, the unicorn and the phoenix, the practice 
and special utility of various forms of magic, all with equal acceptance. 
Plutarch (A.D. 50-125) wrote on the nature of the Moon and on 
Roman mythology, with a suggestion for the comparative study of 
religions. Both he and Diogenes Laertius handed on valuable informa- 
tion about Greek philosophy and philosophers. 


Greek medicine flourished at both Alexandria and Rome. Gelsus 
in the reign of Tiberius wrote a treatise on medicine and surgery, 
describing many surprisingly^ m^idej:n_japeialiQns. He .gives also a 
history of medicine in Alexandria and Rome. His work was lost in 
the Middle Ages, but recovered in time to influence the Renaissance. 
Later on Galen (A.D. 129-200) dissected animals and a few human 
bodies, and investigated by vivisection the action of the heart and 
the spinal cord. His medicifle was built on the idea of spirits of 
various kinds pervading the different parts of the body, and from 
this theory he deduced dogmas which influenced medicine for 1500 
years. Galen's ^vev^ia fivftiKov, translated as spiritus anitnalis, became 
our c animal spirits', the original meaning of which is perhaps some- 
times misunderstood. Galen thought that the principle of life was 
a pneuma, drawn from the world spirit by the act of breathing. He 
held that the blood reached the parts of the body by a tidal ebb 
and flow in" both veins and arteries, a view which persisted till 
Harvey discovered circulation. In the first century A.D. Dioscorides, 
a military physician, wrote on botany and pharmacy, describing 
some six hujidued^antS-and their Jiisditinal^jope^ 
of medicine, being of practical use, especially for the armies, lasted 
longer than pure science and philosophy, which, during^ the second 
century A.D., showed signs of the collapse .ttiajt soon followejd. 

But practical arts of all kinds flourished in Rome. The protection 
of public health, with aqueducts to bring fresh water, sanitary 
appliances, hospitals and a public medical service, military and civil 
engineering, showed the practical genius of the Roman people. 

Diophantus of Alexandria, the greatest Greek writer on algebra, 
lived in the latter half of the third century after Christ. He intro- 
duced abbreviations for quantities and operations that continually 
recur, and thus was able to solve simple equations. After him there 
was no one of the first rank in mathematics or pure science in the 
ancient world. Indeed no advance in knowledge was being made, 
and the only activity shown was in the writing of compendiums and 
commentaries, chiefly on Greek philosophers. 

And these second-hand sources were all, or nearly all, which came 
through the dark ages and lightened the dawn which followed. 


The End of Ancient Learning. To understand why for a thousand 
years Europe made little or no advance in science we must begin by 
examining the scientific and philosophic outlook and the religious 
beliefs which dominated thought during the last period when the 
learning of Athens, Alexandria and Rome was still alive. 

As long as his books were available, Aristotle was accepted as the 
great authority on scientific theory and even fact, and this acceptance 
remained when, in the sixth century, his complete works ceased to 
be read or were lost, and only abbreviated commentaries were 
studied, the most popular being one on Logic. 

In spite of Aristotle's predominance in the little science that 
survived, philosophy took another course. Plato's School at the 
Academy in Athens was by then teaching a mystical Neo-Platonism, 
and Platonism in its mystical Neo-Platonic form became the prevalent 
philosophy. As we shall see presently, this Platonism survived as an 
alternative background even in the later Middle Ages of Aristotelian 
Scholasticism, and, at the time we are now considering, the first few 
centuries of the Christian era, it was predominant. 

Alongside the inquiries of the philosophers, classical Greek mytho- 
logy still represented the official religion, though it showed signs of 
decay. Even at their height, the many and various pagan cults were 
tolerant of each other, and the policy of the Roman Empire upheld 
that tolerance. But the first Christians, taking over the exclusive 
religious outlook of the Jews, refused to conform to the Imperial 
laxity, and thus faced their Roman governors with a difficult problem, 
leading almost inevitably to persecution. But when Christianity 
began to triumph and persecution of its votaries ceased, the need of 
a more definite formulation of its beliefs arose. 

The Fathers of the Church. Thus the first systematic theology 
of the Christian Church was framed by the Early Fathers by inter- 
preting the Christian story in the light of Hebrew Scripture and 


Neo-Platonic philosophy, while underneath still lay the mystery 
religions and more primitive magical rites. In these rites we find 
the widespread ideas of initiation, sacrifice and communion, which 
appear in more developed forms in the mystery religions, arid also 
find the celebration in imagery of the drama of the year growth 
and full life in summer, death in winter, and joyous resurrection in 
each new spring. 

Among the Eastern mystery religions two are of special interest : 
Mithraism, the Persian cult of the soldiers' god Mithras, disputed 
for long with Christianity the possession of the Roman Empire; 
Manichaeism, which held a dualism of the powers of good and evil, 
reappeared in essence again and again as the ages passed. 

Such was the atmosphere in which the Early Fathers sought, as 
their most open and obvious task, to reconcile Greek philosophy and 
Christian doctrines, while traces of magic rites were unconsciously 
interwoven in their synthesis. Foremost among the Fathers was 
Origen (185-254), who proclaimed the essential conformity of the 
ancient learning, especially Alexandrian science, with the Christian 
Faith, and did much to gain converts among the educated and 
intelligent. Origen took a more critical view of the Old and New 
Testaments and a more liberal-minded outlook generally than after- 
wards became orthodox after much embittered controversy. It may 
be held that doctrines which, for any reason, survived were apt to 
be accepted as orthodox, while, as Gibbon says, ' the appellation of 
heretics has always been applied to the less numerous party'. 

Of the Latin Fathers, Saint Augustine (354-430) had most influence 
on Christian thought. He was successively a Manichaean, a Neo- 
Platonist and a Christian, and combined Platonic philosophy with 
the teaching of Saint Paul's Epistles to form the first great Christian 
synthesis of knowledge. It was this combination of Neo-Platonism 
and Pauline Christianity which persisted in the background through 
the predominance of Aristotle when his works were recovered in the 
late Middle Ages. 

Early Christian theology and mystic Neo-Platonism acted and 
reacted, each accusing the other of plagiarism. At first little stress 
was laid on divination and magic, but a century later the Neo- 



Platonists Porphyry and lamblichus and the Christians Jerome and 
Gregory of Tours revelled in the daemoniac and miraculous. 

Again, the personal motive of individual sin, salvation or damna- 
tion, and the prospect of a catastrophic end of the world at the near 
second coming of Christ, replaced the bright Greek spirit and the 
stern Roman joy in Family and State. 

With such an outlook on life and death, it is no wonder that the 
Christian Fathers showed small interest in secular knowledge for its 
own sake. As Saint Ambrose said, ' To discuss the nature and position 
of the earth does not help us in our hope of the life to come 5 ; and the 
followers of Artemon are said 'to lose sight of heaven while they are 
employed in measuring the earth'. Thus part of the Christian world 
passed to an actual hatred of pagan learning. A branch of the 
Library of Alexandria was destroyed by Bishop Theophilus about 
the year 390, and Hypatia, the last mathematician of Alexandria, 
was murdered in 415 with revolting cruelty by a Christian mob, 
instigated, it was believed, by the Patriarch Cyril. 

The Dark Ages. The fall of Rome was not only or even primarily 
an overthrow of civilization by barbarians. It was more the clearing 
away of a doomed and crumbling ruin. The military strength of the 
Empire was weakening; the purity of its blood was being corrupted 
by an influx of oriental and other foreign elements; a failure of the 
gold and silver mines of Spain and Greece reduced the currency and 
caused a fall in prices, which, as in our own day, sent land out of 
cultivation. The Roman Campagna consequently became infested with 
malaria, and large tracts grew uninhabitable. The barbarians came, 
and Rome fell into the dark gloom of the sixth and seventh centuries. 

Almost the only survival was medicine, monastic and other. In 
the sixth century the Benedictines began to read compendiums of 
the works of Hippocrates and Galen, which were soon afterwards 
studied at Salerno, a city on the Bay of Paestum to the south of 
Naples, the first secular home of learning. Salerno was a Greek 
colony and later a Roman health resort, and it is possible that it 
remained an unbroken link between the learning of the ancient and 
that of the modern world. 


Neo-Platonism was given its final form by Proclus (A.D. 41 1-485), 
the last great Athenian philosopher, whose works led from the 
writings of Plato and Aristotle to the mystical beliefs of mediaeval 
Christianity and Islam. 

Again Boethius, a noble Roman who was put to death as a 
Christian in 524, wrote compendiums and commentaries on Plato 
and Aristotle, and on what he called the quadrivium arithmetic, 
geometry, music and astronomy. He was the last to show the true 
spirit of ancient philosophy, and his works form another link between 
the Classics and Mediaevalists. After Boethius the classical spirit 
vanished, and Plato's school at Athens was closed in A.D. 529 by 
order of the Emperor Justinian. 

Curiously enough, countries at a distance from Rome showed some 
of the earliest signs of revival. In Ireland, Scotland and the north 
of England, a literary and artistic development, quickened by 
Christianity, culminated in the work of the Anglo-Saxon monk Bede 
of Jarrow (673-735), an< ^> together with missionary teaching, carried 
some secular learning into more southern lands. Bede's science, as 
that of other mediaevalists, was chiefly drawn from Pliny's Natural 
History, though he added something of his own as, for instance, 
observations on the tides. Then we come to the Abbey schools 
founded by Charlemagne, and Alfred the Great's translations of 
Latin texts into Anglo-Saxon. New nations were forming and 
becoming self-conscious. 

The Arabian School. When European learning was at its lowest 
ebb, culture of mixed Greek, Roman and Jewish origin survived in 
the Imperial Court at Byzantium and in the countries which stretch 
from Syria to the Persian Gulf. The Persian School of Jundishapur 
gave refuge to Nestorian Christians 1 in A.D. 489 and to Neo-Platonists 
when Plato's Academy was closed in 529. In the third century, 
Greek was replaced in Western Asia by the Syriac language, which 
was itself later replaced by Arabic. 

Muhammad and his Arabs between 620 and 650 conquered 
Arabia, Syria, Persia and Egypt. About 780 Harun-al-Rashid, most 
1 Followers of Nestorius, a sect declared heretical. 


famous of the Caliphs, encouraged translations from Greek authors, 
and thus helped to initiate the great period of Arab learning. The 
first task of the Arabs was to recover the hidden and forgotten store 
of Greek knowledge, then to incorporate it in their language, arid 
finally to add their own contributions. 

The Arabs developed an atomic theory based on those of the 
Greeks and Indians. But to the Arabs not only matter, but space 
and time also were atomic the latter being composed of indivisible 
'nows'. Allah creates atoms anew from moment to moment with 
their qualities. If He ceased re-creating, the Universe would vanish 
like a dream. 

The Arab schools of medicine and chemistry were developed in 
the late eighth and in the ninth centuries, when the lead definitely 
passed from Europe to Arabic-speaking lands. The earliest forms of 
practical chemistry are concerned with the arts of life cooking, 
metal-working, the collection of medicinal plants and the extraction 
of drugs. The Arabs too worked at alchemy for seven hundred years, 
searching for the transmutation of metals and an elixir vitae to cure 
all human ills. They were, of course, doomed to failure, but, in their 
search, they discovered many chemical substances and reactions, on 
which the true sciences of chemistry and chemical medicine were 
founded. The results reached Europe chiefly through the Moors in 

The most famous Arabian chemist and alchemist was Abu-Musa- 
Jabir-ibn-Haiyan, who flourished about 776. He is thought to be 
the author of many writings which appeared afterwards in Latin and 
were assigned to a shadowy 'Geber' of uncertain date. Their identity 
or difference cannot be decided until all Jabir's works have been 
translated and studied. Jabir seems to have prepared what we now 
call lead carbonate, and separated arsenic and antimony from their 
sulphides; he described processes for the refinement of metals, the 
dyeing of cloth and leather and the distillation of vinegar to give 
concentrated acetic acid. Metals, he believed, differed because of 
the varying proportions of sulphur and mercury in them. The theory 
that sulphur (fire), mercury (liquidity) and salt (solidity) were the 


primary principles of things lasted as an alternative to the atomic 
theory and the four elements of Empedocles and Aristotle till the 
days of Robert Boyle's Sceptical Chymist published in 1661. 

In the ninth century also, translations into Arabic were made of 
Euclid's Geometry and Ptolemy's Astronomy, thereafter best known by 
its Arabic name of Almagest. The Hindu numerals were completed 
by the invention of a sign for zero, and replaced the clumsy Roman 
figures in Europe. 

Among Muslim astronomers, Muhammad-al-Batani of Antioch 
recalculated the precession of the equinoxes and a new set of astro- 
nomical tables. About the year i ooo, observations on solar and lunar 
eclipses were made at Cairo by Ibn Junis or Yunus, perhaps the 
most eminent Muslim astronomer. 

The greatest period of Arabian science dates from the tenth cen- 
tury, when al-Kindi wrote on philosophy and physics, and the Persian 
physician Abu-Bakr-al-Razi practised in Baghdad and produced a 
treatise on measles and small-pox. He was reckoned the leading 
physician of Islam, a chemist who applied his knowledge to medicine, 
and a physicist who used the hydrostatic balance. But the most 
famous Arabic physicist was Ibn-al-Haitham (965- 1 020) , who worked 
in Egypt chiefly at optics. Translated into Latin, his writings had 
much influence, especially on and through Roger Bacon. In the 
eleventh century al-Hazen was famous in mathematics, and Ibn Slna 
or Avicenna (980-1037) wrote on all the sciences then known. His 
Canon, or compendium of medicine, was one of the highest achieve- 
ments of Arabic culture, and afterwards became the text-book of 
medical studies in the Universities of Europe. A contemporary was 
al-Biruni, philosopher, geographer and astronomer. 

At this time Arabic had become the classical language of learning, 
and Arabic writings carried the prestige which formerly and after- 
wards was given to Greek. In the eleventh century the poet Omar 
Khayyam did important algebraic work, but by the end of that 
century a decline of Arabic and Muslim learning had set in. 

In Spain, where Arabian, Jewish and Christian cultures were 
intermingled, philosophy developed on much the same lines as in 


Christendom a century later. There was the same attempt to reconcile 
the sacred books of the nation with Greek learning, and the same 
contest between theologians who relied on reason and those who 
trusted to revelation or to mystic religious experience, and in either 
case denied the validity of human reason in matters of faith. 

The chief fame of the Spanish- Arabian School is due to Averroes, 
born at Cordova in 1126, to whom religion was a personal and 
inward power, and theology an obstacle. His teaching came into 
conflict with that of orthodox Christian theologians, but, in spite of 
opposition, he became an authority in the Universities, worthy, it 
was said, to be compared with Aristotle as a master of the science of 
proof. Another great Cordovan was the Jewish physician Maimo- 
nides (1135-1204), who was also a mathematician, astronomer and 
philosopher. His chief work was a Jewish Scholasticism, comparable 
with the Arabic Scholasticism of al-Ghazzali of Baghdad and the 
Christian Scholasticism of Saint Thomas Aquinas, each of them an 
attempt to reconcile a particular scheme of theology with the 
philosophy of Aristotle. 

The Revival in Europe. When Arabic learning percolated into 
Europe, it found here and there the way prepared. The Byzantine 
Empire at Constantinople patronized art and literature in the ninth 
and tenth centuries, collecting and preserving many Greek manu- 
scripts. Salerno had developed a school especially of medicine, and 
the encouragement of scholars by Charlemagne and Alfred had so 
much improved teaching in the north that the secular schools began 
to take their modern form of Universities. 

Legal studies revived in Bologna about the year 1000, and soon 
medicine and philosophy were added. A students' Guild or Universitas 
was formed for mutual protection, and undertook also the provision 
of teachers, so that the governing power rested with the students. 
But, early in the twelfth century, a school of dialectic was organized 
by teachers at Paris, and a Community or Universitas of teachers set 
the fashion for most Universities in Northern Europe. Thus at Oxford 
and Cambridge the governance rests with the teachers, while the 
election by the undergraduates of the Rectors in Scottish Universities 
shows a surviving trace of students' control on the model of Bologna. 


The academic subjects of study consisted of an elementary trivium 
grammar, rhetoric and dialectic, dealing with words and a more 
advanced quadrivium arithmetic, geometry, music and astronomy, 
supposed to be concerned with things. Music contained a half- 
mystical doctrine of numbers, geometry a selection of Euclid's pro- 
positions without proofs, while arithmetic and astronomy were used 
chiefly to fix the date of Easter. When later on philosophy also was 
studied, it was merely added as a more advanced part of dialectic. 
All led up to the sacred subject of theology ; mediaeval philosophy, 
it has been said, was but a mixture of logic and theology. 

The controversy between Plato and Aristotle on the nature of 
' universals ' or * intelligible forms 3 passed into the writings of Porphyry 
and Boethius, and so reached the mediaeval mind as the problem of 
classification. How is it that we can classify? Are individuals alone 
real as the nominalists say, the classes or universals existing merely as 
mental concepts, or are the universals apart from the individuals the 
only realities? Or is Aristotle's compromise to be accepted? Are we 
to say universalia ante rem with Plato, universalia in re with Aristotle, or 
universalia post rem with the nominalists? To the Greeks the question 
was important, and it has some bearing on modern physics. But the 
mediaeval mind eventually discovered in it the whole problem of 
Christian dogma. The only difficulty was to determine which alter- 
native was orthodox, and indeed the answer varied from time to 

At first Plato's realism in a mystical Neo-Platonic form was com- 
bined with Christian theology to form the first Mediaeval (as opposed 
to Patristic) synthesis, based on the idea that ultimately the divine 
is the only reality. Then nominalism appeared in Berengarius of 
Tours (999-1088) and in Roscellinus, who reached a Tritheistic 
conception of the Trinity. In Abelard, on the other hand, the Trinity 
was reduced to three aspects of one Divine Being. It will be seen that 
the apparently harmless philosophical problem opened the way to 
very dangerous controversies. 

Abelard showed signs of independence in many directions, saying 
that 'it is necessary to understand in order to believe', which may 
well be compared with Anselm's credo ut intelligam, and Tertullian's 
credo quia impossibile. 


Abelard's desire to understand leads our story to the great enlighten- 
ment of the thirteenth century, but before we pass on we must pause 
to trace the effect on the Middle Ages of the fantastic idea of the 
cosmos as macrocosm and man as microcosm an idea we can see 
in Plato's Timaeus, in Alcmaeon's medicine, and perhaps in older 
legends of Hermes or the Egyptian god Thoth. The mediaeval mind 
seems to have been fascinated with this analogy. Pictures supposed 
to represent it are continually seen in mediaeval art paradise in 
the empyrean space beyond a zone of fire, and hell in the earth 
underfoot. The sun, stars and planets, kept moving by the four winds 
of heaven, are related to the four elements of earth and the four 
humours of man. Drawings derived from these confused imaginings, 
I am told, still decorate certain almanacs beloved of the ignorant. 

The Thirteenth Century and Scholasticism. In the thirteenth 
century an increasing desire for secular knowledge led to the rendering 
of Greek writings into Latin, first by re-translation from the Arabic 
and later by direct translation from the Greek. The former was carried 
on chiefly in Spain from 1 125 to 1280, and the latter at first in Sicily 
and Southern Italy, where lived both Arabs and Greeks, who kept 
up diplomatic and commercial relations with Constantinople. The 
Arabic nations and the Jews dwelling among them had a real interest 
in science, and it was by contact with them that mediaeval Europe 
learned a more rationalist habit of mind. 

Between 1200 and 1225 Aristotle's complete works were recovered 
and translated into Latin, first from Arabic versions and then straight 
from the Greek. In the latter task, one of the most active scholars 
was Robert Grosseteste, Chancellor of Oxford and Bishop of Lincoln, 
while his famous pupil, Roger Bacon, wrote a Greek grammar. Their 
object was not merely literary; they sought primarily to unlock the 
original language of Scripture and Aristotle. 

The effect of the new knowledge on current controversies was 
immediate. Realism remained, but it became less Platonic and less 
dominant. Aristotle's form of realism could be reconciled with 
nominalism, and made a philosophy on which scientific inquiry 
could be based. Aristotle's outlook was at once more rational and 
more scientific than the mystical Neo-Platonism which had come to 


represent ancient philosophy. His range of knowledge, especially 
his knowledge of nature, was far greater than anything then available. 
To absorb and adapt this new material to mediaeval Christian 
thought was a difficult task. Aristotle's works were condemned by a 
Church Council at Paris in 1209, but the flood proved irresistible, 
and in 1225 the University of Paris accepted Aristotle's works as a 
subject of study. 

Two scholars took the foremost place in interpreting Aristotle: 
Albertus Magnus (1206-1280) and his famous pupil Saint Thomas 
Aquinas (1225-1274). Albertus combined Aristotelian philosophy 
with all contemporary knowledge of astronomy, geography, zoology, 
botany and medicine, and Thomas Aquinas continued his work of 
rationalizing both sacred and profane learning. Thomas recognized 
two sources of knowledge : the Christian faith transmitted through 
Scripture, the Fathers and the tradition of the Church, and the truths 
reached by human reason as set forth by Plato and Aristotle. The 
two sources must agree, as both come from God, and a Summa 
Theologiae, as written by Saint Thomas, should comprise the whole 
of knowledge. On this basis was built up the system of Scholasticism. 

Unlike the ' realist ' outlook of earlier days, which feared the use 
of reason by 'nominalists', the Thomist philosophy was founded and 
built up olf reason, and on reason professed to explain the whole of 
existence, with the object of apprehending both God and nature. 

Thomas accepted all Aristotle's logic and science. His logic, based 
on the syllogism, set out to give rigorous proofs from definite and 
certain premises, which to Thomas were intuitive axioms and 
Catholic doctrine : it was ill adapted to guide men in the experimental 
examination of nature. 

With both Aristotle's science and Christian doctrine, Saint Thomas 
Aquinas took over the assumption that man is the centre and object 
of creation, and that the cosmos can be defined in terms of human 
sensation. He also adopted the Ptolemaic system of astronomy with 
its central Earth, though only as a working hypothesis. This caution, 
however, was not followed by his disciples; the geocentric theory 
became part of the orthodox scheme, and afterwards proved a serious 
obstacle to Copernicus and Galileo. But, accepting Thomas's pre- 
mises, his whole system, worked out with consummate skill, hung 


together convincingly, and a criticism of Aristotle's philosophy or 
science became an attack on the Christian faith. 

There was one man of whom thirteenth-century records remain 
who saw the need of experiment. Roger Bacon, born about 1210 
near Ilchester in Somerset, studied at Oxford under Adam Marsh, 
a mathematician, and Robert Grosseteste the Chancellor. 'In our 
days', said Bacon, 'Lord Robert, lately Bishop of Lincoln, and 
Brother Adam Marsh were perfect in all knowledge.' He also names 
Master John of London and Master Peter de Maharn-Curia, a Picard, 
as mathematicians, and Peter also as a master of experiment. 

Grosseteste was the first to invite Greeks to come from the East 
as instructors in the ancient form of their language, still read at 
Constantinople. As said above, Bacon wrote a Greek grammar, and 
argued that ignorance of the original tongues was the cause of the 
errors in theology and philosophy of which he accused the Scholastic 
doctors of the time. He insisted that the only way to verify or disprove 
their statements was to observe and experiment. He also realized 
the importance of mathematics, both as an educational exercise and 
as a tool in experimental science, and this at a time when mathematics 
and astronomy had earned a bad name because they were chiefly 
studied by Muhammedans and Jews. 

Bacon was specially interested in light, possibly through the 
influence of Ibn-al-Haitham. He gave the laws of reflexion, and 
described mirrors and lenses with the general facts of refraction, 
including a theory of the rainbow. He invented some mechanical 
contrivances and described or predicted others, such as self-propelled 
ships and flying machines. He considered burning glasses, magic 
mirrors, gunpowder, magnets, artificial gold and the philosopher's 
stone, in a confused mixture of fact and fiction. 

It is probable that Bacon would only be remembered as a magician 
had not Pope Clement IV told him to write out his work and send 
it to him. This Bacon did, and from these books we know his achieve- 
ments. Unfortunately Clement died, and Bacon, deprived of his 
protection, suffered imprisonment. Much of his work was forgotten ; 
all through the Middle Ages work was done and lost and had to be 


In spite of his modern appreciation of mathematics and experiment 
and his attacks on the Schoolmen, Bacon never cast off the mediaeval 
habit of mind in philosophy and theology. He was a true man of 
science, but born too soon. 

In modern days Roger Bacon's criticism of Scholasticism would 
be accounted effective, but it was too much out of tune with mediaeval 
thought to produce much result at the time. Towards the close of 
the thirteenth and at the beginning of the fourteenth century, attacks 
from a philosophic point of view were made by Duns Scotus and 
William of Occam, who led a revolt against the Scholastic union of 
philosophy and religion, claiming freedom for both. This dualist view 
was linked with a revival of nominalism, with its belief in the sole 
reality of individual things. 

In its turn, the new nominalism with its opposition to Scholasticism 
was banned by the Church, which tried to impose realism as late as 
1473. But the work of Scotus and Occam was a severe blow to the 
dominance of Scholasticism, though in 1879 an Encyclical of Pope 
Leo XIII re-established the wisdom of Saint Thomas Aquinas as the 
official Roman Catholic philosophy. 

The fourteenth and fifteenth centuries saw the growth of a new 
mysticism, especially in Germany. Cardinal Nicholas of Cusa, who 
made advances in mathematics and physics, showed that a growing 
plant took something from the air, and supported the theory of the 
Earth's rotation. He maintained that God must be known by ipiystical ' 
intuition and not by reason. Thus Cusa helped in the final overthrow 
of mediaeval Scholasticism. 

We must not think that Scholasticism did only harm in later ages. 
It is true that it carried Aristotle's philosophy and science forward 
into a time when they proved an obstacle to the birth of modern 
science at the Renaissance. But the Schoolmen kept alive in the 
minds of men the belief in rational order, in cause and effect. As 
Whitehead says: 'Galileo owes more to Aristotle than appears on 
the surface ... he owes to him his clear head and his analytic mind . . . 
the priceless habit of looking for an exact point and of sticking to it 
when found.' 


The Causes. It has sometimes been said that the Renaissance 
produced so great a revolution that its causes cannot be fully under- 
stood. But it is clear that many accidents and activities coincided at 
one time to bring it about. The change began in Italy, partly perhaps 
because the majestic remains of Roman building made it easier for 
men's minds to recover some of the lost Roman culture, but partly 
also because in Italy it was the fashion for ' knights and noble ladies ' 
to live chiefly in the towns where intercourse was easy, and not, as 
in northern lands, on their estates in feudal isolation. 

Navigation was facilitated by the magnetic compass, discovered 
by the Chinese in the eleventh century, and brought to Europe a 
hundred years later. Early in the fifteenth century the Portuguese 
began a great period of exploration, discovering the Azores in 1419 
and later tracing the west coast of Africa. It became generally 
accepted that the Earth was a sphere, and that, as the Greek Posei- 
donius had held, by sailing westward, ships might reach the shores 
of Asia, and bring back to Europe the rich trade of India and Cathay. 
With the support of Ferdinand and Isabella of Spain, Columbus 
sailed from Palos and landed on the Bahamas in 1492. Doubtless 
these discoveries enlarged not only the known world but also the 
minds of men. Moreover, besides the direct growth in material 
resources, when the gold and silver of Mexico and Peru swelled the 
currency, the consequent rise in prices, as always, stimulated industry 
and trade and thus increased wealth, giving opportunity for leisure, 
study and invention. 

When a number of factors are at work, the total result at the 
beginning is only the sum of the separate results, but, when the results 
overlap, cause and effect act and react, and the whole process 
becomes cumulative. And so with the material, moral and intel- 
lectual factors in the changes of the sixteenth century; somewhat 
suddenly they combined in the irresistible torrent of the Renaissance. 

A literary harbinger appeared in Petrarch (1304-1374), who tried 
to restore both a taste for good classical Latin in place of the dog- 


Latin of the Schoolmen, and also the Greek and Roman claim for 
liberty of the reason. 

In the early years of the fifteenth century a growing interest in 
classical literature drew from the East many Greeks, who, from their 
modern tongue, were able to teach the ancient language. This influx 
was quickened by the capture of Constantinople by the Turks in 
1453; more teachers came, bringing manuscripts with them, while 
a search in European libraries disclosed others. Thus Greek again 
became familiar after a lapse of eight or nine hundred years, and the 
humanists who first read it played a chief part in the widening of 
mental horizons which afterwards made science possible. Another 
important factor in the advancement of learning was the invention, 
about the middle of the fifteenth century, of printing with movable 
type, which brought books into many more hands. 

Leonardo da Vinci. The influence of personality in past times 
is often difficult to trace, and it is only since the manuscript note-books 
of Leonardo da Vinci have been deciphered that we are able fully 
to appreciate his universal genius. Leonardo (see Plate III, facing 
p. 29) was born at Vinci between Florence and Pisa in 1452. He 
lived successively in the courts of Florence, Milan and Rome, and 
died in 1519 in France, the servant and friend of Francis I. 

Leonardo was a painter, sculptor, engineer, architect, physicist, 
biologist and philosopher, and in all these subjects supreme. Observa- 
tion and experiment were to him the only true method of science ; 
the opinions of ancient writers could never be conclusive though they 
might be useful as a starting-point; the most helpful of all were the 
writings of Archimedes, and for manuscripts of his works Leonardo 
eagerly sought. 

Leonardo grasped the principle of inertia, 'every body has a weight 
in the direction of its movement'. He understood the impossibility 
of perpetual motion as a source of power, and deduced therefrom 
the law of the lever, which he treated as the primary machine. He 
recovered Archimedes' results in hydrostatics, and dealt also with 
hydrodynamics the flow of water through channels and the propa- 
gation of waves over its surface, waves in air and the laws of sound, 


and recognized that light also showed some of the properties of 

Some of the fossils found on mountains must have been laid down 
in sea water; changes must have occurred in the crust of the Earth, 
and new mountains been thrown up. But no catastrophic happenings 
are needed, the river Po 'will lay down land in the Adriatic as it has 
already formed a great part of Lombardy' a uniformitarian theory 
three centuries before Hutton. 

As a painter and sculptor Leonardo, like Botticelli and Albrecht 
Diirer, was led to anatomy. In the face of prejudice, he dissected 
' more than ten human bodies ', making anatomical drawings which 
are both accurate and works of art. In physiology he explains how 
the blood carries nutriment to the parts of the body and removes 
waste products. It almost looks as though he understood the circula- 
tion of the blood a hundred years before Harvey. He dismisses 
scornfully the follies of astrology, alchemy and magic; to him nature 
is orderly; even in astronomy he holds that the cosmos is a celestial 
machine, and the Earth a star like the others. All this is markedly 
different from Aristotle's belief that the heavenly bodies, unlike our 
Earth, are divine and incorruptible. 

Leonardo says that mathematics are concerned with ideal mental 
concepts and within that realm give certainty. Other sciences should 
begin with observation, use mathematics if possible, and end with 
one clear experiment a good attempt to set forth scientific method. 
As a philosopher, Leonardo seems to have held an idealistic pan- 
theism, though, with a well-balanced mind, he accepted the essential 
Christian doctrine as an outward form for his inward spiritual life. 
But he lived in the brief interval when the Papacy itself was liberal 
and humanist; later his attitude might have been untenable. 

Incidentally he names others, earlier and contemporaneous, who 
were interested in mathematics and scientific experiment. A circle 
of kindred spirits evidently lived in Italy, and we know little of them, 
except from Leonardo's note-books. The Schoolmen prepared men's 
minds by teaching that the world was understandable, but a new 
method was necessary; induction from nature had to replace 
deduction from Aristotle or Thomas Aquinas, and these Italians, 
above all Leonardo, helped to start the change. 


The Reformation. Humanism was brought to the north of Europe 
by students who had worked in Italy. Johann Miiller (1436- 
1476) translated into Latin Ptolemy and other Greek writers, and 
founded an observatory at Niirnberg. His Ephemerides, the pre- 
cursors of our Nautical Almanacs, were used by the Portuguese and 
Spanish explorers. Again, Desiderius Erasmus, chief figure of the 
northern Renaissance, attacked evils such as monastic illiteracy, 
Church abuses and Scholastic pedantry, setting himself to show what 
the Bible really said and meant. 

For a few years, culminating with the reign of Pope Leo X (1513- 
1521), the Vatican was a living centre of ancient culture. But the 
capture of Rome by the Imperial troops in 1527 broke up this intel- 
lectual and artistic life, and soon afterwards the Papacy reversed its 
liberal policy, and became an obstacle to modern learning. Freedom 
of thought had to be won through much tribulation by the rough 
path opened by Martin Luther. 

The Reformers had three chief objects : (i) the re-establishment 
of Church discipline; (2) the reform of doctrine and a return to a 
supposed primitive simplicity; and (3) a loosening of dogmatic 
control and a measure of freedom for the individual judgment based 
on Scripture. The first motive carried the people ; the second was an 
appeal to an older precedent, as in our own day there have been 
appeals to the 'first four centuries'. But the third object is the one 
that concerns us here. Although Calvin was as bad a persecutor of 
free thought as any Roman Inquisitor, he had not the power of the 
Mediaeval Church behind him, and the disintegration of Christen- 
dom, sad though it was from some other points of view, did indirectly 
help to secure liberty of thought and speech. 

Copernicus and Astronomy. Nicolaus Koppernigk (1473-1543), 
whose father was a Pole and mother a German, was a mathematician 
and astronomer, and became famous under his Latinized name of 

The cosmos as described by Hipparchus and Ptolemy accepted 
the common-sense view of the Earth as the centre of all things, 
drawing them to it by gravity, and explained the apparent move- 

DSH 4 


ment of the heavenly bodies by a series of cycles and epicycles. The 
system conformed with Aristotle and even with the facts, but it was 
unpleasantly complicated. 

Even while the Scholasticism of Aristotle and Saint Thomas 
Aquinas was predominant, the form of Neo-Platonism accepted by 
Saint Augustine survived in Italy as an alternative philosophy. It 
contained elements derived from the Pythagoreans, the idea that the 
Earth moved round a central fire, and that the ultimate mystical 
reality was to be found in numbers ; the simpler the relation of the 
numbers the nearer the truth. 

Copernicus spent six years in Italy as a pupil of Novara of Bologna, 
who criticized the Ptolemaic system as too cumbrous. Copernicus 
searched what books were available, and found that, according to 
Cicero, Hicetas thought that the Earth revolved on its axis, and, 
according to Plutarch, others had held the same opinion or even 
thought with Aristarchus that the Earth moved round the Sun. 
Given confidence by this ancient authority, Copernicus found that 
all the phenomena were simply explained, and so hung together that 
nothing could be altered without confusing the whole scheme. 
* Hence for this reason', he says, *I have followed this system.' 

He takes a sphere of fixed stars beyond all as the frame of the 
Universe and gravity as a universal force. Of the moving bodies, 
Saturn completes a circuit in thirty years, Jupiter in twelve, Mars 
in two, then the Earth, with the Moon going round it in an epicycle, 
next Venus circling in nine months and finally Mercury in eighty 
days. ' In the middle of all ... the Sun . . . sitting on a royal throne, 
governs the circumambient family of stars. . ,we find. . .a wonderful 
symmetry in the universe and a definite relation of harmony.' Thus 
to Copernicus, as to Pythagoras and to Plato, the object was to find 
the simplest and most harmonious picture of the heavens. 

Copernicus printed a short abstract of his work in 1530 and the 
complete book, De Revolutionibus Orbium C<lestium y was published in 
1543 with a Preface by Osiander, suggesting that the theory was 
only an aid to mathematical simplicity. This led to a mistaken idea 
that Copernicus himself did not regard it as physical reality, The 
book also met with criticism based on the science of the time. If the 


Earth revolved, would not things thrown upward lag behind? Would 
not loose objects fly away from the ground and the Earth itself 
disintegrate? Therefore the theory only made its way slowly, and 
did not become widely known till Galileo, using his newly invented 

FIG. 8. Diagram of the Universe by Copernicus 

telescope, revealed Jupiter's satellites, a solar system in miniature. 
But by 1616 the Papacy had become alarmed. Galileo was reproved 
and the theory condemned as * false and altogether opposed to Holy 
Scripture', though it might be taught as a mere mathematical 
hypothesis. But the adverse decision was never ratified by the Pope, 
and in 1822 the Sun was given formal sanction to become the centre 
of the planetary system. Galileo's 'persecution' has been exag- 



gerated; he only suffered a mild reprimand and detention and died 
peacefully in his bed. 

Nevertheless the Copernican system brought about a revolution 
in the minds of men. Instead of the Earth being the centre of the 
Universe, it became merely one of the planets, and although this 
change does not necessarily dethrone man from his proud position 
as the object and summit of creation, it does suggest doubts about the 
certainty of that belief. 

Thomas Digges, an English mathematician and engineer, accepted 
the Copernican theory, but not Copernicus' fixed stars. He thought 
the Universe was infinite and the stars scattered through boundless 
space. This view was also held by Giordano Bruno. But Bruno was a 
pantheist, and attacked other orthodox beliefs. For this, and probably 
not for his astronomy, he was condemned by the Inquisition, and 
burned at the stake in 1600, 

The accuracy of astronomical observation, especially of planetary 
motions, was much improved by Tycho Brahe, a Danish noble of 
Copenhagen (i54&-i6oi). The year before his death he was joined 
by John Kepler (1571-1630), to whom he bequeathed his unique 
collection of data. 

Kepler is often represented as solely engaged in searching for laws 
of planetary motion, and verifying three of them ready for a coming 
Newton to explain. But Kepler was after nobler game. Saturated 
with Platonic ideas, he believed that God made the world in accord 
with the principle of perfect numbers; he was really searching for 
ultimate causes the music of the spheres, and the mathematical 
harmonies in the mind of the Creator. 

The three laws he established were: (i) the planets travel in 
ellipses with the Sun in one focus; (2) the area swept out in any orbit 
by the straight line joining the centres of the Sun and a planet is 
proportional to the time; (3) the squares of the periodic times which 
the different planets take to describe their orbits are proportional to 
the cubes of their mean distances from the Sun. He was even more 
pleased by other fancied relations which later observation has not 
confirmed. About 1590 mathematics were much developed by the 


invention of symbolic algebra, the chief credit for which belongs to 
Francois Viete. 

Chemistry and Medicine. It was hoped that the revival of Greek 
learning would cause the same improvement in medicine as in 
literature and philosophy. Doubtless, when physicians turned from 
commentaries to the writings of Hippocrates and Galen themselves, 
a great increase in knowledge occurred, but when this knowledge 
had been discovered, accepted and systematized, men came again 
to rely too much on authority, till once more they began to observe 
and experiment; medicine then became allied with the chemistry 
emerging from alchemy to form a school of iatro-chemists or spagy- 

The Arabs had taken and modified the Pythagorean idea that the 
primary elements were to be found in principles or qualities and not 
in substances. They believed that the fundamental principles were 
those of 'sulphur', that part of a body which made it combustible 
and vanished on burning, 'mercury' which distilled over as liquid, 
and 'salt', any solid residue. This theory passed with other Arab 
learning into Europe. 

Theophrast von Hohenheim (1490-1541), a Swiss physician, wan- 
dered over Europe studying minerals and mechanical contrivances, 
and the diseases and remedies of different nations, before practising 
medicine for a while at Basle, where, from Celsus, the great physician 
of Roman times, he was given the name of Paracelsus, by which he 
is better known. He despised most orthodox men of science, and in 
medicine turried from the authority of Galen and Avicenna to his 
own observation and experience. As a chemist he prepared many 
substances, among them ether, and discovered its anaesthetic pro- 
perties by experiments on chickens, without appreciating its value 
for mankind. 

Van Helmont, mystic and experimenter, born at Brussels in 1577, 
recognized for the first time that there are different kinds of aeriform 
substances, and invented the name 'gas' to describe them. Believing 
that water was the sole element, he planted a willow in a weighed 


quantity of dried earth and supplied it with water only. At the end 
of five years the willow had gained in weight by 164 pounds while 
the earth had lost only 2 ounces. Van Helmont drew the conclusion 
that the new substance of the willow was made of water only, a 
legitimate conclusion indeed until, a century later, it was shown that 
green plants absorb carbon from the carbon dioxide in the air. 

Sanctorius (1561-1636) used an improved thermometer to measure 
the temperature of the human body, and Dubois (1614-1672), better 
known as Sylvius, applying chemistry to medicine, taught that health 
depends on the fluids of the body, opposite in kind, combining with 
each other to form a milder substance the first theory of chemistry 
not based on the phenomena of flame, leading afterwards to a general 
study of acids, alkalies and salts and so to the idea of chemical 

Anatomy, Physiology and Botany. A prejudice against the dis- 
section of human bodies prevented the revival of anatomy till the 
thirteenth century, and in the fourteenth, after the work of Mondino, 
it again became stereotyped. The note-books of Leonardo were not 
made known at the time, and the first modern anatomist of general 
influence was Andreas Vesalius (1515-1564), who published Fabrica 
Humani Corporis in 1543, setting forth not what Galen or Mondino 
taught, but what he himself had observed and was prepared to 
demonstrate. His work on the bones, veins, abdominal organs and 
brain was specially notable, and he was the first to see the importance 
of the shape of the skull in the classification of mankind. Before the 
end of the sixteenth century anatomy was freed from the trammels 
of ancient authority. 

In physiology Vesalius accepted the current ideas that food is 
endowed in the liver with natural spirit, which the heart converts into 
vital spirit and the brain into animal spirit; this last 'is a quality rather 
than an actual thing', and is employed for the operations of the 
'chief soul', and for bodily movement 'by means of nerves, as it were 
by cords.. . .As regards the structure of the brain, the monkey, dog, 
horse, cat and all quadrupeds which I have hitherto examined . . . 
resemble man in almost every particular.' 


Van Helmont held that in plants and brute beasts there is only 
'a certain vital power... the forerunner of a soul'. In man, the 
sensitive soul controls the functions of the body, and acts by means 
of archaei its servants, which work directly on the organs of the body 
by means of ferments not chemical ferments, but mystic agencies 
of another kind. Sylvius also believed in ferments, but his ferments 
were ordinary chemical agents, like the vitriol which causes effer- 
vescence when poured on chalk. This chemical physiology stimulated 
useful work by Sylvius and his pupils. 

In considering the functions of the blood, the doctrines of Galen 
were an obstacle. Galen taught that the arterial and venous blood 
were two separate tides which ebbed and flowed carrying ' vital ' and 

* natural 5 spirits to the tissues. Servetus, physician and theologian, 
who was burned by Calvin at Geneva for his heterodox opinions, 
discovered the circulation of the blood through the lungs, but the 
function of the heart in maintaining the flow through lungs and body 
was only made clear when William Harvey (1578-1657) was led to 
'give his mind to vivisections'. 

Harvey was educated at Gonville and Gaius College, Cambridge, 
and after some years abroad, he returned to England and practised 
as a physician. He was on friendly terms with Charles I, and showed 
him the development of the chick in the egg. It is said that, during 
the battle of Edgehill, in charge of the young princes, he sat under 
a hedge reading a book. With the king he retired to Oxford, and for 
a time he was Warden of Merton. 

In 1628 he published a small but most important volume : Exercitatio 
Anatomica de Motu Cordis et Sanguinis. He points out that in half an 
hour the heart deals with as much blood as is contained in the whole 
body, and that therefore the blood must find its way from the arteries 
to the veins and back to the heart. S I began to think', he says, 

* whether there might not be a motion as it were in a circle. Now this 
I afterwards found to be true ' found that is by observation of the 
heart as seen in the living animal. Harvey treats the problem as one 
of mechanics, and solves it as such. Another book, De Generatione 
Animaliumy appeared in 1651, and described the greatest advance in 
embryology since Aristotle. 


To complete Harvey's work on circulation, the microscope was 
necessary. In 1661 Malpighi of Bologna thus discovered in the lung 
of a frog that the arteries and veins are connected by capillary tubes, 
and not by structureless flesh as had been supposed. Malpighi also 
examined microscopically the glands and other organs, and gave the 
first description of the microscopic changes which appear as the egg 
starts to produce the living bird. 

The Renaissance increased the security of life and led to a simul- 
taneous development in artistic feeling. These factors, with the 
accompanying increase in wealth, encouraged the laying out of 
public and private parks and gardens, and the better cultivation of 
trees, vegetables and flowers. Botanic gardens were founded at Padua 
in 1545 and afterwards at Pisa, Leyden and elsewhere. Medicine too 
started gathering grounds and distilleries, where herbs were grown 
and converted into drugs. 

The revival of scientific botany was delayed by the mediaeval 
doctrine of signatures, whereby the colour or other visible character 
of a plant was thought to disclose the use for which God designed it. 
Plant-lore too was mingled with magic and other superstitions. 

The first to give accurate accounts of plants with drawings from 
nature was Valerius Cordus (1515-1544), who thus made the first 
appreciable advance in systematic botany since Dioscorides fifteen 
hundred years before. Among botanists of the period mention should 
be made of Jean and Gaspard Bauhin, who put together extensive 
catalogues of plants. Other herbals appeared; one was published by 
William Turner in the years 1551 to 1 568, and another, more famous 
but less accurate, by John Gerard in 1597. 

Mediaeval Bestiaries had been compiled, not from nature but from 
Pliny the Elder. A better spirit was now abroad; animals were 
studied and zoological gardens founded, one of the earliest at Lisbon. 

Magnetism and Electricity. William Gilbert of Colchester (1540- 
1603), Fellow of Saint John's College, Cambridge, and later Presi- 
dent of the College of Physicians, gave in his book De Magnete 
all known facts about magnetism, adding many observations of his 



own. The compass needle, discovered by the Chinese in the eleventh 
century, was soon used by Muslim sailors, and appeared in Europe 
a hundred years after its discovery. 

Gilbert investigated the forces between magnets, and showed that 
a magnet, when freely suspended, besides pointing to the north and 
south, dips in England with its north pole downwards through an 
angle depending on the latitude. He concluded that the Earth itself 

FIG. 9. Diagram of declination of iron magnet 

was a magnet, with poles nearly, but not quite, coincident with the 
geographical poles. For a uniform lodes tone, the strength of the 
magnetism was proportional to its quantity or mass perhaps the 
first clear recognition of mass as distinct from weight. 

Gilbert also found that when amber was rubbed it showed forces, 
which he measured with a suspended needle. To describe these 
results, he coined the name 'electricity' from the Greek word 
rjXcKrpov, amber, though he discovered that other substances were 
also active. He imagined that an aethereal, non-material influence 
was emitted by the magnet or electrified substance, embracing neigh- 
bouring bodies and drawing them towards itself. He used similar 
half-mystical ideas to explain the motions of the Sun and planets. 


Philosophy. Though the great predominance of Aristotelian 
Scholasticism had been shaken by Duns Scotus, William of Occam 
and Nicholas of Cusa, it remained very powerful at the time of the 
Renaissance, and the philosophy and science of Aristotle kept much 
of their old prestige. When those with the newer outlook wished to 
experiment in order to test a hypothesis, the orthodox inquirer could 
meet them with a quotation from Aristotle, and sometimes find his 
authority still accepted. . 

It was this position which made so useful the message proclaimed 
to the world by Francis Bacon (1561-1626), Lord Chancellor of 
England, 'to extend more widely the limits of the power and great- 
ness of man*. Bacon held that, by recording and tabulating all 
possible observations and experiments, the relations would emerge 
almost automatically. But in nature there are so many phenomena 
and so many possible experiments that advances are seldom made 
by the pure Baconian method. Insight and imagination must be 
used at an early stage of the inquiry, and a tentative hypothesis 
formed by induction from the facts. Then its consequences must be 
deduced logically and tested for consistency among themselves and 
for concordance with the primary facts and the results of ad hoc 
experiments. Hypothesis after hypothesis may have to be examined 
till one passes all the tests, and, for a time at all events, becomes an 
accepted theory, which can predict phenomena to a high degree of 
probability. The methods of science are more speculative more 
poetical than Bacon thought. Nevertheless he was the first to 
consider formally, if inadequately, the philosophy of inductive science, 
and he supported with statesmanlike eloquence the new experimental 

Rene Descartes (1596-1650), who was born in Touraine and also 
lived in Holland and Sweden, improved the mathematics used in 
physics and founded modern critical philosophy. For the first time 
he applied algebra in the methods of co-ordinate geometry. Straight 
lines OX and T are drawn from at right angles. The position of 
a point P may then be specified by stating the distance OM on x and 
PM ony. Ify increases evenly as x increases, we pass over the diagram 
in a straight line OP. Ify equals x 2 multiplied by a constant, we get 



a parabola OP' and so on. These equations may be treated alge- 
braically and the results interpreted geometrically to solve many 
physical problems. 

Descartes applied mechanics to construct a theory of the cosmos. 
He regarded the physical universe as a closely packed plenum with 
no empty spaces ; motion can then only Y 
occur in closed circuits, for there is no 
vacuum into which a body can pass. On 
these ideas Descartes formed a theory 
of vortices, in which a stone is drawn to 
the earth and a satellite to its planet, 
while the planet and its satellite are 
whirled in a greater vortex round the 
Sun. At a later date Newton proved 
mathematically that the necessary pro- 
perties of these Cartesian vortices were Q MX 
inconsistent with observation, but they FlG I0 Co-ordinate geometry 
formed nevertheless a bold attempt to by Ren6 Descartes 
reduce the colossal problem of the sky to terrestrial dynamics. In 
Descartes' scheme God as First Cause started the machine, which 
then runs spontaneously. 

Descartes was the first to formulate complete dualism, with an 
entire separation of soul and body, mind and matter. Previously the 
soul was regarded as of the nature of air or fire, and mind and matter 
differed only in degree and not in kind. Descartes, to whom mind 
was immaterial and matter was really inert and dead, thus made it 
possible to consider the human body as a mechanism without 
banishing the soul altogether, indeed, though they are completely 
different, thought is as real as matter cogito ergo sum. 

Descartes' system was criticized by the nominalist Thomas Hobbes 
(1588-1679), who would have none of the Cartesian dualism, and 
held that the only reality was matter in motion. Regardless of 
difficulties, Hobbes took sensation, thought and consciousness as due 
to the motion of atoms in the brain, but offered no explanation of 
how the connexion between two apparently quite different types of 
activity comes about. 


Witchcraft. It is strange that, in the time of the Renaissance, 
when knowledge of all kinds made a new start in growth and modern 
experimental science may be said to have begun, there should have 
been a recrudescence of ancient magic in the form of a belief in 
sorcery and witchcraft. 

When the Christian Church first conquered the world, unconscious 
of the effect of the mystery religions in the formulation of its belief in 
earlier times, intelligent men had come to regard magic in its various 
forms as a relic of paganism which was dying out. So the Church 
took a lenient view to call up Satan was not heresy ; it was merely 
sin. But in the later Middle Ages, in Manichaean heresies the Devil 
became a disinherited Lucifer, an object of worship to the oppressed. 
Saint Thomas Aquinas set himself to explain away the lax attitude 
of the early Church, and in 1484 Pope Innocent VIII gave formal 
sanction to the popular belief in sorcery and witchcraft. Thus was 
forged a new weapon to combat heretics they could be declared 
sorcerers and the fury of the mob roused against them. 

After the Reformation the Protestants used the scriptural injunction 
'thou shalt not suffer a witch to live* to vie with Romanists in the 
hunt. On the Continent, where torture was legal, most of those 
accused confessed. In England, where torture was allowed in Pre- 
rogative Courts but not at Common Law, they mostly declared their 
innocence. Very few men ventured their lives by protesting against the 
mania. Perhaps the first was Cornelius Agrippa ; others were John 
Weyer, physician to Duke William of Cleves, and Reginald Scot, a 
Kentish squire who took the modern common-sense view that the 
whole thing is a mixture of ignorance, illusion and false accusation. 
A Jesuit, Father Spec, attended nearly two hundred victims to the 
stake at Wiirzburg. Horrified at the experience, he declared his belief 
that they all were innocent, and that anyone could be made to confess 
by the tortures used. In two hundred years of Europe the number of 
victims is estimated at three-quarters of a million or more a dis- 
graceful episode in the history of mankind. But the civilized world 
discovered that it had ceased to believe in witches before it had 
stopped burning them. The change was chiefly due to the advance 
of science, which was slowly defining the limits of man's mastery 
over nature and the methods whereby it is attained. 


Galileo. If we are asked to name the man who did most to start 
physical science on the triumphant course which lasted for nearly 
three hundred years, we must answer: Galileo Galilei (1564-1642) 
(see Plate IV, facing p. 62). Leonardo, Copernicus and Gilbert, each 
in his different way, foreshadowed the coming revolution, but Galileo 
went farther, and in his writings we recognize for the first time the; 
authentic modern touch. ^He brought the theory of Copernicus tol 
the practical test of the telescope, but above all in his work on 
dynamics he combined observation and induction with mathematical 
deduction tested by experiment, and thus inaugurated the true 
method of physical research. In his work there is no reliance on an 
authoritative and rational scheme as in Scholasticism ; each problem 
is faced in isolation, each fact is accepted as it stands with no desire 
to make it fit into a universal pre-ordained whole; concordance, if 
possible at all, comes slowly and partially; mediaeval Scholasticism 
was rational, modern science is in essence empirical, accepting brute 
facts whether they seem reasonable or not. 

In 1609 Galileo heard a rumour that a Dutchman had made a 
glass that magnified distant objects. From his knowledge of refraction, 
he was able at once to do likewise, and soon made a telescope which 
magnified thirty diameters (see Plate V, facing p. 63). Surprising 
discoveries followed: the surface of the moon, instead of being perfect 
and unblemished as held by Aristotle, was seen to be broken by 
rugged mountains and valleys: countless stars, flashing into sight, 
solved the problem of the Milky Way. Round Jupiter four satellites 
revolved, a model of the Earth and its moon moving round the Sun 
as taught by Copernicus on a priori grounds of mathematical sim- 
plicity. But the Professor of Philosophy at Padua refused to look 
through the telescope, and his colleague at Pisa laboured with logical 
arguments before the Grand Duke to refute Galileo. 
' Galileo's most original and important work was the establishment 
of the science of dynamics on a combined experimental and mathe- 
matical basis. Stcvinus of Bruges had considered the inclined plane 


and the composition of forces, and thus made some advance in statics, 
but men's ideas on motion were a confused medley of Aristotelian 
theory and disconnected observation. It was thought that bodies 
were essentially light or heavy, and therefore rose or fell to find their 
'natural places'. Stevinus, in an experiment afterwards confirmed 
by Galileo, let fall a heavy body and a light body together, and 
showed that they struck the ground practically simultaneously. In 
repeating the experiments more accurately, Baliani, a Captain of 
archers at Genoa, rightly referred the slight difference to the friction 
of the air. Since the forces on the two bodies are measured by their 
weights, there must be some other quantity which resists the setting 
in motion, and the experiments show that in each body it must be 
proportional to the weight. This quantity, as we saw above, was 
recognized also by Gilbert; it is what we call mass, and later it was 
explicitly discussed by Newton. 

Copernicus and Kepler proved that the motion of the planets 
could be described in mathematical terms. Galileo thought that 
bodies on the Earth ' in local motion ' might also move mathematically. 
Watching the bronze lamps, hanging from the roof of the cathedral 
at Pisa, he saw that the swings, whether large or small, occupied 
equal times, and so discovered the principle of the pendulum. 
A falling body moves with increasing speed; what is the law of the 
increase? Galileo first tried the hypothesis that the speed was pro- 
portional to the distance fallen through; but this, he found, involved 
an inconsistency, and he then tried another hypothesis, that the 
speed varied with the time of fall. Galileo deduced its consequences 
to compare with experiment. The speeds being too great for his 
instruments to measure, he used inclined planes, having found that 
a body falling down such a plane acquired the same velocity as 
though it had fallen through the same vertical height. His measure- 
ments agreed with his second hypothesis and its mathematical con- 
sequence that the space described increases with the square of the 

Galileo's inclined planes gave another important result. After 
running down one plane a ball will run up another to the same 
vertical height, and, if the second plane be horizontal, the ball will 


run along it in a straight path till stopped by friction. Thus a moving 
body continues to move in virtue of inertia till some opposing force 
comes into play. It had been supposed that a force was necessary to 
maintain motion; the planets had to be kept going by Aristotle's 
Unmoved Mover, or Kepler's action of the Sun exerted through an 
aether. Galileo's result showed that, when the planets have been set 
in motion, they only need a force to pull them away from a straight 
path, and keep them swinging round the Sun in their orbits. The 
way was opened for Newton. 

Galileo also began the study of the strength of materials, the 
bending of beams and other problems in elasticity, and carried out 
further work on hydrostatics. Also, with the newly invented glass 
tube, he made a thermoscope, in which the expansion of air in a bulb 
measured the temperature. The production and manipulation of 
glass tubes did much for experimental science. 

Galileo, like Kepler, looked for mathematical relations, not how- 
ever in a search for causes, due to mystic numbers, but in order to 
discover the laws by which nature works, caring nothing 'whether 
her reasons be or be not understandable by man' a contrast to 
homocentric Scholasticism, in which the whole cosmos is made for 
man. To Aristotle space and time were somewhat unimportant and 
vague * categories'. Galileo, after his experiments on falling bodies, 
gave them that primary and fundamental character which Newton 
adopted and passed on to his successors. 

Galileo distinguished between primary qualities, such as extension 
or shape, which, he held, cannot be separated from a body, and 
secondary qualities, such as colour or smell, which, following Demo- 
critus, he referred to the senses of the percipient, the observed body 
being merely ' atoms and a void '. Galileo accepted the atomic theory, 
discussing speculatively how differences in the number, weight, shape 
and velocity of atoms may cause differences in taste, smell or sound. 
Galileo's time and space, with his atomic theory and its consequences, 
led later to dualism and materialism in other men, while some have 
referred to Galileo's results many of our present philosophic dis- 
contents. But it may equally be said that Galileo revealed and clarified 
the difficulties obscured or concealed by Aristotle. Galileo confessed 


that he knew nothing about the cause of gravity or the origin of the 
Universe, and declared it better ' to pronounce that wise, ingenuous 
and modest sentence, "I know it not"'. 

Boyle, Huygens and others. The philosophy of Hobbes, founded 
on the science of Galileo, did not escape criticism. The Cambridge 
Platonists pointed out that a theory which made extension and its 
modes the only real properties of bodies could not explain life and 
thought. They tried to reconcile mechanical views with religion 
by an apotheosis of space. Malebranche identified infinite space with 
God himself. Spinoza held that God is the immanent cause of a 
pantheistic Universe, and the Cartesian dualism of mind and matter 
is resolved in a higher unity when viewed sub specie aeternitatis. Thus 
contemporary philosophers tried to escape from their growing diffi- 
culties by invoking the power of God. 

Prevalent theories were well discussed by Sir Kenelm Digby 
(1603-1665), who ridiculed Aristotle's 'essential qualities', and held 
with Galileo that all things could be explained by particles 'working 
by means of local motion'. Again, Galileo's new mathematical 
methods were clearly set forth in the lectures of Isaac Barrow, 
Newton's teacher at Cambridge. Space and time are absolute, 
infinite and eternal, because God is omnipresent and everlasting. 
This seems to be the first definite formulation of the ideas of absolute 
time and space as held by Newton. 

Stevinus had re-opened the subject of hydrostatics by calculating 
the pressure of a liquid at a given depth; Robert Boyle (1627-1691), 
chemist, physicist and philosopher, proved that air is a material 
substance having weight, its volume being inversely proportional to 
the pressure, a relation known as Boyle's Law, rediscovered by 
Mariotte. Boyle observed the effect of a change in atmospheric 
pressure on the boiling point of water, collected many new facts in 
electricity and magnetism, and explained heat as a 'brisk* agitation 
of particles. As a chemist he distinguished element, mixture and 
compound, prepared phosphorus, collected hydrogen in a vessel over 
water, though he called it 'air generated de novo\ and studied the 
form of crystals as a guide to chemical structure. He dealt with the 


chemistry of common things without reference to the still surviving 
half-mystical theories, indeed he rejected both the old idea of four 
elements, and also the ' principles ' or * essences ' of sulphur, mercury 
and salt. In 1661 he published The Sceptical Chymist. . .touching the 
experiments whereby Vulgar Spagirists 1 are wont to endeavour to evince their 
Salt, Sulphur and Mercury to be the True Principles of Things^ In a 
trialogue, Boyle's spokesman explains that he still feels doubts about 
elements or principles, ' notwithstanding the subtile reasonings I have 
met with in the books of the Peripatetiks, 2 and the pretty experiments 
that have been shew'd me in the Laboratories of Chymists'. Gold 
can be alloyed or dissolved in aqua regia and yet recovered in its 
original form; this suggests unalterable atoms of gold surviving 
various combinations rather than vague Aristotelian elements or 
Spagyrist principles. Thus Boyle had grasped the ideas on which 
modern chemistry was afterwards founded. 

Boyle accepted the view that secondary qualities are mere sensa- 
tions, but he justly pointed out that 'there are de facto in the world 
certain sensible and rational beings that we call men', so that their 
sensations, and with them the secondary qualities of all bodies, are 
part of the world in being and therefore as real as the primary 
qualities. The mechanical world and the thinking world (we may 
say) are both parts of the whole problem which philosophy has to 
face. God made the world in the beginning and (Boyle holds) His 
1 general concourse' is continually needed to keep it in being and at 
work. This partial return to the Indian and Arabic idea of continual 
creation and re-creation is also the physical aspect of the Christian 
doctrine of immanence. 

Thus Boyle was an interesting philosopher as well as a distinguished 
physicist and chemist. His diversity is described in an Irish epitaph, 
which, it is said, called him * Father of Chemistry and Uncle of the 
Earl of Cork 5 . 

Blaise Pascal (1623-1662), best known as a theologian, was also 
an experimental physicist. He arranged for a barometer, newly 

1 See p. 53. 

1 Aristotle's School was called Peripatetic from the custom of master and pupils 
walking together in the garden of the Lyceum at Athens. 

DSH 5 


invented by Torricelli, to be carried up the Puy de Dome, when the 
height of the mercury column became less, clearly because the pressure 
of the atmosphere fell, and not through nature's 'abhorrence of a 
vacuum * as taught by the Aristotelians. Pascal was also the originator 
of the theory of probability, which, beginning with games of chance, 
has proved to be of great and still increasing importance in philosophy, 
science and social statistics. Indeed all empirical knowledge may be 
said to be a matter of probability expressible in terms of a bet. 

The most striking advances in dynamics since the work of Galileo 
were made by Ghristiaan Huygens (1629-1695), who published his 
book Horologium Oscillatorium in 1673. Assuming the constancy in 
moving bodies of vis viva, which we now call kinetic energy, he 
deduced the theory of the centre of oscillation and opened a new 
method in mechanics. The work done by a force / moving a body 
through a space s is/jr, and Huygens found that this is equal to the 
vis viva produced, that is \mv 2 . He proved also the relation between 
the length of a pendulum and its time of swing, and dealt with 
circular motion. If a body of mass m describes with velocity v a 
circular path of radius r, by Galileo's result a force must act towards 
the centre. Huygens showed that, in modern language, the accelera- 
tion is v 2 /r, so that the force is mv 2 /r. Newton must have reached the 
same conclusion in 1666, but did not publish it till a later date. 
Huygens also improved telescopes and watches and discovered 
Saturn's rings. 

Scientific Academies. In tracing the intellectual environment of 
Newton and his contemporaries, it is necessary to take into account 
the societies or academies which were then being formed. The new 
learning, striving to push its way against the opposition of the 
Aristotelians, only slowly entered the Universities of Europe. But 
the numbers interested in ' natural philosophy' were growing rapidly, 
and here and there they met together for discussion. At Naples in 
1560 was formed an Accademia Secretorwn Naturae \ from 1603 to 1630 
an Accademia del Lincei existed in Rome, and in 1651 the Accademia 
del Cimento was founded by the Medici at Florence. 

In England a society began to meet in 1645 at Gresham College 


or elsewhere in London, under the name of the Philosophical or 
Invisible College. In 1648, owing to the Civil War, most of its 
members moved to Oxford, but in 1660 it returned to London, and 
in 1662 it was incorporated by a Royal Charter of Charles II as 
'The Royal Society of London for Promoting Natural Knowledge 5 . 
In France a corresponding Acadtmie des Sciences was founded by 
Louis XIV in 1666, and similar institutions followed in other lands. 

The influence of these bodies in facilitating discussion and making 
known the results of research has greatly helped the rapid growth 
of science, especially as most of them soon began to issue periodic 
publications, which superseded the older method of correspondence 
between individuals. rA Journal des Savants appeared at Paris in 1665, 
and three months later it was followed by the Philosophical Transactions \ 
of the Royal Society, at first a private venture of its secretary.^) 

Even in the second half of the seventeenth century, survivals of 
mediaeval thought, especially Aristotelian Scholasticism, contended 
with the new science based on mathematics and experiment. In 
mechanics, after the work of Galileo, the newer outlook was learning 
to express its results in terms of matter and motion. This was helped 
by a revival of the atomic theory, accepted by Galileo, and developed 
by Gassendi. The tendency was hastened by Huygens, though echoes 
of old controversies were still heard. Boyle in 1661 thought it worth 
while to argue against both Scholastic and Spagyrist concepts in 
chemistry, and both alchemy and astrology were still taken seriously. 
When Newton went to Cambridge and was asked what he meant to 
study, he is said to have answered: ' Mathematics, because I wish to 
test judicial astrology. 5 At a later date he possessed a chemical 
laboratory, and it is probable that he spent much more time there 
labouring fruitlessly at alchemy, as well as at more hopeful chemistry, 
than he gave to the dynamics which changed the whole outlook of 

The Greek idea of an aether had been used by Kepler to explain 
how the Sun kept the planets moving, by Descartes as a fluid in which 
to form his vortices, by Gilbert in his theories of electricity and 
magnetism, and by Harvey to enable the Sun to send heat to the 
heart and blood of living animals. But interplanetary aether was 


still confused with Galen's aethereal or psychic spirits, used by the 
mystic to explain the nature of being. The modern distinction between 
mind and matter, soul and body, had not become clear. The 'souP, 
the ' animal spirits ' and similar concepts were regarded as c vapours ' 
or * emanations', things to us material. A unity was thus maintained 
by most men except Descartes, who was the first to see an essential 
difference between inert matter and the thinking mind. The usual 
line seems to have been drawn between solids and liquids on one 
side, and air, fire, aether and spirit on the other. Also nearly all men 
of science and philosophers in the middle of the seventeenth century 
looked on the world from the Christian standpoint; the idea of 
antagonism between religion and science is of a later date. Even 
Hobbes, who was a philosophic materialist and defined religion as 
'accepted superstition' agreed that it should be established and 
enforced by the State. Hobbes was exceptional; almost all men 
adopted the fundamental theistic belief, to which, they thought, any 
theory of the cosmos to be true must conform. 

Newton and Gravitation. Isaac Newton (1642-1727), qui genus 
humanum ingenio superavit, is still accepted as the bearer of the most 
illustrious name in the long roll of science [see frontispiece]. Born 
at Woolsthorpe in Lincolnshire on Christmas Day 1642, the year in 
which Galileo died, he entered Trinity College, Cambridge, in 1661, 
and attended the mathematical lectures of Isaac Barrow. He was 
elected as a Scholar of the College in 1664 and as a Fellow in 1667. 
In 1665 and the following year, driven to Woolsthorpe by plague 
at Cambridge, he meditated on planetary problems. 

For in those days [he says] I was in the prime of my age for inven- 
tion, and minded Mathematics and Philosophy more than at any 
time since. 

It is one of the ironies of history that, after those years, Newton 
did his best to avoid being pushed into work on ' Mathematics and 
Philosophy* or into publication of his results. 

Galileo's work had shown the need of a force acting towards the 
Sun to keep the planets circling in their orbits. Newton is said to 
have seen the clue while idly watching the fall of an apple in the 


Woolsthorpe orchard. He wondered about the cause of the fall, and 
the distance the apparent attraction of the Earth for the apple would 
reach : would it perchance reach the Moon, and explain that body's 
continual fall towards the Earth away from a straight path? 

From Kepler's third law Newton deduced that the forces keeping 
the planets in their orbits must be, at all events approximately, 
inversely as the squares of their distances from the centre about which 
they revolve, and thereby compared the force needed to keep the 
Moon in her orbit with the force of gravity on the surface of the 
Earth, and, says Newton, 'found them answer pretty nearly'. But, 
always averse to publication, he took no step to make his discovery 
known : perhaps to ' answer pretty nearly ' was not good enough. 

But the most probable cause of Newton's delay was that pointed 
out in 1887 by J. G. Adams arid J. W. L. Glaisher. The sizes of the 
Sun and planets are so small compared with the distances between 
them that the whole of each may fairly be treated as concentrated 
in one place. But compared with the size of the apple or its distance 
from the ground, the Earth is gigantic. The problem of calculating 
the combined attraction of all its parts was one of great difficulty. 
Newton solved it in 1685 when he proved mathematically that a 
uniform sphere of gravitating matter attracts bodies outside it as 
though all its mass were concentrated at the centre. This justified 
the simplification whereby the Sun, planets, Earth and Moon were 
taken as massive points. Glaisher says : 

No sooner had Newton proved this superb theorem and we know 
from his own words that he had no expectation of so beautiful a result 
till it emerged from his mathematical investigation than all the 
mechanism of the universe at once lay spread before him ... it was 
now in his power to apply mathematical analysis with absolute pre- 
cision to the actual problems of astronomy. 

The way was then clear for Newton to deal with his old problem 
of the apple and the Moon. Using a new French measurement of 
the Earth's size due to Picard, he found concordance within narrow 
limits, and the proof of identity was complete: the familiar fall of an 
apple to the ground and the majestic sweep of the Moon in her 
orbit are due to one and the same unknown cause. 

Meanwhile the question of gravity was under general discussion, 


especially at the Royal Society. If the planetary orbits, really ellipses, 
are taken as circles, it follows from Huygens' results and Kepler's 
third law that the force must be inversely proportional to the square 
of the distance. 1 But the real paths are ellipses, and no one in London 
seemed able to solve the actual problem. Halley therefore went to 
see Newton at Cambridge, and found that he had worked it out two 
years before, but had lost his notes. However he drafted another 
solution and sent it to Halley with 'much other matter'. Urged by 
Halley, who paid for the publication, Newton wrote out his work, 
and in 1687 issued the Principia, the ' Mathematical Principles of 
Natural Philosophy', the greatest book in the history of science. 

The heavenly bodies, to Aristotle divine, incorruptible, and 
different in kind from our imperfect world, were brought by Newton 
within range of man's inquiry, and shown to move in accordance 
with the dynamical principles established by terrestrial experiments. 
Their behaviour could be deduced from the one assumption that 
every particle of matter attracts every other particle with a force 
proportional to the product of the two masses and inversely propor- 
tional to the square of the distance between them. The movements 
so calculated were found to agree accurately with the observations of 
more than two centuries. Halley proved that even comets move in 
accord with gravity. He calculated the times of appearance of the 
comet named after him, indicating that it was the same as the comet 
pictured in the Bayeux tapestry which was thought to presage disaster 
to the Saxons in 1066. 

Newton also investigated the attraction of the Sun and Moon on 
the waters of the Earth, and placed tidal theory on a sound footing, 
though the complications introduced by land and channels still defy 
complete explanation. 

The proofs in the Principia are given in geometrical form, but it is 
possible that Newton first obtained some of them by new mathe- 
matical methods which he had himself devised. The chief of these 
was his method of fluxions finding the rate of change of one variable 

1 Kepler's third law states that the squares of the periodic times, and therefore 
r 2 /p*, are proportional to r*. Hence v 2 varies as i/r, and & 2 / r which by Huygens* 
proof gives the acceleration and therefore the force, is proportional to i/r*. 


x with another^. Newton wrote this rate as #, but Leibniz, who 
invented an equivalent method, apparently independently, used the 
better notation dxjdy, which was adopted in the further development 
of the differential calculus. But Newton seems to have had an 
amazing power of seeing the solution of a problem by intuition; 
sometimes his proofs may have been merely helps to weaker minds. 

Mass and Weight. The concept of mass as inertia, distinct from 
weight, is implicit in the work of Galileo. It appears explicitly in the 
writings of Gilbert and of Baliani, who refers both to moles andpondus. 
Newton defined mass as ' the quantity of matter in a body as measured 
by the product of its density and bulk 5 , and force as 'any action on 
a body which changes, or tends to change, its state of rest, or of 
uniform motion in a straight line'. He then summarizes his results 
in three laws of motion, the second stating that change of motion, 
which, in modern terms, means rate of change of momentum, is 
proportional to the moving force. 1 

No serious criticism of this formulation appeared till Mach in 1 883 
pointed out that Newton's definitions of mass and density involve a 
logical circle; he defines mass in terms of density, while density can 
only be defined as mass per unit volume. But it is possible to avoid 
this difficulty. If two bodies act on each other, as by mutual gravita- 
tion or by a coiled spring joining them, the ratio of their opposite 
accelerations depends only on something in the bodies which we may 
if we please call mass. We can then define the relative masses of the 
two bodies as the inverse ratio of their accelerations, and the force 
between them as the product of either mass and its own acceleration. 
The logical circle is thus avoided. 

We can also escape from it in another way. We have ideas derived 
from experience about space or length and about time; our muscular 
sense similarly gives us the idea of force. Equal forces, as roughly 
measured by this sense, are found to produce unequal accelerations 
on different pieces of matter, and the inertia of each piece, its 
resistance to the force/, may be called its mass, and may be defined 
as the inverse of the acceleration produced by a given force, or 

1 The rate of change of velocity is called acceleration, and the rate of change of 
momentum, mv y is therefore ma, so that force is mass multiplied by acceleration. 


m=~//a. This may bring psychology into physics, but it is interesting 
to note that it is possible to avoid a logical circle in physics by doing 
so. Next we find by experiment that the relative masses of two bodies 
as thus defined are roughly constant ; then we can make the hypothesis 
that this rough constancy is rigorously true, or better, true to a high 
degree of accuracy, and use M as a third fundamental unit to those 
of length L and time T. All the innumerable deductions from this 
hypothesis of constancy proved exactly true till recent days. 

Mass being settled, there remains the problem of its relation to 
weight, the force by which a body is drawn towards the Earth. The 
answer is implicitly given by the experiments on falling bodies carried 
out by Stevin, Galileo and Baliani, which showed that a heavy and 
a light body fall together, that is, their accelerations are the same and 
equal to about 16 feet per second in every second of time. If W\ 
and W 2 be the weights, we have by experiment <x. l =<x. 2) that is 

W l W 2 W, m, , . , i u 

*= - or T7F= > the weights are proportional to the masses. 

m l m 2 W 2 m 2 5 ^ F 

Newton verified this result more accurately by showing that pen- 
dulums of the same length have the same time of swing, whatever 
be their mass or material. Since weight hastens the swing and mass 
retards it, Newton's result shows that weight and mass must be 
proportional. He pointed out how surprising it is that gravity thus 
proceeds from a cause depending not on the surface but on the 
'quantity of the solid matter* the bodies contain; gravity must 
penetrate to the centres of the Sun and planets. 

Mach also pointed out that the dynamical work of Galileo, 
Huygens and Newton only means the discovery of one fundamental 
result. In his experiments on falling bodies, Galileo found that the 
velocity increased with the time, v = a.t, so that mv=ft y that is, the 
increase in momentum is measured by the product of the force and 

the time, which gives the Newtonian lawy= = ma. Now half the 

final velocity is the average velocity, and this multiplied by the time 
gives the space traversed, so that Galileo's v = ct.t or Newton's mv=ft 
becomes Huygens' %mv 2 ==/y, which states that the vis viva, our kinetic 
energy, is equal to the work done (p. 66). As Mach said, only one 
fundamental principle had been discovered. 


But if Galileo had happened first on the fact that the square of 
the velocity increased with the space traversed, or v 2 = 20^ , he would 
have thought that \mv 2 =fs , Huygens 5 equation of work and energy, 
was the primary and important relation. It was merely the accident 
of history which gave that place to force and momentum, and caused 
delay in the use of the concepts of work and energy. 

Optics and Light. The law of refraction, that the sines of the 
angles of incidence and refraction bear a constant ratio, had been 
discovered by Snell in 1621, while the colours seen in the rainbow 
and in cut glass were, of course, familiar to men. In 1666 Newton 
'procured a triangular glass prism to try the celebrated phenomena 
of colours', and his first paper, published in 1672, was on light. 

Newton showed that white light is made up of light of various 
colours, differently refracted by passing through the prism, the most 
refracted being violet and the least red. On these results he solved 
the problem of the rainbow, and explained the colours which dis- 
turbed the vision through the then known refracting telescopes, but 
he concluded erroneously that colour could not be prevented without 
at the same time destroying the refraction which gave magnification. 
To evade the difficulty he invented a reflecting telescope. 

He examined the colours of thin plates, well known in bubbles and 
other films. By pressing a glass prism on to a lens of known curvature, 
the colours were formed into circles which he could measure, since 
called 'Newton's rings'. Using light of one colour only, the rings 
became alternately light and dark; it was then clear that the colours 
with white light were due to the abstraction of one colour after 
another in turn. He also repeated and extended experiments made 
by Grimaldi, who had found that narrow beams of light are bent at 
the edges of obstacles, making the shadows larger than expected and 
showing fringes of colour. Newton proved that the bending is 
increased by passing the light through a narrow slit, and made careful 
observations and measurements. He also carried further Huygens' 
experiments on the double refraction of Iceland spar, and pointed 
out that they proved that a ray of light cannot be symmetrical but 
must be different on its different sides. 

In considering the nature of light, another discovery, made by 


Roemer, was important. When the Earth is between the Sun and 
Jupiter, the eclipses of his satellites appear about fifteen minutes 
earlier than when the Earth is beyond the Sun, and the light has to 
cross the Earth's orbit. Thus light does not travel instantaneously, 
but needs a finite time. 

The nature of light has always been a subject of wonder and 
speculation. The idea that light consists of particles can be traced 
back to the Greeks particles either coming from the visible object 
or projected from the eye to feel the object, though Aristotle held that 
light was action in a medium. Descartes thought it was a pressure 
transmitted through his plenum, and Hooke suggested that it was a 
rapid vibration in a medium, a theory worked out in some detail by 

Newton, in dealing with the passage of heat through a vacuum, 
asked in his queries: 

Is not the Heat convey'd through the Vacuum by the Vibrations 
of a much subtler Medium than Air . . . and exceedingly more elastick 
and active? 

But the fact that normally light travels in straight lines made 
Newton think that primarily it must consist of projected particles, 
though to explain the other properties he had to suppose that the 
particles stirred up vibrations in the medium which conveys radiant 
heat vibrations which put the particles into ' Fits of easy Reflexion 
and easy Transmission' alternately. Thus he gave to his particles 
some of the properties of waves. 

Now it is a remarkable fact that, after a century of a pure wave 
theory of light and forty years of electric particles, physicists are now 
finding that these particles are associated with waves of extremely short 
wave length (see p. 1 52) . Indeed this modern view of electron particles 
with their trains of waves is very much like Newton's inspired guess, 
His amazing insight into nature is once more demonstrated. 

Newton fitted up a laboratory in the garden behind his rooms 
in Trinity College, and there spent much time in chemical and 
alchemical experiments. He wrote no book or even paper on this 


subject; all that remain are his manuscript notes, and some of the 
queries at the end of his Optics. He seems to have been chiefly 
interested in metals, in chemical affinity and in the structure of 
matter. Thus he states that the most fusible alloy of lead, tin and 
bismuth contains those metals in the "proportion of 5 : 7 : 12. In 
query 3 1 he writes : 

When Salt of Tartar runs per deliquium is not this done by an 
Attraction between the Particles of the Water which float in the Air 
in the form of Vapours ? And why does not common Salt, or Salt- 
petre, or Vitriol, run per deliquiwn, but for want of such an Attraction? 

Newton and Philosophy. Newton carried farther Galileo's method 
of scientific investigation. Postponing the question of why things 
happen, he concentrates on the problem of how. This is clearly seen 
in his work on gravity. For although Newton was often said to 
have established * action at a distance', in fact he regarded such an 
idea as absurd. He proved that bodies moved as though particles 
attracted each other, but he clearly and often states that he does not 
know why, or by what mechanism, gravity works. That is a separate 
problem which comes at a later stage of the inquiry. Indeed it may 
never be solved, for science deals with appearance and not necessarily 
with reality. 

Again the same distinction is seen in Newton's queries about 
chemical affinity: 

Have not the small Particles of Bodies certain Powers, Virtues or 
Forces, by which they act . . . upon one another for producing a great 
part of the Phaenomena of Nature?. . .How these Attractions may 
be perform'd I do not here consider. What I call Attraction may be 
perform'd by impulse, or by some other means unknown to me. 

The first step in scientific research, as carried on by Galileo and 
Newton, is to examine known facts and frame a hypothesis to reduce 
them to order the process of induction. The logical consequences 
of the hypothesis must then be deduced by mathematics or otherwise 
and compared with observation or experiment. If they agree, the 
hypothesis may be called a theory, and used to suggest further 
inquiry, observation and experiment, for, as has been well said, the 


larger becomes the sphere of knowledge, the greater grows its area 
of contact with the unknown. 

Newton's dynamics and astronomy involve the ideas of absolute 
space and time, though we can see now, in our era of relativity, that 
those ideas do not necessarily follow from the phenomena. Newton 
also, like Galileo, accepted the atomic theory, though the time had 
not yet come to put it in the definite numerical form framed by 
Dalton a century later. 

The work of Galileo and Newton, which went so far to express 
dynamical and even some physical phenomena in terms of time, 
space and moving particles of matter, undoubtedly suggested, when 
translated into philosophy, a mechanical or materialist creed, and, 
as we shall see later, this was its outcome in the eighteenth century, 
especially in France, where it helped forward first deism and then 
atheism. But to Newton and his contemporaries that conclusion 
would have been quite foreign. Firstly, Newton himself, as shown 
above, clearly distinguished between a successful mathematical 
description of natural phenomena and a philosophical explanation 
of their causes. Secondly, Newton and his immediate followers 
regarded the new discoveries as a revelation of the power and wisdom 
of God. Newton wrote: 

This most beautiful System of the Sun, Planets and Comets could 
only proceed from the counsel and dominion of an intelligent and 
powerful Being. . . God . . . endures for ever and is everywhere present, 
and, by existing always and everywhere, he constitutes duration and 

Thus to Newton God is not only a First Cause, but is also immanent 
in Nature. Newton sums up : 

All these things being considered, it seems probable to me that 
God in the Beginning formed matter in solid, massy, hard, impene- 
trable, moveable 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. 

During his early years in Cambridge, while he 'minded Mathe- 
matics and Philosophy', Newton studied mystical writings and much 
theological literature as well as treatises on alchemy, which often 


showed mystical leanings. His theological opinions were unorthodox, 
and, though he was a Fellow of his College, he never took Holy 
Orders. But it is clear that he had a firm belief in God, and felt the 
utmost confidence that his scientific work went to confirm that belief. 

Newton in London. Newton played an important part in 
defending the University against the attack on its independence by 
James II. He was elected to the Convention Parliament which 
settled the succession of the Crown, and was again elected in 1701. 

In 1693 ne suffered from a nervous breakdown, and his friends 
decided that it would be well for him to leave Cambridge. They 
obtained for him the post of Warden of the Mint, and later he became 
Master, the highest office there. He gave up his chemical and 
alchemical researches, and put the papers concerning them into a 
locked box. 

His move to London marked a complete change in his life. His 
scientific achievements won for him a pre-eminent position, and for 
twenty-four years, from 1 703 till his death, he was President of the 
Royal Society, which gained much authority by his unique powers 
and reputation. In spite of the absence of mind which marked his 
early years, his work at the Mint showed that he had become an 
able and efficient man of affairs, though he was always nervously 
intolerant of criticism or opposition. 

His niece Catherine Barton, a witty and beautiful woman, kept 
house for him, and it was on this second part of his life that the 
eighteenth century built up its Newtonian legend. Catherine married 
John Conduitt; their only child became the wife of Viscount 
Lymington and the Lymingtons' son succeeded to the Earldom of 
Portsmouth. Thus Newton's belongings passed into the possession 
of the Wallop family. 1 

1 In 1872 the fifth Lord Portsmouth gave some of Newton's scientific papers to 
the Cambridge University Library. At a later date some more of his books and 
papers were sold. Part of the papers were acquired by Lord Keynes; the books 
were bought by the Pilgrim Trust, and have now (1943) been presented to 
Trinity College. 


Philosophy. Some writers of the time of Newton and after, 
writers who were primarily philosophers, either touched explicitly 
on science, or, at all events, dealt with branches of philosophy with 
scientific implications. Of these men John Locke (1632-1704), 
though most of his life fell in the seventeenth century, belonged in 
spirit to a later age, and may well serve to introduce it. 

Locke practised as a physician; he wrote against Scholastic ideas 
in medicine and in favour of observation as used by his friend 
Dr Sydenham. But Locke's chief work was his Essay Concerning 
Human Understanding, in which he argues that thoughts are due to 
experience, either sensations of external things, or reflexions on the 
operations of our minds. We know nothing of substances except their 
attributes, and those only from sense impressions. When these attri- 
butes show themselves in a constant connexion, we gain the idea of 
an underlying substance, the existence of which in some form seems to 
Locke a fair inference from our success in co-ordinating appearances. 
To fix abstract ideas by means of words involves danger, because the 
meaning of words may change an early criticism of language. 
Locke also began introspective psychology, watching steadily the 
operations of his own mind. He concluded that knowledge is the 
discernment of agreement, either of our thoughts among themselves 
or with external phenomena; but these external relations can only 
be established by induction from specific instances, and a knowledge 
of nature can only be an affair of probability, liable to be upset by 
new facts. In political, philosophic and religious thought, Locke 
upheld a moderate and rational liberalism. He insisted on the 
toleration of various religious opinions in that age a great proof of 

Newton's science and Locke's philosophy together led George 
Berkeley, Bishop of Cloyne, to accept the Newtonian picture of the 
world, but to point out that it is only a picture of the world revealed 
by the senses, and only the senses which make it real; the material 
world is made real only by being apprehended by some living mind. 


God must exist, because the material world to be a real world in 
the absence of human minds needs to be continually realized and 
regulated by Him. 

To the plain man this seems a denial of the existence of matter. It 
has led to much criticism, good and bad, beginning with Dr Johnson, 
who thought he could refute Berkeley by kicking a stone, and con- 
tinuing till it inspired a recent writer of Limericks. But it does seem 
true that the world we know is only made real by the senses; we cannot 
know the world of reality which may or may not lie beneath, though, 
with Locke, we may think its existence a fair inference from the 
knowledge of appearance revealed by the senses. 

David Hume (1711-1776) went farther and denied reality to 
mind as well as to matter; all that he left real was a succession of 
4 impressions and ideas '. He argued that the empiricists, in appealing 
exclusively to sense experience, made it impossible to pass to the 
inductive inference of universal laws. Hume held that to look on 
one happening as the cause of another is merely an instinct, perhaps 
founded on coincidence and unwarranted. Both Locke and Hume 
regarded metaphysical reality as beyond the reach of human reason. 
Hume also separated reason and faith, as the late mediaevalists 
revolted against the rational synthesis of Scholasticism. 

Scepticism as regards the possibility of a knowledge of reality was 
held also by Kant (1724-1804) and extended to all the principles of 1 
science and philosophy. The world of science is the world revealed 
by the senses, the world of appearance, not necessarily the world of 
ultimate reality. Leibniz thought that pure reason could unfold 
external, unchanging truth; Kant set himself to save as much of 
Leibniz's pure reason as Hume had left standing. Kant maintained 
we could still believe that the moral sense is as real as the starry 
heaven, indeed more real, the one form in which reality discloses 
itself to the human mind. 

Leaving the writings of the professional philosophers, we turn to 
the influence of the Newtonian system on the general thought of the 
eighteenth century, especially in France, where it found its way into 
the famous Encyclopedic. As we have seen, Newton and his friends 


regarded his picture of the Universe as a revelation of the glory of 
God, and biologists such as Ray echoed their words; but it must be 
confessed that Newton's work produced a very different effect on 
Voltaire and those of a like way of thinking. Their general wave of 
sceptical religious thought got a powerful reinforcement from 
Newton's success in explaining the mechanism of the heavens, and 
from the possibility of extending similar mechanical principles to 
other branches of science. Naturally they exaggerated: Laplace 
conceived a mind able to foretell the progress of nature for all eternity 
if but the masses and their velocities were given. Few would be so 
bold nowadays, when a principle of indeterminacy is hovering over 
the perplexed thoughts of physicists. But Voltaire wrote 

It would be very singular that all nature, all the planets, should 
obey eternal laws, and that there should be a little animal, five feet 
high, who, in contempt of these laws, could act as he pleased, solely 
according to his caprice. 

Voltaire ignored the problems of the meaning of natural laws, of 
the functions of life and of the human mind, and the possible scope 
still left for free will. But doubtless he was expressing vividly the 
current French opinions about the philosophic and religious bearings 
of Newtonian science. Laplace told Napoleon that he had no need 
of the hypothesis of a Creator, though Lagrange made the cpmment 
that it was a good hypothesis, it explained many things. In England, 
where the eighteenth-century Church was tolerant, and men more 
used to holding simultaneously beliefs at the moment apparently 
incompatible, the mechanical outlook never became so common 
as in more logical lands. Newton's countrymen for the most part 
accepted both Newton's science and their accustomed religion; the 
idea of antagonism only became prevalent in the nineteenth century. 

Meanwhile in France a current of popular thought was running 
towards materialism, a philosophy easily understood, as old as the 
Greek Atomists and recently expounded by Hobbes. The word 
materialism is often used in a loose sense to mean atheism, or indeed 
any view we dislike. But here it is used in its strict meaning a belief 
that dead matter in the form of solid impenetrable Newtonian 
particles (or perhaps of their modern derivatives) is the sole ultimate 


reality; that thought and consciousness are but by-products of 

The allied, but not identical, theory of mechanical determinism 
was also taken over by the French materialists, while Holbach argued 
that, since man, a material being, thinks, matter itself is capable of 
thought. This seems an assumption of the very thing to be explained, 
a mere restatement of the problem. For rough, everyday work, and 
for investigating the details of science, an assumption of materialism 
is useful, but there is danger that it should be taken as the philosophy 
of science as a whole, and gain the prestige which the success of 
science gives. In fact, matter, like all other concepts of science, is 
only known to us through its effect on our senses, and we are brought 
back to the problem of knowledge. Even in the eighteenth century, 
Locke, Berkeley and Hume had shown that materialism, at all 
events in its then form, should have failed to satisfy. We shall meet 
materialism again, especially in Germany, during the nineteenth 

Mathematics and Astronomy. A controversy about priority 
between Newton and Leibniz caused an unfortunate separation 
between English and Continental mathematicians. The Englishmen, 
using either geometry or Newton's method of fluxions, did com- 
paratively little towards developing the differential calculus and its 
consequences, which were carried forward abroad by James Ber- 
nouilli, Euler and others. But useful results were obtained in England 
by Taylor and Maclaurin in the expansion of certain mathematical 

Newton's work was made known in France especially by Mauper- 
tuis, while Voltaire wrote a popular account. For a time France was 
the chief centre of scientific activity. Lagrange (1736-1813) created 
the calculus of variations, and systematized the subject of differential 
equations work which proved of use in physical and astronomical 
problems. In his treatise Mfchanique Analytique he treated the whole 
of mechanics on the principles of conservation of energy and virtual 
velocity what is gained in power is lost in speed. Maupertuis gave 
the name of 'action' to the sum of the products of space (or length) 

DSH 6 


and velocity, and showed that light always went by the path of least 
action. We shall meet an allied form of 'action 5 in quantum physics. 
The Newtonian system was extended by Pierre Simon Laplace 
(1749-1827), who, beginning as the son of a cottager, skilfully guided 
himself to end as a Marquis of the Restoration. He treated problems 
of attraction by Lagrange's method, and proved that the solar 
system was stable, perturbations of one planet due to other planets 
or comets being only temporary and correcting themselves. He 
framed a nebular theory, whereby the system of Sun and planets was 
formed from a rotating mass of incandescent gas, an idea which had 
also occurred to Kant. Modern investigation shows that the theory 
fails for the solar system, but may be true for the much largtr 
aggregates of stars seen in formation in spiral nebulae. 

Newton had shown that the velocity of a wave is equal to the square 
root of the elasticity concerned divided by the density. Taking the 
usual elasticity of air, this formula gives too small a figure for the 
velocity of sound. Laplace traced the discrepancy to heat, which, 
developed by the sudden compression and absorbed by the following 
expansion, increases the elasticity of air and therefore the velocity of 

Gravitational astronomy has followed the lines laid down by 
Newton and Laplace. An apparently final test was given in 1846 by 
the successful prediction by J. C. Adams and Leverrier of the presence 
of an unknown planet, afterwards called Neptune, from the per- 
turbations of another, Uranus. The success of Newton's formulation 
is astonishing; it is only the most powerful modern apparatus that 
can show certain minute discrepancies in favour of Einstein. But, 
to a very high degree of accuracy, Newton's work stands; it is 
absorbed in something wider but not superseded. It was completed 
in another direction by the determination of the gravitational con- 
stant: Maskelyne observed the deviation of the plumb-line on the 
opposite sides of a mountain, and Henry Cavendish ( 1 73 1-1810), used 
Michell's torsion balance to measure the attraction between two balls. 
Kepler's observations gave a model of the solar system, but the 
scale of the model was not known till some one distance had been 
measured in terrestrial units. We shall give recent values in a later 


chapter; but fairly good results were found by Richer in 1672 
(p. 88). Among other results was an estimation of the velocity of 
light by Bradley in 1729 from the aberration of the stars as the Earth 
moves in its orbit. 

Chemistry. In the early years of the eighteenth century Hom- 
berg, linking with the ideas of Sylvius, studied the reactions of acids 
and alkalies to form salts work which afterwards led to theories of 
chemical structure. In 1732 Boerhaave of Leyden published the best 
chemical treatise of the time and thus helped to co-ordinate existing 

Most early work on chemistry sprang from a desire to explain the 
phenomena of flame. When bodies are burnt, it seems that something 
escapes. This something, for long called sulphur, was given the name! 
of * phlogiston', the principle of fire, by Stahl (1660-1734), physician' 
to the king of Prussia. Rey and Boyle had shown that when metals 
were burnt the solid increased in weight; thus, as Venel pointed out, 
phlogiston must possess a negative weight a return to Aristotle's 
idea of a body essentially light. Chemistry, ignoring the achieve- 
ments of physics, learned to express itself in terms of phlogiston, 
which dominated the chemical thought of the latter part of the 
eighteenth century. 

Meanwhile many new substances were discovered. Oxygen had 
been obtained from saltpetre by Borch in 1678, and it was again 
prepared and collected over water in 1 729 by Hales, who still thought 
it was air modified by the presence of some other substance. But 
about 1 755 Joseph Black of Edinburgh discovered that a new pon- 
derable gas, distinct from air, was combined in the alkalies. He 
described it as 'fixed air' ; it was what we now call carbon dioxide or 
carbonic acid. In 1774 Scheele discovered chlorine. Joseph Priestley 
(1733-1804) prepared oxygen by heating mercuric oxide, and redis- 
covered its unique power of supporting combustion and respiration. 
Cavendish demonstrated the compound nature of water in 1781, 
thus finally banishing it from the list of elements, though he still 
called its constituent gases phlogiston and dephlogisticated air. 

Thus we see men of the eighteenth century collecting chemical 



facts and slowly feeling their way forward under the hampering 
restriction of false assumptions and theories, till there came the hour 
and the man. Antoine Laurent Lavoisier (1743-1794)? who was 
guillotined with other farmers of the taxes because ' the Republic had 
no need of savants', had repeated the experiments of Priestley and 
Cavendish, weighing accurately his reagents and products. He 
found that, though matter may alter its form and properties in a 
series of chemical actions, its total amount as measured by the balance 
is unchanged. The constituents of water, which Lavoisier named 
hydrogen and oxygen, were gases with the ordinary properties of 
mass and weight. The concept of phlogiston with its negative weight 
vanished from science, and the principles of Galileo and Newton were 
carried over into chemistry. 

Physiology, Zoology and Botany. The physiology of breathing 
and its connexion with combustion had been studied in the seven- 
teenth century, specially by Boyle, Hooke, Lower and Mayow. They 
proved that air is not homogeneous, but contains an active principle 
spiritus nitro~aereus needed both for breathing and burning, our 
modern oxygen. Metals when burned increase in weight by the 
absorption of this spirit. Lower showed that the change in the colour 
of blood from purple to red took place not in the heart but in the 
lungs, where the blood came into contact with air and absorbed its 
vital particles. Much of this sound work was forgotten till the 
chemical facts and their interpretation were rediscovered in the 
eighteenth century by Priestley and Lavoisier. 

We have seen that Sylvius threw over van Helmont's spiritualistic 
ideas of the control of the body by a sensitive soul working through 
archaei) and tried to explain bodily functions by effervescences of the 
same kind as that produced when vitriol is poured on to chalk. 

But the pendulum now swung the other way. Stahl maintained 
that changes in the living body were fundamentally different from 
ordinary chemical reactions, being governed by a sensitive soul on 
a plane above physics and chemistry. Sensation and its concomitants 
are modes of motion directed by the sensitive soul. Stahl was a 
forerunner of modern vitalists, though they found it necessary to 


convert his very definite * sensitive soul' into a much vaguer * vital 

These physiological questions were discussed in Institution's Medicae 
(1708) by Boerhaave, one of the greatest physicians of modern times. 
Blood pressure was first measured by Hales, who also after Ray 
investigated the pressure of the sap in trees. 

One new practice introduced in the eighteenth century is important, 
among other reasons, because it foreshadowed modern methods of 
securing immunity from specific diseases. In 1718 Lady Mary 
Wortley Montagu introduced from Constantinople the practice of 
inoculation for small-pox with pus from a light case, and thus began 
the control of one of the most prevalent and deadly of diseases.' 
Towards the end of the century, Benjamin Jesty acted on the common 
belief that dairymaids who suffered from the lighter cow-pox did not 
catch small-pox. Apparently independently, Edward Jenner, a 
country doctor at Berkeley, investigated the subject scientifically, 
and devised the method of vaccination, whereby the benefits of 
immunity are obtained without the risks involved in the older process 
of inoculation from small-pox itself. 

It has been said that the year 1 757 marks the dividing line between 
modern physiology and all that went before, because in that year 
was published the first volume of the Elementa Physiologiae of Albrecht 
von Haller (1708-1777), the eighth and last volume appearing in 
1 765. In this great work Haller gives a systematic account of the then 
state of physiological knowledge. He himself studied the mechanics 
of respiration, the development of the embryo and muscular irri- 
tability. From observation of disease and experiments on animals, 
he concluded that the nerves alone feel; they are therefore the only 
instruments of sensation, as, by their action on the muscles, they are 
the only instruments of motion. All nerves are gathered into the 
medulla cerebri in the central parts of the brain, so it too must feel and 
present to the mind the impressions which the nerves have collected 
and brought. Von Haller thought the nerves were tubes containing 
a special fluid, and that, since sensation and movement have their 
source in the medulla of the brain, the medulla is the seat of the 


About this time there was an increase in the number of animals 
obtained for royal menageries, and Buffon (1707-1788) wrote a 
comprehensive Natural History of Animals. He regarded a classi- 
fication which placed man among animals as c une verite humiliante 
pour 1'homme', but said that had it not been for the express state- 
ments in the Bible, one might be tempted to seek a common origin 
for the horse and the ass, the man and the monkey. 

The microscope threw new light on the structure and functions of 
the organs of animals, and also revealed the existence of vast numbers 
of minute living beings both animal and vegetable. In ancient and 
mediaeval times, men believed that living things might arise spon- 
taneously, frogs, for instance, by the action of sunshine on mud. But 
doubts had been raised by Redi, who showed that, if the flesh of a 
dead animal were protected from insects, no grubs or maggots 
appeared in it. Redi's work was repeated by the Abbe Spallanzani 
(1729-1799), who moreover proved that not even minute forms of 
life appeared in decoctions first boiled and then protected from the air. 

The application in the seventeenth century of the microscope to 
the study of plants, especially by Grew and Malpighi, began to give 
correct ideas about their structure. In 1676 Grew recognized the 
stamens as the male organs, referring the original idea to Sir Thomas 
Millington. Others followed, making it clear that, in the absence of 
pollen from the stamens, no fertilization of the ovum or setting of 
seed is possible. 

A recent biography by Dr C. E. Raven has made clear the 
important part played by John Ray (1627-1705), botanist, zoologist, 
the first scientific entomologist and a writer on the relations between 
religion and science. Ray gave up his Fellowship and other offices 
at Trinity College, Cambridge, because, though he had not signed 
the Covenant and remained a Churchman, he did not approve the 
Act of Uniformity. He left Cambridge and retired to his birthplace, 
Black Notley in Essex. He travelled through the counties of England 
and through parts of Europe, often with Francis Willughby, studying 
and making lists of the plants and animals. He also wrote many 
books, among them a History of Plants, a History of Insects and Synopses. 


of animals, birds, reptiles and fishes. In his books on plants he paid 
special attention to their medicinal qualities. 

In flowering plants the first leaves growing from the embryo, since 
termed cotyledons, are either single, as in grasses and lilies, or double, 
as in trees and many other plants. Ray recognized the importance 
of this difference between monocotyledons and dicotyledons as 
dividing flowering plants into two great groups, and much improved 
classification in other ways, using all characters fruit, flower, leaf, 
etc. in order to group together plants with real natural affinities. 
As regards animals, Ray not only studied their external characters 
but also their comparative anatomy. He examined fossils, and 
concluded that they 'were originally the shells or bones of living 
fishes and other animals bred in the sea' an enlightened view at 
a time when fossils were generally regarded either as due to a vague 
'plastic force' in nature or as deposited by Noah's deluge. 

He rejected magic and witchcraft, and all superstitious explanations 
of occurrences, holding to natural causes as revealed by observation. 
Ray's philosophy is shown in his book The Wisdom of God in the Works 
of Creation, in which, as a biologist, he supports the view of Newton 
and his disciples as astronomers. Together they succeeded in banishing 
the idea, continually recurring from Augustine to Luther, that nature 
is on a plane irrelevant if not hostile to religion, its beauty a tempta- 
tion, its study a waste of time. But Ray writes : 

There is no occupation more worthy and delightful than to 
template the beauteous works of nature and honour the infinite 
wisdom and goodness of God, 


In systematic botany Ray was followed by Linnaeus (Carl von 
Linne*, 1707-1778), who framed a convenient scheme of double 
nomenclature and founded a system of classification on the sex-organs 
of plants, a system that endured till replaced by the modern plan 
which, returning in the light of evolution to the ideas of Ray, tries 
to group plants in their natural relations by a study of all their 
characters. Linnaeus also dealt with the varieties of men, placing 
them with apes, lemurs and bats in an order of 'Primates', and 
dividing them into four groups by skin colour and other differences. 


It was partly Ray's work which inspired Gilbert White (1720- 
1793), naturalist, who, after a long study of animals and plants 
round his home in Hampshire, published in 1 789 a famous literary 
English classic The Natural History ofSelborne. These two, Ray and 
White, helped the development of our English love of the country 
and its life which shines so clearly from Gilbert White of Selborne 
to Edward Grey of Fallodon. 

Unfortunately at this time there was little intercourse between men 
of science and practical gardeners and breeders, who by hybridization 
and selection were producing new varieties of plants and animals. 
To horticulturalists the spontaneous appearance of large variations 
was well known. In animals Bakewell improved by selection the old 
long-horned cattle and Leicester sheep, while the brothers Colling 
established the famous shorthorn breed of cattle. The knowledge of 
these men would have been of great scientific value to biologists. . 

Geography and Geology. In the seventeenth and eighteenth 
centuries systematic exploration of the world began to be put on a 
scientific basis. Apparently the first man sent on a voyage to carry 
out definite astronomical measurements was Jean Richer, who went 
to Cayenne in French Guiana in 1672-3 under the auspices of 
Colbert, the famous Minister of Louis XIV, { to make astronomical 
observations of utility to navigation 5 . The chief problems set were 
the movements of the Sun and planets, refraction and parallax. From 
the known relative distances, these observations would give the 
absolute distances, and the most striking of Richer's results was the 
revelation of the enormous sizes* of the Sun and the larger planets 
and the dimensions of the solar system itself: the Earth and man on 
it shrank into insignificance. These measurements, together with 
Picard's new and more correct estimation of the Earth's diameter, 
did much to increase the accuracy of astronomical knowledge. 

Some years later, William Dampier (1651-1715), after early 
voyages, went to Jamaica and, for a time, perforce sailed with the 
buccaneers. He crossed the Pacific Ocean and came home by way 
of Sumatra and Madras. He kept a Journal, and in 1697 published 
a Book of Voyages which had a phenomenal success. In 1698 he 


was commissioned by the Admiralty to command the ship Roebuck 
in exploring 'New Holland', that is Australia. The ship was small 
and in bad condition; it sank off the island of Ascension on the way 
home. Nevertheless this was the first voyage planned in England for 
the purpose of scientific exploration. Dampier not only recorded 
accurate observations on physical geography, flora and fauna, but 
he also increased existing knowledge of hydrography, meteorology 
and terrestrial magnetism. 

Dampier's books of voyages set the fashion for a flood of travel 
literature, beginning with Defoe's Robinson Crusoe and Swift's Gulliver's 
Travels. The voyages of Dampier, Cabot and others helped intel- 
lectual development, especially in France, and led to writings about 
island Utopias, Le Bon Sauvage and other such fancies. In England 
the story of the Garden of Eden also contributed to the growth of 
the idea that men of old were better than now, and the ' noble savage ' 
a finer being than civilized man ideas false indeed, but leading 
later to the scientific study of anthropology. 

Thus interest in exploration steadily increased, and, at the instance 
of the Royal Society, James Cook (1728-1779) was sent out in 1768 
by the Admiralty in command of the ship Endeavour to observe a 
transit of Venus at Tahiti in the South Pacific, having on board two 
men of science, Banks 1 and Solander. Cook's later voyages of dis- 
covery, undertaken to find an antarctic continent, failed in this object, 
but gave other information of scientific value, as well as new know- 
ledge of the coasts of Australia and New Zealand and of the Pacific 
Ocean. In the earlier voyage, thirty men died out of eighty-five, 
chiefly from scurvy; in the latter only one died of disease out of 1 18. 
Cook and his surgeon took many precautions, including oranges and 
lemons for the crew and other fresh food when available. 

Meanwhile the science and art of navigation were much improved. 
The determination of latitude is fairly simple by observation of the 
mid-day altitude of the Sun, but longitude could only be found when 
the position of the Moon could be predicted by Newton's lunar 

1 Afterwards Sir Joseph Banks, a man of fortune and an enthusiastic systematic 
botanist, who filled the Presidential Chair of the Royal Society for forty-two years, 
a longer term than that of anyone else in its history. 


theory, and only made easy and accurate when John Harrison 
improved the chronometer in 1761-2 by compensating the effect of 
changes in temperature by the unequal expansion of two metals. 
Greenwich time could then be taken on board each ship and com- 
pared with astronomical events. 

All this growing knowledge of the Earth led naturally to a study 
of its structure, and to speculation about its history, in fact, to 
Geology. The large collection of John Woodward, left in 1728 by 
him to Cambridge University, did much to show, as already held 
by Leonardo, Ray and others, that fossils were animal and vegetable 
remains. In 1674 Perrault had proved that the rain falling on the 
ground was enough to explain the flow of springs and rivers, and 
Guettard (1715-1786) pointed out how much observed weathering 
changed the face of the Earth. But the facts were still forced into 
conformity with Biblical Cosmogonies involving cataclysmic origins 
by fire or flood. 

James Hutton, a Scottish landowner and farmer, after studying 
land at home and abroad, published in 1785 a Theory of the Earth in 
which he showed that the stratification of rocks and the embedding 
of fossils were still going on in sea, river and lake. 'No powers are to 
be employed that are not natural to the globe, no actions to be 
admitted except those of which we know the principle', a precept 
known as Hutton's Uniformitarian Theory. 

After Hutton, William Smith assigned relative ages to rocks by 
noting their fossilized contents, and Cuvier reconstructed extinct 
mammals from fossils and bones, comparing existing animals with 
fossil forms, thus showing that the past as well as the present must 
be brought into account in studying the development of living 

Machinery. The most important practical invention of the 
eighteenth century was the steam-engine, which in the nineteenth 
revolutionized transport. The steam-engine was produced and im- 
proved by empirical methods; it cannot be claimed that its invention 
was due to the application of^cientific principles. The first practical 
stationary steam-engine was due to Newcomen; it was improved by 


Smeaton and principally used for pumping in the Cornish mines. 
The chief drawback to these early models was the waste involved in 
cooling the steam-cylinder at each stroke, and the steam-engine only 
became reasonably efficient when James Watt in 1 777 used a separate 
condensing cylinder kept always cold, and soon after converted linear 
into rotary motion by a crank shaft. Several primitive paddle-boats 
foreshadowed the steam-ships of the next century. Land transport 
was made much easier by better roads, on which fast stage coaches 
and well-made waggons were replacing the saddle and pack-horses 
of earlier times. 

Building was facilitated by measurement of the strength of 
materials; processes for bleaching and dyeing improved in the light 
of growing chemical knowledge and weaving machinery was much 
developed. The great changes in agriculture were chiefly due to the 
enclosures going on, whereby mediaeval methods of joint cultivation 
passed into modern systems of rotation of crops carried out on separate 
farms. Ploughs were improved, a primitive form of reaper tried, and 
a drill for sowing corn in rows designed by Jethro Tull. 

This summary, of course, is not meant to be complete; it deals only 
with a few of the more important advances. During the eighteenth 
century the arts of life were developed in countless directions, but 
the changes, though great, were not revolutionary; the face of 
England was little altered. 


The Scientific Age. The greatest difference between the nine- 
teenth century and those that came before, at least in the subjects of 
the present book, is to be sought in the change in the relative position 
of science and industry. Hitherto invention and other improvements 
in the arts of life had proceeded for the most part independently of 
science, or set the pace for science to follow and problems for science 
to solve. The instances where science led the way and practice 
followed, as, for example, in improvements in navigation, are few in 
number; but in the nineteenth century they become numerous. 
A scientific knowledge of electricity led to the electric telegraph, 
Faraday's experiments in electro-magnetism to the dynamo and the 
great industry" of electrical engineering, and Maxwell's electro- 
magnetic equations, after fifty years' experiment, to wireless telephony 
and broadcasting. These instances are but examples taken from one 
department of science; they could be multiplied almost indefinitely; 
the nineteenth century was the beginning of the scientific age. 

Science itself made great advances, especially in physics and 
chemistry. In their various branches the explanations of new dis- 
coveries fitted together, giving confidence in the Whole, and it came 
to be believed that the main lines of scientific theory had been laid 
down once for all, and that it. only remained to carry measurements 
to the higher degree of accuracy represented by another decimal 
place, and to frame some reasonably credible theory of the structure 
of the luminiferous aether. But from 1895 onwards X-rays, electrons, 
quanta and relativity produced a complete revolution in physical 
science. It became clear that Newtonian and nineteenth-century 
physics were only valid within certain limits of size and velocity; 
below atomic dimensions and at velocities approaching that of light, 
the former ideas failed, and a wider generalization became necessary, 
in which the older scheme appeared as a special case, applicable to 
large-scale phenomena and slowly moving masses. 


To construct a quantitative science, definite units are necessary. 
The multiplicity of weights and measures, by which Britain is still 
afflicted, was replaced in France by a logical jecimal system. Begin- 
ning in 1791, the measurements and legislation were finished by 
1799, and the system made compulsory as from 1820, not perhaps 
with complete success. 

The unit of length, the metre, was meant to be the ten millionth 
part of an earth quadrant, but practically it is the distance between 
two marks made on a certain metallic bar. The kilogram, meant to 
be the weight of a cubic decimetre of water, is now a mass equal to 
that of a platinum-iridium standard made in 1 799. The second is 
defined as the 1/86,400 part of the mean solar day. Although the 
first two are now known to be not exactly what was meant, they are 
near enough for most practical purposes. 

About 1870 it was agreed to use for scientific measurements the 
centimetre (one hundredth part of a metre), the gram (one thousandth 
part of a kilogram) and the second; this is usually known as the 
C.G.S. system of units. 

From these units others are derived. That of velocity is one centi- 
metre per second, with dimensions length divided by time L/T, 
acceleration L/T 2 , force ML/T 2 , the unit being that needed to give 
the mass of one gram unit acceleration and called the dyne, while 
energy is force multiplied by length, ML 2 /T 2 , the c.o.s. unit being 
called the erg. Electric and magnetic units also were built up by 
Gauss on this basis. 

Heat and Energy. The scientific concept of heat is derived from 
our sense-perception, and the thermometer enables us to define a 
scale with which to measure its intensity. Galileo invented the first 
thermometer and Amontons first used mercury. Different scales 
were introduced by Fahrenheit, Reaumur and Celsius. The idea of 
heat as a quantity was suggested by observation in distilleries, but it 
was Joseph Black (1728-1799) who cleared up the still existing con- 
fusion between heat and temperature, calling them quantity and 
intensity of heat. He studied the change of state from ice to water 
and water to steam, finding that, in each change, much heat was 


absorbed with no rise in temperature ; heat, as he said, was rendered 
latent. He explained the different amounts of heat needed by different 
substances to produce the same rise in temperature by assigning to 
each substance a * specific heat', and showed how to measure quan- 
tities of heat in a calorimeter a vessel containing a known weight 
of water with a thermometer immersed in it. 

It is evident that these experiments needed a theory of heat laying 
stress on the idea of a quantity which remained constant as the heat 
passed from one body to another. Although Cavendish, Boyle and 
Newton had regarded heat as a vibratory motion of the particles of 
substances, that view did not lend itself, before the days of the theory 
of energy, to the idea of a quantity remaining constant. It was better 
to take the alternative hypothesis that heat was a subtle, invisible, 
weightless fluid, passing freely between the particles of bodies, and 
this caloric theory served well till the middle years of the century. 
Sometimes science can be advanced better by a false hypothesis 
which meets the immediate needs of the time. 

The calorists explained the heat developed by friction by sup- 
posing that the filings or abrasions, or the main body after friction, 
had a less specific heat, so that heat was, as it were, squeezed out. 
Though the American Benjamin Thompson, who in Bavaria blos- 
somed forth as Count Rumford, had shown in 1798 by experiments 
on the boring of cannon that the heat developed was proportional 
to the work done, and had no relation to the amount of shavings, 
his work was forgotten or ignored, and the caloric theory flourished. 

But by 1840 it had become apparent that some of the powers of 
nature were mutually convertible. Assuming that when air is com- 
pressed all the work appears as heat, J. R. Mayer calculated the 
mechanical equivalent of a unit of heat. Sir W. R. Grove, Judge 
and man of science, wrote on the Correlation of Physical Forces, and 
von Helmholtz (1821-1894), the great German mathematician, 
physicist and physiologist, published Ueber die Erkaltung der Kraft. 
The idea of correlation was in the air, 

, tfrom 1840 to 1850 James Prescott Joule (1818-1889) was engaged 
in measuring experimentally the heat liberated by mechanical and 
electrical work. He found that, however the work was done, the 


expenditure of the same amount of work produced the same quantity 
of heat. To warm one pound of water through one degree Fahrenheit 
needed about 772 foot pounds of work a figure afterwards corrected 
to 778. 

A troublesome double meaning in the word 'force', which had 
been pointed out by Young, was cleared up when Rankine and 
William Thomson (Lord Kelvin, 1824-1907) used the word 'energy 5 
in a specialized sense to denote the power of doing work, and 
measured, if the transformation is complete, by the work done. 
Joule's experiments showed that the total amount of energy in an 
isolated system is constant, the quantity lost in work reappearing as 
heat. Thus the somewhat vague ' correlation of forces ' became the 
quite definite 'conservation of energy'. 

It is well to compare this result with the constancy of mass in 
Newtonian dynamics and in the chemistry of Lavoisier. When we 
strive to bring order into a welter of unco-ordinated phenomena, to 
start, that is, a new science, quantities that have this character of 
permanence inevitably obtrude themselves in our minds. We use 
them to frame our explanatory scheme, as mass is used in dynamics 
and chemistry. In studying the relations of heat and work within 
the limits of the older physics, another quantity emerges, chiefly 
because of its constancy. We call it energy ; use it in our investigations, 
and laboriously and doubtfully Joule rediscovers its constancy. And 
so we learn to recognize the conservation of energy as the first law 
of thermodynamics and place it alongside the conservation of mass. 
This was a great discovery, but it had its dangers ; some men believed 
that matter was indestructible and eternal; the amount of energy in 
the Universe constant and immutable. The principles were converted 
from safe guides for a few steps in empirical science into metaphysical 
dogmas of doubtful validity. We shall see in the sequel reasons to 
suppose that a new outlook on these subjects has become necessary. 

If heat is a form of energy, accepted from Joule's work, it must 
consist in motion of the molecules. This kinetic theory, given in early 
forms by Bernouilli, Waterston and Joule, was first adequately 
expounded by Clausius in 1857. 


The chances of molecular collision will produce molecules moving 
in all directions with all velocities, the average value of which was 
calculated by Joule; for hydrogen it is 1844 metres (more than a mile) 
a second, and for oxygen 461 metres. But Maxwell and Boltzmann 
applied to the velocities a law of error derived by Laplace and by 
Gauss from Pascal's theory of probability. The number of molecules 

Fio. 1 1 . Curve of error 

moving within a certain range of velocity is shown by the diagram. 
The horizontal ordinate x denotes the velocity, and the vertical 
ordinate^ the number of molecules moving with it. It will be seen 
how fast the numbers fall off as we pass from the most probable 
value where the numbers are greatest. This curve of error and its 
modifications are now of great use in many branches of science. It is 
impossible to predict the velocity of a particular molecule or the 
length of life of an individual man, but, with a sufficient number of 
molecules or men, we can deal with them statistically, and say how 
many will move within certain velocities, or how many will die in 
a given year statistical determinism but individual uncertainty. 
Maxwell and Boltzmann also showed that, on the kinetic theory, 


the total energy of a molecule should be divided equally among its 
degrees of freedom, that is the number of co-ordinates needed to 
specify its position and condition. From this it follows that the ratio 
of the specific heats of a gas at constant pressure and at constant 
volume is 1-67 for three degrees of freedom and 1-4 for five figures 
confirmed experimentally for gases with monatomic and diatomic 
molecules respectively. 

Boyle's law, which states that the volume of a gas varies inversely 
as the pressure, may be written as 

if temperature is also brought in. At high pressures or low tempera- 
tures gases depart from this ideal relation. Molecular attraction, 
which depends on the square of the density, or the inverse square of 

the volume, will convert p into p-^-^y and the volume b occupied 

by the molecules themselves will reduce the varying volume to v b. 
Thus Van der Waals in 1873 obtained the equation 

About 1869 Andrews investigated the continuity of the gaseous 
and liquid states, and showed that above a certain critical tempera- 
ture, characteristic of each gas, no pressure, however great, will cause 
liquefaction. Liquefaction then is a problem of cooling the gas below 
its critical point. With this knowledge, gas after gas was condensed, 1 
till Dewar liquefied hydrogen in 1898, and Kamerlingh Onnes 
liquefied helium, the last gas to surrender, in 1908. 

Thermodynamics. The study of heat and energy was naturally 
extended to elucidate the laws of heat-engines. In 1824 Sadi Garnot, 
the son of the ' Organiser of Victory ' in Republican France, imagined 
the simplest ideal case a frictionless engine in which there is no loss 
of heat by conduction, etc. The engine must be supposed taken round 
a complete cycle, so that the working substance, steam, air, or what- 
ever it be, is brought back to its initial state. Garnot's theory was put 
into modern form by Clausius and William Thomson. The latter 

DSH 7 


showed that all such ideal engines must have the same efficiency, 
independently of the form of the engine or the nature of the working 
substance, and depending only on the temperatures T of the source 
and t of the condenser. We may therefore use an imaginary ideal 
engine to define temperature, and say that the ratio of T to t is 
measured by the ratio of H to A, where H is the heat absorbed from 
the source, and h that given up to the condenser in the ideal engine. 

In this way Thomson obtained a thermodynamic or absolute scale 
of temperature. If all the heat is converted into work, t becomes 
zero, and we get an absolute zero of temperature, below which nothing 
can be cooled. He and Joule together, improving on an experiment 
carried out by Gay-Lussac in 1807, showed that when a gas expands 
without doing work the change of temperature is very small. This 
proved that the ideal scale of temperature was practically the same 
as the scale of the air or hydrogen thermometer, which can easily be 

When changes are going on between heat and other forms of 
energy, even in ideal conditions heat passes from hot to cold bodies, 
and, in actual conditions, there are irreversible losses by conduction 
and radiation as well. These observations can be put in various forms 
to express a second law of thermodynamics : e.g. { heat cannot of 
itself pass from a colder to a warmer body'. It follows that, in an 
isolated system, heat becomes less and less available for the per- 
formance of useful work. This process was named the dissipation of 
energy. It was put in a different but equivalent form by Clausius^ 
who showed that a mathematical function he named entrBpy^was 
always tending to increase, and when it reached a maximum an 
isolated system must be in equilibrium. From these results it was 
argued that finally all the energy of the Universe would run down 
into heat uniformly distributed, and no further conversion into other 
energies be possible in a dead Universe. This is a very big extension 
of the thesis, and we shall see later that recent discoveries have 
somewhat modified it. Moreover, even at the time one theoretical 
way of escape was found by James Clerk Maxwell (1831-1879), 
who pointed out that energy could be reconcentrated by a being, 
whom he called a demon, with faculties fine enough to follow and 


control individual molecules. By opening or shutting a frictionless 
trap-door, he (or she) could collect fast moving molecules on one 
side and slow ones on the other, and thus re-create a difference of 

Thermodynamics were carried farther by Willard Gibbs (1877) 
with equations which showed that, in a system not isolated but 
isothermal, that is kept at constant temperature, equilibrium is 
reached when another function, which he called the thermodynamic 
potential, is a minimum. 

By the use of these two functions, entropy and thermodynamic 
potential, together with an equation connecting latent heat with 
temperature, pressure and volume, it is possible to put the whole 
theory of physical and chemical equilibrium on a sound basis, the 
equilibrium between different phases being described by a Phase 

The Wave Theory of Light. Thomas Young (1773-1829) over- 
came some of the difficulties in the way of regarding light as waves 
in an aether. He studied the coloured or light and dark bands 
produced by the interference of two overlapping parts of a beam of 
light passed through two pin-holes in a screen. If one part has to 
travel half a wave-length farther than the other, the crest of one wave 
will coincide with the trough of the next, and the wave be there 
destroyed. From the dimensions of the apparatus and of the inter- 
ference bands, he calculated the wave-lengths, and found them to be 
about the one fifty thousandth part of an inch, very small compared 
with the sizes of ordinary obstacles. A mathematical investigation 
shows that for such small waves it is only elements in the direct path 
that produce an effect; the light travels in straight lines except at 
the edges of shadows. 

Hooke had suggested that the waves of light might be transverse 
to the direction of the beam, and this idea was taken up by Fresnel 
(1788-1827). The vibrations of ordinary light in a plane at right 
angles to the rays are complex, but in plane polarized light they are 
linear, and if a polariscope lets through one such ray it will not let 
through one polarized at right angles. Fresnel, Green, MacCullagh, 



Cauchy, Stokes and others developed the wave theory to a high 
degree, getting remarkable concordance between theory and experi- 

In order to carry the waves, a medium or aether had to be invented, 
and, to explain transverse vibrations, that aether must have rigidity. 
Many elastic solid theories of the aether followed, the chief difficulty 
being to accept at the same time rigidity and the absence of resistance 
to the motion of the planets. But when Maxwell showed that light 
was an electro-magnetic wave, the aether ceased to be necessarily 

Spectrum Analysis. Galileo and Newton showed that our 
dynamical laws hold good throughout the bodies of the solar system. 
To complete the proof of identity, it was necessary to show similarity 
in structure and composition an apparently hopeless task. 

In 1752 Melvill found that light from flames tinged with metals or 
salts when passed through a prism gave spectra of characteristic 
bright lines, and in 1823 Herschel suggested that such lines could be 
used as a test for the presence of the metals. This led to a long series 
of observations, in which spectral lines were mapped and recorded. 
Including the discovery of new elements, spectrum analysis has 
yielded many important results, culminating with the evidence on 
which rest our modern theories of atomic structure. 

In 1802 Wollaston discovered that the luminous band of the Sun's 
spectrum was crossed by a number of dark lines. In 1814 Fraunhofer 
rediscovered and mapped them carefully. Foucault, and indepen- 
dently Bunsen and Kirchhoff, showed that, if complete white light 
be passed through a flame containing sodium, the dark line called D 
appears explaining its presence in the solar spectrum. The intense 
light from within the Sun, passing through the cooler envelope, loses 
the sodium light. Many elements known to us on the Earth have 
thus been shown to occur in the Sun and stars. Conversely helium 
was first discovered in the Sun and afterwards found in a rare mineral 
on the Earth. As Stokes pointed out, the dark lines are an example 
of resonance; a system will absorb vibrations in tune with those it 
will itself emit. If a source of sound or light is approaching the 


observer, the frequency is increased, if receding it is lowered. This, 
called the 'Doppler' effect, is used to measure stellar velocities in 
the line of sight. The visible spectrum is only a small part of solar 
radiation. There are long infra-red heat-waves and short ultra-violet 
ones with intense chemical activity. (See also p. 148.) 

Spectra can be formed by gratings as well as by prisms. A grating 
is made by ruling a number of parallel scratches on a glass plate or 
on a metal mirror. At the correct angle, the scratches cut out all 
but appropriate waves, thus producing a spectrum. 

Maxwell showed that light should exert a minute pressure on a 
surface on which it falls, and this pressure has been demonstrated 
experimentally; it is of great importance in cosmical physics. It also 
allows thermodynamics to be applied to radiation, showing that a 
black body should radiate in proportion to the fourth power of the 
absolute temperature, as previously found practically by Stefan. 
From these results, theoretical and practical, the temperature of the 
surface of the Sun can be estimated by measuring the rate of emission 
of heat. 

Electric Currents. During the eighteenth century, many experi- 
ments were made on statical electricity obtained by friction, and its 
identity with lightning was demonstrated by Benjamin Franklin and 
others. The difference between conductors and insulators was also 
established, while Coulomb, Priestley and Cavendish proved that 
electric and magnetic forces diminished as the square of the distance. 
This enabled Gauss to include them with gravitation in a general 
mathematical treatment of the inverse square law. To Gauss we also 
owe a scientific system of electric units, for instance : a unit electric 
charge repels an equal similar charge at unit distance (one centi- 
metre) in air with unit force (one dyne). If air be replaced by another 
medium, the electric or magnetic forces will be diminished in a ratio 
called the dielectric constant or the magnetic permeability. 

In 1800 Volta of Pavia, extending an experiment of Galvani, found 
that a series of little cells containing brine or dilute acid, in which 
were dipped plates of zinc and copper, gave a current, proved by 
Wollaston to be electric, with tension much less than that of frictional 


electricity, and quantity much more. Nicholson and Carlisle showed 
that the current evolved hydrogen and oxygen when passed through 
water new and striking evidence for the compound nature of that 
substance, and the first experiment in electro-chemistry. The con- 
nexion thus revealed between electricity and chemistry caused much 
speculation. Berzelius regarded every compound as formed by the 
union of two oppositely electrified parts. In 1807 Sir Humphry Davy 
(1778-1829) decomposed soda and potash, thought to be elements, 
and separated the remarkable metals sodium and potassium. The 
products of decomposition appear only at the terminals, and Grotthus 
and Glausius explained that fact by imagining a free exchange of 
partners along lines through the liquid, the opposite atoms at the 
ends of the chain being set free. 

The next great advance was made by Michael Faraday (1791- 
1867), who had been Davy's assistant in the laboratory of the Royal 
Institution. Faraday, in 1833, with Whewell's advice, introduced a 
new terminology which we still use electrolysis, ions, anode, cathode, 
etc. He reduced the complexity of the subject to two simple state- 
ments: the mass liberated is proportional (i) to the strength of the 
current and to the time it flows, that is, to the total amount of 
electricity passing through the liquid; and (2) to the chemical 
equivalent weight. For instance, when one ampere flows for a second 
through an acid solution, 1-044 x io~ 5 gram of hydrogen is liberated, 
while from the solution of a silver salt 0-001118 gram of silver is 
deposited. The weight of silver is easy to measure and may be used 
as a practical definition of the ampere. 

Faraday's work shows that we must regard the flow of electricity 
through conducting liquids as the carrying of charges by moving 
atoms or ions positive charges in one direction and negative in the 
other. At a later date Helmholtz pointed out that it follows that 
electricity, like matter, is atomic, the fundamental unit being the 
charge on one monovalent ion. 

Other properties of currents soon discovered were the heating effect, 
now used in lighting and warming our houses, and the deflexion of 
a magnetic needle, described by Oersted in 1820. This result was 
extended by Amp&re, who showed that currents also exert forces on 
each other, while a circular coil gives a magnetic force at its centre 


equal to 27rc/r, a result which enables us to measure a current in 
absolute c.o.s. units. Ampere's work led to the invention of a practical 
electric telegraph. 

About 1827 G. S. Ohm (1787-1854) replaced the prevalent vague 
ideas of 'quantity 5 and 'tension' by definite conceptions of current 
strength and electromotive force. He showed that the current was 


proportional to the E.M.F., that is c=yE ^, where y is a constant 

known as the conductivity, and R its reciprocal the resistance, a rela- 
tion known as Ohm's Law. 

Electro-magnetism. In 1831 Faraday discovered that, when an 
electric current is started or stopped in a coil of wire, a small transient 
current is produced in another neighbouring coil. He also rotated 
a copper disc between the poles of a magnet, and obtained a steady 
electric current by touching the axle and periphery with wires from 
a galvanometer. This was the first dynamo, afterwards the basis of 
electrical engineering. 

Faraday realized the importance of the medium across which 
electric and magnetic forces stretch; he imagined lines of force, or 
chains of particles in 'dielectric polarization'. His ideas were put 
into mathematical form from 1864 onwards by Clerk Maxwell. As 
a change in 'dielectric polarization' spreads through a medium, it 
travels as an electromagnetic wave, which, Maxwell showed, moved 
with a velocity V=I/VJJLK ) where //, and K are the magnetic per- 
meability and dielectric constant of the medium. Since the electric 
and magnetic forces depend on /* and /c, the units derived from them 
also so depend, and by comparing the electro-static to the electro- 
magnetic units the value of v can be found. It proved to be about 
3 x io 10 centimetres, or 186,000 miles, a second, equal to the velocity 
of light. Maxwell concluded that light is an electro-magnetic wave, 
so that one aether will carry both. At the time this strengthened 
belief in the aether, though it was uncertain whether electric 
waves were mechanical vibrations in a quasi-rigid solid, or light 
electro-magnetic oscillations, the meaning of which remained 
unknown. Electro-magnetic waves were first demonstrated experi- 
mentally by Hertz in 1887, but the aether, if there be an aether, is 


now crowded with 'wireless waves' a consequence of Maxwell's 
equations and, however they are conveyed, it is certainly not ' on 
the air*. 

The Atomic Theory. From the days of Democritus onward the 
atomic idea in a vague form appeared at intervals. Boyle and Newton 
used it in their physical speculations, but, at the beginning of the 
nineteenth century, Dalton made it into a definite quantitative 
theory, based on the numerical facts of chemical combination. 

Lavoisier and others had proved that a chemical compound how- 
ever obtained is always made up of the same amount of the same 
constituent parts water, for instance, always consists of one part of 
hydrogen combined with eight of oxygen, giving 8 as the 'combining 
weight' of oxygen. Nevertheless, some chemists, among them Ber- 
tholet, did not believe in this constancy. But John Dalton ( 1 766- 
1844) saw that the properties of gases were best explained by atoms, 
and then pointed out that, on this theory, the combining weights in 
chemical combination gave the relative weights of the atoms also. 
He drew up a list of twenty such atomic weights. This formulation 
was too simple ; Dalton thought that, if only one compound of two 
elements was known, it was fair to assume it was formed atom for 
atom. This is not always true, indeed it put Dalton wrong about water. 

Gay-Lussac showed that gases combine in volumes that bear simple 
ratios to each other, and Avogadro pointed out that this must apply 
also to the numbers of their combining atoms. In 1858 Cannizzaro 
saw that it was necessary to distinguish between the chemical atom, 
the smallest part of matter which can enter into chemical action, 
and the physical molecule, the smallest particle which can exist in 
the free state. The simplest form of Avogadro's hypothesis is to 
suppose that equal volumes of gases at the same temperature and 
pressure contain the same number of molecules, a result which follows 
also from the kinetic theory of gases. In the formation of water from 
its elements we have two volumes of hydrogen combining with one 
of oxygen to form two of water vapour. The simplest theory which 
will explain these facts is to suppose that each molecule of hydrogen 
or oxygen contains two atoms, and that 


two atoms of hydrogen combining with one of oxygen to form one 
molecule of water. Oxygen is therefore said to be a divalent element. 
The concept of valency has been much used in chemical theory. 
From the considerations given above it follows that the atomic weight 
of oxygen is not 8 but 16. Thus Dalton's combining weights need to 
be considered in the light of other experiments before we can assign 
to the elements their true atomic weights. This was first done sys- 
tematically by Gannizzaro. 

The number of elements known has grown from Dalton's 20 to 92, 
each new method of research disclosing elements previously unknown. 
The results of spectrum analysis and electric currents have already 
been described. In 1895 the third Lord Rayleigh observed that 
nitrogen separated from the air had a density slightly greater than 
that of nitrogen extracted from its compounds, and he and Sir William 
Ramsay traced the difference to the presence in air of a heavier, 
chemically inert gas which they named 'argon'. Four other inert 
gases helium, krypton, neon and xenon were soon afterwards 
discovered, and, with argon, placed as a group of zero valency. 

A connexion between atomic weights and physical and chemical 
properties was sought by several chemists, the most successful being 
the Russian Mendeteeff (1834-1907). On arranging the elements in 
order of ascending atomic weights, a periodicity appeared, each 
eighth element having somewhat similar properties. The table gave 
a means of assigning correct atomic weights to elements of doubtful 
valency. Blanks in the table were filled hypothetically by Mendeleeff, 
who thus predicted the existence and properties of unknown elements, 
some of which were afterwards discovered. As measured chemically, 
many elements (but not all) have atomic weights approaching whole 
numbers. This suggested to Prout and others that all elements were 
composed of hydrogen, or at all events of some common basis. But 
this idea was beyond the theoretical and experimental powers of the 
time to test, and remained for a later age to verify. 

Organic Chemistry. The bodies of plants and animals are com- 
posed of complex chemical substances for the most part based on the 
remarkable element carbon, the atoms of which can combine with 
each other. For long it was thought that these substances could only 


be formed by vital action, but the preparation of urea from cyanic 
acid and ammonia by Wohler in 1828 showed that one such sub- 
stance at all events could be partly made in the laboratory. Other 
artificial productions followed, and Emil Fischer in 1887 built up 
fructose (fruit sugar) and glucose (grape sugar) from their elements. 

The method of determining the percentage composition is due to 
Lavoisier, Berzelius, Liebig and others. The compound is burned in 
the oxygen from copper oxide and the products of combustion, such 
as water and carbon dioxide, weighed. In this way the composition 
of innumerable organic bodies has been determined. One surprising 
result was the discovery that certain compounds, quite different in 
physical and chemical properties, had the same percentage com- 
position for example, urea and ammonium cyanate. Berzelius 
(1779-1848) explained this isomerism as due to differences in the 
connexions between the atoms in the molecule. The same pheno- 
menon is seen in charcoal and the diamond; they both consist of 

Thus empirical formulae, such as G 2 H 6 O for alcohol, became 
constitutional formulae like 

H H 

I I 

I I 
H H 

for the same substance. In 1865 Kekute showed that the properties 
of benzene, C 6 H 6 , indicated a closed ring of the six carbon atoms. 
If one or more of the hydrogen atoms are replaced by other atoms 
or groups of atoms, the more complex aromatic compounds can be 
represented. By these structural formulae, organic chemistry has 
been rationalized; from the possibilities suggested by the formulae, 
new compounds have been predicted and isolated. 

The chemistry of coal-tar has developed into an enormous industry. 
Unverdorben and later Hofmann isolated from tar a substance to 
which the name of aniline was given, and in 1856 W. H. Perkin 
(Senior) obtained aniline purple or mauve, the first aniline dye, soon 
followed by countless others, especially in Germany. In 1878 E. and 


O. Fischer studied their constitution, and found the basis of many 
of them in triphenylmethane. About 1897 indigotin made from 
phenylglycine began to drive natural indigo off the market. Synthetic 
organic drugs appeared with antipyrene (1883), phenacetin (1887) 
and acetyl salicylic acid or aspirin (1899). Then came Ehrlich's 
salvarsan and other specific remedies described later. 

In 1844 Mitscherlich, who had previously pointed out the con- 
nexion between atomic constitution and crystalline form, showed 
that isomers of tartaric acid, though possessing the same structural 
formulae, had different optical properties. In 1848 Pasteur (1822- 
J 895), when recrystallizing racemates, got two varieties of crystal, 
related to each other as a right hand to a left hand or an object to 
its image. When the two kinds of crystals were picked out, separated 
and redissolved, one solution was found to rotate the plane of 
polarization of light to the right and the other to the left. Many of 
the substances obtained from living bodies are optically active in 
this way, while, if they are synthesized in the laboratory, they are 

In 1863 Wislicenus and in 1874 Le Bel and Van't Hoff inferred 
that the atoms in the molecules of the two varieties must be arranged 
differently in space, giving formulae related 
to each other as object and image. They 
pictured a carbon atom G at the centre of a 
tetrahedron, with four or more different 
atoms or group of atoms linked to it what is 
called an asymmetric carbon atom. Similar 
phenomena have been found with a few other 
elements, especially nitrogen. 

A group of atoms, or radical, such for in- r> 3 

stance as hydroxyl OH, may hold together Fio. 12. Asymmetric 
through a series of reactions. This suggested carbon atom 

a theory of types, according to which chemical compounds were once 

Gradually an enormous number of organic compounds have been 
isolated, and many synthesized from their elements. Liebig grouped 
them as members or derivatives of one or other of three great classes: 


(1) Proteins, containing carbon, hydrogen, nitrogen, oxygen, and 
sometimes sulphur and phosphorus. 

(2) Fats, containing carbon, hydrogen and oxygen. 

(3) Carbohydrates, containing carbon, hydrogen and oxygen, the 
hydrogen and oxygen being present in the proportions in which they 
form water. 

Of these compounds the proteins are the most complex. They 
break down into constituents known as amino-acids. In 1883 Gurtius 
built up a substance which gave a protein-like reaction. Fischer 
examined it, and devised several methods of combining amino-acids 
into bodies resembling the peptones which are formed by the action 
of digestive ferments on proteins. Thus, before the end of the century, 
progress had been made towards determining the nature and possible 
methods of synthesis of some constituents of living organisms. More- 
over, the knowledge gained in rationalizing organic chemistry made 
clearer many problems in other branches of chemical science. 

Chemical Action. The causes and mechanism of chemical affinity 
and chemical action have been discussed from early times, and 
Newton gave much attention to the subject. In 1850 Wilhelmy 
measured the rate of ' inversion ' of cane sugar in presence of an acid 
the dissociation of molecules of sucrose into the simpler ones of 
dextrose and laevulose. He found that, as the concentration of the 
cane sugar got less, the amount changing also diminished in a 
geometrical progression. This means that the number of molecules 
dissociating is proportional to the number present at any instant 
as indeed we should expect if the molecules dissociated independently 
of each other in what is called a monomolecular reaction. 

But if two molecules react with each other a dimolecular reaction 
the rate of change must depend on the frequency of collision, a 
frequency proportional to the product of the concentrations or active 
masses of the two reagents; if the molecular concentrations are equal, 
this product will be the square of the concentration. 

As Bertholet discovered, some actions are reversible, able to go in 
either direction. If two compounds AB and CD are forming AD 
and CB 9 and the reverse change is also going on, equilibrium must 


clearly be reached when the rates of the opposite reactions are equal. 
The process is written as 

AB + CD^AD + CB. 

This dynamical equilibrium was first formulated by A. W. Williamson 
in 1850. A fuller statement of the mass law was given by Guldberg 
and Waage in 1864 and by Van't Hoff in 1877. 

The inversion of cane sugar goes much faster in presence of an 
acid. The acid facilitates the action but is itself unchanged, and was 
called by Berzelius a 'catalyst'; similarly, finely divided platinum 
brings about the combination of hydrogen and oxygen. Many such 
actions are known both in chemistry and in physiological processes, 
where the catalysts are called enzymes or hormones. Catalysts are 
also now frequently used in industrial chemistry. 

Solution. The solution of substances in water and other liquids 
is familiar. Sugar dissolves freely, while metals are insoluble. Air is 
only slightly soluble in water, but ammonia and hydric chloride are 
very soluble. Some solutions, such as most of those of salts and 
mineral acids, conduct electricity well, while pure water and solutions 
of sugar have very low conductivity. 

Faraday's work proved that electrolytic conduction is a motion in 
opposite directions of positively and negatively electrified ions, every 
ion of the same chemical valency carrying the same charge. In 1859 
Hittorf saw that the unequal dilution of the solution round the two 
electrodes gave a means of comparing the velocities of the opposite 
ions, since the faster moving ion must concentrate more salt round 
the terminal towards which it moves. In 1879 Kolrausch measured 
the conductivity of solutions, using alternating currents and a tele- 
phone instead of a galvanometer, to avoid polarization at the elec- 
trodes. He found that Ohm's law holds good, so that the smallest 
electromotive force produces a current; there must therefore be 
freedom of interchange in the body of the liquid. He also pointed 
out that the conductivity gives a means of finding the sum of the 
opposite ionic velocities, which, combined with Hittorf 's values for 
their ratios, gives the individual velocity of each ion. For a potential 


gradient of one volt per centimetre, hydrogen moves through water 
with a velocity of about 0-003 centimetre per second, while the ions 
of salts range round 0-0006. Oliver Lodge verified the speed of 
hydrogen, and I measured that of some other ions by watching their 
motion if coloured or by the formation of precipitates. 

Pressures are set up in vegetable cells by the passage of water 
through the containing membranes, and Pfeffer measured this so- 
called osmotic pressure for solutions of cane sugar, using artificial 
membranes deposited chemically in the walls of porous pots. Van't 
Hoff pointed out that Pfeffer's results showed that osmotic pressure, 
like gas pressure, varies inversely as the volume, and has about the 
same value as has an equal molecular concentration of a gas. The 
existence of the pressure makes it possible to imagine the osmotic cell 
acting as the cylinder of Carnot's ideal engine, and Van't Hoff was 
thus able to apply thermodynamic reasoning to solutions, opening a 
new field of research. In dilute solutions the osmotic pressure, both 
theoretically and experimentally, has the gas value, but not in strong 
solutions, investigated by the Earl of Berkeley and E. G. J. Hartley. 
Van't Hoff connected osmotic pressure with other properties of 
solutions, such as the depression of the freezing point, more easily 
measured. These relations with gases do not prove that osmotic 
pressure is due to the same cause as gas pressure; thermodynamic 
reasoning gives results, but has nothing to say about mechanism. The 
pressure may be due to impact, to chemical attraction or some other 
unknown cause. 

In 1887 the Swede Arrhenius, knowing that the osmotic pressures 
of electrolytes were abnormally great, so that the pressure in a dilute 
solution of potassium chloride or other binary salt was about twice 
the value for sugar or for a gas, accepted the conclusion that this 
showed the number of pressure-producing particles to be greater 
than in non-electrolytes. He therefore put forward the theory that 
electrolytes are dissociated into ions in solution. For instance, with 
potassium chloride there are some neutral molecules of KC1, and 
some dissociated ions K+ and Cl~. As the solution is diluted, there 
is more dissociation, till all the salt is resolved into its ions, osmotic 
pressure and chemical activity per unit mass increasing pan passu. 


The ions are probably combined with the solvent, perhaps carrying 
aa-atmosphere of the liquid with them as they move. 
^ On these lines, thermodynamics, especially as developed by Willard 
Gibbs (p. 99), and electrical science have been combined in an 
ever-growing extension of theoretical knowledge and of practical 
industrial applications. Moreover, the theory of solution gave the 
idea of ions to those physicists who later on investigated the conduction 
of electricity through gases and revolutionized modern physical science. 

Colloids. The distinction between compounds that will crystal- 
lize, named crystalloids, and those that form much larger solid 
structures, called colloids, was recognized by Thomas Graham in 
1850, and explained by the size of the colloid particles. The solution 
of a crystalloid, sugar (say) or salt, is a homogeneous liquid, but a 
colloid forms a system of two phases, with a surface of separation 
between them. Some colloid particles can be seen in a microscope; 
for others the ultra-microscope is needed. In this the observer looks 
at right angles to a strong beam of light, which is scattered by the 
particles, so that, if they are not much smaller than the wave-length 
of the light used, they show as separate bright discs, kept in oscillatory 
(Brpwnian) movement by the collision of molecules. 
VThe protoplasm which forms the contents of living cells consists 
of colloids, the nucleus being more solid than the remainder; hence 
the importance of colloids in physiology. They appear also in agri- 
cultural science, for soil is now known to be a complex living structure 
of organic and inorganic colloids, in which micro-organisms, bacteria 
and others, play an essential part in breaking down the raw material 
into substances fit for plant food. Again, the colloids in clay control 
its physical texture, which only becomes porous and fertile when the 
plastic clay is coagulated. 

Colloid particles move in an electric field, and must therefore 
carry electric charges. Sir W. B. Hardy found that, when the sur- 
rounding liquid was slowly changed from acid to alkaline, the charges 
on certain colloids were reversed. At the 'iso-electric point', where 
the charge was neutralized, the system became unstable and the 
colloid was coagulated. 


It was known to Faraday and to Graham that some colloid 
solutions are coagulated by salts. In 1895 Linder and Picton found 
that the average coagulative power of mono-valent, di-valent and 
tri-valent ions were in the ratios of i : 35 : 1023. In 1899 I investi- 
gated the problem on the theory of probability. The electric charge 
on an ion is proportional to its chemical valency, and so it will need 
the conjunction of two tri-valent ions, three di-valent or six mono- 
valent ions to bring the same charge near a colloid particle. Calcula- 
tion shows that the coagulative powers should be as i : x : x 2 , where 
x is some unknown number depending on the structure of the system. 
Putting # = 32, we get i : 32 : 1024 to compare with the observed 
values. This can only be an approximate result; it ignores disturbing 
factors. But the method explains the high effect of tri-valent ions, 
and similar principles of probability are applicable to chemical 
reaction itself. 

The properties of colloids are connected with the phenomena of 
surface films. The thermodynamics of films were first studied by 
Willard Gibbs and their molecular structure by Rayleigh, Langmuir, 
Rideal and N. K. Adam. Some films are so thin that they consist 
of a monomolecular layer. Thus we reach what may be called a two- 
dimensional world. 


Biology and its Effects. In the seventeenth and eighteenth 
centuries it was astronomy that affected most profoundly the minds 
both of philosophers and of ordinary men. Copernicus dethroned 
the Earth from its ancient position as the centre of the Universe, 
while Galileo and Newton proved that the heavenly bodies, no 
longer divine and incorruptible, move in accordance with terrestrial 
dynamics. Man's outlook on the cosmos was revolutionized. 

In the nineteenth century this change had been assimilated and 
no longer caused distress. Physicists banished philosophy from their 
laboratories, and did their work by the light of a common-sense 
realism, never doubting that their discoveries showed the actual 
structure of the world. Mach pointed out that science does but create 
a model of what our senses tell us about nature, but few men of 
science listened. 

The next revolution in scientific and philosophic thought came 
from biology, with Darwin as its chief figure. The old theory of 
evolution was made credible by his concept of natural selection, and 
man was forced to recognize his true place in the animal kingdom. 
Then evolutionary ideas spread from biology to other departments 
of knowledge. 

Physiology. In the second half of the eighteenth century, the 
difficulty of explaining physiological processes led to the almost 
universal adoption of vitalism, the theory that living matter is above 
the range of physics and chemistry. But by the middle of the nine- 
teenth century success in applying physical and chemical methods 
to biology, aided by the invention of physiological apparatus, swung 
opinion in the other direction. For most studies in physiology it 
seems necessary to accept physics and chemistry at all events as 
guides to the elucidation of details. The problerrTbf organisms as 
wholes is different and more complex. 

In the early years of the nineteenth century, Johannes Muller 
collected all available physiological knowledge in his Outlines of 


Physiology and himself worked on nervous action. He proved that 
sensation depends on the nature of the sense organ and not on the 
mode of stimulation; light, pressure or mechanical irritation, acting 
through the optic nerve on the retina, all produce luminous sensa- 
tions, thus confirming the philosophic view that man's unaided 
senses give him no real knowledge of the external world. 

During 1833 the American army surgeon Beaumont published 
facts about digestion observed in a patient with a gun-shot wound 
which left a hole into his stomach. Claude Bernard (1813-1878) 
studied the same condition in animals, and showed that pancreatic 
juice disintegrates the fats discharged by the stomach into the 
duodenum, decomposes them into fatty acids and glycerine, converts 
starch into sugar and dissolves proteins. 

Dumas and Boussingault taught that, while plants absorb inorganic 
bodies and build them up into organic substances, animals, essentially 
parasitic, live by breaking down these substances into simpler com- 
pounds. But Bernard proved by experiments on dogs that the liver 
forms the carbohydrate dextrose from the blood, and also dis- 
covered that the liver produces a starch-like substance, named by 
him glycogen, which gives dextrose by a process of fermentation. 
Thus he showed that animals can build up some organic substances, 
though that function is generally performed by plants. 

Bernard also explained the poisonous action of carbon monoxide 
gas by showing that it irreversibly displaces oxygen from the haemo- 
globin in the red blood corpuscles; the haemoglobin then becomes 
inert and can no longer carry oxygen to the tissues of the body. 
Bernard held that the function of the vital mechanism was to keep 
constant the conditions of the internal environment. 

Schleiden in plants and later Schwann in animals established the 
theory that their tissues are made up of vast numbers of separate 
cells, tracing them to their origins in the embryos. Harvey and 
Wolff had put embryology on a sound basis, and it was taken up 
again by von Baer (1792-1876), who traced the multiplication and 
differentiation of cells in embryonic development. He rediscovered 
the ovum in mammals, and did much to create modern embryology. 
He opposed a prevalent theory that the history of the individual 
recapitulates the history of the species. 


Von Mohl examined the contents of cells and called the plastic 
substance within the cell wall by the name of protoplasm. Schultz 
described the cell as a mass of nucleated protoplasm, the physical 
basis of life. Virchow carried the cell theory into the study of diseased 
tissues, and discovered that the white corpuscles in the blood can 
engulf and destroy poisonous bacteria. 

The general principle of the conservation of energy requires that 
the physical activities of the body must be maintained by the 
chemical and thermal energy of the food taken in. Atwater and 
Bryant, by experiments in America, gave 4-0 calories as the heat value 
of one gram of protein or carbohydrate and 8-9 for fats. T. B. Wood, 
working on farm animals, separated the maintenance ration needed 
to keep the animal in a stationary state from the additional food 
required for growth, milk-production, etc. A man doing no muscular 
work wants food to the equivalent of about 2450 calories a day, and 
one doing heavy labour 5500. l The energy of the food taken in has 
been found to be equal to the output in muscular work, heat and 
excrement, in full accord with the principle of the conservation of 

During the period now under review, much advance was made in 
the study of the nervous system. The localization of the functions of 
the brain had often been suggested, and was investigated by Gall, 
who taught that the grey matter was the active instrument'ortFe 
nervous system and the white matter the connecting links. Majendie 
proved an idea due to Bell, that the anterior and posterior roots of 
spinal nerves had different functions. With Marshall Hall they 
established the difference between volitional and unconscious or 
reflex action. Such common acts of life as'TSreatKihg, sneezmg^fetc. 
nfayTScTtaken as reflexes, and other processes, formerly thought to 
involve complicated mental operations, were held to be reflexes, 
especially by Charcot later in the century. Bernard investigated the 
function of the vaso-motor nerves, showing that they are put into 
action involufitarily by sensory impulses and control the blood 

1 All these figures are expressed in the so-called * great calory*, 1000 times the unit 
used in physics, which is the amount of heat needed to raise, one gram of water 
through one degree Centigrade. 



vessels. E. H. and E. F. Weber discovered inhibiting actions, such as 
the stoppage of the beat of the heart by stimulation of the vagus nerve. 
The study of catalytic actions, as found in inorganic chemistry, 
was extended to many processes going on in living organisms. In 
1878 Kiihne, who did much to trace their action, gave to these 
organic catalysts the name of enzymes (eV ^v'/zfl, in yeast). Like 
other catalysts, enzymes, without themselves being altered, facilitate 
reactions in either direction, as oil helps a machine. Their effect is 
often specific one reaction, one enzyme. They are often colloids 
and may carry electrical charges, indeed ions may act as catalysts, 
as in the inversion of cane sugar in presence of acids. Among the 
more important enzymes are amylase, which decomposes starch, 
pepsin which breaks up proteins in an acid medium as trypsin in an 
alkaline, lipase which decomposes esters and so on. We shall find 
later that this subject is of growing importance, especially in the 
study of glands and their secretions. As early as 1884 Schiff found 
that the effects of the removal of the thyroid gland from an animal 
could be overcome if the animal were fed with an extract from the 
gland. This result was soon applied to the variety of human idiocy 
known as cretinism, which was found to be due to a failure in the 
thyroid gland, and many children who in former times would have 
been hopeless imbeciles for life have been made into intelligent and 
happy beings. 

Bacteriology. About 1838 Cagniard de Latour and also 
Schwann discovered that the yeast used in fermentation consists of 
minute living cells. Schwann also proved that putrefaction was a 
similar process, and showed that neither fermentation nor putre- 
faction would occur if the substance were heated to destroy living 
organisms and afterwards protected from air save that which had 
passed through red-hot tubes. 

A^ Louis Pasteur (1822-1895) confirmed these results, and extended 
them to the souring of beer and wine, the silk-worm disease, and 
(the greatest benefit of all) to rabies in animals and hydrophobia in 
mankind. As Jehner produced immunity from small-pox by vac- 
cination, so Pasteur found by experiment on dogs that he could give 


them immunity from rabies by inoculation with attenuated poison, 
and thus found a cure for men who had been bitten. Each of these 
affections or diseases is due to a specific microbe or bacterium, though 
some enzymes expressed from them produce the same effect, 

Lister, applying Pasteur's discoveries to surgery, used first phenol 
(carbolic acid) as an antiseptic, and then found an aseptic treatment 
in careful cleanliness. Lister's methods, together with the discovery 
of anaesthetics by Davy, Morton and Simpson, made safe many 
surgical operations previously impossible. 

Koch found that the spores of the anthrax bacilli were more 
resistant than the bacilli themselves, an observation important in the 
technique of bacteriology. He also discovered the micro-organism 
responsible for tuberculosis. The life-history of some pathogenic 
organisms is complex; they may need several kinds of host. This is 
true of malaria, carried by mosquitoes, and of Maltese fever, the 
microbe of which passes part of its life in goats. 

We shall describe later the many discoveries of ultra-microscopic 
viruses; but one such, responsible for tobacco disease, was investi- 
gated by Ivanovski in 1892, and another by Loftier and Frosch in 
1893. The latter found that the infection of foot-and-mouth disease 
would pass freely through a filter which stopped ordinary bacteria, 
and would still affect animals in series. The nature of these viruses 
is still uncertain. 

It is clear that essential parts of our knowledge of the organs and 
functions of the human body, with all their beneficial effects, on 
medicine and surgery, could only have been reached by experiments 
on animals, carried on from early days till the present. Those who 
try to stop further advance by this method take on themselves a 
fearful moral responsibility, not lightened by their frequent ignorance 
of the facts. 

The Carbon and Nitrogen Cycles. The relations between plants 
and animals were studied further by several investigators, leading 
up to the*work of Liebjg T _ , Plants are built up by the action in 
sunlight of the green colouring matter chlorophyll, which uses the 
Sun's energy to decompose the carbon dioxide in the air, liberating 


oxygen and combining the carbon in the complex organic molecules 
of plant tissues. In the absorption spectrum of chlorophyll, the 
maximum absorption coincides with the maximum energy of the 
solar spectrum a remarkable adaptation, however produced, of 
means to ends. 

Animals live either on plants or on each other, and so all are 
ultimately dependent on the energy of the Sun. In breathing they 
oxidize carbon compounds into carbon dioxide and the derivatives 
they need; other substances are excreted, and the residual energy 
appears as bodily heat. Plants also slowly give out carbon dioxide, 
though in sunlight this is masked by the reverse process. Thus both 
animals, and to a lesser degree plants, return to the air the carbon 
dioxide which plants have removed. The waste organic solid products 
are deposited in the ground, where they are attacked by teeming 
bacteria and are broken down into harmless (indeed useful) inorganic 
bodies, while more carbon dioxide is poured into the air. Thus the 
carbon cycle is completed. 

The corresponding cycle for nitrogen was worked out at a later 
date. In his Georgics, Virgil recommends the farmer to grow beans, 
vetch or lupins before wheat, but the reason for the success of this 
sound advice was only discovered in 1888 by Hellriegel and Wilfarth. 
The roots of leguminous plants produce nodules containing bacteria 
which can fix nitrogen from the atmosphere, convert it into protein 
and pass it on to the plant. Moreover, Vinogradsky found in the soil 
bacteria which obtain nitrogen direct from the air. Waste nitro- 
genous products are converted in the soil, again with the help of 
bacteria, into ammonium salts and finally into nitrates, the best form 
of nitrogen for plant food. Soil is a live physical, chemical and 
biological structure which needs mineral salts as well as humus to 
keep its balance. 

Liebig demonstrated the importance of mineral salts in agriculture, 
but he overlooked the need for nitrogen. This was discovered by 
Boussingault, and by Gilbert and Lawes of Rothamsted, who intro- 
duced artificial manures to the farmer. 

Geography and Geology. In 1784 the Ordnance Department 
measured a baseline on Hounslow Heath and began trigonometrical 


surveys, which enabled d'Anville and others to make accurate maps. 
Von Humboldt studied the variations of the Earth's magnetic force 
and the magnetic storms he was the first to observe. 

Reviving the practice of sending out exploratory expeditions, in 
1831 the Beagle was despatched for scientific observations round 
Patagonia and Tierra del Fuego, with Charles Darwin on board as 
official naturalist. A few years later Joseph Hooker joined Sir James 
Ross in his Antarctic voyage, and in 1846 T. H. Huxley sailed as 
surgeon on the Rattlesnake and spent several years surveying and 
charting in Australian waters. Thus three men, who had much to do 
with the coming and establishment of the theory of evolution, served 
an apprenticeship on voyages of scientific exploration. Finally in 
1872 the Challenger was sent to cruise for some years in the Atlantic 
and Pacific to take records of oceanography, meteorology and natural 
history. Maury of the United States navy took up the problems of 
winds and currents as they were left a century and a half earlier by 
Dampier, and improved the navigation of ocean routes. A study of 
the life of the sea revealed countless forms, from the drifting micro- 
scopic matter named 4 plankton ' by Henson to the fish that follow it 
for food. 

Hutton's uniformitarian theory was much strengthened when 
Sir Charles Lyell collected in his Principles of Geology (1830-1833) 
all available evidence about the formation of strata and the origin 
of fossils. Fossils indicate changes of climate at definite times, in this 
supported by the evidence of glaciation found by Agassiz and Buck- 
land about 1840. Flint implements and carved pieces of bone and 
ivory enabled Lyell in 1863 to place man in his position in the series 
of organic types, and to show that his existence on the Earth must 
have extended over much longer ages than those contemplated by 
the Biblical Chronology current at the time. Much evidence has 
accumulated since Lyell's day, and it now seems likely that men 
appeared on the Earth somewhere between one and ten million 
years ago. 1 

Evolution and Natural Selection. The idea of evolution was 
known to some of the Greek philosophers. The Atomists seem to have 

1 Sec Chapter i, p. I . 


thought that each species arose independently, but, in their belief 
that only those types survived which were fitted to the environment, 
they touched the concept of natural selection. By the time of 
Aristotle, speculation had suggested that more perfect types had not 
only followed less perfect ones but actually had developed from them. 
But all this was guessing; no real evidence was forthcoming. 

When, in modern times, the idea of evolution was revived, it 
appeared in the writings of the philosophers Bacon, Descartes, 
Leibniz and Kant though some of them, Hegel for instance, took 
evolution in an ideal sense. But Herbert Spencer was preaching a 
full evolutionary doctrine in the years just before Darwin's book was 
published, while most naturalists would have none of it. Nevertheless, 
a few biologists ran counter to the prevailing view, and pointed to 
such facts as the essential unity of structure in all warm-blooded 

The first complete theory was that of Lamarck (1744-1829), who 
thought that modifications due to the environment, if constant and 
lasting, would be inherited and produce a new type. Though no 
evidence for such inheritance was available, the theory gave a working 
hypothesis for naturalists to use, and many of the social and philan- 
thropic efforts of the nineteenth century were framed on the tacit 
assumption that acquired improvements wouldj^elnherited. Similar 
views were advocated by Saint-Hilaire and by Robert Chambers, 
whose book Vestiges of Creation helped to prepare men for the 
acceptance of evolution. 

But the man whose book gave both Darwin and Wallace the clue 
was the Rev. Robert Malthus (1766-1834), sometime curate of 
Albury in Surrey. The English people were increasing rapidly, and 
Malthus argued that the human race tends to outrun its means 
of subsistence unless the redundant individuals are eliminated. 

This may not always be true, but Darwin writes : 

In October 1838 I happened to read for amusement Malthus on 
Population, and being well prepared to appreciate the struggle for 
existence which everywhere goes on from long continued observation 
of the habits of animals and plants, it at once struck me that under 
these circumstances favourable variations would tend to be preserved, 


and unfavourable ones to be destroyed. The result of this would be 
the formation of new species. Here then I had a theory by which 
to work. 

Darwin spent twenty years collecting countless facts and making 
experiments on breeding and variation in plants and animals. 
By 1844 he had convinced himself that species are not immutable, 
but worked on to get further evidence. On 1 8 June 1858 he received 
from Alfred Russel Wallace a paper written in Ternate in the space 
of three days after reading Malthus's book. Darwin saw at once that 
Wallace had hit upon the essence of his own theory, and placed 
himself in the hands of Lyell and Hooker, who arranged with the 
Linnaean Society to read on i July 1858 Wallace's paper together 
with a letter from Darwin to Asa Gray dated 1857 and an abstract of 
his theory written in 1844. Then Darwin wrote out an account of his 
labours, and on 24 November 1859 published his great book The 
Origin of Species. 

Charles Robert Darwin (1809-1882) [see Plate VI, facing p. 122] 
was the son of an able doctor, Robert Waring Darwin of Shrewsbury, 
and grandson of Erasmus Darwin, who had ideas about evolution, 
and of Josiah Wedgwood, the potter of Etruria, who also showed 
the scientific ability which has now appeared in five generations of 

In any race of plants or animals, the individuals differ from each 
other in innate qualities. Darwin offered no explanation of these 
variations, but merely accepted their existence. When the pressure 
of numbers or the competition for mates is great, any variation in 
structure which is of use in the struggle has 'survival value', and 
gives its possessor an improved chance of prolonging life and leaving 
offspring. That variation therefore tends to spread through the race 
by the elimination of those who do not possess it, and a new variety 
or even species may be established. As Huxley said, this idea was 
wholly unknown till 1858. 

Huxley, Asa Gray, Lubbock and Carpenter accepted Darwin's 
theory at once, and Lyell was convinced by 1864. Huxley called 
himself * Darwin's bulldog', and said the book was like a flash of 
lightning in the darkness. He wrote: 


It did the immense service of freeing us from the dilemma Refuse 
to accept the Creation hypothesis, and what have you to propose 
that can be accepted by any cautious reasoner? In 1857 I had no 
answer ready, and I do not think that anyone else had. A year later 
we reproached ourselves with dulness for being perplexed with such 
an enquiry. My reflection when I first made myself master of the 
central idea of the Origin was ' How extremely stupid not to have 
thought of that ! ' 

The hypothesis of natural selection may not be a complete explana- 
tion, but it led to a greater thing than itself an acceptance of the 
theory of organic evolution, which the years have but confirmed. 
Yet at first some naturalists joined the opposition, and the famous 
anatomist Sir Richard Owen wrote an adverse review. To the many, 
who were unable to judge the biological evidence, the effect of the 
theory of evolution seemed incredible as well as devastating, to run 
counter to common sense and to overwhelm all philosophic and 
religious landmarks. Even educated man, choosing between the 
Book of Genesis and the Origin of Species, proclaimed with Disraeli 
that he was 'on the side of the Angels'. 

Darwin himself took a modest view. While thinking that natural 
selection was the chief cause of evolution, he did not exclude 
Lamarck's idea that characters acquired by long use or disuse might 
be inherited, though no evidence seemed to be forthcoming. But 
about 1890 Weismann drew a sharp distinction between the body 
(or soma) and the germ cells which it contains. Somatic cells can 
only reproduce cells like themselves, but germ cells give rise not only 
to the germ cells of a new individual but to all the many types of cell 
in his body. Germ cells descend from germ cells in a pure line of 
germ plasm, but somatic cells trace their origin to germ cells; from 
this point of view, the body of each individual is an unimportant 
by-product of his parents' germ cells. The body dies, leaving no 
offspring, but the germ plasm shows an unbroken continuity. The 
products of the germ cells are not likely to be affected by changes in 
the body; so Weismann's doctrine offered an explanation of the 
^apparent non-inheritance of acquired characters. It seems that, in 
spite of philosophers and philanthropists, nature is more than nurture 
and heredity than environment. 


The supporters of pure Darwinism came to regard the minute 
variations as enough to explain natural selection and natural selection 
enough to explain evolution. But animal breeders and horticul- 
turalists knew that sudden large mutations occur, especially after 
crossing, and that new varieties might be established at once. Then 
in 1900 forgotten work by Mendel was rediscovered and a new chapter 

Anthropology. Darwin's work started the study of man on a 
novel course, the idea of evolution underlying it all. Huxley's study 
of human skulls was inspired by the Darwinian controversy, and 
began the exact measurement of physical characters. The explorers 
who brought back plants and animals often brought also the indus- 
trial and artistic products of other peoples and the ceremonial objects 
of their religions or descriptions thereof. There was much material 
ready waiting for the anthropologist. 

Since Lyell described what was known in his day of man in the 
geological record, many discoveries have been made. In the nine- 
teenth century pictures of bison, prehistoric mammoths and other 
animals were found on the walls of caves. At Neanderthal in 1856 
and at Spy in 1886 relics of primitive types of men appeared, and in 
1893 Dubois discovered in the late Pliocene deposits in Java, bones 
which some think are those of a being intermediate in structure 
between anthropoid apes and early men. Man cannot be descended 
from any form of ape now existing, but he is at least a distant cousin 
of some of them. 

Statistical methods were applied to men in the seventeenth century 
by a study of the Bills of Mortality, especially by Sir William Petty 
and John Graunt. The subject was again advanced by tye Belgian 
astronomer Quetelet in 1835 and later. He found that the chest 
measurements of Scottish soldiers (Fig. 13, p. 124) or the heights of 
French conscripts varied round the average as the bullets round the 
centre of a target, or the runs of luck at a gaming table. Graphically, 
as in the diagram, the curve, except that it is symmetrical on both sides, 
resembles that showing the velocities of molecules in a gas (p. 96). 
Similar considerations apply to such economic activities as insurance. 



In 1869 Darwin's cousin Francis Gal ton applied these principles 
to mental qualities. Tracing the distribution of marks in an examina- 
tion, he found the same laws as for physical qualities or molecular 
velocities. Most men have mediocre intellectual powers, and, as we 
pass towards genius at one end and idiocy at the other, the numbers 
fall off as the curve shows. A Senior Wrangler obtained on the average 
about thirty times the number of marks of the lowest honours man, 
while the pass men, had they taken the same examination, would 






34 36 38 40 42 44 
FIG. 13. Inches of chest measurement 


presumably have got still fewer marks. The differences in ability are 
clearly enormous, and the democratic idea that men are born equal 
is demonstrably false. 

By searching books of reference, Gal ton examined the inheritance 
of ability; &r instance he found that the chance of the son of a judge 
showing great ability was about five hundred times as high as that 
of a man taken at random, and for the judge's father it was nearly 
as much. While no prediction can be made about individuals, on the 
average of large numbers the inheritance of ability is certain. 

Thus we must give up the idea that the nation consists of a number 
of individuals of equal potential capacity, only waiting for education 
and opportunity, and look on it as an interwoven network of strains 


of various innate hereditary qualities, strains differing in character 
and value, and increasing or disappearing chiefly in accordance with 
natural or artificial selection. Almost any action, social, economic 
or legislative, will favour some of these strains at the expense of others, 
and alter the average biological character of the nation. This subject 
will be pursued in the light of more recent information in Chapter rx. 

Nineteenth-Century Science and Philosophy. Till the days of 
Kant philosophers framed their systems in the light of physical 
science, but Hegel and the Hegelians, starting from a priori philosophy, 
constructed a theory of nature which seemed to men of science 
fantastic. In turn Hegel attacked physicists, and especially Newton 
as their exemplar. The poet Goethe, too, who had done good work 
in animal and vegetable anatomy, where the facts lay on the surface, 
failed when he touched physics. A flash of poetic insight assured him 
that white light must be simpler and purer than coloured, and 
Newton's theory wrong. He refused to consider facts disclosed by 
experiments and inferences drawn from them; the senses must reveal 
at once the truth about nature. Thus for a time the philosophers 
scorned the scientists and the scientists ignored the philosophers; 
thinking they were keeping clear of metaphysics, they accepted 
uncritically the structure of nature built by science as ultimate reality. 
Though the philosophy of science was studied in England by Boole, 
Jevons, Clifford and Spencer, they had little influence among 
scientists. Even when in 1883 Mach, treating mechanics from the 
historical point of view, and reviving the teaching of the philosophers 
from Locke to Kant, pointed out that science does but construct a 
model of what our senses tell us about nature, few listened. The 
separation between science and philosophy remained complete. 

But soon in its turn science began again to influence philosophy. 
Lavoisier's proof that mass persisted through a series of chemical 
changes was brought into prominence to support the common-sense 
view that matter is real, and the striking success of physics and 
chemistry drew uncritical men to believe in matter and energy as 
ultimate realities. 

This led in Germany to a revival of the materialism prevalent in 


France a hundred years before. Some based their belief on physiology 
and psychology, but Biichner's book Kraft und Staff showed that the 
idea of the reality of force and matter was an essential part of this 
philosophy. The establishment of the principle of the conservation of 
energy, when it came, was used to support the philosophic theory of 
mechanism and determinism. 

William Thomson's proof that, in an isolated system, energy must 
continually become less available, and Clausius' entropy increase 
(p. 98), was extended, perhaps unwarrantably, to the cosmic 
problem, and used to predict a 'dead universe' new evidence, some 
thought, for the spread of determinism and atheism. But, on the 
alternative hypothesis, man's soul, being immaterial and immortal, 
need not mind the dissolution of a physical universe. 

Materialism and allied beliefs were most prevalent in Germany, 
but in some other continental countries ecclesiastical conservatism 
found means to suppress these views, till the struggle for political 
liberty was combined with that for intellectual freedom, and cul- 
minated in the revolutionary outbreaks of 1848. In the following 
years the industrial changes, which had already gone far in England, 
began to extend to the Continent. Science, especially chemistry, 
came to touch ordinary life more closely. In practical England, this 
process had little effect on religious orthodoxy, but in logical France 
and metaphysical Germany, it helped to swell the rising tide of 
mechanical and materialist philosophy. 

And it was in Germany that Darwin's explanation of evolution by 
the principle of natural selection, when accepted by Haeckel and 
other biologists, went to build up a thoroughgoing Darwinismus and 
most strongly reinforced the materialist tendencies in both philosophy 
and political theory, the latter being used by some as a basis for 
the ideas of communism. Thus natural selection ceased to be 
merely a tentative scientific theory, and became the basis of a philo- 
sophy of evolution. Meanwhile Darwin's own methods of careful 
observation and experiment fell into abeyance. 

But, however much exaggeration was worked into a Darwinian 
philosophy, and however the inheritance of small variations and 
natural selection acting on them failed to explain the details of change 


Df species, the revolution in thought due to the acceptance of the 
general principle of evolution was immense. Instead of a stationary 
world of living beings and a stationary human society, a dynamic 
picture of continual change emerged. The geological record showed 
a gradual change from simpler to more complex organisms, and from 
an ape-like precursor to homo sapiens. It was therefore perhaps natural 
to suppose that evolution should continue to mark progress both in 
natural history and in human morphology and human society; men 
ignored the fact that ' survival of the fittest ' meant only fittest for the 
existing environment, and the possibility that adaptation to that 
environment might proceed in a downward direction. In morpho- 
logy and sociology, evolution at first engendered a somewhat shallow 

Psychology. The mind of man can be studied in two ways, 
rationally or empirically. If we accept some metaphysical system of 
the Universe, say that of the Roman Church or that of the German 
materialists, we can deduce rationally the place of the human mind 
in that system. On the other hand, making no assumptions, we can 
investigate mind by empirical observation, either by introspection 
with Locke, or by objective observation and experiment. This last 
method makes psychology a branch of natural science. 

Early in the nineteenth century German universities were still 
combining rational psychology with cosmology and theology. In 
England and Scotland empirical psychology had appeared, and at 
first, led by Mill and Bain, followed the introspective method. In 
France mind was already being examined by external means as a 
physiological and pathological problem. 

And about the middle of the century physical methods became 
general. Helmholtz studied physiological acoustics and the physio- 
logical basis of music and speech. E. H, Weber observed the limits 
of sensation, and found that the increase in stimulus necessary to 
cause an equal increase in sensation must rise in geometrical pro- 
gression. Wundt made measurements on the sensation of time. Darwin 
studied the expression of emotion in animals and man. 

Physical science is analytic, and may regard a problem successively 


from different aspects, mechanical, chemical or physiological, in each 
resolving the subject of study into simple concepts such as atoms or 
electrons. But biology, while using physical methods, also sees in 
each living being an organic whole, and each man feels a deep-seated 
consciousness of unity of being. Since each man's mind is fully 
accessible only to himself, this consciousness of unity cannot be 
investigated adequately by the methods of natural science; neverthe- 
less the fact of organism is important. 

In the human being physical and psychical phenomena clearly run 
parallel they are simultaneous if not connected. The theory of 
psycho-physical parallelism, which can be traced back to Descartes, 
regards consciousness as an epi-phenomenon of the changes in the 
nervous system, which are more accessible to examination. Whether 
the two are distinct or connected and, if connected, whether the 
nervous system or the consciousness is the master, remains a problem 
perhaps insoluble. Again, is the feeling of unity a reflexion of a 
reality, and has the mind or soul an independent existence, or is it 
built up by the grouping together of sensations, perceptions and 
memories? Such are the questions posed, but not yet answered, by 


Genetics. Once more the roles are reversed. During the last 
fifty years, biology, though adding greatly to knowledge, has followed 
along lines already laid down, while physics and chemistry, absorbing 
the system of Galileo, Newton and Dalton in wider generalizations, 
have revolutionized both science and philosophy. ^ 

For the most part, naturalists, accepting Darwin's work as final, 
had given up experimenting on variation, though some, like de Vries 
and William Batesori^ 1861-192 6), were beginning to examine scien- 
tifically the large and sudden mutations familiar to practical horti- 
culturalists. But in 1900 came the rediscovery of Mendel's forgotten 
writings, buried for forty years in the volumes of a local society. 

G. J. Mendel (1822-1884), Abbot of the Konigskloster at Briinn, 
made a series of experiments on the cross-breeding of the tall and 
dwarf varieties of green peas. All the hybrids were tall, outwardly 
resembling the tall parents, but when they were bred among them- 
selves, on the average of large numbers three-quarters of the progeny 
were tall and one-quarter dwarf. The dwarfs in turn all bred true, 
while the others again produced pure dwarfs, pure tails and mixed 
tails. The facts are explained if we suppose that the germ cells ol 
the original plants bear tallness or dwarfness as a pair of contrasted 
characters, and that tallness is 'dominant', so that it always shows 
if present, while dwarfness is 'recessive', and only shows if brought 
in from both sides. Then the probabilities of the conjunctions of 
different germ cells agree with the observed facts. Thus these biological 
qualities are reduced to indivisible units, and their behaviour to an 
exercise in the theory of probability. It is interesting to compare this 
result with the atomic and molecular theory and the recent quantum 
theory in physics. In neither case can we predict the fate of a single 
unit, but, among large numbers, the probable distribution can be 

Many Mendelian characters have now been traced in plants and 
animals. They seldom show such simple relations as in green peas; 

DSH 9 


characters may be linked in pairs, so that one cannot appear without 
the other, or they may be incompatible and never be present together. 

Investigations into cell structure by T. H. Morgan and others 
showed that within each cell-nucleus is a definite number of thread- 
like bodies which have been named chromosomes. If two germ cells 
unite, the fertilized ovum will contain double the original number of 
chromosomes. When the ovum divides, every chromosome divides 
likewise, the two parts going to the two daughter cells. Thus every 
body-cell contains a double set of chromosomes derived equally from 
the twoparents. In the germ cells, at the last stage of transformation, 
the icnromosomes unite in pairs, and the number is halved. The agree- 
ment of these cell phenomena with Mendelian inheritance was noticed 
by several people and it was put into definite form by Sutton. 

Morgan and his colleagues in New York have worked out these 
relations more fully in the fruit-fly Drosophila, in which generations 
of large numbers succeed each other at intervals of ten days. They 
have found a numerical correspondence between the number of 
groups of hereditary qualities and the number of pairs of chromo- 
somes, each being four. In the garden pea the number is seven, in 
wheat eight, in the mouse twenty, in man probably twenty-four. 
Even with twenty pairs of chromosomes, there will be over a million 
possible kinds of germ cells. It is easy to understand why no two 
individuals are identical. 

The number of chromosomes in a reproductive cell is considered 
basic and is called the 'haploid 5 number. When fertilization occurs 
and two haploid numbers are brought together by the, union of two 
nuclei, the resulting new individual is said to be 'diploid', but more 
than two haploid sets may appear. This polyploidy occurs in wheat, 
oats and cultivated fruits. Sweet cherries are diploids, plums hexa- 
ploids, while apples may be complex diploids or triploids. If a 
polyploid has an odd number of chromosomes which cannot be 
halved equally in the formation of reproductive cells, irregularities 
in chromosome distribution may take place, generally leading to 
sterility. Many varieties of fruit, Cox's Orange Pippin among apples, 
various plums, and all sweet cherries are unable to fertilize themselves, 
and need the near presence of some other variety to set their fruit. 


Sex determination has been shown to depend on two factors, 
hereditary and developmental; the chromosomes which fix sex have, 
in some cases, been identified microscopically, while Crew has 
described the reversal of sex characters in fowls. 

Again, so called genes may prevent the development of certain 
substances or qualities ; some of these are fatal to the organism, as in 
plants which inherit genes inhibiting chlorophyll formation. Here 
genetics and biochemistry interact. The biophysicist and biochemist 
describe life as far as may be in physical and chemical terms, but 
many phenomena still elude this method. As Sherrington insists, 
bodily organs develop before their function can be used; the complex 
structure of the eye is built up before the eye can see. 

Fertilization shows two steps stimulation of the ovum and the 
union of the opposite nuclei, and stimulation can sometimes be 
performed parthenogenetically. If an ovum divides by falling into 
halves, it forms 'identical twins', while, if two ova are fertilized 
simultaneously, 'fraternal twins' result, and they may be no more 
alike than any two children of the same parents. 

Heredity has also been examined further by the statistical study 
of large numbers initiated by Quetelet (p. 123) and complications 
due to mixture of different groups detected. Karl Pearson and others 
have traced the inheritance of qualities by measuring them in parents 
and offspring. If a group of men exceed the normal stature by four 
inches, their sons will on the average of large numbers exceed it by 
two inches half as much. This relation is expressed by saying that 
the coefficient of correlation is one half or 0-5. If the sons had reverted 
to the normal, there would have been no correlation and the coeffi- 
cient would be zero. Most hereditary qualities have coefficients of 
correlation ranging round 0-5. De Vilmorin, a member of a long- 
established family of French seedsmen, got better results in breeding 
plants by selecting as parents not from the qualities of individuals, 
but from those of lines which show continued good characters. The 
same holds true in breeding animals. It is a fallacy for a prospective 
bridegroom to say * I am not marrying her family'. The children may 
be all too likely to show that he has perforce done so. 



Though at one time there was controversy between Mendelians 
and Biometricians, in any complete study of heredity, as R. A. Fisher 
has shown, there is room statistically for both methods of inquiry. 

The theory of evolution has become more and more firmly estab- 
lished as fresh geological evidence has accumulated. Some biologists 
still hold to Darwin's natural selection, acting on small variations, 
and some look to Mendelian mutations. But others feel that neither 
explanation gives an adequate cause for the present transmutation 
of species. It may be that living beings were more plastic in former 
ages, and are too fixed nowadays to show the fundamental changes 
necessary to produce new species, though the superficial modifications 
which give new varieties are still possible. 

\ A survival of the fittest is no use to a nation unless the fittest have 
a preponderating number of children. An examination of books of 
reference in 1909 by my wife and myself showed that in England the 
landed, professional and upper commercial classes had diminished 
their output of children to less than one half of what it was in the 
years before 1870. An almost equal fall was shown by the statistics 
of Friendly Societies, whose members are mostly skilled artisans. On 
the other hand, miners and unskilled labourers were maintaining the 
numbers of their children, as were unfortunately the feeble-minded. 
It seems likely then that the differential birth rate is tending to breed 
out ability. Scholarships may supply the deficiency for a time, but 
the amount of ability in the country is limited. If it all be picked out 
and raised from the ranks, it may partially be sterilized by a decreased 
birth rate. Again, legislation, passed with other objects in view, may 
favour or depress special strains in the population. Death dues, for 
instance, are destroying the old landed families, on whom the nation 
has relied for unpaid work in the counties, and underpaid work in 
the Church, the Army and the Navy. 

Much new evidence is now available about the effects of light and 
heat on the germination of seeds and the growth of plants. Maxima 
and minima of light and temperature are needed at some stages, and 
a process of * vernalization* has been developed, whereby growing 
seeds are cooled for a time and the season of fruiting controlled. The 
subject of ecology, dealing with the relations of plants and animals 


with their inorganic environment and with other living creatures, is 
rapidly expanding. 

Geology and Oceanography. Information on human evolution 
has recently been obtained by the discovery of fossil man-like apes 
and ape-like men. Early forms of anthropoid apes were found in the 
Egyptian Fayum and the foot-hills of the Himalayas, and in 1912 
Dawson and Woodward discovered at Piltdown in Sussex man-like 
remains in Pleistocene deposits. It is possible too that the Chinese 
specimens named Pithecanthropus Pekinensis may be members of the 
group from which later types of men descend, while Neanderthal 
men were an aberrant line. Neolithic men came later, bringing with 
them into Western Europe traces of the world civilizations of Egypt 
and Mesopotamia. Considering fossils in general, Cambrian rocks, 
such as are found in North Wales, contain examples of most groups, 
but below Cambrian levels fossils fail. Somewhere between 500 
million and 2000 million years ago, life appeared on the Earth how 
we do not know. 

V/The recent application of physical methods, such as an accurate 
measurement of gravity, has given information about regions of the 
Earth lying below the surfaces of the ground and sea. Seismic 
observations show that waves due to near earthquakes have travelled 
mainly through the crust of the Earth, while those from distant 
disturbances have traversed deeper regions. Indications suggest that 
the crust is shallow, perhaps 25 miles thick, while the central core, 
which may be chiefly liquid iron, has a radius more than half that 
of the Earth itself. 

Artificial waves can be made by firing explosives, and, by noting 
the time of their echoes, the depth of the sea, or of discontinuities in 
the strata, or the distance of a buoy, can be found. 

In the migration of fish there is usually a movement to a definite 
area for spawning, then a reverse movement in search of food. For 
instance, the salmon deposits its eggs in the upper reaches of rivers, 
the young move down to the sea, and when mature go back to the same 


rivers, thus showing individual memory. The European eel spends its 
adult life in fresh water, and migrates thousands of miles to spawn 
in the deeps of the Sargasso Sea. Many sea fish feed on diatoms and 
other minute organisms, collectively known as plankton; the drift of 
which shows where food and therefore fish will later be found. 

Biochemistry, Physiology and Psychology. In 1912 (Sir) Frederick 
Gowland Hopkins showed that young rats, fed on chemically pure 
food, ceased to grow till minute quantities of fresh milk were added. 
Milk therefore contains substances necessary for growth and health, 
substances which Hopkins called ' accessory food factors ', later known 
as vitamins. The most striking character of vitamins is the fact that 
minute quantities are enough to produce their beneficial effects. 
Those first investigated were given the letters A, B, G and D. 

Vitamins A and D are present in animal fats, such as butter and 
cod-liver oil, and in green plants. A protects from infection; D is 
necessary for the calcification of bones and protection from rickets, 
and can be made by the action of ultra-violet light; B is found in the 
husks of various grains, in yeast, etc., and protects from diseases such 
as beri-beri and polyneuritis ; G is present in fresh green plants and 
in fruits such as the lemon, and protects from scurvy. / 

Much information about vitamins has been found more recently. 
Vitamin A, proved by von Euler in 1929 to be allied to the vegetable 
pigment carotene, an unsaturated alcohol, is necessary for the health 
of the central nervous system, the retina and the skin; night blindness 
is an early symptom of vitamin A deficiency. 

The first vitamin to be identified chemically was the anti-rachitic D ; 
it is a complex alcohol known as ergosterol, and was isolated in 1927. 
Vitamin E maintains mammalian fertility; K is required for the 
normal coagulation of blood and so as a guard against the 'bleeding 
disease', haemophilia; chemically both these two are quinone 

Vitamin B has proved to be a mixture; the anti-neuritic Bj or 
aneurin, found in yeast, etc., has been isolated in a crystalline form 
and proved to be a pyrimidine-thiazole compound. Some patients 
need the mass action of the pure Bj for a cure from neuritis. Five 


other constituents of the B complex have been described. Vitamin G 
is ascorbic acid, a reducing compound C 6 H 8 O 6 , allied to sugar. Its 
formation precedes chlorophyll and carotinoids in germinating seeds. 
In the animal body it is present in large amounts in two of the endo- 
crine glands, the pituitary and the adrenal cortex. This is only a 
very short account of the many investigations which have been made 
since the discovery of vitamins. 

Since Fischer synthesized mono-saccharide sugars (p. 106) investi- 
gations on the structure of di-saccharides such as cane sugar have 
been made by others, and ring formulae have been proposed. 
Fischer's work on amino-acids has also been followed up. But the 
most complex polypeptides yet prepared, with molecular weights 
somewhat exceeding 1300, are still far from proteins. By measure- 
ments of osmotic pressure and rates of sedimentation, proteins have 
been found to fall into two groups, with molecular weights that are 
simple multiples of 35,000 and 400,000 respectively. Indications of 
their structure have been given by X-ray examination, but no protein 
has yet been synthesized. This gap between the laboratory and life 
remains open. 

X-ray photographs have also helped to explain in molecular terms 
the fibrous nature of such things as cellulose and the myosin of 
muscle (p. 135). Langmuir has related the constitutional formulae 
of organic compounds to their physical properties, while he and 
Adam have extended these methods to surface films. F. G. Donnan 
formulated in 1911 a theory of equilibria in membranes permeable 
to one kind of ion, which explains the phenomena of osmotic pressure 
and electric potential in such substances as the colloids of proteins. 

The chemistry of blood includes the study of haematin, the structure 
of which has four rings linked by an iron atom, and combined with 
the protein globin to form the oxygen-carrying substance haemo- 
globin. In plants, Willstatter has shown that the nucleus of the 
chlorophyll molecule is similar to haematin with a magnesium atom 
replacing iron. He found two chlorophylls with slightly different 
composition, and in 1934 he gave diagrams of their structural 


Oxidation in the tissues has been shown by Wieland to be carried 
on by specific enzymes, called dehydrogenases. They are present in 
all living tissues and able to liberate hydrogen to combine with 
oxygen. Muscular contraction was shown by Hopkins and W. M. 
Fletcher in 1907 to depend on the breakdown of glycogen to lactic 
acid. This process has since been analysed into eight chemical stages 
catalysed by at least ten enzymes. 

Besides oxidation in the tissues there are also changes involving 
the addition of water and the shedding of amino-groups. The excre- 
tion of these bodies in the form of urea has been shown by Krebs to 
require a complicated cycle of reactions. Carbon dioxide is carried 
in the blood as bicarbonate, and Meldrum and Roughton have shown 
that it is released in the lungs by an enzyme, carbonic anhydrase. 

In 1902 Bayliss and Starling found that pancreatic secretion is 
induced by a chemical substance formed in the intestine and carried 
to the pancreas by the blood. This led to the detection of other 
similar internal secretions, which Hardy named hormones (op/x,acej, 
I rouse to activity). They are each secreted in one gland or organ 
and carried by the blood to others, for instance insulin, discovered in 
1922 by Banting and Best by experiments on dogs, and used to obviate 
the effects of diabetes. The thyroid gland has already been considered 
(p. 1 1 6), but the work on other endocrines, that is the glands which 
form hormones by internal secretion, is so voluminous that it is now 
treated as a separate subject and called endocrinology. In this the 
co-ordinating role of the pituitary gland is specially important, 
particularly in the phenomena of sex. 

The hormone adrenalin is discharged into the blood in conditions 
such as fright or anaesthesia, which stimulate the splanchnic nerves, 
Conversely, the injection of adrenalin produces the physical 
symptoms of emotion or fear. 

In the study of the nervous system the pioneer work was done by 
Sir Charles Sherrington from 1906 onwards. Messages pass by the 
peripheral nerve fibres from the sense organs or receptors to the 
central nervous system and from it to the muscles and glands. But 
how are the incoming messages co-ordinated and the outgoing con- 


trolled in such a way that the animal responds as a whole with 
appropriate movements ? Sherrington has shown that much of this 
'integrative action 5 of the nervous system can be made intelligible by 
a study of the simple reflexes and their interaction. An incoming 
message may have a dual effect, exciting certain nerves and depressing 
or inhibiting others, sometimes helped by the adjustment of the time 

Experiments on nerve-impulses are facilitated by modern physical 
instruments. Single nerve-fibres can be examined, and minute heat 
effects have been detected by A. V. Hill, Gasser and Erlanger. 

The highest part of the nervous system, the brain, is connected 
with sight and hearing, putting the animal into touch with distant 
objects. Mental functions have their seat in a part of the brain called 
the cerebrum, and especially in its cortex, which has been mapped 
out and its local reactions studied especially by Horsley, Head and 
Sherrington. Another part of the brain, the cerebellum, is connected 
with balance, posture and movement, acting in response to stimuli 
received from the muscles of the body and from the labyrinth of 
the ear. 

The involuntary nervous system, which controls the unconscious 
bodily functions, was first studied thoroughly by Gaskell and Langley. 
Pavlov held that here psychological ideas were unnecessary. The 
simple unconditioned reflexes pass into complex reflexes conditioned 
by other factors, but the method of observing stimulation and resultant 
action may still be applied. This does not touch the problem of the 
nature of the intervening consciousness, but it has led, in the hands 
of Lloyd Morgan and J. B. Watson, to a school of psychology called 
behaviourism, which ignores consciousness in its investigations. Freud 
too held to a strict determinism, explaining our most trivial mistakes 
and our most cherished beliefs by the operation of instinctive forces 
which grow with the body and may cause mental ill-health if their 
development is checked or distorted. 

All this work, culminating in behaviourism and Freud's deter- 
minism, has led to a mechanistic trend in recent psychology, which 
seeks to build up the individual from an accumulation of experiences 
and memories. But one may point out that to the behaviourist a man 


is only a nexus of stimuli and responses because the method of investi- 
gation by its own definitions and axioms is merely the study of the 
relations between stimuli and responses; it deliberately excludes 
consciousness and its problems. Some physiologists and philosophers 
point to purpose in the action of living beings as wholes, and the 
adaptation of embryonic organs to their final functions, as evidence for 
a modern form of vitalism. Perhaps we are still subject to the swings 
of the pendulum. The modern concept of organism recalls Aristotle's 
dictum that the animal body is not the mere sum of its parts. 

Physiology and biochemistry are working their way into medicine. 
Besides the instances already mentioned, we may cite as other 
examples Minot's use of liver extract to cure pernicious anaemia, and 
the avoidance of miners' cramp by drinking salt water instead of 
fresh. Heavy labour carries away salt in the sweat, and fresh water 
dilutes the body fluids too much. 

Viruses and Immunity. The first description of an ultra-micro- 
scopic, non-filterable virus was due to Ivanovski, who discovered 
one in tobacco-mosaic in 1892. Many others have since been 
found in both plants and animals. Small-pox, yellow fever, measles, 
influenza and the common cold, in cattle foot-and-mouth disease, 
in dogs distemper, in plants tulip-break, potato-leaf-roll and tobacco- 
mosaic are recognized as due to viruses. 

The sizes of the virus particles have now been estimated in several 
ways. Filters can be made of collodion films with minute pores of 
regular size, measured by observing the rate of flow of water through 
a given area of film. Other methods depend on photography, on an 
ultra-violet or electron microscope, or on a high-power centrifuge. 
Particles range from 300 millimicrons, an approach to bacteria, to 
about 10 millimicrons in foot-and-mouth disease, a millimicron being 
the millionth of a millimetre. 

Is the virus a minute living organism or a large chemical molecule? 
W. M. Stanley of Princetor; obtained from tobacco virus a protein 
of high molecular weight which had the virus properties and also 
crystalline affinities, and other viruses are regular crystals. But they 
have some of the properties of living organisms; the diseases they 


cause are infectious, and the virus particles reproduce themselves in 
the new host. They seem to be borderline entities, and perhaps, as 
further evidence accumulates, they may throw light on the origin of 
life; but that is not yet. 

The methods by which viruses travel are various. In an animal 
host, they may move through the blood, nerves or lymph, and the 
transmission from one host to another is often a complex process. 
Tobacco-necrosis is carried by an air-borne virus. Some viruses are 
carried by insects, such as the green-fly or thrips, while the viruses 
of louping-ill in sheep and red-water in cattle are conveyed by ticks. 
Kenneth Smith has found a plant disease to produce which two 
viruses are needed, one borne by insects and one otherwise. 

An infectious disease is often found to make the patient immune 
from further attacks, the classical instance being the mild cow-pox 
which protects from the virulent disease (p. 116), probably by the 
formation of the same protective substances which are effective after 
small-pox itself. The body reacts to the injection of bacteria and many 
other proteins by making substances which can neutralize the poison; 
they are known as 'anti-bodies'. The substances causing this reaction 
are called 'antigens'. Heidelberger and Kdndal have given some 
evidence of combination in definite chemical proportions between 
antigen and anti-body, but the action has also been explained as the 
union of oppositely charged colloidal particles. 

Paul Ehrlich ( 1 854-1 9 15), responsible for much of the early work on 
immunity, produced in 1912 an arsenic compound, which he named 
'salvarsan', with a specific destructive action on the micro-organism 
producing syphilis, and in 1924 Fourneau obtained a derivative of 
carbamide which destroys the parasite of sleeping sickness. A series 
of synthetic drugs, based on sulphanilamide, have been found to 
control diseases due to streptococci and pneumococci, some acting, 
as Fildes has shown, by depriving the bacteria of substances necessary 
for their growth. Fleming's penicillin, made from mould, is specially 
powerful; sulphaguanidine is a specific remedy for dysentery. 

Dunkin and Laidlaw found that the virus of distemper, weakened 
by formaldehyde, gave considerable immunity to dogs, confirmed by 
subsequent injections of virus. Some virus diseases, foot-and-mouth 


in cattle and influenza in man, show a variety of different strains, 
and immunity to one strain may not protect from others. This makes 
it difficult to secure protection. 

Anthropology. Physical anthropology is, I suppose, a branch 
of natural history. Social anthropology touches on one side psycho- 
logy and on others geography, sociology and comparative religion. 

Mankind show marked differences in different parts of the world, 
the chief distinguishing feature being skin-colour, to which other 
characters are attached. The population of Europe has been divided 
into three races. In the north, and especially round the shores of 
the Baltic, are found tall, fair people with long-shaped skulls, who 
have been called Nordic. In the south, near the Mediterranean, and 
stretching up the lands of the Western Atlantic, are short, dark men 
also with long-shaped skulls, the Mediterranean race, while pushing 
between them are the Alpine people with Asiatic affinities, stocky, 
of medium colouring, with broad round skulls. The three races are 
only found in purity in small areas, but they are revealed by a general 
study, which shows a gradual approach to the type as we move 
towards its chief home. 

It was formerly thought that similar civilizations might arise 
spontaneously in different parts of the world, but studies of various 
arts have favoured the alternative view that they often indicate a 
common origin. For instance, the widespread custom of erecting 
monoliths and other stone structures orientated in relation to the 
Sun and stars, which is seen from Egypt to Stonehenge, shows a 
connexion, not necessarily of race, but of civilization, perhaps due 
to the intermingling of peoples, or close intercourse in trade. 

A vast collection of facts about primitive people in ancient and 
modern times has been put together by Sir James Frazer in his great 
book the Golden Bough, while the psychology of existing savage races 
has been studied by anthropologists like Rivers who have lived 
among them. Rivers introduced a new method; having found that 
the general terms in which former observers put their questions were 
quite unintelligible to the savage mind, he asked single questions and 
generalized afterwards. For instance, it is useless to ask a man if he 


can marry his deceased wife's sister. One must first inquire 'Can 
you marry that woman?' and then 'What relation are you to her 
and she to you?' 

The old view of religion was that it was a body of doctrine, theology 
if the religion was one's own, or mythology if that of other people. 
Ritual was merely a form in which these beliefs were expressed 
publicly. Greek religion, for example, to the nineteenth century 
meant Greek mythology, though neither Greek nor Roman had any 
creed or dogma. But underlying the mythology were the Greek 
mysteries, and with them a system of ritual containing magical 
elements. Ritual is prior to and dominant over any definite belief. 
Compare this with some forms of modern psychology which say 
* I react to outer stimuli and so I come to think.' 

The relations of magic to religion and science are still uncertain. 
Some hold that magic is the common matrix out of which both 
religion and science arose, but Frazer thinks that they grew in series 
magic, religion and then science. Rivers says that mana y a vague 
sense of awe and mystery, is a more primitive source of magic and 
religion than the animism described by Tylor. Magic is an attempt 
to get control over nature: the savage wants the Sun to shine, and 
so dances a Sun-dance. Sometimes he is related to some animal, 
which becomes endowed with sanctity it may be taboo and must 
not be touched, it may be that by eating its flesh he will acquire its 
strength. A very widespread magic is that which, by rehearsing 
the drama of the year, hopes to secure fertility for crops, beasts and 

When this fails, or otherwise ceases to satisfy, men turn to gods. 
At a high level, Tammuz of the Babylonians became Adonis of the 
Greeks. Tammuz is the spouse of Ishtar the great mother, goddess of 
fertility, and the union of Adonis and Aphrodite was necessary in 
Greece for the fertility of the Earth. These underlying rites of magic 
and mystery religions sought mystic union with nature or the divine 
through rites of initiation and communion. By eating the body of 
a god, corn for a corn god, the savage shares his attributes and powers. 
Drinking wine in the rites of the vine-god Dionysos is not revelry 
but a sacrament. 


The Physical Revolution. During the last five years of the 
nineteenth century, a complete change in physical science began. 
The chemical atom, revealed by Dalton ninety years before, and 
accepted as the indivisible unit of matter, was shattered into frag- 
ments by J. J. Thomson and Rutherford. Then the facts of spectra 
led Planck to the theory that radiation is emitted in gushes or quanta, 
while Bohr and others imagined models of the atom in which New- 
tonian dynamics no longer held, and, models discarded, explanations 
had finally to be left in the equations of a new science of wave- 
mechanics. Newton's ideas of absolute space and time and his scheme 
of gravitational forces, which had replaceo^Aristotle's teaching and 
ruled mechanics and astronomy for two centuries, were superseded 
by iJinstein; time and space became relative to the observer, and 
gravity a curvature in a space-time continuum. &V f 

The first shadow of the coming events was the accidental discovery 
by Rontgen in 1895 that covered photographic plates became fogged 
if electric discharges were passed through highly exhausted glass 
bulbs in their neighbourhood. Rays of some sort let us call them 
X-rays must be produced in the bulb, and pass through the glass 
and through the opaque coverings of the photographic plates. The 
tremendous benefits which this discovery has conferred on mankind 
through medicine and surgery will be known to all my readers. 

When X-rays pass through a gas, they make it a conductor of 
electricity, and this process was jointly investigated by Thomson and 
Rutherford. If the rays were cut off, the conductivity persisted for 
a time and then died away. It was also removed at once by passing 
the gas through glass wool or between two plates oppositely electrified. 
The facts could be explained by supposing that the conductivity was 
due to ions as in liquids, but that in gases they had to be formed by 
some ionizing agency such as X-rays, and, if left alone, gradually 
recombined and neutralized each other. 


Cathode Rays and Electrons. It has been known since 1869 
that when a glass tube with platinum electrodes is very highly 
exhausted with an air pump, and an electric discharge passed through 
it, rays (since called cathode rays) fly off in straight lines from the 
negative electrode or cathode. It is these that give rise to X-rays 
where they strike solid objects. Cathode rays were thought to be 
either waves of the same nature as light or flights of negatively 
electrified particles, the latter alternative chiefly because they are 
deflected from their straight path by a magnetic force. Assuming 
the particle theory, the deflexion will be proportional to the electric 
charge and inversely proportional to the mass of the particles, that 
is proportional to e/m, the ratio of charge to mass. But it must also 
depend on the velocity v with which the particles move, so, taking 
e/m as one quantity, we have two unknowns, e/m and v y and shall 
want two equations to determine them. Several physicists, among 
them Wiechert and Kaufmann, measured the magnetic deflexion, 
and guessing, or getting indirect evidence of other properties, obtained 
values for e/m and z>, the latter about one- tenth that of light, and the 
value of e/m much greater than for the hydrogen ion in liquid 
electrolysis. Next J. J. Thomson ( 1 856- 1 940, Professor at Cambridge, 
later Sir Joseph Thomson, O.M.), directing the rays into an insulated 
cylinder, measured the negative charge they delivered and the heat 
developed when they struck a thermo-couple. The latter quantity 
gave the kinetic energy of the rays, which involves their velocity and 
supplies the second equation needed to determine both e\m and v. 

But, in October 1897, Thomson got clearer results by a better 
method. If the cathode-ray stream consists of charged particles, they 
should be deflected by an electric as well as by a magnetic force. 
Attempts to get this deflexion had hitherto failed or proved incon- 
clusive; but Thomson succeeded with the glass apparatus shown in 
the diagram, C is the cathode, A the anode, pierced by a slit which 
lets through a beam of rays which is further cut down by a second 
slit at B. The narrow pencil thus obtained fell on a fluorescent screen 
or photographic plate at^, after passing between two insulated metal 
plates at D and E. These plates, connected with the opposite poles 
of a high-tension battery, set up an electric force between them, and 


an electro-magnet, surrounding the whole apparatus, could be used 
to produce a magnetic field also acting on the rays. The electric 
deflexion from p to p' gave a second value for e/m 9 so that both e/m 
and v were determined. The measurements again showed that e/m 
was much greater than the corresponding value for the hydrogen ion 
in liquids, later work giving a ratio of 1837. Thus it became clear 
that either the charge was greater or the mass less than for hydrogen. 
Thomson thought that the mass must be less, but sought further proof. 
Much indirect evidence had accumulated suggesting that the 
charge on a gaseous ion was the same as on a monovalent ion in 
liquids, and this was now made definite. C. T. R. Wilson had shown 

FIG. 14. Thomson's apparatus for cathode rays 

that ions, like dust particles, act as cloud nuclei for the condensation 
of drops of water in moist air, and Thomson in 1899 usec " this action 
to find the electric charge carried. Then Townsend measured the 
rates of diffusion of ions through gases, and from his results again 
calculated the charge. All measurements agreed in showing that 
gaseous ions carry the same charge as monovalent ions in liquids. 

Finally Thomson measured both e/m and v for the same ions 
those ejected when ultra-violet light falls on a zinc plate and got the 
same result. The proof was complete. Moreover, while the velocity 
varies, e/m is the same whatever be the nature of the electrodes or of 
the residual gas. The cathode ray particles, which Thomson called 
at first by the Newtonian name of 'corpuscles', are the common basis 
of matter sought by men from the Greeks onwards. 

This discovery linked up with another line of research. On 
Maxwell's theory, light is an electro : magnetic wave, and must be 
emitted by vibrating electric systems. Lorentz therefore framed a 
theory of matter, in which parts of atoms are electric units, the 


vibrations starting light. This was supported by a discovery of 
Zeeman, who in 1896 found that lines in the spectrum of sodium 
were broadened by a strong magnetic field. From the broadening, 
it was possible again to calculate e/m. The same figure was obtained. 
To his electric unit Lorentz gave Johnston Stoney's name of ' electron ', 
and later on this name was implicitly accepted by Thomson. 

Thomson's picture of the atom was a uniform sphere of positive 
electricity, in which electrons are either at rest or revolving in 
planetary Newtonian orbits. When an atom loses an electron, the 
electron becomes a negative ion, while the residue is an atom posi- 
tively electrified or a positive ion. One electron would place itself 
at the centre of the sphere, two at the opposite ends of a diameter, 
three at the corners of a triangle and so on, but with seven or eight 
the system becomes unstable, and a second shell of electrons is formed. 
This was held to explain chemical valency, and the recurrence of 
properties in the Periodic Table at each eighth element. But 
Thomson's sphere of positive electricity had to give way to Ruther- 
ford's theory of a nucleus, and Thomson's essentially Newtonian 
outlook pass into newer, less comprehensible ideas. 

Radio-activity. X-rays produce marked effects on phospho- 
rescent substances, and soon after Rontgen's discovery a search began 
for bodies which conversely might emit any sort of rays. In 1896 
Henri Becquerel found that salts of uranium, and uranium itself, 
continually give out rays which affect a photographic plate through 
black paper and other screens, and were soon afterwards found to 
act like X-rays in making gases conductors of electricity. 

In 1900 M. and Mme Curie made a systematic search of chemical 
elements and compounds and of natural substances. They found that 
pitchblende and other uranium minerals were more active than the 
element. Using radio-activity itself as a test and guide, they separated 
by chemical means a surprisingly active substance which they called 
radium. Other observers followed with elements which were named 
polonium and actinium. The amount of radium in pitchblende is 
very small, many tons of the mineral yielding only a small fraction of 
a gram of a salt of radium. 


In 1899 Rutherford (see Plate VII, facing p. 123) of Montreal, 
later of Manchester, and finally Lord Rutherford of Nelson, O.M., 
Sir J. J. Thomson's successor at Cambridge, discovered that the 
radiation from uranium consists of three kinds of rays to which he 
gave the Greek letters a, jS and y. The a rays, the most powerful at 
short range, will only go through thin screens; the j9 rays through 
half a millimetre of aluminium before their intensity is halved, and 
the y rays through much more. By measuring their magnetic 
deflexion a rays have been found to be atoms of helium carrying a 
double positive charge, jS rays negative electrons, while y rays have 
proved to be waves like light, but with enormously shorter wave- 

Crookes found that uranium, precipitated from solution by ammo- 
nium carbonate, gave a small quantity of an active substance which 
he named uranium X, the residual uranium being for a time less 
active. Rutherford and his colleagues discovered many such chemical 
changes, yielding from radium and thorium, among other products, 
radio-active gases which they called emanations. Radio-activity was 
found always to be accompanied by chemical change, new elements 
appearing and a rays, or /? and y rays, being shot off. The pedigree 
of the family beginning with uranium and containing radium, has 
been traced for fifteen generations before it ends in the inactive 
element lead. 

The rate of decay in activity of these bodies varies enormously. 
Uranium would take 4*5 x io 9 years to fall to half value, radium 
1600 years, radium emanation 3-82 days, radium A 3-05 minutes, 
and radium G io~ 6 second. Some give out only a rays and others 
jS and y rays. Each single change proceeds so that the rate of decay 
during each short interval of time is proportional to the activity at 
the beginning of the interval. This is the same law of change as that 
shown by a chemical compound dissociating molecule by molecule 
into simpler products. 

In 1903 Curie and Laborde discovered the remarkable fact that 
the compounds of radium continually emit heat, and calculated that 
one gram of radium would give about 100 gram-calories of heat per 
hour. They found the emission of heat was not changed by high or 


low temperatures. The amount of energy thus liberated is many 
thousand times more than that of the most violent chemical action 

Thus we have chemical changes of monomolecular type, giving a 
new element at each change and an enormous output of energy. 
Taking all these properties into account, Rutherford and Soddy in 
1903 explained the facts by the theory that radio-activity is due to 
an explosive disintegration of the elementary atoms, in which an 
atom here and there out of millions explodes, flinging off an a particle, 
or a jS particle and a y ray, leaving a different atom behind. 

The atomic theory from Democritus to Dalton had no hope of 
dealing with atoms singly; it could only treat them statistically in 
large, indeed gigantic, numbers; the kinetic theory of gases indicates 
that the number of molecules in one cubic centimetre is about 
2'7Xio 19 . But radio-activity gave several ways of detecting the 
presence of single atoms. Firstly, Grookes observed with a magnifying 
lens scintillations on a fluorescent screen of zinc sulphide exposed to 
a speck of radium bromide shooting out a rays, that is atoms of 
helium; each atom as it strikes the screen gives a flash of light. 
Secondly, Rutherford counted the kicks of an electrometer needle as 
a particles shoot through a gas, producing ions as they pass. Thirdly, 
G. T. R. Wilson used a rays to ionize a moist gas, the ions forming 
nuclei of condensation, so that each a particle gives a cloud-track in 
the gas. From the number of a particles the 'life' of the radium, that 
is the time it takes to halve its activity, can be calculated. 

The cloud-tracks of <x rays are usually straight, but sometimes a 
sharp change in direction is seen (see Plate VIII, facing p. 148). The 
forces exerted by electrons on the much more massive a particle 
cannot be enough to produce such a turn, but it is explained at once 
if we imagine with Rutherford that the positive electricity, which 
Thomson supposed distributed evenly over a comparatively large 
sphere, is concentrated in a very dense minute nucleus at the centre. 
If the atom is that of hydrogen, the nucleus, which is then called a 
proton, has about 1837 times the mass of an electron. This heavy 
nucleus, with the mass of an atom, is massive enough to stop and 


turn a colliding a particle of the same order of mass. The hydrogen 
atom has one electron outside the nucleus. At first, with Newtonian 
preconceptions, it was thought that the electron circled round in a 
planetary orbit; this idea has been abandoned, but before describing 
its successor we must follow other lines of research. 

X-Rays and Atomic Numbers. The X-rays discovered by Rontgen 
are not refracted like ordinary light, and show little trace of reflexion 
or polarization. Unlike cathode rays or a and j8 rays, they are not 
deflected by magnetic or electric forces. But in 1912 Laue suggested 
that if X-rays were light of very short wave-length, they might be 
diffracted by the regular layers of atoms in a crystal, as light is 
diffracted by the regular scratches on a grating (p. 101), and a 
spectrum might result. This suggestion was verified experimentally 
by Friedrich and Kipping, and carried farther by Sir William and 
Sir Lawrence Bragg. Beginning with rock salt, a simple cubic type 
of crystal, the Braggs found spectral lines on a more diffuse back- 
ground, lines which showed that the distance between the layers of 
atoms was 2*81 x io~ 8 centimetre, and that the characteristic X-rays 
emitted from a target of palladium had a wave-length of 0-576 x io~ 8 
centimetre, only the one ten-thousandth part of the wave-length of 
sodium light. Electro-magnetic radiation is now known from the 
longest waves used in wireless telegraphy to the short waves of X and 
y rays, a range of about 60 octaves, of which only about one octave 
is visible light. 

The work on sodium and potassium chlorides showed no trace of 
NaCl or KG1 molecules; the crystals are made of alternate positive 
and negative ions. Extension to more complex inorganic bodies 
confirmed this view, the silicates for instance are silicon-oxygen 
skeletons enclosing positive ions. But organic chemistry is properly 
based on the concept of the molecule, and X-ray analysis has shown 
that the structural formulae of the chemist are correct. Again, the 
crystals of metals and alloys have been analysed, and several observers 
(Herzog, Astbury, Bernal, etc.) have examined complex biochemical 
substances such as cellulose, keratin and proteins. 

When the target bombarded by cathode rays was changed from 


Plate VIII. Tracks of a particles in oxygen, one showing a fork due to collision 
with an oxygen nucleus. The short branch of the fork was produced by the recoiling 
oxygen nucleus and the long branch by the deflected a particle. Measurements of 
the angles of deflection of the two branches showed that momentum and enenry 
were conserved in the collision. 

Plate IX 

The Spiral Nebula in Canes Venatici 


one metal to another, and the X-rays examined by using a crystal 
of potassium ferro-cyariide as a grating, H. G. J. Moseley found that 
the square root of the frequency of vibration (ft) of the strongest 
characteristic line in the spectrum increases by the same amount on 
passing from element to element in the Periodic Table. If vX that 
is wi, be multiplied by a constant adjusted to bring this step-by-step 
increase to unity, Moseley got a series of atomic numbers for solid 
elements from aluminium 13 to gold 79. Fitting in the other known 
elements, it was found that, from hydrogen i to uranium 92 (atomic 
weight 238'2), there were only four or five gaps for undiscovered 
elements, and some of these have since been filled. It is sad to record 
that the brilliant young physicist Moseley, soon after this great 
discovery, was killed in the first world war an incalculable loss to 
England and to science. 

Positive Rays and Isotopes. Cathode-ray particles are carriers 
of negative electricity, or rather perhaps are themselves disembodied 
negative electrons. In an exhausted tube the anode also is a source 
of rays. If holes are bored in a cathode placed opposite the anode, 
the rays go through the holes and can be detected on the far side. 
Their magnetic and electric deflexions were measured in 1898, first 
by Wien and then by Thomson, and showed that they were particles 
carrying positive charges with masses comparable with those of 
ordinary atoms and molecules. 

In 1910-11 Thomson used a large vessel very highly exhausted, 
with a long narrow tube through the cathode. This gave a very small 
pencil of rays which was recorded on a photographic plate inside the 
apparatus. The magnetic and electric forces were arranged at right 
angles to each other. The magnetic deflexion is inversely proportional 
to the velocity of the particles and the electric deflexion inversely to 
the square of the velocity. Hence, if identical particles of differing 
velocities exist in the rays, a parabola will be photographed on the 
plate (p. 59). The lines which appear depend on the nature of the 
residual gas in the apparatus. With hydrogen the fundamental line 
gives a value of io 4 for e/m, or io~ 4 for m/e, the same as for the 
hydrogen ion in liquid electrolytes. A second line has double this 


value for m\e, and indicates a hydrogen molecule with twice the mass 
of the atom carrying a single electric charge. 

With the gas neon, to which chemical measurements give an 
atomic weight of 20-2, Thomson found two lines, indicating weights 
of 20 and 22. This suggested that neon as usually prepared is a 
mixture of two elements, identical in chemical properties but of 
different atomic weights. Such elements also appear in radio- 
activity, and were called by Soddy 'isotopes' (ICTO-TOTTO?, occupying 
the same place in the chemical table). 

Thomson's experiments were carried farther by F. W. Aston, who 
obtained regular 'mass spectra' of many elements. Taking the atomic 
weight of oxygen as 1 6, the atomic weights of all other elements are 
very nearly whole numbers ; chlorine, for instance, which chemically 
is 35^46, was shown to consist of a mixture of two isotopes 35 and 37. 
When Aston's first apparatus (now in the Science Museum at South 
Kensington) was brought into action, results poured out. In 1933 
Aston said : ' At the present time out of all the elements known to 
exist in reasonable quantities, only eighteen remain without analysis ', 
and by 1935 about 250 stable isotopes were known. For practically 
every atomic weight up to 210 an element has been found; thus 
Prout's hypothesis has been confirmed. Some numbers harbour more 
than one element 'isobars', atoms of the same weight but different 
chemical properties. 

To the hydrogen nucleus or proton, Aston gave a mass of 1-0076 
now corrected to i '00837. In 1932 Urey, by a process of fractioniza- 
tion, discovered that a heavy isotope of hydrogen with mass 2, double 
the normal detected by Aston, was present in ordinary hydrogen to 
the amount of i in 4000. It is now called 'deuterium' and its ion a 
'deuteron'. By electrolysing water, Washburn obtained a new sub- 
stance, heavy water, in which hydrogen is replaced by the isotope. 
Heavy water was isolated by Lewis; it is about u per cent denser 
than ordinary water. 

The Structure of the Atom. If electrons in the atom revolved 
in Newtonian planetary orbits, they would emit radiant energy, and 
the orbit would contract with a consequent quickening of the period 


of rotation and of the frequency of the emitted waves. Atoms in all 
stages would exist, and therefore in all spectra radiation of every 
frequency should be found, instead of only the radiation of a few 
definite frequencies as seen in the line spectra of many chemical 

To meet these difficulties, Planck in 1901 devised a quantum 
theory, according to which radiation is not continuous but is emitted 
in gushes, so that, like matter, it exists only in indivisible units or 
atoms, not all of the same size, but with sizes proportional to the 
frequency of the radiation. High frequency ultra-violet radiation can 
only radiate when it has a large amount of energy available, so that 
the chance of many units being radiated is small, and the total 
amount is small also. On the other hand, the low frequency infra-red 
radiations possess small units, and the chances favour their emission, 
but, as they are small, the total amount radiated is again small. For 
some special range of intermediate frequency, where the unit is of 
intermediate size, the chances may be favourable to a maximum 
emission of energy. Thus the quantum theory, like many physical and 
chemical problems, is an exercise in probability. 

In 1923 Compton put forward the idea of a unit of radiation 
comparable with the electron and proton; he called it a photon. 
The quantum of energy E is proportional to the frequency v, that is 
inversely as the period of vibration T. So 

zr A h 
JE = Av = y., 

where h is Planck's constant, =ET, that product of energy and time 
which is called 'action'. This is a true natural unit, independent of 
anything variable, like the atom or the electron. 

The quantum theory was much strengthened when it was also 
applied successfully to explain the variation in specific heat. Einstein 
pointed out that the rate of absorption would depend on the size of 
the unit, and therefore on the frequency of vibration and so on the 
temperature. This application has been carried farther by Nernst 
and Lindemann l and by Debye. 

1 Now Lord Cherwell. 


The chief difficulty in quantum theory is to explain the inter- 
ference between parts of a beam of light which seems to require a 
long train of uniform waves. The most hopeful attempts to reconcile 
the difference are found in a combination of waves and particles, 
for which there is experimental evidence, and in a recent theory of 

The application of quantum theory to the problem of atomic 
structure was first made by Niels Bohr of Copenhagen, when working 
in Rutherford's laboratory in Manchester. In the complex spectrum 
of hydrogen, regularities appear if we examine, not the usual wave- 
lengths of its luminous lines, but the number of waves in a centimetre, 
and Bohr was able to explain these regularities on the quantum 

If action is absorbed in quantum units, only a certain number of 
all the conceivable orbits will be used by the electrons. In the smallest 
orbit the action will be one unit or A, in the next zh and so on. If an 
electron leaves one path, it must jump instantaneously to another, 
apparently without passing through the intervening space. Here, for 
the first time, we leave Newtonian dynamics, and open a new chapter 
in physical science. 

By assuming four possible orbits for the single hydrogen electron, 
Bohr explained the facts of its coarser spectrum. But Bohr's atom 
failed to account for the finer details of the spectrum of neutral helium 
and the great complexity of the spectra of heavier elements. By 1925 
it was becoming clear that Bohr's theory, so successful for a time, was 

Nevertheless the idea of different energy levels is supported by the 
facts of ionization. Lenard in 1902 showed that an electron must 
possess a certain minimum energy before it would ionize a gas. 
Franck and Hertz found that maxima of ionization occur at multiples 
of a definite voltage. At the same points new lines or groups of lines 
may appear in the spectra. 

The double aspect of electrons as particles and waves was demon- 
strated experimentally in 1923 by Davisson and Kunsman and in 
1927 by Davisson and Germer working in America, and later in that 
year by Sir G. P. Thomson, son of Sir J. J. Thomson. He passed a 


narrow beam of electrons through an exceedingly thin sheet of metal, 
thinner than the finest gold leaf. A photographic plate on the far side 
showed a series of diffraction rings like those obtained when light is 
passed through a thin glass plate or a soap film. This indicates that 
a moving electron is accompanied by a train of waves, the wave- 
length being found to be about the millionth part of that of visible 
light. Waves and electrons must vibrate in unison, hence, even experi- 
mentally, the electron has a structure and more minute parts. 
Mathematical investigation proves that the energy of the electron is 
proportional to the frequency of the oscillations, and that the product 
of the momentum of the electron and the wave-length is constant. 
It will be seen with astonishment how closely this latest concept of 
electron and attendant wave-train resembles Newton's theory of light, 
with its corpuscles and waves that put them into "fits of easy reflexion 
and easy transmission". 

We can only examine atoms from outside, observing the radiation 
or radio-active particles which enter or leave; we cannot say that 
any given internal mechanism, such as that imagined by Bohr, is 
the only mechanism that will produce the external effects. But in 
1925 Heisenberg framed a new mathematical theory of quantum 
mechanics, based only on the frequencies and amplitudes of the 
emitted radiation and on the energy levels of the atomic system. 
The theory gives the main lines of the hydrogen spectrum and the 
influence on it of electric and magnetic fields. 

In 1926 Schrodinger extended certain work of de Broglie on high 
quanta. Taking material particles as wave-systems, he got equations 
mathematically similar to those of Heisenberg. The velocity of a 
single wave is not the same as the velocity of a group of waves or 
storm, which appears to us as a particle, while the frequencies mani- 
fest themselves as energies. Thus we return to the constant relation 
between frequency and energy first seen in Planck's constant h. 
Schrodinger obtained concordances between his equations and the 
spectrum lines even in complex atoms. 

When one of the wave-groups is small, there is no doubt where to 
place the electron which is its manifestation. But, as the group 


expands, the electron can be put anywhere within it, so that there 
is an uncertainty in its position. The more accurately we attempt to 
specify the position of a particle, the less accurately can the velocity 
be determined and vice versa. The product of the two uncertainties, 
approximately at any rate, brings us back once more to the quantum 
constant h. Thus twenty-five years after the atom was resolved into 
electrons, electrons themselves were resolved into an unknown type 
of radiation or into a disembodied wave-system. The last trace of the 
old, hard, massy atom has disappeared, mechanical models of the 
atom have failed, and the ultimate concepts of physics have, it seems, 
to be left in the decent obscurity of mathematical equations. 

The Transmutation of Elements. For some years after the 
acceptance of the atomic explosion theory of radio-activity, all 
attempts to initiate or control radio-active transformations failed. 
But in 1919 Rutherford discovered that bombardment with a rays 
induces atomic changes in nitrogen, with the emission of fast-moving 
hydrogen nuclei or protons, the existence of which was confirmed 
by Blackett, who photographed their paths in a cloud chamber. This 
discovery began an immense development in controlled atomic 
transformations. Between 1921 and 1924 Rutherford and Ghadwick 
disintegrated most elements from boron to potassium. 

When beryllium was bombarded, Bothe obtained rays even more 
penetrating than the y rays of radium, and in 1932 Chadwick found 
that the main part of this radiation consisted, not of y waves but of 
swift uncharged particles about equal in mass to hydrogen atoms. 
They are now called neutrons, and, being uncharged, pass freely 
through atoms without causing ionization. But, as Feather, Harkins 
and Fermi have shown, neutrons, especially slow neutrons, entering 
easily into nuclei, are very effective in causing transmutation. 

Yet another type of radiation, always passing through space, has 
been detected. The charge on an electroscope leaks away faster when 
it is raised above the Earth's surface and more slowly when sunk in 
water, the radiation being more penetrating than any terrestrial ray 
The intensity is the same day and night, and the rays arrive in the 
southern hemisphere when the Milky Way is not visible. Thus the) 


cannot come from Sun or stars, but must originate in outer space. 
Their energies were measured by Carl Anderson and Millikan, who 
passed them through an intense magnetic field and measured the 
deflexion, finding energies ranging round 6 thousand million electron- 
volts, the electron-volt being the energy change when one electron 
falls through a potential difference of one volt. In 1932 Anderson 
discovered positive particles with the mass of negative electrons. 
These particles are now called positrons. 

When photons strike the nucleus of a heavy atom, a positive- 
negative electron-pair appears in a cloud chamber. Their joint energy 
is about i '6 million electron-volts when the energy of the photons 
was 2-6 millions. The difference of i million e- volts measures the 
energy involved in the conversion of photons of radiation into an 
electron-pair of matter. Conversely if a positron and an electron 
annihilate each other, two photons of electro-magnetic radiation 
shoot out in opposite directions. In 1938 Anderson and Neddermeyer 
confirmed a supposition that highly penetrating particles exist having 
masses intermediate between electrons and protons about that of 
200 electrons, a proton being almost 2000. The intermediate particles 
have been called mesotrons. The mode of origin of the cosmic rays 
is still uncertain. 

Thus it will be seen how complex the structure of matter must be; 
we have the following types of particles : 

Mass in 
Name electron unite Electric charge 

Electron or jS particle i e 

Positron i +e 

Mesotron 200 e 

Proton 1800 +e 

Neutron 1800 o 

Deuteron 3600 +e 

a particle 7200 +ze 

Besides these particles, which are reckoned as material, there is 
the photon, the unit of radiation. It is clear that matter is a won- 
derful and mysterious thing, too complex to be represented in atomic 
models, so that, as we have seen, its description may have ultimately 
to be left in a series of wave-equations. 


The quantity of a rays obtained from radio-active substances is 
very small, and artificial methods of producing more effective a rays, 
long sought, have now been found. By passing an electric discharge 
through hydrogen or its isotope deuterium, a copious supply of 
protons and deuterons can be obtained, but, to give them velocity, 
a very strong electric field is necessary. This was applied by Cock- 
croft and Walton, and now powerful apparatus is available. Again, 
E. Lawrence of California has invented a new form of accelerating 
apparatus called a 'cyclotron'. Ions pass through an alternating 
electric field and a magnetic field at right angles, which makes the 
proton or deuteron describe a spiral path of steadily increasing radius, 
and enter and leave the electric field at regular intervals. For one 
frequency of the alternating potential, the ions always enter the field 
when the electric force is in the direction to accelerate them. In this 
way Lawrence got intense streams of protons and deuterons, equiva- 
lent to the a rays from 16 kilograms of radium. 

With these instruments many transmutations have already been 
performed. To take an example, Lawrence and his colleagues, by 
bombarding bismuth, have converted it into a radio-active isotope 
identical with the natural radio-active element radium E, which has 
a time of half-decay of 5 days. Again, sodium (atomic weight 23) 
or its salts give a radio-active isotope of weight 24. This radio-sodium 
changes with the emission of one p particle, into magnesium, also 24, 
the period of half-decay being 15 hours. In the course of these recent 
researches more than 250 new radio-active substances have been 
recorded. In such transmutations as these, the dream of the mediaeval 
alchemist has come true. 

Some of the energy changes in theSe forced transmutations are 
greater than those in natural radio-activity. For instance, a deuteron 
of energy 21,000 electron-volts will transmute an atom of lithium 
into beryllium with an emission of energy of 22-5 million electron- 
volts. This looks at first sight like a limitless source of atomic energy. 
But only about one deuteron in io 8 is effective, so that, on balance, 
more energy has to be supplied than is emitted. A similar catch 
appears in every case yet examined, and, even if it could be obtained, 
it might be dangerous to put the destructive power of atomic energy 


into the hands of man. Nevertheless, the advance of knowledge 
cannot be stopped, and science is not responsible if a bad use is made 
of some of the gifts it brings. 

Electro-magnetic Waves. Clerk Maxwell published his electro- 
magnetic equations in 1864, and Hertz produced and demonstrated 
electro-magnetic waves in 1887 (p. 103). Rutherford and others 
carried the work farther in later years, sending signals over a mile 
or two, but it only led to a practical outcome when two inventions 
were adopted. Marconi used an aerial wire or antenna to increase 
the energy despatched and collect that energy at the receiving station, 
and Sir O. W. Richardson investigated the emission of electrons 
from hot metals and so made possible the thermionic valve. 

Hertz and other early experimenters used the waves from an 
induction coil, waves which are heavily damped and rapidly die 
away, but for radio-transmission a train of continuous, undamped 
waves is needed. If a hot wire inside an exhausted bulb be connected 
with the negative terminal of a battery, and a metal plate with the 
positive terminal, a continuous negative current, carried by the 
electrons, will pass from wire to plate, though if the terminals be 
reversed no appreciable current will flow. Thus the thermionic valve 
acts as a rectifier, letting one half of an alternating current pass and 
stopping the other half. If a grid of wire gauze be put between wire 
and plate and be positively electrified, it will help the emission of 
electrons and increase the thermionic current, but, if it be negative, 
it will decrease it. If it alternates in potential, the current also will 
oscillate, an alternating current being thus superposed on a direct 
one. These alternations are passed through the primary circuit of 
a transformer, the secondary being connected back to give the grid 
its proper alternating potential. The thermionic valve is used both 
to emit a steady, undamped train of waves and also to rectify them 
when received. By interrupting these rectified currents and passing 
them through a telephone, a sound of corresponding pitch is obtained 
and radio-speech made possible. 

The radiation can be divided into an earth wave, gliding over the 
surface of the ground, and a sky wave, starting above the horizontal. 


The latter wave can be carried long distances, because it is reflected 
or refracted by a conducting layer in the upper atmosphere, ionized 
by the Sun's rays. This is called the ionosphere, or the Kennelly- 
Heaviside layer from those who first suggested its existence. From 
the behaviour of long-distance waves, much information about the 
ionosphere has been obtained. It was first located by wireless waves 
by Appleton and Barnett, and in 1926 an upper layer was discovered 
by Appleton, and shown to be the more effective in deflecting short 
radio-waves. These experiments were an early instance of radio- 

Another invention using modern discoveries is the electron micro- 
scope. The ordinary microscope fails to give clear definition when the 
size of the object approaches the wave-length of light. The ultra- 
microscope (see p. i n ) carries vision somewhat farther, but the train 
of waves accompanying an electron has wave-lengths about the 
millionth part of that of light. 

The function of the lenses in a microscope is to bend the rays of 
light coming from the object and focus them for the eye. Highly 
accelerated electrons can similarly be bent by a properly adjusted 
magnetic field and focused on a fluorescent screen or photographic 
plate inside the apparatus. Objects much smaller than those other- 
wise visible are thus clearly seen. The minute beings which devour 
bacteria have been revealed, and, in the near future, a great extension 
of knowledge will thus be won. Viruses should easily be seen, and a 
vision of molecules or even atoms seems within the bounds of possi- 

Relativity. In 1676 Romer discovered that light needed time 
for its propagation. He observed the eclipses of the satellites of Jupiter 
when the Earth was approaching or receding, and found a velocity 
of 192,000 miles a second. In 1728 Bradley again measured the 
velocity by observing the aberration of light from the stars as the 
Earth moves in its orbit. In 1849 Fizeau passed a beam of light 
through one of the blanks in a toothed wheel and reflected it back 
from a mirror 3 or 4 miles away. When the wheel was at rest, the 
return beam passed through the same gap, but, when the wheel was 


revolving fast enough, the beam struck the next tooth and became 
invisible. Then Foucault measured the velocity by means of a rapidly 
rotating mirror. The best modern results give a value of 186,300 miles, 
or 2-998 x io 10 centimetres a second in vacuo, very nearly 3 x io 10 . 

If there be a luminiferous aether, its effect on light should disclose 
its motion. If the Earth moves through the aether without disturbing 
it, Earth and aether will be in relative motion, and light should travel 
faster with the aether stream than against it, and faster to and fro 
across the stream than up and down it. On these lines Michelson 
and Morley in 1887 designed an apparatus to test the problem. They 
could find no difference when the light took one of the alternative 
paths; in this experiment there was no appreciable relative motion 
of Earth and aether; the Earth seems to drag the aether with it. 

But, in calculating the velocity of light from aberration, it is assumed 
that the aether is undisturbed by the passage of the Earth. Moreover 
in 1893 Lodge rotated two parallel heavy steel plates and passed 
light between them. He could find no change in the velocity of the 
light when the plates were at rest and when they were rotating 
rapidly. Thus there is an unresolved discrepancy. 

G. F. Fitzgerald suggested that if matter be electrical in essence, 
or even bound together by electric forces, it might contract as it 
passed through an electro-magnetic aether. The necessary contraction 
is very small, and could not be observed with scales, because they 
too would contract. Michelson and Morley 's apparatus might change 
in dimensions so as to mask the effect expected. Whatever the cause, 
every attempt to find a change in velocity failed. 

But in 1905 an entirely new direction was given to thought on this 
subject by Albert Einstein, who pointed out that the ideas of absolute 
space and time were metaphysical concepts and did not necessarily 
follow from the observations and experiments of physics. The Fitz- 
gerald contraction would be invisible to us moving with the scales 
and suffering corresponding changes, but it might be measurable by 
an observer moving differently. Time and space then are not absolute 
but relative to the observer, and are such that light always travels 
relatively to any observer with the same velocity. That is the first 
experimental law of the new physics. 


The mass of a moving body will increase in the same proportion 
as its length in the direction of motion is shortened. It can be shown 

/ / 02 

that, on the principle of relativity, m = m Q / */ i 2 , where v is the 

/ v c 

velocity of the body, c that of light, and m Q the mass when at rest. 
This result can be tested by observations on )3 particles and has been 
shown to agree with the measurements by Kaufmann. Again, on 
the principle of relativity, mass and energy are equivalent, a mass m 
expressed as energy being me 2 . This too is in conformity with Maxwell's 
theory of waves, which possess momentum equal to E/c, where E is 
their energy. Momentum being me, we get again E=mc 2 . 

Space and time then are relative to the observer; but in 1908 
Minkowski pointed out that space and time compensate each other, 
so that a combination of the two, where time is a fourth dimension 
to the three of space, is the same for all observers. Other quantities 
that remain absolute are number, thermodynamic entropy and 
action, that product of energy and time that gives us the quantum. 
In reversible physics events can occur in either direction, but in the 
second law of thermodynamics, and the irreversible rise of the entropy 
of an isolated system towards a maximum, we have a physical process 
which can only proceed in one direction, like the remorseless march 
of time in the human mind. 

In Minkowski's space-time there are natural paths like the straight 
paths of freely moving bodies in three-dimensional space. Since a 
projectile falls to the Earth and the planets circle round the Sun, we 
see that near matter these natural paths must be curved, and there 
must be a curvature in space-time. 

Calculation shows that the consequences of this theory are the same 
as those of Newton's to the usual order of accuracy of observation. 
But in one or two cases it is just possible to devise a crucial experi- 
ment. The deflexion of a ray of light by the Sun is twice as great on 
Einstein's theory as on Newton's. During the eclipse of 1919, 
Eddington in the Gulf of Guinea and Crommelin in Brazil photo- 
graphed the image of a star just outside the Sun's disc. Compared 
with stars farther away from the Sun the image of the near star was 
displaced to the amount foretold by Einstein. Secondly a discrepancy 


of 42 seconds of arc per century in the orbit of Mercury left by the 
Newtonian theory was at once explained by Einstein, who calculated 
a change of 43 seconds of arc. Eddington has linked gravitation with 
electricity and quantum theory by comparing the theoretical with 
the observed values of many physical constants. He obtained very 
striking concordances. It seems that all these modern concepts may 
before long be brought together in one new physical synthesis. 



The Solar System. Newtonian astronomy was chiefly concerned 
with the solar system, minute compared with the stellar universe, but 
gigantic to ourselves. Kepler gave us a model of the system, but 
the scale of the model was not known till some one distance was 
measured in terrestrial units. For instance, when the planet Venus 
passes between the Earth and the Sun, its time of transit over the 
Sun as observed at two places on the Earth gives a means of deter- 
mining by trigonometry the distance of the Sun. This proves to be 
93 million miles, which light can traverse in 8-3 minutes. The most 
distant known planet, Pluto, discovered by Tombaugh in 1930, 
moves round the Sun in 248 years, the diameter of the orbit being 
7350 million miles, which gives the size of the solar system as now 

There has often been discussion on the possibility of life on other 
worlds; this problem reduces to a consideration of the conditions on 
the other planets of the solar system. One of the most important of 
these conditions is the nature of the atmosphere round each planet. 
Molecules of the gases will escape from gravitational attraction if 
their velocity of movement is more than a critical value called the 
'velocity of escape', which can be calculated from the mass and size 
of the planet. The moon has lost practically all its atmosphere, Mars 
and Venus have atmospheres comparable with that of the Earth, 
while the large planets Jupiter, Saturn, Uranus and Neptune 
have much more -than the Earth. On Venus carbon dioxide is 
plentiful; but apparently there is no vegetation and no oxygen, and 
life is not yet possible, whereas on Mars conditions favourable to life 
are over, or, at all events, drawing to a close. Planets much farther 
from the Sun than the Earth are probably too cold to support life. 

The Stars and Nebulae. Beyond the orbit of the planet Pluto 
lies a great gulf of space. The few nearest stars may be seen to move 
against the background of those more distant as the Earth passes in 
six months from one side of its orbit to the other. In 1832 and fol- 


lowing years, measurements of this parallax were made. The nearest 
star, a faint speck called Proximo, Centauri, was found to be 24 million 
million (2-4 x io 13 ) miles away from us, a distance traversed by light 
in 4- 1 years, and 3000 times the diameter of Pluto's orbit. 

The naked eye can see a few thousand stars. They were classed by 
Hipparchus in six 'magnitudes' according to their apparent bright- 
ness. For those whose distances are known, we can calculate the 
apparent magnitude the star would have at a standard distance and 
this is called the absolute magnitude. In the loo-inch reflecting 
telescope at the Mount Wilson Observatory in America, a number 
of stars estimated at about 100 million are visible, and hundreds of 
times more must exist. There are many double stars, first discovered 
by Herschel; some are too near each other to be separated by a 
telescope, but can be resolved spectroscopically by observing the 
shift in the spectral lines as the two stars are alternately approaching 
or receding from us (p. i o i ) . If both stars of the doublet are luminous, 
the lines are doubled. If one is invisible, sometimes it periodically 
hides the other, and thus again the double nature of the pair can be 
detected. If visual and also spectroscopic measurements are possible, 
a very complete specification can be obtained, giving the individual 
orbits and masses. Other variable stars cannot be explained by 
eclipses, as, for instance, 8 Gephei. These 'Cepheid' stars show a 
relation between the period of variation and the luminosity or abso- 
lute magnitude. This relation is so regular that measurement of the 
periods of other similar stars at unknown distances can be used to 
estimate their absolute magnitudes. An observation of the apparent 
magnitude then gives the distance a method applicable to stars too 
far away to show any parallax. 

Stars are most numerous in a band stretching across the heavens 
in a great circle. It is called the Galaxy or Milky Way. We and our 
Sun are within it but not at the centre. This, our stellar system, forms 
a vast lens-shaped collection of stars of which the Sun is one. The 
size is so huge that light would take 300,000 years to traverse the 
longest diameter. In the galaxy there are two great streams of stars 
moving in different directions, while the galaxy itself is rotating about 
a centre. The stars of which the masses can be determined do not 


seem to differ much, mostly ranging from one half to three times the 
mass of the Sun. 

Beyond our stellar system lie other galaxies, 'island Universes', of 
which our own is but one. Most impressive of all are the multitudes 
of great spiral nebulae, star-systems in the making. They are gigantic; 
though formed of tenuous gas, one of them might form a thousand 
million Suns. Estimates of their distances give to the farthest 500 
million light-years; they lie far beyond the confines of our stellar 
system (see Plate IX, facing p. 149). 

The Structure of Stars. A system of classification of stars by 
their spectra was introduced by Father Secchi in Rome about 1867, 
and has been much extended and improved at the Harvard Observa- 
tory in America. A list has been drawn up in which the bluer stars 
come first, and the different types of spectra, indicating various 
elements and temperatures, are grouped together. Again, if a black 
body, taken as a perfect radiator, is heated, the character as well as 
the intensity of the radiation changes. For each temperature there 
is a characteristic curve between radiant energy and wave-length, 
showing a maximum at one particular wave-length. As the tem- 
perature rises, the position of the maximum shifts towards the blue, 
and thus the temperature can be estimated. The temperatures of the 
outermost radiating layers of stars range from 1650 G. to 23,000 C. 

Knowing the size and average density of the Sun or a star, and 
assuming that it is gaseous, Eddington calculated the rate of increase 
of pressure with depth below the surface. At any level, the pressure 
from above is supported by the elasticity of the gas below and the 
pressure of its radiation. These quantities are known and depend on 
the internal temperature, and so the temperature can be estimated. 
To support the enormous pressure within the Sun or another similar 
star, the internal temperature must be very high reaching tens of 
millions of degrees Centigrade. Sir R. H. Fowler has shown that in 
stellar atoms some electrons must stay in orbits of high energy; the 
pressure required to decrease the volume is then increased, and the 
internal temperature needed to balance the pressure is less; at the 
centre of the Sun about 20 million degrees. These figures are, of 


course, altogether different from the temperatures of the outermost 
radiating layers at a few thousand degrees only. 

Sirius, the brightest star in the sky, is linked with a companion 
which has a mass about four-fifths of that of the Sun, and gives little 
light. But in 1914 Adams saw from Mount Wilson that it was white- 
hot, so that its low emission must be due to small size. Its heavy mass 
and small size indicates the surprising density of a ton to the cubic 
inch at the time an incredible result. But Einstein's theory requires 
that the spectral lines should be shifted towards the red by an amount 
proportional to the mass divided by the radius. Adams examined 
the spectrum and again got the same enormous density, and other 
dense stars have now been found. 

With temperatures of millions of degrees, the maximum energy in 
a star is far above the visible spectrum and consists of X-rays and 
y rays, which are very effective ionizing agencies. Inside a star then 
the atoms will be ionized, that is stripped of their outer electrons; 
this is so, even in ordinary stars, while in the very dense stars it is 
probable that the atoms consist of nuclei only, stripped bare of even 
the innermost ring of electrons. 

Stellar Evolution. When classed in absolute magnitudes, there 
are stars of all values, but more in the highest and lowest groups than 
in the intermediate ones. Those in the two more populous grades 
bright and faint are called giants and dwarfs respectively. It was 
thought that they indicated the course of evolution of every star, 
which, beginning large and diffuse, shrinks with rising temperature, 
owing to gravitational contraction and radio-activity. It reaches a 
maximum output as a giant, and then cools, going through the same 
changes in reverse order with much less luminosity, which, since 
temperatures are the same, means smaller size; the star has become 
a dwarf a small star, with little radiation. This scheme has been 
modified by bringing in the new physical ideas. 

The probable age of stars was formerly estimated as five to ten 
millions of millions of years, but we shall see some reason to reduce 
this to some ten thousand millions. To provide for such ages as these, 
enormous supplies of radiant energy are needed, much more than 


gravitational contraction or radio-activity can supply. Einstein's 
theory suggested that the source might be found in the conversion 
of matter into radiation by methods we shall describe presently. 
Radiation exerts pressure, and therefore possesses momentum, by 
which the Sun loses mass at the rate of 360,000 million tons a day. 
It must have lost mass faster when larger and younger, and thus an 
upper limit can be found for its age, a limit of somewhere about 
eight million million years, agreeing well with the earlier independent 
estimate for the ages of the stars. 

Kant and later Laplace tried to explain the origin of the solar 
system by imagining a nebula shrinking and revolving under its own 
gravitation. At various stages it was supposed to leave behind rings 
of matter which condensed into globular planets. But, as Chamberlin 
showed, for a mass of gas of the required dimensions, gravity would 
not overcome the diffusive effects of molecular velocities and radiation 
pressure, and Sir James Jeans has indicated that planetary condensa- 
tions would not be formed. "" ~~ * 

^ have bodies a million times larger 

than that imagined by Laplace, and on this scale gravitation will 
overcome both gas pressure and radiation pressure, and the nebula, 
instead of scattering, contracts and spins faster as Laplace supposed. 
The theory fails for the comparatively small solar system, but succeeds 
for a gigantic stellar galaxy. 

Jeam]ia^4xr^ved^ mathematically that a mass of rotating gas will 
form a double convex lens, the edge of which becomes unstable and 
forms two whirling arms. In them local condensations will occur, 
each of the appropriate size to form a star within the limits of size 
we know stars to possess. Spiral nebulae are the forerunners of 
stellar systems. 

But our solar system, small enough for diffusive effects to take 
charge, gives another problem, A globule on the arm of a spiral 
nebula, if rotation is fast enough to cause disruption, is more likely, 
according to Jeans' mathematics, to form a double star with two 
partners wahZhlg TOimd euCll Oilier. But if, Jeans and Moulton and 
Chamberlin suggest, two smaller stars canTeliear eacH other in the 
gaseous stage, tidal waves would be formed, and, if the stars ap- 


preached within a certain critical distance, such a wave would shoot 
out a long arm of matter, which might break up into bodies like the 
Earth and the other planets. This would happen but rarely, and, 
even in the millions of galaxies, not many such systems are to be 

The spectra of spiral nebulae show most known lines displaced 
towards the red. By Doppler's principle this indicates retrocession. 
The velocity is greater in proportion to the distance, and the pheno- 
menon is sometimes described as an expanding Universe. 

Double stars show their structure by spectral lines oscillating in 
time with the revolution of the two stars. But, in some cases, the 
calcium or the sodium lines do not share in this periodic motion, 
but only move with our galaxy of stars. Calcium and sodium, and 
possibly other elements, therefore, are scattered through space, 
perhaps condensing in places into cosmic clouds. The density is in 
general extremely small, about io~ 24 , one atom to a cubic centi- 
metre. With this scattered tenuous matter, there are also the cosmic 
rays observed by Millikan and others, which, the evidence shows, 
come to us from outer space, either from the tenuous matter or from 
spiral nebulae. 

It will be remembered that, on Einstein's relativity theory of 
gravitation, the presence of matter or an electro-magnetic field pro- 
duces something analogous to curvature in the four-dimensional 
space-time continuum. Since there is matter scattered about the 
Universe, in the forms of stars, nebulae and cosmic clouds, we get 
this curvature, and if we regard time as flowing evenly onward, space 
itself must be curved and the Universe finite. Light emitted from 
one place and travelling forward long enough would return to its 
starting point. Einstein's estimate gives the radius of space as 
9-3 x io 26 G.G.S. units, or about a thousand million light-years. 

The final problem is to discover the source of the energy radiated 
by stars, including our own Sun, in whose light we live and move 
and have our being. The internal temperatures run to tens of millions 
of degrees, and the total output is too great to be supplied by gravita- 
tional contraction and the radio-activity of any terrestrial elements. 
Perhaps some more complex and vigorous radio-active elements 


exist in stars and emit more heat, but it seems that the conversion of 
matter into radiation is probably the chief source of the enormous 
output of energy. 

Einstein's relation between energy and mass, E=mc 2 , where c is 
the velocity of light, 3X io 10 centimetres a second, shows that one 
gram is equivalent to gx io 20 ergs of energy. If we suppose a com- 
plete conversion, as by the mutual extinction of protons and electrons, 
the energy liberated would give the Sun an age of i'5Xio 13 
(15 million million) years. But, as there is no direct evidence for 
this theory, some prefer an alternative explanation. 

The energy changes which accompany the transmutation of 
elements by bombardment in modern apparatus such as the cyclo- 
tron, and Aston's accurate measurement of atomic weights with the 
mass-spectrograph, show what large amounts of energy are involved 
in the conversion of hydrogen into other elements and give means 
of calculating them. For instance, the atomic weight of hydrogen is 
1-00813 (oxygen = 1 6) and helium is 4-00389, so that four gram- 
atoms of hydrogen, or 4*03252, yield one gram-atom of helium and 
leave a mass of 0-02863 to be converted into radiation. This gives 
for me 2 0-25767 x io 20 ergs of energy. If we take one gram-atom of 
hydrogen instead of four, we should get 6-4 x io 18 ergs, which is 
equivalent to about 200,000 kilowatt hours. The energy is of course 
less than that of complete conversion, but if io per cent of the Sun's 
mass suffers transmutation from hydrogen into not-hydrogen, enough 
energy would be liberated to support the radiation for some ten 
thousand million years, This would be somewhat increased by the 
heat liberated by gravitational contraction and radio-activity. The 
stability which this theory gives to the Sun and stars is a great point 
in its favour. 

The Beginning and End of the Universe. Kelvin's principle of 
the dissipation of energy, equivalent to Clausius' maximum entropy, 
was extended, from the isolated system for which it was proved, to 
cover the physical Universe. Whether this extrapolation was justified 
is another question. If the principle can be taken as applying on so 
much larger a scale, and if the Universe can fairly be treated as 


isolated, it follows that all temperature differences will continue to 
decrease, and the energy consequently become less and less available 
for the performance of useful work. This process will continue till all 
cosmic energy has become heat uniformly distributed at a constant 
temperature, and no further operations are possible in a dead 

The new developments in physics and astronomy demand that 
fresh consideration should be given to this problem. However great 
be the output of energy of the stars, as long as it is finite, there must 
be not only an end but also a beginning. Jeans holds that ' everything 
points with overwhelming force to a definite event, or series of events, 
of creation at some time or times not infinitely remote'. The facts of 
artificial radio-activity, and the need for explaining the energy of the 
radiation from the Sun and stars, have forced us to believe that matter 
is continually passing into radiation. If this process goes on to the 
end, as Jeans says, * there would be neither sunlight nor starlight, but 
only a cool glow of radiation uniformly diffused through space'. 
Thus, though the process is quite different, the outcome is the same 
as that formerly deduced from the law of dissipation of energy in 
the end no further action can occur and the Universe is dead. 

Some people find the idea of the death of the physical Universe 
an intolerable thought. Perhaps to try to satisfy them, search has 
been made for natural means whereby the dissipation of energy or 
the destruction of matter might be reversed. Possibly there may be 
some physical process which plays the part of Maxwell's demon 
(p. 98), and separates out fast moving molecules. Again, there is 
another story which seems conceivable, though enormously unlikely, 
which runs as follows. If infinite time is available, all improbable 
things may happen. Chance concentrations of molecules might 
reverse the effect of random shuffling and undo the deadly work of 
the second law of thermodynamics; chance concentrations of radiant 
energy might saturate a part of space, and matter, perhaps one of 
our spiral nebulae, might crystallize out and start a new cycle. The 
probability against such a happening is fantastically great, but infinity 
is greater. However long it is necessary to wait for such a chance to 
occur, eternity is longer. Can we thus explain the course of past 


creation, and, when the present Universe has passed, apparently for 
ever, into 'a cool glow of radiation', may we imagine a new begin- 
ning? Probably not probably something less unlikely would inter- 
vene this side of eternity. 

It has been suggested that the second law of thermodynamics holds 
good only in an expanding Universe, and Tolman has formulated 
a scheme of relativistic thermodynamics in a contracting Universe 
in which the second law is reversed. This suggests the possibility of 
a pulsating Universe, in which we chance to be living in a phase of 
expansion and need not contemplate a beginning or an end. But 
these ideas are speculative, and the probabilities favour the dissipa- 
tion of energy, and the transmutation of matter into a * cool glow of 
radiation uniformly diffused through space'. There may be changes 
or reversals before or when this end is reached, but they are beyond 
the range of our present science. 

Conclusion. And now we have to sum up the lessons we have 
learned and the outlook we have reached. Fifty years ago most men 
of science would have proclaimed a far more confident faith than 
their successors can preach to-day. Then it seemed that physics had 
laid down the main lines of inquiry once for all, and need only look 
to increased accuracy of measurement and a credible description of 
the luminiferous and electro-magnetic aether. Mach and Karl 
Pearson were teaching that science gave only a conceptual model of 
phenomena, but most men held a crude belief thaVphysics revealed 
ultimate reality about matter and energy, and that natural selection 
fully explained organic evolution. Others went further and, carrying 
science into metaphysics, combined Kraft und Stqff with Darwinismus 
to formulate a philosophy of determinism and even of materialism. 

To-day much of this nineteenth-century vision has vanished. 
Matter has ceased to be hard, impenetrable, material atoms, and 
become an amazingly complex structure, in which protons, electrons, 
positrons and neutrons jostle each other while waiting for new 
particles to be discovered. Radiation is no longer a train of regular 
mechanical waves in a semi-rigid medium or electro-magnetic waves 
in aether, but is now regarded as gushes or quanta of 'action', an 
incomprehensible product of energy and time. The heavier atoms 


are radio-active, and explode spontaneously, while some lighter ones 
are made radio-active by bombardment with a particles, and both 
are transmuted into other elements. All terrestrial atoms are open 
structures, in which empty space far transcends that occupied, though 
in dense stars the electrons are stripped off, leaving nuclei only 
tons to the cubic inch. 

Even with all this complexity, matter cannot be represented by 
particles only. The particles have to be imagined as accompanied 
by waves, or, to go farther, as themselves described by wave- 
mechanics. In a wave-group, there is an essential uncertainty in 
either the position or the velocity of a particle. The certainty of the 
older physics was part of the evidence on which philosophic deter- 
minism was built, and the principle of uncertainty destroys that part 
of the evidence, though of course it does not establish the opposite 
doctrine of human free-will. 

The stellar Universe is far larger than was formerly realized. Our 
galaxy of stars is only one out of millions, the spiral nebulae being 
stellar galaxies in the making, some being so far away that their 
light takes hundreds of millions of years to reach us. ' 

Thus the Universe is both larger and more complex than once 
appeared. We are not, as we thought, just about to understand it all. 
The larger the sphere of knowledge, the greater the area of contact 
with the unknown, and the farther we push into the unknown the 
less easy is it to represent what we find there in simple, understandable 
terms. Much of it must be left in mathematical equations. And, in 
any case, science can only build a model of nature, leaving to philo- 
sophy the problem of the possible reality which may or may not 
stand behind it. 

The philosophy of Hegel revived the idea that a knowledge of the 
real world could be obtained a priori by logic. Such beliefs echo down 
the ages from Parmenides, Zeno and Plato. At the other extreme 
Francis Bacon exalted pure experiment, and held that, by an almost 
mechanical process, general laws could bejsstablished with certainty. 
But, in fact, scientific discovery involves botlimduction and deduction. 
First the right mental concepts must be pickedout from the confused 
medley of phenomena. For instance, Aristotle's ideas of substance 
and qualities, natural places, etc. were useless as basic concepts for 


dynamics, and only led, if they led anywhere, to false conclusions. 
No advance was possible till Galileo and Newton, discarding the 
whole Aristotelian scheme, chose, as new fundamental ideas, length, 
time and mass, and thus were able to think in terms of matter and 
motion. This choice of concepts is itself a form of induction, and the 
most important step in framing scientific knowledge. '** Next, guesses 
at relations between the concepts, founded on preliminary observa- 
tion, must be made.vTheir logical consequences must then be deduced 
by mathematics or otherwise, and these must be tested by further 
observation or experiment. An empirical rule, resting on facts alone, 
does not bring the conviction which follows an explanation of the 
law by an accepted theory. Even then, and more so with induction 
alone, the laws are only probably true, though the probability in 
favour of some of them may be so great as to approach, though never 
reach, certainty.^ A few years ago we all should have been willing 
to bet heavy odds that Newton's laws of gravity and the constancy 
of the chemical elements were accurately true, yet Einstein and 
Rutherford have proved us wrong. 

Scientific philosophy has been much advanced by the application 
of mathematics. Lobatchevsky invented non-Euclidean geometry; 
Weierstrass proved that continuity does not involve infinitesimals; 
Cantor framed a theory of continuity and infinity which resolved 
Zeno's ancient paradoxes; Frege showed that arithmetic follows from 
logic ; Russell and Whitehead traced fundamentals in their Principles 
of Mathematics. The new semi-realism, founded on these (with 
other) considerations, gives up the hope of explaining phenomena 
from a comprehensive theory of the Universe, as indeed science did 
when breaking with Scholasticism in the seventeenth century. 
'Philosophy now fits its knowledge together piecemeal as does science, 
formulating hypotheses in the same way. But it goes beyond Mach's 
pure phenomenalism, and holds that science is concerned in some 
way with persisting realities. Nevertheless, as seen above, mental con- 
cepts are necessary for scientific analysis^and the relations which are 
called 'laws of nature* are relations between mental concepts and not 
between concrete realities. <3To suppose the latter is to fall into what 
Whitehead calls the * Fallacy of Misplaced Concreteness*. The doc- 
trine of mechanical determinism, he holds, only applies to abstract 


concepts; the concrete entities of the world are complete organisms, 
in which the structure of the whole influences the characters of the 
parts; mental states are part of the organism and enter into the whole 
and so into its parts. 

In the seventeenth century two systems were simultaneously in 
being Aristotelian and Newtonian. And a few years ago we had 
reverted to a similar dichotomy. The classical Newtonian dynamics 
still gave a useful method of solving many problems, though for 
others relativity and the quantum theory were necessary. As Sir 
William Bragg said, we freely used the classical theory on Mondays, 
Wednesdays and Fridays and the quantum theory on Tuesdays, 
Thursdays and Saturdays. But Eddington has now put together a new 
quantum synthesis, which points the way to a complete acceptance 
of the new views with the classical theory as a limiting case. 

The older physics included a firm belief in cause and effect,^ belief 
which began with the Greek atomists more than two thousand years 
ago. Even when the kinetic theory of gases dealt with the pressures 
due to molecular bombardment, the molecules were considered 
statistically in large numbers, and their joint effects were determined 
and calculable. But when G. T. R. Wilson and Rutherford began 
to trace individual atoms, prediction failed; there was no means of 
knowing which radio-active atom would explode next. Perhaps 
further investigation may reveal the finer structure of the atoms and 
bring each one into the realm of law and the region of prediction. 
But there is no sign of it as yet; all we can do is to calculate prob- 
abilities, and set forth the odds on one atom exploding in the next 
hour. Even if each atom became calculable as a whole, we cannot 
fix both the position and the velocity of its electrons; a fundamental 
principle of uncertainty seems to lie at the base of our model of nature. 
Vf he regularities of science may be put into it by our methods of 
observation or experimentVror instance, white light is an irregular 
disturbance into which regularity is put by our examination with 
prism or grating. Atoms can only be examined by external inter- 
ference which must disturb their normal structure: Rutherford may 
have created the nucleus he thought he was discovering. From the 
latest point of view, substance vanishes, and we are left with form, 
in quantum theory with waves and in relativity with curvature. 



Many references to sources for this book will be found in A History of 
Science and its Relations with Philosophy and Religion, by Sir William Cecil 
Dampier (Cambridge, 1929, 1930 and 1942). 

More detailed accounts within the limits of time indicated will be 
found in four books : 

Science since 1500, by H. T. Pledge (London, 1939). 

A Short History of Science to the Nineteenth Century, by Charles Singer (Oxford, 

A History of Science, Technology and Philosophy in the Sixteenth, Seventeenth and 
Eighteenth Centuries, by A. Wolf (London, 1935, two volumes). 

The most complete book of reference is Introduction to the History of Science, 
by G. Sarton (Washington, Vol. i, 1927; Vol. n, 1931, bringing it to 1300). 
Other volumes in preparation. 

Cambridge Readings in the Literature of Science, by W. C. Dampier- Whetham 
and Margaret Dampier Whetham, now Mrs Bruce Anderson (Cambridge, 

Current Literature will be found in the periodical Isis (Burlington, 

Vermont, U.S.A.). 


A Short Account of the History of Mathematics, by W. W. Rouse Ball (London, 

A History of Mathematics, by F. Cajori (London, 1919). 

The History of Mathematics in Europe, by J. W. N. Sullivan (Oxford, 1925). 

History of Greek Mathematics, by Sir T. L. Heath (Oxford, 1921), shortened 
in his Manual of Greek Mathematics (Oxford, 1931). 


History of Greek Astronomy, by Sir T. L. Heath (Oxford, 1913). 
History of Astronomy during the Nineteenth Century, by Agnes M. Clerke 
(London, 1902). 

A Hundred Tears of Astronomy, by R. L. Waterfield (London, 1938). 
General Astronomy, by H. Spencer Jones (London, 1923). 
The Birth and Death of the Sun, by G. Gamow (London, 1941)- 


A Short History of Physics, by H. Buckley (London, 1927). 
A History of Physics, by F. Cajori (London, 1929). 

The Recent Development of Physical Science, by W. C. Dampier- Whetham 
(London, 5th ed. 1924). 



A Short History of Chemistry, by J. R. Partington (London, 1937), and 
Origins and Development of Applied Chemistry (London, 1935). 
A Hundred Tears of Chemistry, by A. Findlay (London, 1937). 


A Short History of Biology and A Short History of Medicine, by C. Singer 
(Oxford, 1931 and 1928). 

The History of Biological Theories, by E. Radl (Eng. Trans., Oxford, 1930). 

The History of Biology, by E. Nordenskiold (London, 1929). 

History of Botany, 1530-1860, by J. von Sachs (Oxford, 1906), and 1860- 
1900, by J. R. Green (Oxford, 1909). 

Introduction to the History of Medicine, by F. H. Garrison (Philadelphia, 
4th ed. 1929). 


Abelard, 41, 42 

Aberration of light, 158 

Ability, inheritance of, 124 

Abram, 7 

Absolute temperature, 98 

Accademia Secretorum Naturae, etc., 66 

Achaeans, 15 

Achilles and the tortoise, 20 

Acquired characters, 122 

Actinium, 145 

Action, 81, 82, 151, 152, 160, 170 

Adam, N. K., 112, 135 

Adams, J. G., 69, 82 

Adaptation, 118 

Adonis, 141 

Adrenalin, 136 

Aeschylus, 16 

Aether, 67, 68, 100, 103; motion of, 159 

Agassiz, 1 19 

Agrippa, Cornelius, 60 

al-Batani, 39 

Albertus Magnus, 43 

al-Biruni, 39 

Albury, 120 

Alchemy, 31-2, 38, 48, 156 

Alcmaeon, 19, 22, 41 

Alexander, 12, 22, 24, 30 

Alfred the Great, 37, 40 

al-Ghazzali, 40 

al-Haitham, 39, 44 

al-Hazen, 39 

al-Kindi, 39 

Almagest, 39 

Alpine race, 8 

al-Razi, 39 

Amber, 57 

Amino- acids, 108, 135 

Amontons, 93 

Ampere, 102, 103 

Anaemia, 138 

Anaesthetics, 53 

Analinc, 106 

Anatomy, 48 

Anatomy, Physiology and Botany, 54-6 

Anaxagoras, 17 

Anaximander, 17 

Ancient Learning, end of, 34 

Anderson, Carl, 155 

Andrews, 97 

Animal spirits, 33, 54, 68 

Animals, experiments on, 55, 85, 114, 

116, 117, 136 
Anselm, 41 

Anthropoid apes, 123, 133 
Anthropology, 123-5, H ^ 1 
Antigens, 139 
Antipyrene, 107 
Aphrodite, 141 
Apollonius, 31 
Apple, Newton's, 68, 69 
Appleton, Sir E. V., 158 
Aquinas, St Thomas, 22, 40, 43, 45, 48, 

50, 60 

Arabia, 7, 12 
Arabian School, 37-40 
Arabic language, 37 
Archaei, 84 

Archimedes, 23, 27, 28, 47 
Argon, 105 

Aristarchus, 19, 27, 50 
Aristotle, 17, 18, 21, 22-24, 26, 34, 37, 

41, 42, 43, 45, 48, 50, 63, 74, 120, 

138, 142, 171, 172, 173 
Arithmetic, 9 
Aromatic compounds, 106 
Arrhenius, no 
Aryan people, 14 
Ascorbic acid, 135 
Aspirin, 107 
Assyrians, 7 
Astbury, 148 
Aston, 1 8, 150, 1 68 
Astrology, 13, 25, 29, 31, 48, 67 
Astronomy, 9, 13, 68-71, 81-3, 162-73 
Asymmetric atoms, 107 
Athena Academy, 34, 37 
Atomic energy, 156 
Atomic numbers, 149 



Atomic numbers and X-rays, 1 48 
Atomic theory, 14, 18, 22, 25, 38, 104-5, 

147, 148, 155, 165, i?i 
Atomic weights, 104 
Atomists, 17-18, 80, 119, 173 
Atoms, 76, 128 
Atwater and Bryant, 1 15 
Augustine, St, 35, 49 
Australia, 89, 119 
Averroes, 40 

Avicenna (Ibn Sina), 39, 53 
Avogadro, 104 
Azores, 46 

Babylonia, 12-14, 24 

Bacon, Francis, 58, 120, 171 

Bacon, Roger, 39, 42, 44, 45 

Bacteria, 115, 117, 118 

Bacteriology, 116-17 

Baer, von, 114 

Baghdad, 39, 40 

Bahamas, 46 

Bain, 127 

Bakewell, 88 

Baliani, 62, 70, 72 

Banks, Sir Joseph, 89 

Banting and Best, 136 

Barnett, 158 

Barometer, 65, 66 

Barrow, Isaac, 64, 68 

Barton, Catherine, 77 

Base-line, 118 

Basle, 53 

Bateson, William, 129 

Bauhin, J. and G., 56 

Bayliss, 136 

Beagle, 119 

Beaumont, 114 

Becquerel, Henri, 145 

Bede of Jarrow, 37 

Beginning and End of the Universe, 


Behaviourism, 137 
Bell, 115 
Benzene, 106 
Berengarius, 41 
Bcri-Beri, 134 
Berkeley, Bishop, 78, 79, 81 
Berkeley, Earl of, no 


Bernal, 148 

Bernard, Claude, 114, 115 
Bernouilli, James, 81, 95 
Berossus, 29 
Bertholet, 104 
Beryllium, 154 
Berzelius, 102, 106, 109 
Bestiaries, 56 
Bibliography, 174-5 
Bills of Mortality, 123 
Biochemistry, Physiology and Psycho- 
logy, 134-8 

Biology and its Effects, 1 13 
Birth-rate, 132 
Black, Joseph, 83, 93 
Black Notley, 86 
Blackett, 154 

Blood corpuscles, 114, 115, 138 
Boerhaave, 83, 85 
Boethius, 37, 41 
Bohr, Niels, 18, 142, 152, 153 
Bologna, 40, 56 
Boltzmann, 96 
Boole, 125 
Borch, 83 

Botanic Gardens, 56 
Botany, 33 
Bothe, 154 
Botticelli, 48 
Boussard, 9 
Boussingault, 114, 118 
Boyle, Hon. Robert, 64, 83, 84, 94, 104 
Boyle's Law, 97 
Bradley, 83, 158 

Bragg, Sir W. and Sir L., 148, 173 
Brahe, Tycho, 52 
Brain, 30, 85, 137 
Brazil, 160 
Britain, 30 
Bronze Age, 2, 6 
Brownian Movement, in 
Brunn, 129 
Bruno, Giordano, 52 
Brussells, 53 
Buccaneers, 88 
Biichner, 126 
Buckland, 119 
Buddha, 14 
Buffon, 86 

i 7 8 


Bunsen, 100 

Byzantium (Constantinople), 37, 40, 42, 


Cabot, 89 

Cagniard-de-Latour, 116 

Calendar, 10, 13 

Caloric theory, 94 

Calorie, 115 

Calorimeter, 94 

Calvin, 49, 55 

Cambridge, 40, 55, 70 

Cambridge Platonists, 64 

Cambridge University Library, 77 

Cambyses, 12 

Cannizzaro, 104, 105 

Cantor, 172 

Carbohydrates, 108, 115 

Carbon, 105, 107 

Carbon and nitrogen cycles, 1 1 7 

Carbon dioxide, 83, 117, n 8, 136 

Carbon monoxide, 114 

Carnot, Sadi, 97 

Carnot's engine, 97, no 

Carotene, 134 

Carpenter, 121 

Catalysts, 109 

Cathode Rays and Electrons, 143-5 

Cattle, breeding of, 88 

Cave man, 2, 3 

Cavendish, Henry, 82, 84, 94, 101 

Cayenne, 88 

Cells, living, 114 

Cellulose, 135, 149 

Celsius, 93 

Celsus, 33, 53 

c.o.s. units, 93 

Chadwick, 154 

Challenger, 119 

Chambcrlin, 166 

Chambers, Robert, 120 

Champollion, 9 

Charcot, 115 

Charlemagne, 37, 40 

Charles I, 55 

Chemical action, 108-9, "2 

Chemical affinity, 75, 108 

Chemical elements, 64, 105 

Chemistry, 38, 83, 84 

Chemistry, industrial, 106, 107, 109 

Chemistry and Medicine, 53-4 

China, 7, 14 

Chlorine, 83 

Chlorophyll, 117, n 8, 135 

Christians, early, 34 

Chromosomes, 130, 131 

Chronometer, 90 

Church, Fathers of, 34 

Cicero, 28, 32, 54 

Circulation of the blood, 33, 48, 55 

Classification, 41 

Clausius, 95, 97, 98, 102, 126, 168 

Clay, in 

Clement IV, Pope, 44 

Cleopatra, 12, 29 

Clifford, 125 

Cloud nuclei, 144, 147 

Cnidos, 20 

Cnossus, 14, 15 

Coaches, stage, 91 

Coagulation, in, 112, 134 

Coal-tar, 106 

Cockcroft, 156 

Colbert, 88 

Colchester, 56 

Colloids, 111-12, 116, 139 

Columbus, 30, 46 

Combining volumes of gases, 104 

Combining weights, 104 

Combustion, 106 

Composition, percentage, 106 

Compton, 151 

Conclusion, 170-3 

Concreteness, fallacy of, 172 

Conductivity of gases, 145 

Conductivity of liquids, 109 

Conductors and insulators, 101 

Conduitt, John, 77 

Consciousness, 128, 137 

Conservation of Energy, 95, 115, 126 

Constantinople, 85; and see Byzantium 

Cook, James, 89 

Co-ordinate geometry, 58 

Copenhagen, 52, 152 

Copernicus, 19, 43, 49~53 6l > 62 

Cordus, Valerius, 56 

Cork, Earl of, 65 

Corpuscles, 144 



Correlation of forces, 94 

Cos, 20 

Cosmic clouds, 167 

Cosmic physics, 101 

Cosmic rays, 154, 155, 167 

Cotyledons, 87 

Coulomb, 101 

Creation, 122, 169, 170 

Crete, 12, 14-15 

Crew, 131 

Crommelin, 160 

Crookes, Sir William, 146, 147 

Crystalloids, in 

Crystals, 107 

Curie, M. et Mme, 145, 146 

Curtius, 1 08 

Curvature in space-time, 167 

Cuvier, 90 

Cyclotron, 156 

Cyril the Patriarch, 36 

Cyrus, 12 

Dalton, John, 18, 104, 105, 129, 142 

Dampier, W. C. D., no, 112 

Dampier, William, 88, 89, 119 

d'Anville, 119 

Dark Ages, 36-7 

Darwin, Charles Robert, 113, 119, 120, 

121, 122, 123, 126, 127, 132 
Darwin, Erasmus, 121 
Darwin, R. W., 121 
Darwinismus, 126 
Davisson, 152 

Davy, Sir Humphry, 102, 117 
Dawson, 133 

Death of the Universe, 169 
deBroglie, 153 
Debye, 151 
Decay, rate of, 146 
Decimal system, 9, 13 
Decimal units, 93 
Declination, diagram of, 57 
Deflexion, electric and magnetic, 143, 


Defoe, 89 

Degrees of freedom, 97 
Dchydrogenases, 136 
Democritus, 17, 1 8, 22, 23, 25, 104 
Demon, Maxwell's, 98, 99, 169 

Density, 23, 27, 71 

Descartes, Rene*, 58, 59, 67, 68, 74, 120, 


Determinism, 137, 170, 172 
Deuterium, 150 
Deuteron, 150 
de Vilmorin, 131 
de Vries, 129 
Dewar, Sir James, 97 
Dextrose, 114 
Diana Nemorensis, 4 
Dielectric constant, 103 
Differential equations, 81 
Diffraction, 148, 153 
Digby, Sir Kenelm, 64 

Digges, Thomas, 52 

Diogenes the Babylonian, 32 

Dionysos, 141 

Diophantus, 33 

Dioscorides, 33, 56 

Disraeli, 122 

Dissipation of energy, 98, 168, 169 

Distemper, 139 

Dominance, 129 

Donnan, F. G., 135 

Doppler, 101, 167 

Dorians, 15 

Dreams, 6 

Drosophila, 130 

Dualism, 59 

Dubois (Sylvius), 54, 123 

Dumas, 114 

Duns Scotus, 45, 58 
Diirer, Albrecht, 48 
Dynamics, 61-3 
Dynamo, 103 

Earth, size of, 30 

Earth solidification, i 

Earthquakes, 133 

Easter, date of, 41 

Eclipses, 13, 20 

Ecology, 132 

Ecphantus, 30 

Eddington, Sir Arthur, 1 60, 1 6 1 , 1 64, 1 73 

Eels, life of, 134 

Effervescence, 84 

Egypt, 8-12, 24, 133, 140 



Ehrlich, Paul, 107, 139 
Eighteenth Century, 78-91 
Einstein, Albert, 26, 82, 151, 159, 160, 

161, 165, 166, 168, 172 
fj xotvi^ 24 

Electric charge, 102, in, 112 
Electric current, 101-3 
Electric units, 101 
Electrical engineering, 103 
Electrochemical equivalent, 102 
Electro-chemistry, 102 
Electrolysis, 102, 109, no 
Electro-magnetic waves, 103, 144, 148, 


Electro-magnetism, 103-4 
Electromotive force, 103 
^Xacrpov, 57 

Electron microscope, 1 38, 1 58 
Electrons, 128, 147, 148 
Electron-volts, 155 
Elements, 17 
Eleusinian mysteries, 1 6 
Embalming, 11 
Embryology, 114 
Empedocles, 17 
Encyclopedic, 79 
Endeavour , 89 
Endocrinology, 136 
Energy, 95, 160, 167, 168; kinetic, 66, 

95, 9 6 
Engels, 126 

Engine, theory of, 97, 98, 1 10 
England, 37 

Entropy, 98, 126, 160, 168 
Enzymes, 109, 116, 136 
Eoliths, 2 
Ephemerides, 49 
Epicurus, 17, 25, 26 
Equilibrium, physical and chemical, 99, 


Equinoxes, 29 
Erasistratus, 30 
Erasmus, Desiderius, 49 
Eratosthenes, 30 
Ergosterol, 134 
Erlanger, 137 
Error, curve of, 96, 124 
Ether, 53 
Etruria, 121 

Euclid, 26, 27, 29, 39, 41, 172 

Eudemus, 30 

Eulcr, 81, 134 

Euphrates, 7 

Europe, peoples of, 8, 15, 140 

Evans, Sir Arthur, 14 

Evolution and Natural Selection, 113, 

Expanding Universe, 167 

Fahrenheit, 93 

Faraday, Michael, 92, 102, 103, 109, 112 

Fathers of the Church, 34-6 

Fats, 108, 114, 115 

Feather, N., 154 

Ferdinand and Isabella, 46 

Ferments, 55, 108, 114, 116 

Fermi, 154 

Fertilization, 131 

Fildes, P., 139 

Films, 112, 135 

Fire, 2, 5, 83 

Fischer, Emil, 106, 108, 135 

Fischer, O., 107 

Fish, migration of, 133 

Fisher, R, A., 132 

Fitzgerald, G. F., 159 

Fizeau, 158 

Fleming, A., 139 

Fletcher, Sir W. M., 136 

Flint implements, 2, 119 

Florence, 66 

Fluxions, method of, 70, 71, 8 1 

Foot and mouth disease, 138, 139 

Formulae, empirical and constitutional, 

1 06 

Fossils, 48, 119 
Foucault, 100, 159 
Fourneau, 139 
Fourth dimension, 160 
Fowler, Sir R. H., 164 
Franck, 152 

Franklin, Benjamin, 101 
Fraunhofer, 100 
Frazer, Sir James, 4, 140, 141 
Free will, 171 

Freedom, degrees of, 97, 99 
Freezing point, 1 10 
Frege, 172 



French Guiana, 88 
Fresnel, 99 
Freud, 137 
Friedrich, 148 
Fructose, 106 
Fruits, genetics of, 130 

Galen, 33, 36, 53, 55, 68 

Galileo, 22, 24, 43, 45, 5*> 6i-4 68, 70, 

72, 73> 75> 84, 93> 100, 129, 172 
Galileo and Newton, 61-77 
Gall, 115, 

Galton, Sir Francis, 124 
Galvani, 101 
Gas, 53 

Gases, kinetic theory of, 66, 95, 96, 97 
Gaskell, 137 
Gassendi, 67 
Gasser, 137 
Gauss, 96, 101 
Gay-Lussac, 98, 104 
Geber, 38 
Genes, 130, 131 
Genetics, 129-33 
Geneva, 55 

Geography and Geology, 88-90, 1 1 8, 1 1 9 
Geological periods, i 
Geology and Oceanography, 88, 89, 


Geometry, deductive, 26 
Geometry, non-Euclidean, 172 
Gerard, John, 56 
Germ cells, 122, 129, 130 
Germer, 152 
Gibbon, 35 

Gibbs, Willard, 99, 1 1 1 
Gilbert, William, 56, 57, 62, 67, 71 
Gilbert and Lawes, 1 1 8 
Glaisher,J. W. L., 69 
Glands, 116 
Glucose, 1 06 
Glycerine, 114 
Glycogen, 114, 136 
Gnomon, 17 
Goethe, 125 
Golden Bough, 4, 140 
Gonville and Caius College, 55 
Graham, Thomas, in, 112 
Gratings, optical, 101, 148, 149 

Graunt,John, 123 

Gravity, 69, 82 

Gray, Asa, 121 

Greece and Rome, 16-33 

Greek medicine, 20 

Greek religion, 16 

Green, 99 

Gregory XIII, Pope, 11 

Gregory of Tours, 36 

Grew, N., 86 

Grey, Edward (Viscount), 88 

Grimaldi, 73 

Grosseteste, 42, 44 

Grotthus, 102 

Grove, Sir W. R., 94 

Guettard, 90 

Guinea, Gulf of, 160 

Guldberg and Waage, 109 

Gulliver's Travels, 89 

Haeckel, 126 

Haematin, 135 

Haemoglobin, 114, 135 

Haemophilia, 135 

Hales, Stephen, 83, 85 

Haller, A. von, 85 

Halley, 70 

Hanno, 30 

Haploid number, 130 

Hardy, Sir W. B., in, 136 

Harkins, 154 

Harun-al-Rashid, 37 

Harrison, John, 90 

Hartley, E. G. J., no 

Harvard observatory, 164 

Harvey, William, 33, 48, 55, 67, 114 

Head, Sir Henry, 137 

Heat and Energy, 64, 66, 74, 93-7 

Heath, Sir Thos., 28 

Heaviside, 158 

Hecateus, 20 

Hegel, 120, 125, 171 

Heidelberger, 139 

Heisenberg, 153 

Helium, 97, 100, 105, 152 

Hellenistic Period, 24-6 

Hellriegel and Wilfarth, 118 

Helmholtz, H. von, 102, 127 

Helmont, van, 53, 54, 55, 84 



Henson, 119 

Heraclitus, 18, 19 

Herbals, 56 

Heresy, 35, 60 

Hermes, 41 

Hero, 31 

Herodotus, 20 

Herophilus, 29, 30 

Herschel, 100, 163 

Hertz, 103, 152, 157 

Herzog, 148 

Hicetas, 50 

Hiero, 27, 28 

Hieroglyphs, 9 

Hilfield, 6 

Hill, A. V., 137 

Hindu numerals, 39 

Hipparchus, 21, 27, 28, 29, 49, 163 

Hippocrates, 20, 22, 36, 53 

History, Dawn of, 7 

Hittorf, 109 

Hobbes, Thomas, 59, 64, 68, 80 

Hofmann, 106 

Hohenheim, T. von (Paracelsus), 53 

Homberg, 83 

Homer and Hesiod, 16 

Hooke, 74, 84, 99 

Hooker, Sir Joseph, 119, 121 

Hopkins, Sir F. G., 134, 136 

Hormones, 109, 136 

Horsley, Sir Victor, 137 

Horus, 9 

Hounslow Heath, 118 

Humboldt, von, 119 

Hume, David, 79, 81 

Hutton, James, 48, 90 

Huxley, T. H., 119, 121, 123 

Huygens, 64, 66, 67, 69, 72, 73, 74 

Hybridization, 88 

Hydrodynamics, 47 

Hydrogen, atomic weight of, 167; 

liquefied, 97 

Hydrogen spectrum, 152, 153 
Hydrophobia, 116 
Hydrostatics, 47 
Hypatia, 36 

lamblichus, 36 
I-am-hotep, n 

latrochemists (Spagyrists) , 53, 65 

Ibn-Junis (Yunus), 39 

Ibn-Sina, 39, 53 

Ice Age, 3, 119 

Immanence, 65 

Immunity, 139 

India, 14, 30 

Indigo, 107 

Indus, 7 

Influenza, 140 

Inheritance, 120, 131, 132 

Innocent VIII, Pope, 60 

Inoculation, 85, 139 

Inquisition, 52 

Interference, 99, 148, 152, 153 

Introspection, 127 

Inverse Square Law, 69, 70, 101 

Inversion of sugar, 108 

Ionian philosophers, 16-17 

Ionosphere, 158 

Ions, 102, 109, no, 142, 144 

Ireland, 37 

Iron age, 7, 14 

Ishtar, 141 

Island universes, 164, 166 

Isobars, 150 

Iso-electric point, in 

Isomerism, 106 

Isotopes, 150 

Ivanovski, 117, 1 38 

Jabir-ibn-Haiyan, 38 

Jamaica, 88 

James II, 77 

Java, 123 

Jeans, 166 

Jenner, Edward, 85, 116 

Jerome, 36 

Jesty, Benjamin, 85 

Jevons, 125 

John of London, 44 

Johnson, Dr, 79 

Joule, J. P., 94, 95. 96, 98 

Jundishapur, 37 

Jupiter's satellites, 61, 158 

Justinian, 37 

Kamerlingh Onnes, 97 
Kant, 79, 82, 120, 125, 166 



Karnak, n 

Kaufmann, 143, 160 

Kekul6, 1 06 

Kendal, 139 

Kennelly-Heaviside layer, 158 

Kepler, John, 52, 62, 67, 70, 82, 162 

Keratin, 148 

Keynes (Lord), 77 

Kilogram, 93 

Kinetic theory, 66, 95, 96, 97, 147 

Kipping, 148 

Kirchhoff, 100 

Koch, 117 

Kolrausch, 109 

Krebs, 136 

Krypton, 105 

Kuhne, 116 

Kunsman, 152 

Laborde, 146 

Lagrange, 80, 81, 82 

Laidlaw, Sir P., 139 

Lamarck, 120, 122 

Landed families, 132 

Langley, 137 

Langmuir, 112, 135 

Language, 78 

Laplace, P. S. (Marquis de), 80, 82, 96, 

1 66 

Latent heat, 94, 99 
Latitude, 89 
Laue, 148 

Lavoisier, A. L., 84, 95, 104, 106, 125 
Lawes and Gilbert, 118 
Lawrence, A. E., 156 
Laws of Nature, 58, 75, 172 
Lead, 146 
Le Bel, 107 

Leguminous plants, 1 1 8 
Leibniz, 79, 81, 120 
Lenard, 152 
Leo X, Pope, 49 
Leo XIII, Pope, 45 
Leonardo da Vinci, 28, 47-8, 54, 90 
Leucippus, 17 
Lever, theory of, 27, 47 
Leverrier, 82 
Lewis, 150 
Leyden, 56, 83 

Library of Alexandria, 30, 36 

Liebig, 106, 107, 117, 118 

Life, basis of, 84, 115, 128, 138 

Life on other worlds, 162 

Light, theory of, 99-100, 153; velocity 

of, 74, 83, 103, 158, 159 
Limericks, 79 

Lindemann (Lord Cherwell), 151 
Linder and Picton, 1 1 2 
Linnaeus (Carl von Linn6), 87 
Liquefaction, 97 
Lisbon, 56 
Lister (Lord) ,117 
Lobatchevsky, 172 
Local motion, 62 
Locke, John, 78, 81, 125, 127 
Lodge, Sir Oliver, no, 1 59 
Loffler and Frosch, 1 1 7 
Longitude, 89 
Loom, 12 
Lorentz, 144, 145 
Lot, 7 

Louis XIV, 88 
Lower, 84 

Lubbock (Lord Avebury), 121 
Lucretius, 17, 18, 25, 32 
Lunar theory, 89, 90 
Luther, Martin, 49 
Lyell, Sir Charles, 119, 121, 123 
Lymington (Viscount), 77 

MacGullagh, 99 

Mach, E., 71, 72, 113, 125, 170, 172 

Machinery, 90-1 

Maclaurin, 81 

Macrocosm, 19, 20, 21, 25, 42 

Madras, 88 

Magic, 4, 5, 16, 25, 35, 48, 56, 60, 87, 141 

Magnetic compass, 46, 57 

Magnetic permeability, 103 

Magnetic storms, 119 

Magnetism and Electricity, 56-7 

Maimonides, 40 

Maintenance ration, 115 

Majendie, 115 

Malaria, 36, 1 1 7 

Malebranche, 64 

Malpighi, 56, 86 

Maltese fever, 117 



Malthas, Robert, 120, 121 

Mammoths, 3, 4 

Man, age of, i, 119 

Manichaeism, 35, 60 

Maps, 30, 119 

Marcus Aurelius, 32 

Mariotte, 64 

Marsh, Adam, 44 

Marshall Hall, 115 

Marx, 126 

Mass, 47, 57, 62, 63, 71, 160 

Mass law, 1 09 

Materialism, 80, 81, 125, 126, 170 

Materials, strength of, 63, 91 

Mathematics, 48 

Mathematics and Astronomy, 81-3 

Maupertuis, $i 

Maury, 119 

Maxwell, James Clerk, 92, 96, 98, 99, 

100, 101, 103, 104, 144, 157, 160, 169 
Mayer, J. R., 94 
Mayo, 84 

Medicine, u, 20, 33, 36, 38 
Mediterranean race, 8, 15, 140 
Mela, Pomponius, 32 
Meldrum, 136 
Melvill, 100 
Memphis, 9 
Menageries, 86 

Mendel, Abbot G. J., 123, 129, 130 
Mendele'eff, 105 

Mendclians and Biometricians, 132 
Menes, 9 

Mental power, 124 
Mercuric oxide, 83 
Mercury, orbit of, 161 
Merton College, 55 
Mesopotamia, 133 
Mesotrons, 155 
Meteorology, 119 
Metre, 93 
Mexico, 46 
Michell, 82 

Michelson and Morley, 1 59 
Microcosm, 19, 20, 21, 25, 42 
Microscope, 86; electron, 138, 158; 

ultra, in 
Middle Ages, 34-45 
Migration offish, 133 

Milky Way, 154, 163 

Mill,J.S., 127 

Millikan, 155, 167 

Millington, Sir Thomas, 86 

Miners' cramp, 138 

Minkowski, 160 

Minos, 15 

Minot, 138 

Mint, 77 

Mithras, 35 

Mitscherlich, 107 

Mohl, 115 

Molecules, 104 

Mondino, 54 

Monomolecular change, 147 

Montagu, Lady Mary Wortley, 85 

Moon, 61, 69, 89 

Morgan, Lloyd, 137 

Morgan, T. H., 130 

Morton, 1 1 7 

Moseley, H. G.J., 18, 149 

Moulton, 1 66 

Mount Wilson Observatory, 163, 165 

Mousterian civilization, 3 

Muhammad, 37 

Muller, Johan, 49, 1 1 3 

Museum of Alexandria, 29, 30, 36 

Mutations, 129 

Myosin, 135 

Mystery religions, 25, 35, 141 

Mysticism, 45 

Mythology, 16, 140, 141 

Naples, 66 

Napoleon, 80 

Natural History of Selborne, 88 

Natural philosophy, 66, 70 

Natural selection, 120-3 

Navigation, 46, 88, 89, 90, 119 

Neanderthal man, 3, 123, 133 

Nebulae, spiral, 82, 164, 167 

Nebular theory, 82, 166 

Neddermeyer, 155 

Nemi, 4 

Neolithic man, 2, 5, 133 

Neon, 105, 150 

Neo-Platonism, 34, 35, 37, 41, 42, 50 

Neptune, 82 

Nernst, 151 



Nervous system, 85, 114, 115, 116, 128, 

134^136, 13? 
Nestorius, 37 
Neutrons, 154 
Newcomen, 90 

New Holland (Australia), 89, 119 
New Physics and Chemistry, 141-61 
Newton, Sir Isaac, 21, 22, 24, 29, 59, 
62, 63, 64, 66, 68-77, 81, 82, 84, 87, 
89 94 95> ioo> i04> Io8 > I2 5 129, 
142, 152, 153, 160, 161, 162, 172, 


Nicholas of Cusa, 45, 58 

Nicholson and Carlisle, 102 

Night blindness, 134 

Nile, 7, 8, 10 

Nineteenth-Century Biology, 113-28 

Nineteenth-century Science and Philo- 
sophy, 124-7 

Nitrogen cycle, 1 1 8 

Nomads, 7 

Nominalism, 24, 41, 42, 45 

Nordic race, 8, 15, 140 

Novara, 50 

Number, 18, 19, 50, 52 

Nurnberg, 49 

Occam, William of, 45, 58 

Oceanography, 89, 119, 133 

Ochus, 12 

Oersted, 102 

Ohm, G. S., 103 

Ohm's Law, 103, 109 

Old Testament, 7, 8 

Omar Khayyam, 39 

Optics and Light, 73-5 

Organic Chemistry, 105-8 

Organism, 113, 128, 138, 173 

Origen, 35 

Origin of Species, 121, 122 

Origins, i 

Orphic mysteries, 16 

Orthodoxy, 35 

Oscillation, centre of, 66 

Osiander, 50 

Osmotic pressure, no, 135 

Owen, Sir Richard, 122 

Oxford, 40, 55 

Oxygen, 83, 84 

Padua, 56 

Palaeoliths, 2, 3 

Palos, 46 

Palstave, 6 

Pancreas, 114 

Paracelsus (see Hohenheim), 53 

Parallax of stars, 163 

Paris, 40, 43, 67 

Parliament, 77 

Parmenides, 171 

Parthenogenesis, 131 

Particles, list of, 1 55 

Pascal, Blaise, 65, 66, 96 

Pasteur, Louis, 107, 116, 117 

Paul, St, 35 

Pavlov, 137 

Pearson, Karl, 131, 170 

Peas, green, 129 

Pendulum, 62, 66 

Peptones, 108 

Penicillin, 139 

Periodic table, 105, 149 

Perkin, W. H., 106 

Pernicious anaemia, 138 

Perrault, 90 

Persia, 7 

Peru, 46 

Peter de Maharn-Curia, 44 

Petrarch, 46 

Petty, Sir William, 123 

Pfeffer, no 

Pharmacy, 33 

Phase Rule, 99 

Phenacetin, 107 

Phenomenalism, 172 

Phenylglycinc, 107 

Philae, 12 

Philip of Macedon, 22 

Philosophy, 58-9, 78-81, 172 

Phlogiston, 83, 84 

Photons, 151, 155 

Physical constants, 161 

Physics and Chemistry of the Nineteenth 

Century, 92-112 
Physiological apparatus, 1 1 3 
Physiology, 30, 48, 113, n 6, 134-8 
Physiology, Zoology and Botany, 84-8 
Picard, 69 
Pictures in caves, 2, 3, 4 

1 86 


Pilgrim Trust, 77 

Pillars of Hercules, 30 

Piltdown, 133 

Pisa, 56 

Pitchblende, 145 

Pithecanthropus Pekinensis, 133 

Planck, 142, 151, 153 

Planets, 162, 167 

Plankton, 119, 134 

Plants, classification of, 87 

Plants and Animals, 114, 117, 1 18 

Plato, 16,21,22,23,26,31, 37,41, 42, 171 

Platonism, 34, 35, 52 

Pliny, 32, 37, 56 

Plutarch, 28, 32, 50 

Pluto, 162, 163 

Polarization, electric, 109 

Polarization of light, 99, 107 

Polonium, 145 

Polyneuritis, 134 

Polypeptides, 135 

Polyploidy, 130 

Porphyry, 36, 41 

Portsmouth, Earl of, 77 

Portuguese exploration, 46 

Poseidonius, 30, 32, 46 

Positive electricity, 145 

Positive Rays and Isotopes, 149-50 

Positrons, 155 

Potassium, 102 

Potential thermodynamic, 99 

Pottery, 8, 14 

Prehistory, 1-7 

Pressure of light, 101 

Prices, 36, 46 

Priestley, Joseph, 83, 84, 101 

Primary and Secondary qualities, 63, 65 

Principia, 70 

Principles, primary, 38, 39, 65 

Printing, 47 

Probability, theory of, 66, 96, 112, 129, 


Proclus, 37 

Proteins, 108, 114, 115, 135, 148 
Protons, 147, 148 
Protoplasm, nr, 115 
Prout, 105, 150 
Proxima centauri, 163 
Psychology, 72, 78, 127, 128 
Psycho-physical parallelism, 128 

Ptolemy I, 29 

Ptolemy the Astronomer, 2 1 , 29, 30, 39, 


Ptolemy Epiphanes, 9 
Putrifaction, 116 
Puy-de-D6me, 66 
Pyramids, 12 
Pythagoras, 18, 19, 26 
Pythagoreans, 18-20, 50 
Pytheas, 30 

Quadrivium, 37, 41 
Quantum mechanics, 153 
Quantum theory, 142, 151, 153 
Quetelet, 123, 131 

Rabies, 116 

Racemates, 107 

Radiation, 142, 151, 169, 170 

Radicals, 107 

Radio-activity, 145-8 

Radio-location, 158 

Radio-speech, 157 

Radium, 145, 156 

Rainbow, 73 

Rankin, 95 

Rattlesnake, 119 

Raven, G. E., 86 

Ray, John, 85, 86, 87,88, 90 

Rayleigh, 112 

Rays, a, )3, y, 146 

Realism, 23, 41, 42, 45 

Reality, 78, 79, 170, 171 

Reaumur, 93 

Recent Biology, 129-41 

Recessive characters, 129 

Redi, 86 

Reflex action, 115 

Reflexes, 137 

Reformation, 49 

Regularities of science, 1 73 

Relativity, 158-61 

Renaissance, 46-60 

Resistance, electric, 103 

Resonance, 100 

Reversible processes, 160 

Reversible reactions, 1 08, 109 

Rey, 83 

Richardson, Sir O. W., 157 

Richer, 83, 88 



Rickets, 134 
Rideal, 112 
Rings, Newton's, 73 
Ritual, 1 6, 140 
Rivers, 7 

Rivers, W. H., 4, 140, 141 
Robinson Crusoe, 89 
Roebuck, 89 
Roemer, 74, 158 
Roman Age, 32-3 
Rome, 33, 36, 49, 66, 164 
Rontgen, 142, 145 
Rosetta stone, 9 
Ross, Sir James, 1 1 9 
Rothamsted, 1 1 8 
Roughton, 136 
Royal Institution, 102 
Royal Society, 66, 67, 77, 89 
Rumford, Count, 94 
Russell, Bertrand (Earl), 172 
Rutherford, Lord, 18, 142, 145, 146, 
H7> 154, i57> 172, 173 

Saint-Hilaire, 120 

Salerno, 36, 40 

Salvarsan, 107, 139 

Sanctorius, 54 

Sargasso Sea, 134 

Saturn's rings, 66 

Sceptical Chymist, 65 

Scheele, 83 

Schiff, u 6 

Schleiden, 114 

Scholasticism, 22, 34, 40, 42-5, 49, 50, 

58,67, 172 
Schrodinger, 153 
Schwann, 114, 116 
Scientific Academies, 66-8 
Scientific Age, 92-3 
Scot, Reginald, 60 
Scotland, 37 
Scurvy, 89, 134 
Secchi, Father, 164 
Second, 93 
Seleucus, 28 
Semi-realism, 172 
Semites, 7 
Seneca, 32 
Sensation, 114, 127 
Sepia, 23 

Servetus, 55 

Sex determination, 1 3 1 

Sheep, breeding of, 88 

Sherrington, Sir Charles, 131, 136, 


Signatures, doctrine of, 56 
Silkworm disease, 116, 138 

Simpson, 117 

Sirius, 165 

Smallpox, 85, 135 

Smeaton, 91 

Smith, Kenneth, 139 

Smith, William, 90 

Snell, 73 

Socrates and Plato, 20-22 

Soddy, 147, 149 

Sodium, 1 02 

Soil, structure of, 1 1 1, 1 18 

Solander, 89 

Solar system, 88, 162, 166 

Solution, 109-11 

Sophocles, 1 6 

Sound, 82, 127 

Space, 26, 38, 76, 142, 159, 160, 167 

Spagyrists, 53, 65 

Spain, 39, 42 

Spallanzani, Abb, 86 

Specific gravity, 23, 27, 47 

Specific heat, 94, 151 

Spectrum analysis, 100-1 

Spec, Father, 60 

Speech, 127 

Spencer, Herbert, 120, 125 

Spinoza, 64 

Spirits of the Wild, 5 

Spiritus nitro-aereus, 84 

Spontaneous generation, 86 

Spy, 123 

Stahl, 83, 84 

Standards of length, etc., 13 

Stanley, W. M., 138 

Starch, 114 

Starling, 136 

Stars, age of, 165; cepheid, 163; classi- 
fication of, 164; double, 163, 167; 
energy of, 165, 166; giant and dwarf, 
165; heavy, 165; magnitudes of, 163; 
and nebulae, 162-4; number of, 163; 
spectra of, 164; streams of, 163; 
temperatures of, 164; variable, 163 



Statistics, 96, 123, 173 

Steam engine, 90 

Steam ships, 91 

Stellar evolution, 165, 168 

Stellar Universe, 162-73 

Stellar velocities, 101 

Stevinus (Stevin), 6 1, 62, 72 

St John's College, Cambridge, 56 

Stoicism, 25, 32 

Stokes, Sir G. G., 100 

Stonehengc, 140 

Stoney, Johnston, 145 

Structure of atom, 150-4 

Structure of stars, 164-5 

Sugar, 135 

Sulphaguanidine, 139 

Sulphanilamidc, 139 

Sumatra, 88 

Sumer, 12 

Sun, age of, 166, 167; distance of, 162; 

energy of, 117, 118, 167, 169 
Sun and moon, 28, 29, 50 
Survival of the fittest, 127, 132 
Sutton, 130 
Swift, 89 
Sydenham, 78 

Sylvius (Dubois), 54, 55, 83, 84 
Synthetic drugs, 139 
Syracuse, 28 
Syria, 8, 12 
Syriac language, 37 

Tahiti, 89 

Tammuz, 141 

Taoism, 14 

Tartaric acid, 107 

Taylor, 81 

Telescope, 61 

Temperature, 93, 98 

Temperatures of Sun and stars, 101 

Tertullian, 41 

Thales, 16, 26 

Theophilus, 30, 36 

Thermionic valve, 157 

Thermodynamics, 95, 97-9, 101, no, 
in, 112; Second Law of, 169, 170 

Thermometer, 93 

Thompson, Benjamin (Count Rum- 
ford), 94 

Thomson, Sir G. P., 152 

Thomson, Sir J. J., 18, 142, 143, 144* 

145, 146, 147, 149 
Thomson, William (Lord Kelvin), 95, 

97,98, 126, 1 68 
Thoth, 9, 41 
Thucydides, 20 
Thyroid gland, 1 16 
Tiberius, 33 
Tides, 32, 70 
Tigris, 7 

Time, 38, 76, 142, 159, 160 
Toleration, 34, 78 
Tolman, 170 
Tombaugh, 162 
Torricelli, 66 
Torsion balance, 82 
Torture, 60 
Townsend, Sir J., 144 
Transmutation of elements, 1 54-7 
Travel literature, 89 
Trigonometrical Surveys, 118-19 
Trinity College, Cambridge, 68, 74, 77, 


Triphenyl methane, 107 
Trivium, 41 
Turner, William, 56 
Twins, 131 
Tylor, 141 
Types, theory of, 107 

Ultra-microscope, 1 1 1 

Uncertainty, principle of, 154, 171, 173 

Uniformitarian theory, 48, 90, 119 

Uniformity, Act of, 86 

Universals, 41 

Universe, contracting, 170; diagram of, 

51 ; energy of, 95, 98; expanding, 167 ; 

limits of, 167 
Universities, 40, 66 
Unverdorben, 106 
Ur of the Chaldees, 12 
Uranium, 145, 146 
Uranium X, 146 
Uranus, 82 
Urea, 106 

Vaccination, 85, 1 1 6 
Valency, 105, 112 



Van der Waals, 97 

Van't Hoff, 107, 109, no 

Variation, calculus of, 81 

Varro, 32 

Velocity of escape, 162 

Venel, 83 

Venus, transit of, 89, 162 

Vernalization, 132 

Vesalius, Andreas, 54 

Viete, Francois, 53 

Vinogradsky, 1 18 

Virchow, 115 

Virgil, 32, 118 

Viruses, 117 

Viruses and Immunity, 138-40 

Vitalism, 84, 115, 128, 138 

Vitamins, 134, 135 

Volta, 101 

Voltaire, 80, 81 

Wallace, A. R., 120, 121 

Wallop family, 77 

Walton, 156 

Washburn, 150 

Water, 53, 83, 84, 102, 104; heavy, 150 

Waterston, 95 

Watson, J. B., 137 

Watt, James, 91 

Wave-length of light, 99 

Wave mechanics, 152 

Wave theory of light, 99-100 

Waves, 47, 48, 82, 103 

Weber, E. H. and E. F,, 116, 127 

Wedgwood, Josiah, 121 

Weierstrass, 172 

Weight, 71, 72 

Weismann, 122 

Weyer, John, 60 

Wheat, 13, 118 

Whewell, 102 

White, Gilbert, 88 

Whitehead, A. N., 45, 172 

Wiechert, 143 

Wieland, 136 

Wien, 149 

Wilhelmy, 108 

Williamson, A. W., 109 

Willstatter, 135 

Willughby, Francis, 86 

Wilson, G. T. R., 144, 147, 173 

Wislicenus, 107 

Witchcraft, 60 

Wohler, 106 

Wolff, 114 

Wollaston, 100, 101 

Wood, T. B., 115 

Woodward, John, 90, 133 

Woolsthorpe, 68, 69 

Wundt, 127 

Wurzburg, 60 

Xenon, 105 

Xenophanes, 16 

Xenophon, 21 

X-rays, 135, 142, 143, 145, H9 

X-rays and Atomic Numbers, 148-9 

Young, Thomas, 9, 95, 99 

Zeeman, 145 

Zeno of Citium, 25, 32 

Zeno of Elea, 20, 171, 1 72 

w. LEWIS, M.A.