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BIOLOGY LIBRARY

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FIFTY YEAES OF SCIENCE

FIFTY TEARS OF SCIENCE

BEING THE ADDRESS DELIVERED AT YORK

TO THE BRITISH ASSOCIATION

AUGUST 1881

BY

SIR JOHN LUBBOCK, BART., M.P.

PRESIDENT OF THE ASSOCIATION

MACMILLAN AND CO.

1882

BIOLOGY UBRARf

LONDON t PRINTED BY

SPOTTISWOODE AND CO., NEW-STREET SQUARB
AND PARLIAMENT STREET

V.

ADDEESS

TO THE

BEITISH ASSOCIATION, 1881.

IN the name of the British Association, which for the
time I very unworthily represent, I beg to tender to
you, my Lord Mayor, and through you to the City of
York, our cordial thanks for your hospitable invitation
and hearty welcome.

We feel, indeed, that in coming to York we are
coming home. Gratefully as we acknowledge, and
much as we appreciate the kindness we have ex-
perienced elsewhere, and the friendly relations which
exist between this Association and most — I might even
say, all — our great cities, yet Sir R. Murchison truly
observed at the close of our first meeting in 1831, that
to York, ' as the cradle of the Association, we shall ever
look back with gratitude ; and whether we meet here-
after on the banks of the Isis, the Cam, or the Forth, to
this spot we shall still fondly revert.' Indeed, it would
have been a matter of much regret to all of us, if we
had not been able on this, our fiftieth anniversary, to
hold our meeting in our mother city.

My Lord Mayor, before going further, I must ex-
press my regret, especially when I call to mind the

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ivi3676£0

2 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

illustrious men who have preceded me in this chair,
that it has not fallen to one of my eminent friends
around me, to preside on this auspicious occasion.
Conscious, however, as I am of my own deficiencies, I
feel that I must not waste time in dwelling on them,
more especially as in doing so I should but give them
greater prominence. I will, therefore, only make one
earnest appeal to your kind indulgence.

The connection of the British Association with the
City of York does not depend merely on the fact that
our first meeting was held here. It originated in a
letter addressed by Sir D. Brewster to Professor Phillips,
as Secretary to your York Philosophical Society, by
whom the idea was warmly taken up. The first meet-
ing was held on September 26, 1831, the chair
being occupied by Lord Milton, who delivered an
address, after which Mr. William Vernon Harcourt,
Chairman of the Committee of Management, submitted
to the meeting a code of rules which had been so
maturely considered, and so wisely framed, that they
have remained substantially the same down to the
present day.

Of those who organised and took part in that first
meeting, few, alas! remain. Brewster and Phillips,
Harcourt and Lord Milton, Lyell and Murchison, all
have passed away, but their memories live among us.
Some few, indeed, of those present at our first meeting,
we rejoice to see here to-day, including one of the five
members constituting the original organising Com-
mittee, our venerable Vice- President, Archdeacon
Creyke.

The constitution and objects of the Association were

THE PROGRESS OP SCIENCE. 3

so ably described by Mr. Spottiswoode, at Dublin, and
are so well known to you, that I will not d \vell on them
this evening. The excellent President of the Royal
Society, in the same address, suggested that the past
history of the Association would form an appropriate
theme for the present meeting. The history of the
Association, however, is really the history of science,
and I long shrank from the attempt to give even a
panoramic survey of a subject so vast and so difficult ;
nor should I have ventured to make any such attempt,
but that I knew I could rely on the assistance of friends
in every department of science.

Certainly, however, this is an opportunity on which
it may be well for us to consider what have been the
principal scientific results of the last half-century,
dwelling especially on those with which this Associa-
tion is more directly concerned, either as being the work
of our own members, or as having been made known at
our meetings. I have, moreover, especially taken those
discoveries which the Royal Society has deemed worthy
of a medal. It is of course impossible within the
limits of a single address to do more than allude to a
few of these, and that very briefly. In dealing with so
large a subject I first hoped that I might take our
annual volumes as a text-book. This, however, I at
once found to be quite impossible. For instance, the
first volume commences with a Report on Astronomy,
by Sir G. Airy ; I may be pardoned, I trust, for ex-
pressing my pleasure at finding that the second was
one by my father, on the Tides, prepared like the pre-
ceding at the request of the Council ; then comes one
on Meteorology by Forbes ; Radiant Heat, by Baden

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4 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

Powell ; Optics, by Brewster ; Mineralogy, by Whewell,
and so on. My best course will therefore be to take our
different Sections one by one, and endeavour to bring
before you a few of the principal results which have
been obtained in each department.

The Biological Section is that with which I have
been most intimately associated, and with which it is,
perhaps, natural that I should begin.

Fifty years ago it was the general opinion that
animals and plants came into existence just as we now
see them. We took pleasure in their beauty ; their
adaptation to their habits and mode of life in many
cases could not be overlooked or misunderstood.
Nevertheless, the book of Nature was like some richly
illuminated missal, written in an unknown tongue.
The graceful forms of the letters, the beauty of the
colouring, excited our wonder and admiration ; but of
the true meaning little was known to us ; indeed we
scarcely realised that there was any meaning to decipher.
Now glimpses of the truth are gradually revealing
themselves ; we perceive that there is a reason — and in
many cases we know what that reason is — for every
difference in form, in size, and in colour ; for every bone
and every feather, almost for every hair. Moreover, each
problem which is solved opens out vistas, as it were, of
others perhaps even more interesting. With this impor-
tant change the name of our illustrious countryman,
Darwin, is intimately associated, and the year 1859 will
always be memorable in science as having produced his
work on ' The Origin of Species.' In the previous year
he and Wallace had published short papers, in which

BIOLOGY. THE DARWINIAN THEORY. 5

"they clearly state the theory of natural selection, at
which they had simultaneously and independently
arrived. We cannot wonder that Darwin's views
should have at first excited great opposition. Never-
theless from the first they met with powerful support,
especially, in this country, from Hooker, Huxley, and
Herbert Spencer. The theory is based on four
axioms : —

' 1. That no two animals or plants in nature are
identical in all respects.

' 2. That the offspring tend to inherit the peculiar-
ities of their parents.

i 3. That of those which come into existence, only a
small number reach maturity.

' 4. That those, which are, on the whole, best
adapted to the circumstances in which they are placed,
are most likely to leave descendants/

Darwin commenced his work by discussing the
causes and extent of variability in animals, and the
origin of domestic varieties ; he showed the impossibility
of distinguishing between varieties and species, and
pointed out the wide differences which man has pro-
duced in some cases — as, for instance, in our domestic
pigeons, all unquestionably descended from a com-
mon stock. He dwelt on the struggle for existence
(since become a household world), which, inevitably
resulting in the survival of the fittest, tends gradually
to adapt any race of animals to the conditions in which
it occurs.

While thus, however, showing the great importance
of natural selection, he attributed to it no exclusive in-
fluence, but fully admitted that other causes — the use

6 ADDRESS TO THE BUHTSI1 ASSOCIATION, 1881.

and disuse of organs, sexual selection, &c. — had to be
taken into consideration. Passing on to the difficulties
of his theory, he accounted for the absence of inter-
mediate varieties between species, to a great extent, by
the imperfection of the geological record. Here, how-
ever, I must observe that, as I have elsewhere remarked,
those who rely on the absence of links between different
species really argue in a vicious circle, because wherever
such links do exist they regard the whole chain as a
single species. The dog and jackal, for instance, are
now regarded as. two species, but if a series of links
were discovered between them they would be united
into one. Hence in this sense there never can be links
between any two species, because as soon as the links
are discovered the species are united. Every variable
species consists, in fact, of a number of closely connected
links.

But if the geological record be imperfect, it is still
very instructive. The further paleontology has pro-
gressed, the more it has tended to fill up the gaps
between existing groups and species : while the careful
study of living forms has brought into prominence the
variations dependent on food, climate, habitat, and other
conditions, and shown that many species long supposed
to be absolutely distinct are so closely linked together
by intermediate forms that it is difficult to draw a satis-
factory line between them. Thus the European and
American bisons are connected by the Bison priscus of
Prehistoric Europe ; the grizzly bear and the brown
bear, as Bask has shown, are apparently the modern
representatives of the cave bear ; Flower has pointed
out the palasontological evidence of gradual modification

THE PRINCIPLES OF CLASSIFICATION. 7

of animal forms in the Artiodactyles ; and we may
almost say, as a general rule, that the earliest known
mammalia belong to less specialised types than our
existing species. They are not well-marked Carnivores,
Rodents, Marsupials, &c., but rather constitute a group
of generalised forms from which our present well-marked
orders appear to have diverged. Among the Inverte-
brata, Carpenter and Williamson have proved that it is
almost impossible to divide the Foraminifera into well-
marked species ; and, lastly, among plants, there are
large genera, as, for instance, Rubus and Hieracium.
with reference to the species of which no two botanists
are agreed.

The principles of classification point also in the
same direction, and are based more and more on the
theory of descent. Biologists endeavour to arrange
animals on what is called the ' natural system.' No one
now places whales among fish, bats among birds, or
shrews with mice, notwithstanding their external simi-
larity ; and Darwin maintained that ' community of
descent was the hidden bond which naturalists had
been unconsciously seeking.7 How else, indeed, can we
explain the fact that the framework of bones is so
similar in the arm of a man, the wing of a bat, the fore-
leg of a horse, and the fin of a porpoise — that the neck
of a giraffe and that of an elephant contain the same
number of vertebras ?

Strong evidence is, moreover, afforded by embryo-
logy ; by the presence of rudimentary organs and tran-
sient characters, as, for instance, the existence in the
calf of certain teeth which never cut the gums, the
shrivelled and useless wings of some beetles, the presence

8 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

of a series of arteries in the embryos of the higher
Vertebrata exactly similar to those which supply the
gills in fishes, even the spots on the young blackbird,
the stripes on the lion's cub ; these, and innumerable
other facts of the same character, appear to be incom-
patible with the idea that each species was specially and
independently created ; and to prove, on the contrary,
that the embryonic stages of species show us more or
less clearly the structure of their ancestors.

Darwin's views, however, are still much misunder-
stood. I believe there are thousands who consider that
according to his theory a sheep might turn into a cow,
or a zebra into a horse. No one would more confidently
withstand any such hypothesis, his view being, of
course, not that the one could be changed into the
other, but that both are descended from a common
ancestor.

No one, at any rate, will question the immense im-
pulse which Darwin has given to the study of natural
history, the number of new views he has opened up,
and the additional interest which he has aroused in, and
contributed to, Biology. When we were young we
knew that the leopard had spots, the tiger was striped,
and the lion tawny ; but why this was so it did not
occur to us to ask ; and if we had asked no one could
have answered. Now we see at a glance that the
stripes of the tiger have reference to its life among
jungle-grasses ; the lion is sandy, like the desert ;
while the markings of the leopard resemble spots of
sunshine glancing through the leaves. Again, Wallace
in his charming essays on natural selection has shown
how the same philosophy may be applied even to birds'

EMBRYOLOGY. 9

nests — how, for instance, open nests have led to the
dull colour of hen birds ; the only British exception
being the kingfisher, which, as we know, nests in river-
banks. Lower still, among insects, Weismann has
taught us that even the markings of caterpillars are full
of interesting lessons ; while, in other cases, specially
among butterflies, Bates has made known to us the
curious phenomena of mimicry.

The science of embryology may almost be said to
have been created in the last half- century. Fifty
years ago it was a very general opinion that animals
which are unlike when mature, were dissimilar from the
beginning. It is to Yon Baer, the discoverer of the
mammalian ovum, that we owe the great generalisation
that the development of the egg is in the main a pro-
gress from the general to the special, that zoological
affinity is the expression of similarity of development,
and that the different great types of animal structure
are the result of different modes of development — in
fact, that embryology is the key to the laws of animal
development.

Thus the young of existing species resemble in many
cases the mature forms which flourished in ancient
times. Huxley has traced up the genealogy of the
horse to the Miocene Anchitherium, and his views
have since been remarkably confirmed by Marsh's dis-
covery of the Pliohippus, Protohippus, Miohippus, and
Mesohippus, leading down from the Eohippus of the
early tertiary strata. In the same way Boyd-Dawkins
and Gaudry have called attention to the fact that just as
the individual stag gradually acquires more and more com-
plex antlers : having at first only a single prong, in the

10 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

next year two points, in the following three, and so on ;
so the genus, as a whole, in Middle Miocene times, had
two pronged horns ; in the Upper Miocene, three ; and
that it is not till the Upper Pliocene that we find any
species with the magnificent antlers of our modern deer.
It seems to he now generally admitted that birds have
come down to us through the Dinosaurians, and, as
Huxley has shown, the profound break once supposed
to exist between birds and reptiles has been bridged
over by the discovery of reptilian birds and bird-like
reptiles ; so that, in feet, birds are modified reptiles. The
remarkable genus Peripatus, so well studied by Moseley,
tends to connect the annulose and articulate types.

Again, the structural resemblances between Am-
phioxus and the Ascidians had been pointed out by
Goodsir; and Kowalevskyin 1866 showed that these
were not mere analogies, but indicated a real affinity.
These observations, in the words of Allen Thomson,
* have produced a change little short of revolutionary in
embryological and zoological views, leading as they do
to the support of the hypothesis that the Ascidian is an
earlier stage in the phylogenetic history of the mammal
and other vertebrates.'

The larval forms which occur in so many groups,
and of which the Insects afford us the most familiar ex-
amples, are, in Ithe words of Quatrefeges, embryos, which
lead an independent life. In such cases as these, external
conditions act upon the larvae as they do upon the
mature form ; hence we have two classes of changes,
adaptational or adaptive, and developmental. These
and many other facts must be taken into consideration ;
nevexthdees naturalists are now generally agreed that

THE GA5TBLSA THEORY. 11

embry ological characters are of high value as guides in
classification, and it may, I think, be regarded as wefl-
established that, just as the contents and srqotnre of
rocks teach us die past history of the earth, so is die
gradual development of the species indicated by Ae
structure of the embryo and its developmental changes.

When the supporters of Darwin are told that Ins
theory is incredible, they may fairly ask why it is im-
possible that a species in the coarse of hundreds of
thousands of years should have passed through changes
which occupy only a lew days or weeks in the fife-
history of each individual ?

The pht-MJimgiMA of yolk segmentation, first observed
by Pre vest and Dumas, are now known to be, in some form
or other, invariably the precursors of emhtyonic develop-
ment ; while they reproduce, as the first stages in the
formation of die higher animals^ the main and essential
features in the lite-history of the lowest forms. The
'blastoderm,7 as it is called, or first germ of the embryo
in the egg, divides itself into two layers, corresponding,
as Huxley has shown, to the two layers into which the
body of the Ccelenterata may be divided. Xot only go,

but most embrvosat an earivsta^e of development have

j i

the form of a cup, the walk of which are formed by die
two layers of the blastoderm. Kowalevsky was the first
to show the prevalence of this embryonic form, and sub-
sequently Lankester and Haeckel put forward the hypo-
thesis that it was the embryonic repetition of an
ancestral type, from which all die higher forms are
descended. The cavity of the cap is supposed to be the
stomach of this simple oqj^nism, ai*l the opening of die
cup the mouth. The inner layer of the wall of the cnp

12 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

constitutes the digestive membrane, and the outer the
skin. To this form Haeckel gave the name Gastraea.
It is, perhaps, doubtful whether the theory of Lankester
and Haeckel can be accepted in precisely the form they
propounded it ; but it has had an important influence
on the progress of embryology. I cannot quit the
science of embryology without alluding to the very
admirable work on ' Comparative Embryology ' by our
new general secretary, Mr. Balfour, and also the ' Ele-
ments of Embryology ' which he had previously
published in conjunction with Dr. M. Foster.

In 1842 Steenstrup published his celebrated work
on the ' Alternation of Generations/ in which he
showed that many species are represented by two
perfectly distinct types or broods, differing in form,
structure, and habits ; that in one of them males are
entirely wanting, and that the reproduction is effected
by fission, or by buds, which, however, are in some
cases structurally indistinguishable from eggs. Steen-
strup's illustrations were mainly taken from marine or
parasitic species, of very great interest, but not gene-
rally familiar, excepting to naturalists. It has since
been shown that the common Cynips or Gallfly is also
a case in point. It had long been known that in some
genera belonging to this group, males are entirely
wanting, and it has now been shown by Bassett, and
more thoroughly by Adler, that some of these species
are double-brooded ; the two broods having been con-
sidered as distinct genera.

Thus an insect known as Neuroterus lenticularis,
of which females only occur, produces the familiar
oak-spangles so common on the under-sicles of oak-

ALTERNATION OF GENERATIONS. 13

leaves, from which emerge, not Neuroterus lenticularis,
but an insect hitherto considered as a distinct species,
belonging even to a different genus, Spathegaster bac-
carum. In Spathegaster both sexes occur ; they pro-
duce the currant-like galls found on oaks, and from
these galls Neuroterus is again developed. So also the
King Charles oak-apples produce a species known as
Teras terminal^, which descends to the ground, and
makes small galls on the roots of the oak. From these
emerge an insect known as Biorhiza aptera, which
again gives rise to the common oak-apple.

Many butterflies, again, are dimorphic, existing
under two, or even three, distinct forms — one that of
the winter, the other of the summer brood or broods.
Weismann has adduced strong reasons for thinking
that during the glacial period these species were one-
brooded only, and existed in the present winter form ;
that, as the climate improved, the period of warmth
became sufficient to allow the development of a second
brood, and led to the gradual rise of the summer form.

He and Edwards have shown that, while, by the
application of cold, pupse, which would naturally have
produced the summer form, can be made to assume the
winter dress ; it is, on the contrary, far more difficult
to change the winter into the summer colouring.

In some cases — as for instance in the very curious
Leptodora crystallina (a fresh- water crustacean, in-
habiting deep lakes and reservoirs, and which, as its
name denotes, is almost perfectly transparent) — though
the two forms are almost exactly similar in their mature
state, the mode of development is very different ; for,
while the winter form goes through a well-marked

14 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

metamorphosis, in the summer brood the development
is direct.

It might seem that such enquiries as these could
hardly have any practical bearing. Yet it is not im-
probable that they may lead to very important results.
For instance, it would appear that the fluke which
produces the rot in sheep, passes one phase of its
existence in snails or slugs, and we are not without
hopes that the researches, in which our lamented friend
Prof. Eolleston was engaged at the time of his death,
and which Mr. Thomas is continuing, will lead, if not to
the extirpation, at any rate to the diminution, of a pest
from which our farmers have so grievously suffered.

It was in the year 1839 that Schwann and Schleiden
demonstrated the intimate relation in which animals
and plants stand to each other, by showing the identity
of the laws of development of the elementary parts in
the two kingdoms of organic nature. Analogies indeed
had been previously pointed out ; the presence of cel-
lular tissue in certain parts of animals was known, but
Caspar F. Wolff's brilliant memoir had been nearly for-
gotten ; and the tendency of microscopical investigation
had rather been to encourage the belief that no real
similarity existed ; that the cellular tissue of animals
was essentially different from that of plants. This had
arisen chiefly, perhaps, because fully formed tissues were
compared, and it was mainly the study of the growth of
cells which led to the demonstration of the general law
of development for all organic elementary tissues.

As regards descriptive biology, by far the greater
number of species now recorded have been named and
described within the last half- century, and it is not too

INCREASE IN NUMBER OF KNOWN SPECIES. 15

much to say that not a day passes without adding new
species to our lists. A comparison, for instance, of the
edition of Cuvier's ' Regne Animal/ published in 1828,
as compared with the present state of our knowledge,
is most striking.

Dr. Giinther has been good enough to make a calcu-
lation for me. The numbers, of course, are only ap-
proximate, but it appears that while the total number
of animals described up to 1831 was not more than
70,000, the number now is at least 320,000.

Lastly, to show how large a field still remains for
exploration, I may add that Mr. Waterhouse estimates
that our Museums contain not fewer than 12,000 species
of insects which have not yet been described, while
our collections do not probably contain anything like
one-half of those actually in existence. Further than
this, the anatomy and habits even of those which
have been described offer an inexhaustible field for
research, and it is not going too far to say that there
is not a single species which would not amply repay
the devotion of a lifetime.

One remarkable feature in the modern progress of
biological science has been the application of improved
methods of observation and experiment ; and the em-
ployment in physiological research of the exact mea-
surements employed by the experimental physicist. Our
microscopes have been greatly improved : achromatic
object-glasses were introduced by Lister in 1829 ; the
binocular arrangement by Wenham in 1856 ; while
immersion lenses, first suggested by Amici, and since
carried out under the formula of Abbe, are most valuable.
The use of chemical re- agents in microscopical investiga-

16 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

tions has proved most instructive, and another very
important method of investigation has been the power
of obtaining very thin slices by imbedding the object
to be examined in paraffin or some other soft substance.
In this manner we can now obtain, say, fifty separate
sections of the egg of a beetle, or the brain of a bee.

At the close of the last century, Sprengel published
a most suggestive work on flowers, in which he pointed
out the curious relation existing between these and
insects, and showed that the latter carry the pollen
from flower to flower. His observations, however,
attracted little notice until Darwin called attention to
the subject in 1862. It had long been known that the
cowslip and primrose exist under two forms, about
equally numerous, and differing from one another in
the arrangements of their stamens and pistils ; the one
form having the stamens on the summit of the flower
and the stigma half-way down ; while in the other the
relative positions are reversed, the stigma being at the
summit of the tube and the stamens half-way down.
This difference had, however, been regarded as a case of
mere variability ; but Darwin showed it to be a beauti-
ful provision, the result of which is that insects fertilise
each flower with pollen brought from a different plant ;
and he proved that flowers fertilised with pollen from
the other form yield more seed than if fertilised with
pollen of the same form, even if taken from a different
plant.

Attention having been thus directed to the question,
an astonishing variety of most beautiful contrivances
have been observed and described by many botanists,
especially Hooker, Axel, Delpino, Hildebrand, Bennett,

RELATION BETWEEN PLANTS AND INSECTS. 17

Fritz M tiller, and above all Hermann Miiller and Darwin
himself. The general result is that to insects, and
especially to bees, we owe the beauty of our gardens,
the sweetness of our fields. To their beneficent, though
unconscious action, flowers owe their scent and colour,
their honey — nay, in many cases, even their form.
Their present shape and varied arrangements, their
brilliant colours, their honey, and their sweet scent are
all due to the selection exercised by insects.

In these cases the relation between plants and
insects is one of mutual advantage. In many species,
however, plants present us with complex arrangements
adapted to protect them from insects ; such, for in-
stance, are in many cases the resinous glands which
render leaves unpalatable ; the thickets of hairs and
other precautions which prevent flowers from being
robbed of their honey by ants. Again, more than a
century ago, our countryman, Ellis, described an
American plant, Dionsea, in which the leaves are
somewhat concave, with long lateral spines, and a joint
in the middle, which closes up with a jerk, like a rat-
trap, the moment any unwary insect alights on them.
The plant, in fact, actually captures and devours in-
sects. This observation also remained as an isolated
fact until within the last few years, when Darwin,
Hooker, and others have shown that many other
species have curious and very varied contrivances for
supplying themselves with animal food.

As regards the progress of botany in other directions,
Mr. Thiselton Dyer has been kind enough to assist me
in endeavouring to place the principal facts before you.
Some of the most fascinating branches of botany —

c

18 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

morphology, histology, and physiology scarcely existed
before 1830. In the two former branches the discoveries
of von Mohl are pre-eminent. He first observed
cell-division in 1835, and detected the presence of starch
in chlorophyll-corpuscles in 1837, while he first de-
scribed protoplasm, now so familiar to us, at least by
name, in 1846. In the same year Amici discovered the
existence of the embryonic vesicle in the embryo sac,
which develops into the embryo when fertilised by the
entrance of the pollen-tube into the micropyle. The
existence of sexual reproduction in the lower plants was
doubtful, or at least doubted by some eminent authorities,
as recently as 1853, when the actual process of fertilisa-
tion in the common bladderwrack of our shores was
observed by Thuret, while the reproduction of the larger
fungi was first worked out by De Bary in 1863.

As regards lichens, Schwendener proposed, in 1869,
the startling theory, now however accepted by some of
the highest authorities, that lichens are not autonomous
organisms, but commensal associations of a fungus
parasitic on an alga. With reference to the higher
Cryptogams, it is hardly too much to say that the whole
of our exact knowledge of their life-history has been
obtained during the last half-century. Thus in the
case of ferns the male organs, or antheridia, were first
discovered by Nageli in 1844, and the archegonia, or
female organs, by Suminski in 1848. The early stages
in the development of mosses were worked out by
Valentine in 1833. Lastly, the principle of Alternation
of Generations in plants was discovered by Hofmeister.
This eminent naturalist also, in 1851-4, pointed out
the homologies of the reproductive processes in mosses,
vascular cryptogams, gymnosperms, and angiosperms.

SYSTEMATIC AND GEOGRAPHICAL BOTANY. 19

Geographical Botany can hardly be said to have had
any scientific status anterior to the publication of the
1 Origin of Species/ The way had been paved, how-
ever, by A. de Candolle and the well-known essay of
Edward Forbes — i On the Distribution of the Plants
and Animals of the British Isles/ — by Sir J. Hooker's
introductory essay to the i Flora of New Zealand/ and
by Hooker and Thomson's introductory essay to the
1 Flora Indica.' One result of these researches has been
to give the coup-de-grdce to the theory of an Atlantis.
Lastly, in a lecture delivered to the Geographical
Society in 1878, Thiselton Dyer himself has summed
up the present state of the subject, and contributed an
important addition to our knowledge of plant-distribu-
tion by showing how its main features may be ex-
plained by migration in latitude from north to south
without recourse being had to a submerged southern
continent for explaining the features common to South
Africa, Australia, and America.

The fact that systematic and geographical botany
have claimed a preponderating share of the attention of
British phytologists, is no doubt in great measure due
to the ever-expanding area of the British Empire, and
the rich botanical treasures which we are continually
receiving from India and our numerous colonies. The
series of Indian and Colonial Floras, published under
the direction of the authorities at Kew, and the l Genera
Plantarum ' of Bentham and Hooker, are certainly an
honour to our country. To similar causes we may
trace the rise and rapid progress of economic botany,
to which the late Sir W. Hooker so greatly contri-
buted.

c 2

20 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

In vegetable physiology some of the most striking
researches have been on the effect produced by rays of
light of different refrangibility. Daubeny, Draper, and
Sachs have shown that the light of the red end of the
spectrum is more effective than that of the blue, so far
as the decomposition of carbon dioxide (carbonic acid)
is concerned.

Nothing could have appeared less likely than that
researches into the theory of spontaneous generation
should have led to practical improvements in medical
science. Yet such has been the case. Only a few
years ago Bacteria seemed mere scientific curiosities.
It had long been known that an infusion — say, of hay —
would, if exposed to the atmosphere, le found, after a
certain time, to teem with living forms. Even those
few who still believe that life would be spontaneously
generated in such an infusion, will admit that these
minute organisms are, if not entirely, yet mainly, de-
rived from germs floating in our atmosphere ; and if
precautions are taken to exclude such germs, as in the
careful experiments especially of Pasteur, Tyndall, and
Roberts, everyone will grant that in ninety-nine cases
out of a hundred no such development of life will take
place. In 1836-7 Cagniard de la Tour and Schwann
independently showed that fermentation was no mere
chemical process, but was due to the presence of a
microscopic plant. But, more than this, it has been
gradually established that putrefaction is also the work
of microscopic organisms. Thirty years, however,
elapsed before these important discoveries received any
practical application.

At length, however, these facts have led to most

MICROSCOPIC ORGANISMS CAUSES OF DISEASE. 21

important results in Surgery. One reason why com-
pound fractures are so dangerous is because, the skin
being broken, the air obtains access to the wound,
bringing with it innumerable germs, which too often
set up putrefying action. Lister first made a practical
application of these observations. He set himself to
find some substance capable of killing the germs with-
out being itself too potent a caustic, and he found that
dilute carbolic acid fulfilled these conditions. This
discovery has enabled many operations to be per-
formed which would previously have been almost hope-
less.

The same idea seems destined to prove as useful in
Medicine as in Surgery. There is great reason to sup-
pose that many diseases, especially those of a zymotic
character, have their origin in the germs of special
organisms. We know that fevers run a certain definite
course. The parasitic organisms are at first few, but
gradually multiply at the expense of the patient, and
then die out again. Indeed, it seems to be thoroughly
established that many diseases are due to the excessive
multiplication of microscopic organisms, and we are not
without hope that means will be discovered by which,
without injury to the patient, these terrible, though
minute, enemies may be destroyed, and the disease thus
stayed. Bacillus anthracis, for instance, is now known
to be the cause of splenic fever, which is so fatal to
cattle, and is also communicable to man. At Bradford,
for instance, it is only too well known as the wool -
sorter's disease. If, however, matter containing the
Bacillus be treated in a particular manner, and cattle
be then inoculated with it, they are found to acquire an

22 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

immunity from the fever. The interesting researches
of Burdon- Sander son, Greenfield, Koch, Pasteur, Tous-
saint, and others, seem to justify the hope that we may
be able to modify these and other germs, and then by
appropriate inoculation to protect ourselves against
fever and other acute diseases.

Terrier's researches in continuation of those of
Fritsch and Hitzig have enabled us to localise the
function of various parts of the brain. His results
have not only proved of great importance in surgery,
and in many cases led to successful operations by point-
ing out the exact source of the mischief, but an exact
knowledge of the brain is also of the greatest importance
in the treatment of nervous diseases. Echeverria has
collected 165 cases of traumatic epilepsy, of which 64
per cent, were cured by removing a portion of the
skull, the site for the operation and the exact locality
of the injury being indicated by cerebral localisation.

The history of Anaesthetics is a most remarkable
illustration how long we may be on the very verge of
a most important discovery. Ether, which, as we all
know, produces perfect insensibility to pain, was dis-
covered as long ago as 1540. The anaesthetic property
of nitrous oxide, now so extensively used, was observed
in 1800 by Sir H. Davy, who actually experimented on
himself, and had one of his teeth painlessly extracted
when under its influence. He even suggests that ' as
nitrous oxide gas seems capable of destroying pain, it
could probably be used with advantage in surgical
operations.' Nay, this property of nitrous oxide was
habitually explained and illustrated in the chemical
lectures given in hospitals, and yet for fifty years the

ANESTHETICS.— ANCIENT CONDITION OF MAN. 23

gas was never used in actual operations. No one did
more to promote the use of anaesthetics than Sir James
Y. Simpson, who introduced chloroform, a substance
which was discovered in 1831, and which for a while
almost entirely superseded ether and nitrous oxide,
though with improved methods of administration, the
latter are now coming into favour again.

The only other reference to Physiology which time
permits me to make, is the great discovery of the reflex
action, as it is called, of the nervous centres. Reflex
actions had been long ago observed, and it had been
shown by Whytt and Hales that they were more or less
independent .of volition. But the general opinion was
that these movements indicated some feeble power of
sensation independently of the brain, and it was not till
the year 1832 that the ' reflex action ' of certain nervous
centres was made known to us by Marshall Hall, and
almost at the same period by Johannes Miiller.

Few branches of science have made more rapid pro-
gress in the last half- century than that which deals with
the ancient condition of Man. When our Association
was founded it was generally considered that the human
race suddenly appeared on the scene, about 6,000 years
ago, after the disappearance of the extinct mammalia,
and when Europe, both as regards physical conditions
and the other animals by which it was inhabited, was
pretty much in the same state as in the period covered
by Greek and Roman history. Since then the perse-
vering researches of Layard, Rawlinson, Botta and
others have made known to us, not only the statues and
palaces, of the ancient Assyrian monarchs, but even

24 ADDRESS TO THE BIU1ISII ASSOCIATION, 1881.

their libraries ; the cuneiform characters have been de-
ciphered, and we can not only see, but read, in the
British Museum, the actual contemporary records, on
burnt clay cylinders, of the events recorded in the his-
torical books of the Old Testament and in the pages of
Herodotus. The researches in Egypt also seem to have
satisfactorily established the fact that the pyramids
themselves are at least 6,000 years old, while it is ob-
vious that the Assyrian and Egyptian monarchies can-
not suddenly have attained to the wealth and power,
the state of social organisation, and progress in the
arts, of which we have before us, preserved by the sand
of the desert from the ravages of man, such wonderful
proofs.

In Europe, the writings of the earliest historians
and poets indicated that, before iron came into general
use, there was a time when bronze was the ordinary
material of weapons, axes, and other cutting imple-
ments, and though it seemed a priori improbable that a
compound of copper and tin should have preceded the
simple metal iron, nevertheless the researches of archae-
ologists have shown that there really was in Europe a
' Bronze Age,' which at the dawn of history was just
giving way to that of l Iron/

The contents of ancient graves, buried in many cases
so that their owner might carry some at least of his
wealth with him to the world of spirits, have proved
very instructive. More especially the results obtained
by Nilsson in Scandinavia, by Hoare and Borlase, Bate-
man, Greenwell, and Pitt Rivers, in our own country,
and the contents of the rich cemetery at Hallstadt, left
no room for doubt as to the existence of a Bronze Age ;

THE BRONZE AND STONE AGES. 25

but we get a completer idea of the condition of Man at
this period from the Swiss lake- villages, first made
known to us by Keller, and subsequently studied by
Morlot, Troyon, Desor, Riitimeyer, Heer, and other
Swiss archaeologists. Along the shallow edges of the
Swiss lakes there flourished, once upon a time, many
populous villages or towns, built on platforms supported
by piles, exactly as many Malayan villages are now.
Under these circumstances innumerable objects were
one by one dropped into the water ; sometimes whole
villages were burnt, and their contents submerged ; and
thus we have been able to recover, from the waters of
oblivion in which they had rested for more than 2,000
years, not only the arms and tools of this ancient
people, the bones of their animals, their pottery and
ornaments, but the stuffs they wore, the grain they
had stored up for future use, even fruits and cakes of
bread.

But this bronze-using people were not the earliest
occupants of Europe. The contents of ancient tombs
give evidence of a time when metal was unknown.
This also was confirmed by the evidence then un-
expectedly received from the Swiss lakes. By the side
of the bronze-age villages were others, not less exten-
sive, in which, while implements of stone and bone
were discovered literally by thousands, not a trace of
metal was met with. The shell-mounds or refuse-heaps
accumulated by the ancient fishermen along the shores
of Denmark, and carefully examined by Steenstrup,
Worsaae, and other Danish naturalists, fully confirmed
the existence of a * Stone Age.'

We have still much to learn, I need hardly say,

26 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

about this Stone- age people, but it is surprising how
much has been made out. Evans truly observes, in his
admirable work on ' Ancient Stone Implements/ ' that
so far as external appliances are concerned, they are
almost as fully represented as would be those of any
existing savage nation by the researches of a painstak-
ing traveller.' We have their axes, adzes, chisels,
borers, scrapers, and various other tools, and we know
how they made and how they used them ; we have
their personal ornaments and implements of war ; we
have their cooking utensils ; we know what they ate
and what they wore; lastly, we know their mode of
sepulture and funeral customs. They hunted the deer
and horse, the bison and urus, the bear and the wolf,
but the reindeer had already retreated to the- North.

No bones of the reindeer, no fragment of any of the
extinct mammalia have been found in any of the Swiss
lake-villages or in any of the thousands of tumuli which
have been opened in our own country or in Central and
Southern Europe. Yet the contents of caves and of
river-gravels afford abundant evidence that there was a
time when the mammoth and rhinoceros, the musk-ox
and reindeer, the cave lion and hyena, the great bear
and the gigantic Irish elk wandered in our woods and
valleys, and the hippopotamus floated in our rivers;
when England and France were united, and the Thames
and the Rhine had a common estuary. This was long
supposed to be before the advent of man. At length,
however, the discoveries of Boucher de Perthes in the
valley of the Somme, supported as they are by the
researches of many continental naturalists, and in our
own country of MacEnery and Godwin Austen, Prest-

THE PAL/EOLITIIIC AND NEOLITHIC AGES. 27

wich and Lyell, Vivian and Pengelly, Christy, Evans,
and many more, have proved that man formed a
humble part of this strange assembly.

Nay, even at this early period there were at least
two distinct races of men in Europe ; one of them — as
Boyd-Dawkins has pointed out — closely resembling
the modern Esquimaux in form, in his weapons and
implements, probably in his clothing, as well as in so
many of the animals with which he was associated.

At this stage Man appears to have been ignorant
of pottery, to have had no knowledge of agriculture,
no domestic animals, except perhaps the dog. His
weapons were the axe, the spear, and the javelin ; I
do not believe he knew the use of the bow, though he
was probably acquainted with the lance. He was, of
course, ignorant of metal, and his stone implements,
though skilfully formed, were of quite different shapes
from those of the second Stone age, and were never
ground. This earlier Stone period, when man co-
existed with these extinct mammalia, is known as the
Palaeolithic, or Early Stone Age, in opposition to the
Neolithic, or Newer Stone Age.

The remains of the mammalia which co-existed
with man in pre-historic times have been most care-
fully studied by Owen, Lartet, Riitimeyer, Falconer,
Busk, Boyd-Dawkins, and others. The presence of the
mammoth, the reindeer, and especially of the musk-ox,
indicates a severe, not to say an arctic, climate — the
existence of which, moreover, was proved by other
considerations ; while, on the contrary, the hippo-
potamus requires considerable warmth. How, then, is
this association to be explained ?

28 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

While the climate of the globe is, no doubt, much
affected by geographical conditions, the cold of the
glacial period was, I believe, mainly due to the eccen-
tricity of the earth's orbit combined with the oblique
effects of precession of the ecliptic. The result of the
latter condition is a period of 21,000 years, during one
half of which the northern hemisphere is warmer than
the southern, while during the other 10,500 years the
reverse is the case. At present we are in the former
phase, and there is, we know, a vast accumulation of
ice at the south pole. But when the earth's orbit is
nearly circular, as it is at present, the difference between
the two hemispheres is not very great ; while on the
contrary, as the eccentricity of the orbit increases, the
contrast between them increases also. This eccentricity
is continually oscillating within certain limits which
Croll and subsequently Stone have calculated for the last
million years. At present the eccentricity is *016 and
the mean temperature of the coldest month in London
is about 40°. Such has been the state of things for
nearly 100,000 years ; but before that there was a
period, beginning 300,000 years ago, when the eccen-
tricity of the orbit varied from *26 to *57. The result
of this would be greatly to increase the effect due to the
obliquity of the orbit ; at certain periods the climate
would be much warmer than at present, while at others
the number of days in winter would be twenty more,
and of summer twenty less, than now. while the mean
temperature of the coldest month would be lowered
20°. We thus get something like a date for the last
glacial epoch, and we see that it was not simply a
period of cold, but rather one of extremes, each beat of

CONDITION OF MAN IN PRE-IIISTORIC TIMES. 29

the pendulum of temperature lasting for no less than
21.000 years. This explains the fact that, as Morlot
showed in 1854, the glacial deposits of Switzerland,
and, as we now know, those of Scotland, are not a
single uniform layer, but a succession of strata indi-
cating very different conditions. I agree also with
Croll and Geikie in thinking that these considerations
explain the apparent anomaly of the co -existence in the
same gravels of arctic and tropical animals ; the former
having lived in the cold, while the latter flourished in
the hot, periods.

It is, I think, now well established that man in-
habited Europe during the milder periods of the glacial
epoch. Some high authorities indeed consider that we
have evidence of his presence in pre- glacial and even in
Miocene times, but I confess that I am not satisfied on
this point. Even the more recent period carries back
the record of man's existence to a distance so great as
altogether to change our views of ancient history.

Nor is it only as regards the antiquity and material
condition of man in pre-historic times that great pro-
gress has been made. If time permitted I should have
been glad to have dwelt on the origin and development
of language, of custom, and of law. On all of these
the comparison of the various lower races still inhabiting
so large a portion of the earth's surface, has thrown
much light ; while even in the most cultivated nations
we find survivals, curious fancies, and lingering ideas ;
the fossil remains as it were of former customs and
religions, embedded in our modern civilisation, like the
relics of extinct animals in the crust of the earth.

30 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

In geology the formation of our Association coin-
cided with the appearance of Lyell's l Principles of
Geology/ the first volume of which was published in
1830 and the second in 1832. At that time the re-
ceived opinion was that the phenomena of Geology could
only be explained by violent periodical convulsions,
and a high intensity of terrestrial energy culminating
in repeated catastrophes. Hutton and Play fair had
indeed maintained that such causes as those now in
operation, would, if only time enough were allowed,
account for the geological structure of the earth ; never-
theless the opposite view generally prevailed, until
Lyell, with rare sagacity and great eloquence, with a
wealth of illustration and most powerful reasoning,
convinced geologists that the forces now in action are
powerful enough, if only time be given, to produce
results quite as stupendous as those which Science
records.

As regards statigraphical geology, at the time of
the first meeting of the British Association at York,
the strata between the carboniferous limestone and the
chalk had been mainly reduced to order and classified,
chiefly through the labours of William Smith. But
the classification of all the strata lying above the chalk
and below the carboniferous limestone respectively,
remained in. a state of the greatest confusion. The
year 1831 marks the period of the commencement of
the joint labours of Sedgwick and Murchison, which
resulted in the establishment of the Cambrian, Silurian,
and Devonian systems. Our Pre- Cambrian strata have
recently been divi led by Hicks into four great groups
of immense thickness, and implying a great lapse of

GEOLOGICAL RESEARCHES. 31

time; but no fossils have yet been discovered in them.
Lyell's classification of the Tertiary deposits ; the
result of the studies which he carried on with the
assistance of Deshayes and others, was published in the
third volume of the ' Principles of Geology ' in 1833.
The establishment of Lyell's divisions of Eocene,
Miocene, and Pliocene, was the starting-point of a most
important series of investigations by Prestwich and
others of these younger deposits ; as well as of the post-
tertiary, quaternary, or drift beds, which are of special
interest from the light they have thrown on the early
history of man.

A full and admirable account of what has recently
been accomplished in this department of science, es-
pecially as regards the palaeozoic rocks, will be found
in Etheridge's late address to the Geological Society.

The thickness of the sedimentary strata implies an
enormous lapse of time, but the amount of subsequent
destruction which has taken place is scarcely less sur-
prising. Ramsay, for instance, has shown that in Wales
from 9,000 to 11,000 feet of solid rock have been re-
moved from large tracts of country. Faults or cracks
there extend for miles, with the strata on one side
raised in some cases as much as 10,000 feet above the
same strata on the other, and yet there . is not on the
surface the slightest vestige of this gigantic dislocation.

The long lines of escarpment again, which stretch
for miles across our country, and were long supposed
to be ancient coast lines, are now ascertained, mainly
through the researches of Whitaker, to be due to the
differential action of aerial causes.

Before 1831 the only geological maps of this

32 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

country were William Smith's general and county maps,
published between the years 1815 and 1824. In the
year 1832 De la Beche made proposals to the Board of
Ordnance to colour the ordnance-maps geologically, and
a sum of 300/. was granted for the purpose. Out of
this small beginning grew the important work of the
Geological Survey.

The cause of slaty cleavage had long been one of
the great difficulties of geology. Sedgwick suggested
that it was produced by the action of crystalline or
polar forces. According to this view miles and miles
of country, comprising great mountain masses, were
neither more nor less than parts of a gigantic crystal.
Sharpe, however, called attention to the fact that shells
and other fossils contained in slate rocks are compressed
in a direction at right angles to the planes of cleavage,
as if the rocks had been seized in the jaws of a gigantic
vice. Sorby first maintained that the cleavage itself
was due to pressure. He observed slate rocks contain-
ing small plates of mica, and that the effect of pressure
would tend to arrange these plates with their flat sur-
faces perpendicu'ar to the direction of the pressure.
Tyndall has since shown that the presence of flat flakes
is not necessary. He proved by experiment that pure
wax could be made by pressure to split into plates of
great tenuity, which he attributes mainly to the lateral
sliding of the particles of the wax over each other ; and
thus the result of pressure on such a mass is to develop
a fissile structure similar to that produced in wax on a
small scale, or on a great one in the slate rocks of Cum-
berland or Wales.

The difficult problem of the conditions under which

THE PHYSICAL STRUCTURE OF THE EARTH. 33

granite and certain other rocks were formed was attacked
by Sorby with great skill in a paper read before the
Geological Society in 1858. The microscopic spaces
in many minerals contain a liquid which does not entirely
fill the hollow, but leaves a small vacuum ; and Sorby
ingeniously pointed out that the rock must have solidi-
fied at least at a temperature high enough to expand
the liquid so as to fill the cavity. Sorby 's important
memoir laid the foundation of microscopic petrography,
which is now not only one of the most promising
branches of geological research, but which has been
successfully applied by Sorby himself, and by Maske-
lyne, to the study of meteorites.

As regards the physical character of the earth, two
theories have been held : one, that of a fluid interior
covered by a thin crust ; the other, of a practically solid
sphere. The former is now generally considered by
physicists to be untenable. Though there is still much
difference of opinion, the prevailing feeling on the sub-
ject has been expressed by Professor Le Conte, who
says, 'the whole theory of igneous agencies — which is
little less than the whole foundation of theoretic geology
— must be reconstructed on the basis of a solid earth.'

In 1837 Agassiz startled the scientific world by his
' Discours sur 1'ancienne extension des Glaciers/ in
which, developing the observation already made by
Charpentier and Venetz, that boulders had been trans-
ported to great distances, and that rocks far away from,
or high above, existing glaciers, are polished and
scratched by the action of ice, he boldly asserted the
existence of a ' glacial period,' during which Switzer-

D

34 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

land and the North of Europe were subjected to great
cold and buried under a vast sheet of ice.

The ancient poets described certain gifted mortals
as privileged to descend into the interior of the earth,
and have exercised their imagination in recounting the
wonders there revealed. As in other cases, however,
the realities of science have proved more varied and sur-
prising than the dreams of fiction. Of the gigantic and
extraordinary animals thus revealed to us, by far the
greatest number have been described during the period
now under review. For instance, the gigantic Cetio-
saurus was described by Owen in 1338, the Dinornis of
New Zealand by the same distinguished naturalist in
1839, the Mylodon in the same year, and the Archsoop-
teryx in 1862.

In America, a large number of remarkable forms
have been discovered, mainly by Marsh, Leidy, and Cope.
Marsh has made known to us the Titanosaurus, of the
American (Colorado) Jurassic beds, which is, perhaps,
the largest land animal yet known, being a hundred
feet in length, and at least thirty in height, though it
seems possible that even these vast dimensions were ex-
ceeded by those of the Atlantosaurus. Nor must I
omit the Hesperornis, described by Marsh in 1872, as a
carnivorous, swimming ostrich, provided with teeth,
which he regards as a character inherited from reptilian
ancestors ; the Ichthyornis, stranger still, with biconcave
vertebrae, like those of fishes, and teeth set in sockets ;
while in the Eocene deposits of the Rocky Mountains
the same indefatigable palaeontologist, among other very
interesting remains, has discovered three new groups of
iv in ark able mammals, the Dinocerata, Tillodontia, and

PALEONTOLOGY. 35

Brontotheridrc. He has also described a number of
small, but very interesting Jurassic mammalia, closely
related to those found in our Stonesfield Slate and
Purbeck beds, for which he has proposed a new order,
1 Prototheria.' Lastly, I may mention the curiously
anomalous Reptilia from South Africa, which have been
made known to us by Professor Owen.

Another important result of recent pakeontological
research is the law of brain-growth. It is not only in
the higher mammalia that we find forms with brains
much larger than any existing, say, in Miocene times.
The rule is almost general that — as Marsh has briefly
stated it — ' all tertiary mammals had small brains.'
We may even carry the generalisation further. The
cretaceous birds had brains one- third smaller than those
of our own day, and the brain -cavities of the Dinosauria
of the Jurassic period are much smaller than in any
existing reptiles.

As giving, in a few words, an idea of the rapid pro-
gress in this department, I may mention that Morris's
1 Catalogue of British Fossils,' published in 1843, con-
tained 5,300 species ; while that now in preparation by
Mr. Etheridge enumerates 15,000.

But if these figures show how rapid our recent pro-
gress has been, they also very forcibly illustrate the
imperfection of the geological record, giving us, I will
not say a measure, but an idea, of the imperfection of
the geological record. The number of all the described
recent species is over 300,000, but certainly not half
are yet on our lists, and we may safely take the total
number of recent species as being not less than 700,000.
But in former times there have been at the very least

D 2

36 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

twelve periods, in each of which by far the greater
number of species were distinct. True, the number of
species was probably not so large in the earlier periods
as at present ; but if we make a liberal allowance for
this, we shall have a total of more than 2,000,000
species, of which about 25,000 only are as yet upon
record ; and many of these are only represented by a
few, some only by a single specimen, or even only by a
fragment.

The progress of palaeontology may also be marked
by the extent to which the existence of groups has been,
if I may so say, carried back in time. Thus I believe
that in 1830 the earliest known quadrupeds were small
marsupials belonging to the Stonesfield Slate ; the
most ancient mammal now known is Microlestes
antiquus from the Keuper of Wiirtemberg : the oldest
bird known in 1831 belonged to the period of the
London Clay, the oldest now known is the Archaeop-
teryx of the Solenhofen Slate, though it is probable
that some at any rate of the footsteps on the Triassic
rocks are those of birds. So again the Amphibia have
been carried back from the Trias to the Coal-measures ;
Fish from the Old Red Sandstone to the Upper Silurian ;
Reptiles to the Trias ; Insects from the Cretaceous to
the Devonian ; Mollusca and Crustacea from the
Silurian to the Lower Cambrian. The rocks below the
Cambrian, though of immense thickness, have afforded
no relics of animal life, if we except the problematical
Eozoon Canadense, so ably studied by Dawson and
Carpenter. But if palaeontology as yet throws no light
on the original forms of life, we must remember that
the simplest and the lowest organisms are so soft and

GEOGRAPHY. 37

perishable that they would leave ' not a wrack behind.'
I will not, however, enlarge on this branch of science,
because we shall have the advantage on Friday of
hearing it treated with the skill of a master.

Passing to the Science of Geography, Mr. Clements
Markham has recently published an excellent summary
of what has been accomplished during the half-century.

As regards the Arctic regions, in the year 1830 the
coast line of Arctic America was only very partially
known, the region between Barrow Strait and the con-
tinent, for instance, being quite unexplored, while the
eastern sides of Greenland and Spitz bergen, and the
coasts of Nova Zembla, were almost unknown. Now
the whole coast of Arctic America has been delineated,
the remarkable archipelago to the north has been ex-
plored, and no less than seven north-west passages —
none of them, however, unfortunately of any practical
value — have been traced. The north-eastern passage,
on the other hand, so far at least as the mouths of the
great Siberian rivers, may perhaps hereafter prove of
commercial importance. In the Antarctic regions,
Enderby and Graham Lands were discovered in 1831-2,
Balleny Islands and SaBrina Land in 1839, while the
fact of the existence of the great southern continent was
established in 1841 by Sir James Ross, who penetrated
in 1842 to 78° IT, the southernmost point ever reached.

In Asia, to quote from Mr. Markham, ' our officers
have mapped the whole of Persia and Afghanistan, sur-
veyed Mesopotamia, and explored the Pamir steppe.
Japan, Borneo, Siam, the Malay peninsula, and the
greater part of China have been brought more com-

38 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

pletely to our knowledge. Eastern Turkestan has been
visited, and trained native explorers have penetrated to
the remotest fountains of the Oxus, and the wild
plateaux of Tibet. Over the northern half of the
Asiatic Continent the Russians have displayed great
activity. They have traversed the wild steppes and
deserts of what on old atlases was called Independent
Tartary, have surveyed the courses of the Jaxartes, the
Oxus, and the Amur, and have navigated the Caspian
and the Sea of Aral. They have pushed their scientific
investigations into the Pamir and Eastern Turkestan,
until at last the British and Russian surveys have been
connected.'

Again, fifty years ago the vast central regions of
Africa were almost a blank upon our best maps. The
rudely drawn lakes and rivers in maps of a more ancient
date had become discredited. These maps did not agree
among themselves, the evidence upon which they were
laid down could not be found, they were in many
respects highly improbable, and they seemed incon-
sistent with what had then been ascertained concerning
the Niger and the Blue and White Niles. At the date
of which I speak, the Sahara had been crossed by
English travellers from the shores of the Mediterranean ;
but the southern desert still formed a bar to travellers
from the Cape, while the accounts of traders, and others
who alone had entered the country from the eastern and
western coasts were considered to form an insufficient
basis for a map.

Since that time the successful crossing of the
Kalahari desert to Lake Ngami has been the prelude to
an era of African discovery. Livingstone explored

HYDROGRAPHY. 39

the basin of the Zambesi, and discovered vast lakes and
waters which have proved to be those of the higher
Congo. Burton and Speke opened the way from the
West Coast, which Speke and Grant pursued into and
down the Nile, and Stanley down the course of the
middle and lower Congo ; while the vast extension of
Egyptian dominion has brought a huge slice of equa-
torial Africa within the limits of semi- civilisation. The
western side of Africa has been attacked at many points.
Alexander and Galton were among the first to make
known to us its western tropical regions immediately
to the north of the Cape Colony ; the Ogowe has been
explored ; the Congo promises to become a centre of
trade, and the navigable portions of the Niger, the
Gambia, and the Senegal are familiarly known.

The progress of discovery in Australia has been
as remarkable as that in Africa. The interior of this
great continent was absolutely unknown to us fifty
years ago, but is now crossed through its centre by the
electric telegraph, and no inconsiderable portion of it is
turned into sheep-farms. It is an interesting fact that
General Sabine, so long one of our most active officers,
and who is still with us, though, unfortunately his
health has for some time prevented him from attending
our meetings, was born on the very day that the first
settler landed in Australia.

In hydrography our charts have been immensely
improved. The study of rivers and of the physical
geography of the sea may indeed almost be said to have
come into existence as a science during the last fifty
years, and in the words of Jansen, it was Maury i who,
by his wind and current charts, his trade- wind, storm,

40 ADDEESS TO THE BRITISH ASSOCIATION, 1881.

and rain charts, and last, but not least, by his work on
the physical geography of the sea, gave the first great
impulse to all subsequent researches/

But the progress in our knowledge of geography is,
and has been, by no means confined to the improve-
ment of our maps, or to the discovery and description
of new regions of the earth ; it has extended to the
causes which have led to the present configuration of
the surface. To a great extent indeed this part of the
subject falls rather within the scope of geology, but I
may here refer, in illustration, to the distribution of
lakes, the phenomena of glaciers, the formation of
volcanic mountains, and the structure and distribution
of coral islands.

. The origin and distribution of lakes is one of the
most interesting problems in physical geography. That
they are not scattered at random, a glance at the map
is sufficient to show. They abound in mountain dis-
tricts, are comparatively rare in equatorial regions,
increasing in number as we go north, so that in Scot-
land and the northern parts of America they are sown
broadcast.

Perhaps a priori the first explanation of the origin
of lates which would suggest itself, would be that they
were formed in hollows resulting from a disturbance of
the strata, which had thrown them into a basin-shaped
form. Lake-basins, however, of this character are, as a
matter of fact, very rare ; as a general rule lakes have
not the form of basin- shaped synclinal hollows, but,
on the contrary, the strike of the strata often runs
right across them. My eminent predecessor, Professor
Ramsay, divides lakes into three classes : — (1) Those

THE ORIGIN OF LAKES. 41

which are due to irregular accumulations of drift, and
which are generally quite shallow ; (2) those which
are formed by moraines ; and (3) those which occupy
true basins scooped by glacier-ice out of the solid rock.
To the latter class belong, in his opinion, most of the
great Swiss and Italian lakes. Professor Ramsay
attributes their excavation to glaciers, because it is of
course obvious that rivers cannot make basin- shaped
hollows surrounded by rock on all sides. Now the
Lake of Geneva, 1,230 feet above the sea, is 984 feet
deep, the Lake of Brienz is 1,850 feet above the sea,
and 2,000 feet deep, so that its bottom is really below
the sea-level. The Italian lakes are even more remark-
able. The Lake of Como, 700 feet above the sea, is 1,929
feet deep. Lago Maggiore, 685 feet above the sea, is
no less than 2,625 feet deep. It will be observed that
these lakes, like many others in mountain regions —
those of Scandinavia, for instance — lie in the direct
channels of the great old glaciers. If the mind is at
first staggered at the magnitude of the scale, we must
remember that the ice which scooped out the valley in
which the Lake of Geneva now reposes, was once at
least 2,700 feet thick ; while the moraines were also of
gigantic magnitude, that of Ivrea, for instance, being no
less than 1,500 feet in height. Professor Ramsay's
theory seems, therefore, to account beautifully for a
large number of interesting facts.

The problem is, however, very complex ; and, while
admitting the force of Professor Ramsay's arguments,
there are, no doubt, other causes which have exercised
a considerable influence in the arrangement and con-
figuration of lakes ; for instance — as has been ably

42 ADDEESS TO THE BRITISH ASSOCIATION, 1881.

argued by our new Secretary, Mr. Bonney — irregular
movements of upheaval along lines athwart the valleys.

Passing from lakes to mountains, two rival theories
with reference to the structure and origin of volcanoes
long struggled for supremacy.

The more general view was that the sheets of lava and
scorise which form volcanic cones — such, for instance,
as JEtna or Vesuvius — were originally nearly horizontal,
and that subsequently a force operating from below, and
exerting a pressure both upwards and outwards from a
central axis towards all points of the compass, uplifted
the whole stratified mass and made it assume a conical
form, giving rise at the same time, in many cases, to a
wide and deep circular opening at the top of the cone,
called by the advocates of this hypothesis a ' crater of
elevation.'

This theory, though, as it seems to us now, it had
already received its death-blow from the admirable
memoirs of Scrope, was yet that most generally adopted
fifty years ago, because it was considered that compact
and crystalline lavas could not have consolidated on a
slope exceeding For 2°. In 1858, however, Sir C. Lyell
conclusively showed that in fact such lavas could con-
solidate at a considerable angle, even in some cases at
more than 30°, and it is now generally admitted that
though the beds of lava, &c., may have sustained a
slight angular elevation since their deposition, still in
the main, volcanic cones have acquired their form by
the accumulation of lava and ashes ejected from one or
more craters.

The problems presented by glaciers are of very great
interest, n 1843 Agassiz and Forbes proved that the

VOLCANOES. GLACIEES. 43

centre of a glacier, like that of a river, moves more
rapidly than its sides. But how and why do glaciers
move at all ? Rendu, afterwards Bishop of Annec,y, in
1841 endeavoured to explain the facts by supposing
that glacier ice enjoys a kind of ductility. The " viscous
theory ' of glaciers was also adopted, and most ably advo-
cated by Forbes, who compared the condition of a glacier
to that of the contents of a tar barrel poured into a slop-
ing channel. We have all, however, seen long narrow
fissures, a mere fraction of an inch in width, stretching
far across glaciers — a condition incompatible with the
ordinary idea of viscosity. The phenomenon of regela-
tion was afterwards applied to the explanation of glacier-
motion. An observation of Faraday's supplied the clue.
He noticed in 1850 that when two pieces of thawing
ice are placed together they unite by freezing at the
place of contact. Following up this suggestion Tyndall
found that if he compressed a block of ice in a mould it
could be made to assume any shape he pleased. A
straight prism, for instance, placed in a groove and sub
mitted to hydraulic pressure, was bent into a trans-
parent semicircle of ice. These experiments seem to
have proved that a glacial valley is a mould through
which the ice is forced, and to which it will accommo-
date itself, while, as Tyndall and Huxley also pointed
out, the ' veined structure of ice ' is produced by
pressure, in the same manner as the cleavage of slate
rocks.

It was in the year 1842 that Darwin published his
great work on i Coral Islands.' The fringing reefs of
coral presented no special difficulty. They could be
obviously accounted for by an elevation of the land,

44 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

so that the coral which had originally grown under
water had been raised above the sea-level. The circular
or oval shape of so many reefs, however, each having a
lagoon in the centre, closely surrounded by a deep
ocean, and rising but a few feet above the sea-level, had
long been a puzzle to the physical geographer. The
favourite theory was that these were the summits of
submarine volcanoes on which the coral had grown.
But as the reef- making coral does not live at greater
depths than about twenty -five fathoms, the immense
number of these reefs formed an almost insuperable ob-
jection to this theory. The Laccadives and Maldives,
for instance — meaning literally the ' lac of islands ' and
the ' thousand islands ' — are a series of such atolls, and
it was impossible to imagine so great a number of craters,
all so nearly of the same altitude. Darwin showed,
moreover, that so far from the ring of corals resting on
a corresponding ridge of rocks, the lagoons, on the con-
trary, now occupy the place which was once the highest
land. He pointed out that some lagoons, as for in-
stance that of Yanikoro, contain an island in the middle ;
while other islands, such as Tahiti, are surrounded by a
margin of smooth water separated from the ocean by a
coral reef. Now if we suppose that Tahiti were to sink
slowly, it would gradually approximate to the condition
of Vanikoro ; and if Vanikoro gradually sank, the
central island would disappear, while on the contrary the
growth of the coral might neutralise the subsidence of the
reef, so that we should have simply an atoll with its
lagoon. The same considerations explain the origin of
the ' barrier reefs,' such as that which runs, for nearly
one thousand miles, along the north-east coast of Aus-

CORAL ISLANDS. THE ABYSSES OF THE OCEAN. 45

tralia. Thus Darwin's theory explained the form and
the approximate identity of altitude of these coral
islands. But it did more than this, because it showed
us that there were great areas in process of subsidence,
which though slow, was of great importance in physical
geography.1

Much information has also been acquired with refer-
ence to the abysses of the ocean, especially from the
voyages of the Porcupine and the Challenger. The
greatest depth yet recorded is near the Ladrone Islands,
where a sounding of 4,575 fathoms was obtained.

Ehrenberg long ago pointed out the similarity of
the calcareous mud now accumulating in our recent
seas to the chalk, and showed that the green sands of
the geologist are largely made up of casts of Foramini-
fera. Clay, however, had been looked on, until the
recent expeditions, as essentially a product of the disin-
tegration of older rocks. Not only, however, are a
large proportion of siliceous and calcareous rocks either
directly or indirectly derived from material which has
once formed a portion of living organisms, but Sir
Wyville Thomson maintains that this is the case with
some clays also. In that case the striking remark of
Linnaeus, that ' fossils are not the children but the
parents of rocks,' will have received remarkable confir-
mation. I should have thought it, I confess, probable
that these clays are, to a considerable extent, composed
of volcanic dust.

It would appear that calcareous deposits resembling
our chalk do not occur at a greater depth than 3,000

1 I ought, perhaps, to mention that Darwin's views have been recently
questioned on some points by Semper and Murray.

46 ADDRESS TO THE BRITISH ASSOCIATION, 1881,

fathoms ; they have not been met with in the abysses
of the ocean. Here the bottom consists of exceedingly
fine clay, sometimes coloured red by oxide of iron,
sometimes chocolate by manganese oxide, and contain-
ing with Foraminifera occasionally large numbers of
siliceous Radiolaria. These strata seem to accumulate
with extreme slowness : this is inferred from the com-
parative abundance of whales' bones and fishes' teeth ;
and from the presence of minute spherical particles,
supposed by Mr. Murray to be of cosmic origin — in
fact, to be the dust of meteorites, which in the course
of ages have fallen on the ocean. Such particles no
doubt occur over the whole surface of the earth, but on
land they soon oxidise, and in shallow water they are
covered up by other deposits. Another interesting
result of recent deep-sea explorations has been to show
that the depths of the ocean are no mere barren soli-
tudes, as was until recent years confidently believed,
but, on the contrary, present us many remarkable
forms of life. We have, however, as yet but thrown
here and there a ray of light down into the ocean

abysses : —

Nor can so short a time sufficient be

To fathom the vast depths of Nature's sea.

In Astronomy, the discovery in 1845 of the planet
Neptune, made independently and almost simulta-
neously by Adams and by Le Yerrier, was certainlv
one of the very greatest triumphs of mathematical
genius. Of the minor planets four only were known in
1831, whilst the number now on the roll amounts to
220. Many astronomers believe in the existence of an
intra-mercurial planet or planets, but this is still an

ASTRONOMY. SPECTRUM ANALYSIS. 47

open question. The Solar System has also been en-
riched by the discovery of an inner ring to Saturn, of
satellites to Mars, and of additional satellites to Saturn,
Uranus, and Neptune.

The most unexpected progress, however, in our
astronomical knowledge during the past half-century
has been due to spectrum analysis.

The dark lines in the spectrum were first seen by
Wollaston, who noticed a few of them ; but they were
independently discovered by Fraunhofer, after whom
they "are justly named, and who, in 1814, mapped no
fewer than 576. The first steps in ' spectrum analysis./
properly so called, were made by Sir J. Herschel,
Fox Talbot, and by Wheatstone. The latter, in a paper
read before this Association in 1835, showed that the
spectrum emitted by the incandescent vapour of metals
was formed of bright lines, and that these lines, while,
as he then supposed, constant for each metal, differed
for different metals. ' We have here,' he said, ' a mode
of discriminating metallic bodies more readily than that
of chemical examination, and which may hereafter be
employed for useful purposes/ Nay, not only can
bodies thus be more readily discriminated, but, as we
now know, the presence of extremely minute portions
can be detected, the -5 o^w^o °f a gram being in some
cases easily perceptible-

It is also easy to see that the* presence of any new
simple substance might be detected, and in this manner
already several new elements have been discovered, as
I shall mention when we come to Chemistry.

But spectrum analysis has led to even grander and
more unexpected triumphs. Fraunhofer himself noticed

48 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

the coincidence between the double dark line D of the
solar spectrum and a double line which he observed in
the spectra of ordinary flames, while Stokes pointed out
to Sir W. Thomson, who taught it in his lectures, that
in both cases these lines were due to the presence of
sodium. To KirchhofF and Bunsen, however, is due the
independent conception and the credit of having first
systematically investigated the relation which exists
between Fraunhofer's lines and the bright lines in the
spectra of incandescent metals. In order to get some
fixed measure by which they might determine and
record the lines characterising any given substance, it
occurred to them that they might use for comparison
the spectrum of the sun. They accordingly arranged
their spectroscope so that one-half of the slit was lighted
by the sun, and the other by the luminous gases they
proposed to examine. It immediately struck them that
the bright lines in the one corresponded with the dark
lines in the other — the bright line of sodium, for in-
stance, with the line or rather lines D-in the sun's
spectrum. The conclusion was obvious. There was
sodium in the sun. It must indeed have been a
glorious moment when that thought flashed across
them, and even by itself well worth all their labour.

But why is the bright line of a sodium flame repre-
sented by a black one in the spectrum of the sun ? To
Angstrom is due the theory that a vapour or gas can
absorb luminous rays of the same refrangibility only
as those which it emits when highly heated ; while
Balfour Stewart independently discovered the same law
with reference to radiant heat.

This is the basis of KirchhofF' s theory of the origin

THE CONSTITUTION OF THE SUN, 49

of Fraunhofer's lines. In the atmosphere of the sun
the vapours of various metals are present, each of which
would give its characteristic lines, but within this at-
mospheric envelope is the still more intensely heated
nucleus of the sun, which emits a brilliant continuous
spectrum containing rays of all degrees of refrangibility.
When the light of this intensely heated nucleus is
transmitted through the surrounding atmosphere, the
bright lines which would be produced by this atmo-
sphere are seen as dark ones.

Kirchhoff and Bunsen thus proved the existence in
the sun of hydrogen, sodium, magnesium, calcium, iron,
nickel, chromium, manganese, titanium, and cobalt ;
since which Angstrom, Thalen, and Lockyer have con-
siderably increased the list.

But it is not merely the chemistry of the heavenly
bodies on which light is thrown by the spectroscope ;
their physical structure and evolutional history are also
illuminated by this wonderful instrument of research.

It used to be supposed that the sun was a dark
body enveloped in a luminous atmosphere. The reverse
now appears to be the truth. The body of the sun, or
photosphere, is intensely brilliant ; round it lies the
solar atmosphere of comparatively cool gases, which
cause the dark lines in the spectrum ; thirdly, the
chromosphere, — a sphere principally of hydrogen, jets
of which are said sometimes to reach to a height of
100,000 miles or more, into the outer coating or corona,
the nature of which is still very doubtful.

Formerly the red flames which represent the higher
regions of the chromosphere could be seen only on the
rare occasions of a total solar eclipse. Janssen and

E

50 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

Lockyer, by the application of the spectroscope, have
enabled us to study this region of the sun at all times.

It is, moreover, obvious that the powerful engine
of investigation afforded us by the spectroscope is by
no means confined to the substances which form part
of our system. The incandescent body can thus be
examined, no matter how great its distance, so long
only as the light is strong enough. That this method-
was theoretically applicable to the light of the stars was
indeed obvious, but the practical difficulties were very
great. Sirius, the brightest of all, is, in round numbers,
a hundred millions of millions of miles from us ; and,
though as big as sixty of our suns, his light when it
reaches us, after a journey of sixteen years, is at most
one two-thousand-millionth part as bright. Neverthe-
less as long ago as 1815 Fraunhofer recognised the
fixed lines in the light of four of the stars, and in 1863
Miller and Huggins in our own country, and Ruther-
ford in America, succeeded in determining the dark
lines in the spectrum of some of the brighter stars, thus
showing that these beautiful and mysterious lights con-
tain many of the material substances with which we
are familiar. In Aldebaran, for instance, we may infer
the presence of hydrogen, sodium, magnesium, iron,
calcium, tellurium, antimony, bismuth, and mercury;
some of which are not yet known to occur in the sun.
As might have been expected, the composition of the
stars is not uniform, and it would appear that they may
be arranged in a few well-marked classes, indicating
differences of temperature, or in other words, of age.
Some recent photographic spectra of stars obtained by
Huggins go very far to justify this view.

THE COMPOSITION OF THE STARS AND NEBULA, 51

Thus we can make the stars teach us their own
composition with light which started from its source in
some cases before we were born — light older than our
Association itself.

Until 1864, the true nature of the unresolved nebulse
was a matter of doubt. In that year, however, Huggins
turned his spectroscope on to a nebula, and made the
unexpected discovery that the spectra of some of these
bodies are discontinuous — that is to say, consist of bright
lines only, indicating that ' in place of an incandescent
solid or liquid body we must probably regard these
objects, or at least their photo- surfaces, as enormous
masses of luminous gas or vapour. For it is from
matter in a gaseous state only that such light as that of
the nebulae is known to be emitted.' So far as obser-
vation has yet gone, nebula) may be divided into two
classes : some giving a continuous spectrum, others one
consisting of bright lines. These latter all appear to
give essentially the same spectrum, consisting of a few
bright lines. Two of them, in Mr. Huggins' opinion,
indicate the presence of hydrogen : one of them agrees
in position with a line characteristic of nitrogen.

But spectrum analysis has even more than this to
tell us. The old methods of observation could deter-
mine the movements of the stars so far only as they
were transverse to us ; they afforded no means of
measuring motion either directly towards or away from
us. Now Doppler suggested in 1841 that the colors
of the stars would assist us in this respect, because they
would be affected by their motion to and from the earth,
just as the sound of a steam- whistle is raised or lowered
as it approaches or recedes from us. Everyone has ob-

E 2

52 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

served that if a train whistles as it passes us, the sound
appears to alter at the moment the engine goes by. This
arises, of course, not from any change in the whistle
itself, but because the number of vibrations which reach
the ear in a given time are increased by the speed of the
train as it approaches, and diminished as it recedes.
So, like the sound, the color would be affected by
such a movement ; but Doppler's method was practi-
cally inapplicable, because the amount of effect on the
color would be utterly insensible ; and even if it were
the method could not, for other reasons, be applied ;
indeed, as we did not know the true color of the stars,
we have no datum line by which to measure.

A change of refrangibility of light, however, does
occur in consequence of relative motion, and Huggins
successfully applied the spectroscope to solve the pro-
blem. He took in the first place the spectroscope of
Sirius, and chose a line known as F, which is due to
hydrogen. Now, if Sirius was motionless, or rather if
it retained a constant distance from the earth, the line
F would occupy exactly the same position in the spec-
trum of Sirius as in that of the sun. On the contrary,
if Sirius were approaching or receding from us, this
line would be slightly shifted either towards the blue
or red end of the spectrum. He found that the line
had moved very slightly towards the red, indicating
that the distance between us and Sirius is increasing at
the rate of about twenty miles a second. So also
Betelgeux, Rigel, Castor, and Regulus are increasing
their distance, while, on the contrary, that of others, as
for instance of Vega, Arcturus, and Pollux, is dimin-
ishino-. The results obtained by Huggins on about

SHOOTING STARS. COMETS. 53

twenty stars have since been confirmed and extended
by Mr. Christie, now Astronomer Royal, in succession
to Sir Gr. Airy, who has long occupied the post with so
much honour to himself and advantage to science.

To examine the spectrum of a shooting star would
seem even more difficult. Alexander Herschel first
succeeded in doing so, and determined the presence of
sodium ; since which Von Konkoly has recognised the
lines of magnesium, carbon, potassium, lithium, and
other substances, and it appears that the shooting stars
are bodies similar in character and composition to the
stony masses which sometimes reach the earth as
aerolites.

Some light has also been thrown upon those mys-
terious visitants, the comets. The researches of Prof.
Newton on the periods of meteoroids led to the remark-
able discovery by Schiaparelli of the identity of the
orbits of some meteor- swarms with those of some
comets. The similarity of orbits is too striking to be
the result of chance, and shows a true cosmical relation
between the bodies. Comets, in fact, are in some cases
at any rate groups of meteoric stones. From the
spectra of the small comets of 1866 and 1868, Huggins
showed that part of their light is emitted by themselves,
and reveals the presence of carbon in some form. A
photographic spectrum of the comet recently visible,
obtained by the same observer, is considered by him to
prove that nitrogen, probably in combination with
carbon, is also present.

No element has yet been found in any meteorite,
which was not previously known as existing in the
earth, but the phenomena which they .exhibit indicate

54 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

that they must have been formed under conditions very
different from "those which prevail on the earth's sur-
face. I may mention, for instance, the peculiar form of
crystallised silica, called by Maskelyne, Asmanite ; and
the whole class of meteorites, consisting of iron gene-
rally alloyed with nickel, which Daubree terms Holo-
siderites. The interesting discovery, however, by
Nordenskiold, in 1870, at Ovifak, of a number of blocks
of iron alloyed with nickel and cobalt, in connection
with basalts containing disseminated iron, has, in the
words of Judd, ' afforded a very important link, placing
the terrestrial and extra-terrestrial rocks in closer rela-
tions with one another.7

We have as yet no sufficient evidence to justify a
conclusion as to whether any substances exist in the
heavenly bodies which do not occur in our earth, though
there are many lines which cannot yet be satisfactorily
referred to any terrestrial element. On the other hand,
some substances which occur on our earth have not yet
been detected in the sun's atmosphere.

Such discoveries as these seemed, not long ago,
entirely beyond our hopes. M. Comte, indeed, in his
' Cours de Philosophic Positive,' as recently as 1842,
laid it down as an axiom regarding the heavenly bodies,
that c Nous concevons la possibilite de determiner leurs
formes, leurs distances, leurs grandeurs et leurs mouve-
ments, tandis que nous ne saurions jamais etudier par
aucun moyen leur composition chimique ou leur struc-
ture miner alogique.' Yet within a few years this
supposed impossibility has been actually accomplished,
showing how unsafe it is to limit the possibilities of
science.

THE HEAT OF THE SUN. 55

It is hardly necessary to point out that, while the
spectrum has taught us so much, we have still even
more to learn. Why should some substances give few,
and others many, lines? Why should the same sub-
stance give different lines at different temperatures?
What are the relations between the lines and the
physical or chemical properties?

We may certainly look for much new knowledge of
the hidden actions of atoms and molecules from future
researches with the spectroscope. It may even, per-
haps, teach us to modify our views of the so-called
simple substances. Prout, long ago, struck by the
remarkable fact that nearly all atomic weights are
simple multiples of the atomic weight of hydrogen,
suggested that hydrogen must be the primordial sub-
stance. Brodie's researches also naturally fell in with
the supposition that the so-called simple substances are
in reality complex, and that their constituents occur
separately in the hottest regions of the solar atmosphere.
Lockyer considers that his researches lend great proba-
bility to this view. The whole subject is one of intense
interest, and we may rejoice that it is occupying the
attention, not only of such men as Abney, Dewar,
Hartley, Liveing, Eoscoe, and Schuster in our own
country, but also of many foreign observers.

When geology so greatly extended our ideas of
past time, the continued heat of the sun became a
question of greater interest than ever. Helmholtz has
shown that, while adopting the nebular hypothesis, we
need not assume that the nebulous matter was originally
incandescent ; but that its present high temperature
may be, and probably is, mainly due to gravitation

56 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

between its parts. It follows that the potential energy
of the sun is far from exhausted, and that with con-
tinued shrinking it will continue to give out light and
heat, with little, if any, diminution for several millions
of years.

Like the sand of the sea, the stars of heaven have
ever been used as effective symbols of number, and the
improvements in our methods of observation have added
fresh force to our original impressions. We now know
that our earth is but a fraction of one out of at least
75,000,000 worlds.

But this is not all. In addition to the luminous
heavenly bodies, we cannot doubt that there are count-
less others, invisible to us from their greater distance,
smaller size, or feebler light ; indeed we know that
there are many dark bodies which now emit no
light or comparatively little. Thus in the case of
Procyon, the existence of an invisible body is proved
by the movement of the visible star. Again I may
refer to the curious phenomena presented by Algol, a
bright star in the head of Medusa. The star shines
without change for two days and thirteen hours ; then,
in three hours and a half, dwindles from a star of the
second to one of the fourth magnitude; and then, in
another three and a half hours, reassumes its original
brilliancy. These changes seem certainly to indicate
the presence of an opaque body, which intercepts at
regular intervals a part of the light emitted by Algol.

Thus the floor of heaven is not only ' thick inlaid
with patines of bright gold/ but studded also with
extinct stars, once probably as brilliant as our own
sun, but now dead and cold, as Helmholtz tells, us that

EXTINCT STARS. PHYSICAL HISTORY OF EARTH. 57

our sun itself will be, some seventeen millions of years
hence.

The connection of Astronomy with the history of
our planet has been a subject of speculation and research
during a great part of the half- century of our existence.
Sir Charles Lyell devoted some of the opening chapters
of his great work to the subject. Haughton has brought
his very original powers to bear on the subject of
secular changes in climate, and CrolFs contributions to
the same subject are of great interest. Last, but not
least, I must not omit to make mention of the series of
massive memoirs (I am happy to say not yet nearly
terminated) by George Darwin on tidal friction, and the
influence of tidal action on the evolution of the solar
system.

I may perhaps just mention, as regards telescopes,
that the largest reflector in 1830 was Sir W. Herschel's
of 4 ft., the largest at present being Lord Rosse's of 6
ft. ; as regards refractors the largest then had a diameter
of 11^ in., while your fellow-townsman Cooke carried
the size to 25 in., and Mr. Grubb, of Dublin, has just
successfully completed one of 27 in. for the Observatory
of Vienna. It is remarkable that the two largest tele-
scopes in the world should both be Irish.

The general result of astronomical researches has
been thus eloquently summed up by Proctor : — i The
sidereal system is altogether more complicated and
more varied in structure than has hitherto been sup-
posed ; in the same region of the stellar depths co-exist
stars of many orders of real magnitude ; all orders of
nebulae, gaseous or stellar, planetary, ring-formed,
elliptical, and spiral, exist within the limits of the

58 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

galaxy ; and lastly, the whole system is alive with
movements, the laws of which may one day be recog-
nised, though at present they appear too complex to
be understood.'

We can, I think, scarcely claim the establishment of
the undulatory theory of light as falling within the
last fifty years ; for though Brewster, in his ' Eeport
on Optics,' published in our first volume, treats the
question as open, and expresses himself still uncon-
vinced, he was, I believe, almost alone in his preference
for the emission theory. The phenomena of interference,
in fact, left hardly any — if any — room for doubt, and
the subject was finally set at rest by Foucault's cele-
brated experiments in 1850. According to the undu-
latory theory the velocity of light ought to be greater
in air than in water, while if the emission theory were
correct the reverse would be the case. The velocity
of light — 186,000 miles in a second — is, however, so
great that, to determine its rate in air, as compared
with that in water, might seem almost hopeless. The
velocity in air was, nevertheless, determined by Fizeau
in 1849, by means of a rapidly revolving wheel. In
the following year Foucault, by means of a revolving
mirror, demonstrated that the velocity of light is greater
in air than in water — thus completing the evidence in
favour of the undulatory theory of light.

The idea is now gaining ground, that, as main-
tained by Clerk -Max well, light itself is an electro-
magnetic disturbance, the luminiferous ether being the
vehicle of both light and electricity.

Wiinsch, as long ago as 1792, had clearly shown

THE THEORY OF COLOR. 59

that the three primary colors were red, green, and
violet ; but his results attracted little notice, and the
general view used to be that there were seven principal
colors — red, orange, yellow, green, blue, indigo, and
violet ; four of which — namely orange, green, indigo,
and violet — were considered to arise from mixtures of
the other three. Red, yellow, and blue were therefore
called the primary colors, and it was supposed that in
order to produce white light these three colors must
always be present.

Helmholtz, however, again showed, in 1852, that a
color to our unaided eyes identical with white, was
produced by combining yellow with indigo. At that
time yellow was considered to be a simple color, and
this, therefore, was regarded as an exception to the
general rule, that a combination of three simple colors
is required to produce white. Again, it was, and indeed
still is, the general impression that a combination of
blue and yellow makes green. This, however, is
entirely a mistake. Of course we all know that yellow
paint and blue paint make green paint : but this results
from absorption of light by the semi-transparent solid
particles of the pigments, and is not a mere mixture of
the colors proceeding unaltered from the yellow and
the blue particles ; moreover, as can easily be shown by
two sheets of colored paper and a piece of window
glass, blue and yellow light, when combined, do not
give a trace of green, but if pure would produce the
effect of white. Green, therefore, is after all not pro-
duced by a mixture of blue and yellow. On the other
hand, Clerk-Maxwell proved in 1860 that yellow could
be produced by a mixture of red and green, which put

60 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

an end to the pretension of yellow to be considered a
primary element of color. From these and other
considerations it would seem, therefore, that the three
primary colors — if such an expression be retained —
are red, green, and viqlet.

The existence of rays beyond the violet, though
almost invisible to our eyes, had long been demonstrated
by their chemical action. Stokes, however, showed in
1852 that their existence might be proved in another
manner, for that there are certain substances which,
when excited by them, emit light visible to our eyes.
To this phenomenon he gave the name of fluorescence.
At the other end of the spectrum Abney has recently
succeeded in photographing a large number of lines in
the infra-red portion, the existence of which was first
proved by Sir William Herschel.

From the rarity, and in many cases the entire
absence, of reference to blue, in ancient literature,
Geiger — adopting and extending a suggestion first
thrown out by Mr. Gladstone — has maintained that,
even as recently as the time of Homer, our ancestors
were blue-blind. Though for my part I am unable to
adopt this view, it is certainly very remarkable that
neither the Kigveda, which consists almost entirely of
hymns to heaven, nor the Zendavesta, the Bible of the
Parsees or fire- worshippers, nor the earlier books of the
Old Testament, nor the Homeric poems, ever allude to
the sky as blue.

On the other hand, from the dawn of poetry, the
splendours of the morning and evening skies have ex-
cited the admiration of mankind. As Euskin says, in
language almost as brilliant as the sky itself, the whole

THE COLOB OF THE SKY. 61

heaven, c from the zenith to the horizon, becomes one
molten, mantling sea of color and fire ; every black
bar turns into massy gold, every ripple and wave into
unsullied shadowless crimson, and purple, and scarlet,
and colors for which there are no words in language,
and no ideas in the mind — things which can only be
conceived while they are visible; the intense hollow
blue of the upper sky melting through it all, showing
here deep, and pure, and lightness ; there, modulated
by the filmy, formless body of the transparent vapour,
till it is lost imperceptibly in its crimson and gold/

But what is the explanation of these gorgeous
colors ? why is the sky blue ? and why are the sunrise
and sunset crimson and gold ? It may be said that the
air is blue, but if so how can the clouds assume their
varied tints ? Briicke showed that very minute particles
suspended in water are blue by reflected light. Tyndall
has taught us that the blue of the sky is due to the re-
flection of the blue rays by the minute particles floating
in the atmosphere. Now if from the white light of the
sun the blue rays are thus selected, those which are
transmitted will be yellow, orange, and red. Where
the distance is short the transmitted light will appear
yellowish. But as the sun sinks towards the horizon
the atmospheric distance increases, and consequently
the number of the scattering particles. They weaken
in succession the violet, the indigo, the blue, and even
disturb the proportions of green. The transmitted
light under such circumstances must pass from yellow
through orange to red, and thus, while we at noon are
admiring the deep blue of the sky, the same rays, robbed
of their blue, are elsewhere lighting up the evening sky
with all the glories of sunset.

62 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

Another remarkable triumph of the last half- century
has been the discovery of photography. At the com-
mencement of the century Wedgwood and Davy ob-
served the effect produced by throwing the images of
objects on paper or leather prepared with nitrate of
silver, but no means were known by which such images
could be fixed. This was first effected by Niepce, but
his processes were open to objections, which prevented
them from coming into general use, and it was not till
1839 that Daguerre invented the process which was
justly named after him. Very soon a further improve-
ment was effected by our countryman Talbot. He not
only fixed his ' Talbotypes ' on paper — in itself a great
convenience — but, by obtaining a negative, rendered it
possible to take off any number of positive, or natural,
copies from one original picture. This process is the
foundation of all the methods now in use ; perhaps the
greatest improvements having been the use of glass
plates, first proposed by Sir John Herschel ; of collodion,
suggested by Le Grey, and practically used by Archer ;
and, more lately, of gelatine, the foundation of the
sensitive film now growing into general use in the
ordinary dry-plate process. Not only have a great
variety of other beautiful processes been invented, but
the delicacy of the sensitive film has been immensely
increased, with the advantage, among others, of diminish-
ing greatly the time necessary for obtaining a picture,
so that even an express train going at full speed can
now be taken. Indeed, with full sunlight g-i^ of a
second is enough, and in photographing the sun itself

of a second is sufficient.
We owe to Wheatstone the conception that the idea

PHOTOGRAPHY. THE NATURE OF HEAT. 63

of solidity is derived from the combination of two
pictures of the same object in slightly different perspec-
tive. This he proved in 1833 by drawing two outlines
of some geometrical figure or other simple object, as
they would appear to either eye respectively, and then
placing them so that they might be seen, one by each eye.
The i stereoscope/ thus produced, has been greatly
popularised by photography.

For 2,000 years the art of lighting had made little
if any progress. Until the close of the last century,
for instance, our lighthouses contained mere fires of
wood or coal, though the construction had vastly im-
proved. The Eddystone lighthouse, for instance, was
built by Smeaton in 1759 ; but for forty 'years its light
consisted of a row of tallow candles stuck in a hoop.
The Argand lamp was the first great improvement,
followed by gas, and in 1863 by the electric light.

Just as light was. long supposed to be due to the
emission of material particles, so heat was regarded as
a material, though ethereal, substance, which was added
to bodies when their temperature was raised.

Davy's celebrated experiment of melting two pieces
of ice by rubbing them against one another in the ex-
hausted receiver of an air-pump had convinced him that
the cause of heat was the motion of the invisible
particles of bodies, as had been long before suggested by
Newton, Boyle, and Hooke. Eumford and Young also
advocated the same view. Nevertheless, the general
opinion, even until the middle of the present century,
was that heat was due to the presence of a subtle fluid
known as ' caloric/ a theory which is now entirely
abandoned.

64 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

Melloni, by the use of the electric pile, vastly in-
creased our knowledge of the phenomena of radiant
heat. His researches were confined to the solid and
liquid forms of matter. Tyndall studied the gases in
this respect, showing that differences greater than those
established by Melloni existed between gases and
vapours, both as regards the absorption and radiation
of heat. He proved, moreover, that the aqueous vapour
of our atmosphere, by checking terrestrial radiation,
augments the earth's temperature, and he considers
that the existence of tropical vegetation — the remains
of which now constitute our coal-beds — may have been
due to the heat retained by the vapours which at that
period were diffused in the earth's atmosphere. Indeed,
but for the vapour in our atmosphere, a single night
would suffice to destroy the whole vegetation of the
temperate regions.

Inspired by a contemplation of Graham Bell's in-
genious experiments with intermittent beams on solid
bodies, Tyndall took a new and original departure ;
and regarding the sounds as due to changes of tempera-
ture he concluded that the same method would prove
applicable to gases. He thus found himself in posses-
sion of a new and independent method of procedure.
It need perhaps be hardly added that, when submitted
to this new test, his former conclusions on the inter-
action of heat and gaseous matter stood their ground.

The determination of the mechanical equivalent of
heat is mainly due to the researches of Mayer and Joule.
Mayer, in 1842, pointed out the mechanical equivalent
of heat as a fundamental datum to be determined by
experiment. Taking the heat produced by the con-

THE MECHANICAL EQUIVALENT OF HEAT. 65

densation of air as the equivalent of the work done in
compressing the air, he obtained a numerical value of the
mechanical equivalent of heat. There was, however, in
these experiments, one weak point. The matter operated
on did not go through a cycle of changes. He assumed
that the production of heat was the only effect of the
work done in compressing the air. Joule had the merit
of being the first to meet this possible source of error.
He ascertained that a weight of 1 Ib. would have to fall
772 feet in order to raise the temperature of 1 Ib. of
water by 1° Fahr. Him subsequently attacked the
problem from the other side, and showed that if all the
heat passing through a steam engine was turned into
work, for every degree Fahr. added to the temperature
of a pound of water, enough work could be done to
raise a weight of 1 Ib. to a height of 772 feet. The
general result is that, though we cannot create energy
we may help ourselves to any extent from the great
storehouse of nature. Wind and water, the coal-bed
and the forest, afford man an inexhaustible supply of
available energy. It used to be considered that there
was an absolute break between the different states of
matter. The continuity of the gaseous, liquid, and
solid conditions was first demonstrated by Andrews
in 1862.

Oxygen and nitrogen have been liquefied in-
dependently, and at the same time, by Cailletet and
Raoul Pictet. Cailletet also succeeded in liquefying air,
and soon afterwards hydrogen was liquefied by Pictet
under a pressure of 650 atmospheres, and a cold of 170°
Cent, below zero. It even became partly solidified, and
he assures us that it fell on the floor with ' the shrill

66 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

noise of metallic hail/ Thus then it was shown
experimentally that there are no such things as abso-
lutely permanent gases.

The kinetic theory of gases, now generally accepted,
refers the elasticity of gases to a motion of translation
of their molecules, and we are assured that in the case
of hydrogen at a temperature of 60° Fahr. they move
at an average rate of 6,225 feet in a second ; while as
regards their size, Loschmidt, who has since been con-
firmed by Stoney and Sir W. Thomson, calculates that
each is at most 5 o 0 0*0 o o o °f an incn m diameter.

We cannot, it would seem at present, hope for any
increase of our knowledge of atoms by any improve-
ment in the microscope. With our present instruments
we can perceive lines ruled on glass of -$ oiro^th of an
inch apart. But, owing to the properties of light itself,
the fringes due to interference begin to produce confu-
sion at distances of y^-g-oo" > an(^ m the brightest part of
the spectrum at little more than 90-*00th they would
make the obscurity more or less complete. If indeed
we could use the blue rays by themselves, their waves
being much shorter, the limit of possible visibility
might be extended to 1 2 ^ Q 0 ; and as Helmholtz has
suggested, this perhaps accounts for Stinde having
actually been able to abtain a photographic image of
lines only Kx/oooth of an inch apart. It would seem
then that, owing to the physical characters of light, we
can, as Sorby has pointed out, scarcely hope for any
great improvement so far as the mere visibility of struc-
ture is concerned, though in other respects no doubt
much may be hoped for. At the same time, Dallinger
and Royston Pigott have shown that, so far as the mere

THE SIZE OF MOLECULES. METEOROLOGY. 67

presence of simple objects is concerned, bodies of even
smaller dimensions can be perceived.

According to the views of Helmholtz, the smallest
particle that could be distinctly defined, when associated
with others, is about -g-o^^n °f an inch. Sorby esti-
mates that a particle of albumen of this size contains
125,000,000 of molecules. In the case of such a simple
compound as water the number would be no less than
8,000,000,000. Even, then, if we could construct
microscopes far more powerful than any we now possess,
they would not enable us to obtain by direct vision any
idea of the ultimate molecules of matter. Sorby calcu-
lates that the smallest sphere of organic matter which
could be clearly defined with our most powerful micro-
scopes would contain many millions of molecules of
albumen and water, and it follows that there may be an
almost infinite number of structural characters in
organic tissues, which we can at present foresee no
mode of examining.

The science of Meteorology has made great pro-
gress ; the weather, which was formerly treated as a
local phenomenon, being now shown to form part of a
vast system of mutually dependent cyclonic and anti-
cyclonic movements. The storm-signals issued at our
ports are very valuable to sailors, while the small
weather-maps, for which we are mainly indebted to
Francis Gralton, and the forecasts, which anyone can
obtain on application either personally or by telegraph at
the Meteorological Office, are also of increasing utility.

Electricity in the year 1831 may be considered to
have just been ripe for its adaptation to practical pur-

™ o

F V

68 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

poses ; it was but a few years previously, in 1819, that
Oersted had discovered the deflective action of the
current on the magnetic needle, that Ampere had laid
the foundation of electro- dynamics, that Schweizzer had
devised the electric coil or multiplier, and that Sturgeon
had constructed the first electro-magnet. It was in
1831 that Faraday, the prince of pure experimentalists,
announced his discoveries of voltaic induction and
magneto-electricity, which with the other three dis-
coveries constitute the principles of nearly all the
telegraph instruments now in use ; and in 1834 our
knowledge of the nature of the electric current had been
much advanced by the interesting experiment of Sir
Charles Wheatstone, proving the velocity of the current
in a metallic conductor to approach that of the wave of
light.

Practical applications of these discoveries were not
long in coming to the fore, and the first telegraph line
on the Great Western Railway from Paddington to
West Dray ton was set up in 1838. In America, Morse
is said to have commenced the development of his re-
cording instrument between the years 1832 and 1837,
while Steinheil, in Germany, during the same period was
engaged upon his somewhat super-refined ink-recorder,
usino- for the first time the earth for completing the
return circuit ; whereas in this country Cooke and
Wheatstone, by adopting the more simple device of
the double-needle instrument, were the first to make
the electric telegraph a- practical institution. Contem-
poraneously with, or immediately succeeding these
pioneers, we find in this country Alexander Bain,
Breguet in France, Schilling in Russia, and Werner

ELECTRICITY. TELEGRAPHY. 69

Siemens in Germany, the last having first, in 1847,
among others, made use of gutta-percha as an insulating
medium for electric conductors, and thus cleared the
way for subterranean and submarine telegraphy.

Four years later, in 1851, submarine telegraphy
became an accomplished fact through the successful
establishment of telegraphic communication between
Dover and Calais. Submarine lines followed in rapid
succession, crossing the English Channel and the Ger-
man Ocean, threading their way through the Mediter-
ranean, Black and Red Seas, until in 1866, after two
abortive attempts, telegraphic communication was suc-
cessfully established between the Old and New Worlds,
beneath the Atlantic Ocean.

In connection with this great enterprise and with
many investigations and suggestions of a highly scien-
tific and important character, the name of Sir William
Thomson will ever be remembered. The ingenuity
displayed in perfecting the means of transmitting in-
telligence through metallic conductors, with the utmost
despatch and certainty as regards the record obtained,
between two points hundreds and even thousands of
miles apart is truly surprising. The instruments de-
vised by Morse, Siemens, and Hughes have also proved
most useful.

Duplex and quadruplex telegraphy, one of the most
striking achievements of modern telegraphy, the result
of the labours of several inventors, should not be
passed over in silence. It not only serves for the
simultaneous communication of telegraphic intelligence
in both directions, but renders it possible for four
instruments to be worked irrespectively of one another,

70 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

through one and the same wire connecting two distant
places.

Another more recent and perhaps still more won-
derful achievement in modern telegraphy is the inven-
tion of the telephone and microphone, by means of
which the human voice is transmitted through the
electric conductor, by mechanism that imposes through
its extreme simplicity. In this connection the names
of Keiss, Graham Bell, Edison, and Hughes are those
chiefly deserving to be recorded.

Whilst electricity has thus furnished us with the
means of flashing our thoughts by record or by voice
from place to place, its use is now gradually extending
for the achievement of such quantitative effects as the
production of light, the transmission of mechanical
power, and the precipitation of metals. The principle
involved in the magneto-electric and dynamo -electric
machines, by which these effects are accomplished, may
be traced to Faraday's discovery in 1831 of the induced
current, but their realisation to the labours of Holmes,
Siemens, Pacinotti, Gramme, and others. In the elec-
tric light, gas-lighting has found a formidable com-
petitor, which appears destined to take its place in public
illumination, and in lighting large halls, works, &c., for
which purposes it combines brilliancy and freedom
from obnoxious products of combustion, with com-
parative cheapness. The electric light seems also to
threaten, when sub- divided in the manner recently
devised by Edison, Swan, and others, to make inroads
into our dwelling-houses.

By the electric transmission of power, we may hope
some day to utilise at a distance such natural sources

THE STORAGE OF FORCE. 71

of energy as the Falls of Niagara, and to work our
cranes, lifts, and machinery of every description by
means of sources of power arranged at convenient
centres. To these applications the Brothers Siemens
have more recently added the propulsion of trains by
currents passing through the rails, the fusion in con-
siderable quantities of highly refractory substances, and
the use of electric centres of light in horticulture as
proposed by Werner and William Siemens. By an
essential improvement by Faure of the Plante Secondary
Battery, the problem of storing electrical energy appears
to have received a practical solution, the real importance
of which is clearly proved by Sir W. Thomson's recent
investigation of the subject.

It would be difficult to assign the limits to which
this development of electrical energy may not be ren-
dered serviceable for the purposes of man.

As regards mathematics I have felt that it would
be impossible for me, even with the kindest help, to
write anything myself. Mr. Spottiswoode, however,
has been so good as to supply me with the following
memorandum.

In a complete survey of the progress of science during the half-
century which has intervened between our first and our present
meeting, the part played by mathematics would form no insignificant
feature. To those indeed who are outside its enchanted circle it is
difficult to realise the intense intellectual energy which actuates its
devotees, or the wide expanse over which that energy ranges. Some
measure, however, of its progress may perhaps be formed by con-
sidering, in one or two cases, from what simple principles some of the
great recent developments have taken their origin.

Consider, for instance, what is known as the principle of signs.
In geometry we are concerned with quantities such as lines and angles;

72 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

and in the old systems a proposition was proved with reference to
a particular figure. This figure might, it is true, be drawn in any
manner within certain ranges of limitation : but if the limits were
exceeded, a new proof, and often a new enunciation, became neces-
sary. Gradually, however, it came to be perceived (e.g. by Carnot, in
his ' Geometrie de Position,') that some propositions were true even
when the quantities were reversed in direction. Hence followed a
recognition of the principle (of signs) that every line should be re-
garded as a directed line, and every angle as measured in a definite
direction. By means of this simple consideration, geometry has
acquired a power similar to that of algebra, viz. of changing the signs
of the quantities and transposing their positions, so as at once, and
without fresh demonstration, to give rise to new propositions.

To take another instance. The properties of triangles, as esta-
blished by Euclid, have always been considered as legitimate elements
of proof; so that, when in any figure two triangles occur, their rela-
tions may be used as steps in a demonstration. But, within the
period of which I am speaking, other general geometrical relations,
e.g. those of a pencil of rays, or of their intersection with a straight
line, have been recognised as serving a similar purpose. With what
extensive results this generalisation has been attended, the Geo-
metrie Superieure of the late M. Chasles, and all the superstructure
built on Anharmonic Ratio as a foundation, will be sufficient evi-
dence.

Once more, the algebraical expression for a line or a plane involves
two sets of quantities, the one relating to the position of any point in
the line or plane, and the other relating to the position of the line or
plane in space. The former set alone were originally considered vari-
able, the latter constant. But as soon as it was seen that either set
might at pleasure be regarded as variable, there was opened out to
mathematicians the whole field of duality within geometry proper,
and the theory of correlative figures which is destined to occupy a
prominent position in the domain of mathematics.

Not unconnected with this is the marvellous extension which the
transformation of geometrical figures has received very largely from
Cremona and the Italian School, and which in the hands of our
countrymen Hirst and the late Professor Clifford, has already brought
forth such abundant fruit. In this, it may be added, there lay-
dormant, it is true, and long unnoticed — the principle whereby
circular may be converted into rectilinear motion, and vice versd —
a problem which until the time of Peaucillier seemed so far from

MATHEMATICS. V3

solution, that one of the greatest mathematicians cf the day thought
that he had proved its entire impossibility. In the hands of Sylvester,
of Kempe, and others, this principle has been developed into a general
theory of link- work, on which the last word has not yet been said.

If time permitted, I might point out how the study of particular
geometric figures, such as curves and surfaces, has been in many
instances replaced by that of systems of figures infinite in number,
and indeed of various degrees of infinitude. Such, for instance, are
Pliicker's complexes and congruencies. I might describe also how
Biemann taught us that surfaces need not present simple extension
without thickness ; but that, without losing their essential geometric
character, they may consist of manifold sheets ; and thus our concep-
tion of space, and our power of interpreting otherwise perplexing
algebraical expressions, become immensely enlarged.

Other generalisations might be mentioned, such as the principle of
continuity, the use of imaginary quantities, the extension of the number
of the dimensions of space, the recognition of systems in which the
axioms of Euclid have no place. But as these were discussed in a
recent address, I need not now do more than remind you that the
germs of the great calculus of Quaternions were first announced by
their author, the late Sir W. E. Hamilton, at one of our meetings.

Passing from geometry proper to the other great branch of mathe-
matical machinery, viz. algebra, it is not too much to say that within
the period now in review there has grown up a modern algebra
which to our founders would have appeared like a confused dream,
and whose very language and terminology would be as an unknown
tongue.

Into this subject I do not propose to lead you far. But, as the
progress which has been made in this direction is certainly not less
than that made in geometry, I will ask your attention to one or two
points which stand notably prominent.

In algebra we use ordinary equations involving one unknown
quantity ; in the application of algebra to geometry we meet with
equations, representing curves or surfaces, and involving two, or
three, unknown quantities respectively \ in the theory of probabilities,
and in other branches of research, we employ still more general ex-
pressions. Now the modern algebra, originating with Cayley and
Sylvester, regards all these diverse expressions as belonging to one
and the same family, and comprises them all under the same general
term ' quantics.' Studied from this point of view, they all alike give
rise to a class of derivative forms, previously unnoticed, but now

74 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

known as invariants, covariants, canonical forms, etc. By means of
these, mathematicians have arrived not only at many properties of the
quantics themselves, but also, at their application to physical pro-
blems. It would be a long and perhaps invidious task to enumerate
the many workers in this fertile field of research, especially in the
schools of Germany and of Italy ; but it is perhaps the less necessary
to do so, because Sylvester, aided by a young and vigorous staff at
Baltimore, is welding many of these results into a homogeneous mass
in the classical memoirs which are appearing from time to time in the
American ' Journal of Mathematics.'

In order to remove any impression that these extensions of algebra
are merely barren speculations of ingenious intellects, I may add
that many of these derivative forms, at least in their elementary
stages, have already found their way into the text-books of mathe-
matics ; and one class in particular, known by the name of deter-
minants, is now introduced as a recognised method of algebra, greatly
to the convenience of all those who become master of its use.

In the extension of mathematics it has happened more than once
that laws have been established so simple in form, and so obvious in
their necessity, as scarcely to require proof. And yet their applica-
tion is often of the highest importance in checking conclusions which
have been drawn from other considerations, as well as in leading to
conclusions which, without their aid, might have been difficult of at-
tainment. The same thing has occurred also in physics ; and notably
in the recognition of what has been termed the ' Law of the Conserva-
tion of Energy.'

Energy has been defined to be ' The capacity, or power, of any
body, or system of bodies, when in a given condition, to do a measur-
able quantity of work.' Such work may either change the condition
of the bodies in question, or it may affect other bodies ; but in either
case energy is expended by the agent upon the recipient in perform-
ance of the work. The law then states that the total amount of
energy in the agents and recipients taken together remains unaltered
by the changes in question.

Now the principle on which the law depends is this : — ' that every
kind of change among the bodies may be expressed numerically in one
standard unit of change, viz., work done, in such wise that the result
of the passage of any system from one condition to another may be
calculated by mere additions and substractions, even when we do not
know how the change came about. This being so, all work done by
a system may be expressed as a diminution of energy of that system,

THE CONSERVATION OF ENERGY. 75

and all work done upon a system as an accession of energy. Conse-
quently, the energy lost by one system in performance of work will be
gained by another in having work done upon it, and the total energy,
as between the two systems, will remain unchanged.

There are two cases, or conditions, of energy which, although sub-
stantially the same, are for convenience regarded separately. These
may be illustrated by the following example. Work may be done
upon a body, and energy communicated to it, by setting it in motion,
e.g. by lifting it against gravity. Suppose this to be done by a spring
and detent ; and suppose further the body, on reaching its highest
point, to be caught so as to rest at that level on a support. Then,
whether we consider the body at the moment of starting, or when
resting on the support, it has equally received an accession of energy
from the spring, and is therefore equally capable of communicating
energy to a third body. But in the one case this is due to the motion
which it has acquired, and in the other to the position at which it
rests, and to its capability of falling again when the support is re-
moved. Energy in the first of these states is called ' Energy of
Motion,' or « Kinetic Energy,' and that in the second state, ' Energy
of Position,' or 'Potential Energy.' In the case supposed, at the
moment of starting, the whole of the energy is kinetic; as the
body rises, the energy becomes partly potential and partly kinetic ;
and when it reaches the highest point the energy has become wholly
potential. If the body be again dropped, the process is reversed.

The history of a discovery, or invention, so simple at first sight, is
often found to be more complicated the more thoroughly it is ex-
amined. That which at first seems to have been due to a single mind
proves to have been the result of the successive actions of many minds.
Attempts more or less successful in the same direction are frequently
traced out j and even unsuccessful efforts may not have been without
influence on minds turned towards the same object. Lastly also,
germs of thought, originally not fully understood, sometimes prove in
the end to have been the first stages of growth towards ultimate fruit.
The history of the law of the conservation of energy forms no excep-
tion to this order of events. There are those who discern even in the
writings of Newton expressions which show that he was in possession
of some ideas which, if followed out in a direct line of thought, would
lead to those now entertained on the subjects of energy and of work.
But however this may be, and whosoever might be reckoned among
the earlier contributors to the general subject of energy, and to the
establishment of its laws, it is certain that within the period of which

76 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

I am now speaking, the names of Seguin, Clausius, Helmholtz, Mayer,
and Colding on the Continent, and those of Grove, Joule, Rankine,
and Thomson in this country, will always be associated with this great
work.

I must not, however, quit this subject without a passing notice of
a conclusion to which Sir William Thomson has come, and in which
he is followed by others who have pursued the transformation of
energy to some of its ultimate consequences. The nature of this will
perhaps be most easily apprehended by reference to a single instance.
In a steam engine, or other engine, in which the motive power de-
pends upon heat, it is well known that the source of power lies not in
the general temperature of the whole, but merely on the difference of
temperature between that of the boiler and that of the condenser.
And the effect of the condenser is to reduce the steam issuing from
the boiler to the same temperature as that of the condenser. When
this is once done, no more work can be got out of the engine, unless
fresh heat be supplied from an outside source to the boiler. The heat
originally communicated to the boiler has become uniformly diffused,
and the energy due to that difference is said to have been dissipated.
The energy remains in a potential condition as regards other bodies ;
but as regards the engine, it is of no further use. Now suppose that
we regard the entire material universe as a gigantic engine, and that
after long use we have exhausted all the fuel (in its most general
sense) in the world ; then all the energy available will have become
dissipated, and we shall have arrived at a condition of things from
which there is no apparent escape. This is what is called the ' Dis-
sipation of Energy.'

Prof. Frankland has been so good as to draw up for
me the following account of the progress of Chemistry
during the last half- century.

Most of the elements had been discovered before 1830, the
majority of the rarer elements since the beginning of the century. In
addition to these the following five have been discovered, three of
them by Mosander, viz. : — lanthanum in 1839, didymium in 1842,
and ebrium in 1843. Ruthenium was discovered by Glaus in 1843,
and niobium by Rose in 1844. Spectrum analysis has added five to
the list, viz. : — Csesium and rubidium, which were discovered by
Bunsen and Kirchhoff in 1860 ; thallium, by Crookes in 1861 ; indium

CHEMISTRY. 77

by Reich and Richter in 1863 ; and gallium, by Lecoq de Boisbaudran
in 1875.

As regards theoretical views, the atomic theory, the foundation of
scientiBc chemistry, had been propounded by Dalton (1804-1808).
The three laws which have been chiefly instrumental in establishing
the true atomic weights of the elements — the law of Avogadro (1811),
that equal volumes of gases under the same conditions of temperature
and pressure contain equal numbers of molecules ; the law of Dulong
and Petit (1819), that the capacities for heat of the atoms of the
various elements are equal ; and Mitscherlich's law of isomorphism
(1819), according to which equal numbers of atoms of elements be-
longing to the same class may replace each other in a compound with-
out altering the crystalline form of the latter, had been enunciated
in quick succession ; but the true application of these three laws,
though in every case distinctly stated by the discoverers, failed to be
generally made, and it was not till the rectification of the atomic
weights by Cannizzaro, in 1858, that these important discoveries bore
fruit.

In organic chemistry the views most generally held about the
year 1830 were expressed in the radical theory of Berzelius. This
theory, which was first stated in its electro-chemical and dualistic
form by its author in 1817, received a further development at his
hands in 1834 after the discovery of the benzoyl-radieal by Liebigand
Wohler. In the same year (1834), however, a discovery was made by
Dumas, which was destined profoundly to modify the electro-chemical
portion of the theory, and even to overthrow the form of it put forth
by Berzelius. Dumas showed that an electro-negative element, such
as chlorine, might replace, atom for atom, an electro-positive element
like hydrogen, in some cases without much alteration in the character
of the compound. This law of substitution has formed a necessary
portion of every chemical theory which has been proposed since its
discovery, and its importance has increased with the progress of the
science. It would take too long to enumerate all the theoretical views
which have prevailed at various times during the past fifty years ;
but the theory which along with the radical theory has exercised most
influence on the development of the views now held, is the theory of
types, first stated by Dumas (1839) and developed in a different form
and amalgamated with the radical theory by Gerhardt and Williamson
(1848-1852). It is, however, the less necessary to refer in detail to
these views, seeing that in the now prevailing theory of atomicity we
possess a generalisation which, while greatly extending the scope of

78 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

chemical science in its power of classifying known and predicting un-
known facts, includes all that was valuable in the generalisations
which preceded it. The study of the behaviour of organo-metallic
compounds in chemical reactions led to the conclusion that various
metallic elements possess a definite capacity of saturation with regard
to the number of atoms of other elements with which they can com-
bine, and demonstrated this regularity of atom-fixing power in the
case of zinc, tin, arsenic and antimony. A serious obstacle, however,
in the way of determining the true atomicities of the elements was
the general employment of the old so-called equivalent weights, which
were by most chemists confounded with the atomic weights. This
difficulty was removed by the rectification of the atomic weights,
which, though begun by Gerhardt as early as 1842, met for a long
time with but little recognition, and was not completed till the sub-
ject was taken up by Cannizarro in 1858. The law of atomicity has
given to chemistry an exactness which it did not previously possess, and
since its discovery and recognition chemical research has moved very
much on the lines laid down by this law.

Chemists have been engaged in determining by means of decompo-
sitions, the molecular architecture, or constitution as it is called, of
various compounds, natural and artificial, and in verifying by synthesis
the correctness of the views thus arrived at.

It was long supposed that an impassable barrier existed between
inorganic and organic substances : that the chemist could make the
former in his laboratory, while the latter could only be produced in
the living bodies of animals or plants — requiring for their construc-
tion not only chemical attractions, but a supposed ' vital force.' It
was not until 1828 that Wb'hler broke down this barrier by the
synthetic production of urea, and since his time this branch of science
in the hands of Hofmann, Wurtz, Berthelot, Butlerow, and others,
has made great strides. Innumerable natural compounds have thus
been produced in the laboratory — ranging from bodies of relatively
simple constitution, such as the alcohols and acids of the fatty series,
to bodies of such complex molecular structure as alizarin (the prin-
cipal coloring matter of madder), coumarin (the odoriferous principle of
the tonqua bean), vanillin, and indigo. The problem of the natural
alkaloids has also been attacked, in some cases with more than partial
success. Methylconine, which occurs along with conine in the hem-
lock, has been recently prepared artificially by Michael and Gundelach,
this being the first instance of the synthesis of a Datura! alkaloid. A
proximate synthesis of atropine, the alkaloid of the deadly nightshade,

UNDISCOVERED SUBSTANCES. 79

has been accomplished by Ladenburg. It seems further probable that
at no distant date the useful alkaloids, such as quinine, may also be
synthesised, inasmuch as quinoline, one of the products of the decom-
position of quinine, and of some of the allied bases, has recently been
prepared by Skraup by a method which admits of its being obtained
in any quantity.

Much also has been done in the way of building up compounds
the existence of which was predicted by theory. Indeed, the extent
to which hitherto undiscovered substances can be predicated is
doubtless the greatest triumph achieved by chemists during the past
fifty years.

As yet, however, only the statical side of chemistry has been de-
veloped. Whilst the physicist has been engaged in tracing, for the
gaseous condition at least, the paths of the molecules and calculating
their velocities, the chemist, whose business is with the atoms within
the molecule, can point to no such scientific conquests. All that he
knows concerning the intramolecular atoms, and all that he expresses
in his constitutional formulae is, the particular relation of union in
which each of these atoms stands to the others — which of them are
directly united (as he expresses it) to other given atoms, and which of
them are in indirect union. Of the relative positions in space occu-
pied by these atoms, and of their modes of motion, he is absolutely
ignorant. In like manner in a chemical reaction the initial and
final conditions of the reacting substances are known, but the
intermediate stages — the modes of change — are for the most part
unexplained.

The feeling that no number, however great, of successfully solved
problems of constitutional chemistry (as at present understood), and
no number of syntheses, however brilliant, of natural compounds could
raise chemistry above the statical stage — that the solution of the
dynamical problem cannot be arrived at by purely chemical means —
has led many chemists to approach the subject from the physical side.
The results which the physico-chemical methods, as exemplified in the
laws already alluded to of Dulong and Petit, Avogadro and Mits-
cherlich, have yielded in the past, offer the best guarantee of their
success in the future. And the advantages of many of the physical
methods are obvious. Every purely chemical examination- — whether
proximate or ultimate — of a compound, presupposes the destruction of
the substance under examination : the chemist ' murders to dissect.'
But observations on the action of a substance on the rays of light, on
the relative volumes occupied by molecular quantities of a substance,

80 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

on its velocity of transpiration in the liquid or gaseous state — these
teach us the habits of the living substance. The rays of light which
have threaded their way between the molecules of a body have under-
gone, in contact with these molecules, various specific and measurable
changes, the nature and amount of which are assuredly conditioned by
the mass, form, and other properties of the molecules : the plane of
polarisation has been caused to rotate ; a particular degree of refrac-
tion has been imparted ; or rays of certain wave-lengths have been
removed by absorption ; their absence being manifested by bands in the
absorption- spectrum of the substance. The volumes occupied by mole-
cular quantities are dependent partly on the size of the molecules and
partly on that of the intermolecular spaces.

The duty of the physical chemist is to endeavour to co-ordinate his
physical observations with the known constitution of compounds, as
already determined by the pure chemist. This endeavour has in
various branches of physical chemistry been to some extent successful.
Le Bel has found that among organic compounds those only possess
action on the plane of polarised light which contain at least one
asymmetric carbon atom — that is to say, a carbon atom which is
united to four different atoms or groups of atoms. The researches of
Landolt, of Gladstone, and of Briihl on the specific refraction of
organic liquids, have shown that from the known constitution of a
liquid organic compound it is possible to calculate its specific refraction.
Noel Hartley, in an examination of the absorption spectra of. organic
liquids for the ultra-violet rays, has demonstrated that certain mole-
cular groupings are represented by particular absorption bands, and
this line of inquiry has been extended with very interesting results to
the ultra red rays by Abney and Festing. It is obvious that these
methods may in turn be employed to determine the unknown consti-
tution of substances. The same holds true of the investigations of
Kopp with regard to the molecular volumes of liquids at their boiling-
points, in which he has established the remarkable fact that some
elements always possess the same atomic volume in combination,
whereas, in the case of certain other elements, the atomic volume
varies in a perfectly definite manner with the mode of combination.
This investigation has lately been extended with the best results by
Thorpe, and by Ramsay. Thermo-chemistry, also, which for a long
time, at least as regards that portion which relates to the heat of forma-
tion of compounds, consisted chiefly of a collection of single equations,
each containing three unknown quantities, is beginning to be inter-
preted by Julius Thomsen, whose experienced work in this field is well

MECHANICS. 81

known. Many other methods of physico-chemical research are being
successfully prosecuted at the present day, but it would go beyond the
bounds of this summary even to enumerate these.

The concordant results obtained by these widely differing methods
show that those chemists who have devoted themselves, frequently
amid the ridicule of their more practical brethren, to ascertaining by
purely chemical methods the constitution of compounds, have not
laboured in vain. But the future doubtless belongs to physical
chemistry.

In connection with the rectification of the atomic weights it may
be mentioned that a so-called natural system of the elements has been
introduced by Mendelejeff (1869), in which the properties of the ele-
ments appear as a periodic function of their atomic weights. By the
aid of this system it has been possible to predict the properties and
atomic weights of undiscovered elements, and in the case of known
elements so determine many atomic weights which had not been fixed
by any of the usual methods. Several of these predictions have been
verified in a remarkable manner. A periodicity in the atomic
weights of elements belonging to the same class had been pointed out
by Newlands about four years before the publication of MendelejefFs
memoir.

In mechanical science the progress has not been less
remarkable than in other branches. Indeed to the im-
provements in mechanics we owe no small part of our
advance in practical civilisation, and of the increase of
our national prosperity during the last fifty years.

This immense development of mechanical science
has been to a great extent a consequence of the new
processes which have been adopted in the manufacture of
iron, for the following data with reference to which I am
mainly indebted to Captain Douglas Galton and Mr.
Rendel. About 1830, Neilson introduced the Hot Blast
in the smelting of iron. At first a temperature of 600° or
700° Fahrenheit was obtained, but Cowper subsequently
applied Siemens' regenerative furnace for heating the
blast, chiefly by means of fumes from the black furnace,

G

82 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

which were formerly wasted ; and the temperature now
practically in use is as much as 1,400°, or even more:
the result is a very great economy of fuel and an in-
crease of the output. For instance, in 1830, a blast
furnace with the cold blast would probably produce
130 tons per week, whereas now, 600 tons a week are
readily obtained.

Bessemer, by his brilliant discovery, which he first
brought before the British Association at Cheltenham
in 1856, showed that Iron and Steel could be produced
by forcing currents of atmospheric air through fluid pig
metal, thus avoiding for the first time the intermediate
process of puddling iron, and converting it by cementa-
tion into steel. Similarly by Siemens7 regenerative
furnace, the pig metal and iron ore is converted directly
into steel, especially mild steel for shipbuilding and
boilers ; and Whit worth, by his fluid compression of
steel, is enabled to produce steel in the highest condition
of density and strength of which the metal is capable.
These changes, by which steel can be produced direct
from the blast furnace instead of by the more cumber-
some processes formerly in use, have been followed by
improvements in the manipulation of the metal.

The inventions of Cort and others were known long
before 1830, but we were then still without the most
powerful tool in the hands of the practical metallurgist,
viz., Nasmyth's steam-hammer.

Steel can now be produced as cheaply as iron was
formerly ; and its substitution for iron as railway
material and in shipbuilding, has resulted in increased
safety in railway travelling, as well as in economy,
from its vastly greater durability. Moreover, the en-

IRON AND STEEL. 83

larged use of iron and steel, which has resulted from
these improvements in its make, has led to the adoption
of mechanical means to supersede hand labour in almost
every branch of trade and agriculture, by which the
power of production has been increased a hundredfold,
while at the same time much higher precision has been
obtained. Sir Joseph Whitworth has done more than
any one else to perfect the machinery of this country
by the continued efforts he has made, during nearly
half-a-century, to introduce accuracy into the standards
of measurement in use in workshops. He tells us
that when he first established his works, no two articles
could be made accurately alike or with interchangeable
parts. He devised a measuring apparatus, by which
his workmen in making standard gauges are accustomed
to take measurements to the 2oooo" °f an inch.

In its more immediate relation to the objects of
this Association, the increased importance of iron and
steel has led to numerous scientific investigations into
its mechanical properties and into the laws which
govern its strength ; into the proper distribution of the
material in construction ; and into the conditions which
govern the friction and adhesion of surfaces. The
names of Eaton Hodgkinson, Fairbairn, Barlow, Rennie,
Scott Russell, Willis, Fleeming Jenkin, and Galton are
prominently associated with these inquiries.

The introduction of iron has, moreover, had a vast
influence on the works of both the civil and military
engineer. Before 1830, Telford had constructed an
iron suspension turnpike-road bridge of 560 feet over
the Menai Straits ; but this bridge was not adapted to
the heavy weights of locomotive engines. At the

o 2

84 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

present time, with steel at his command, Mr. Fowler
is engaged in carrying out the design for a railway
bridge over the Forth, of two spans of 1,700 feet each ;
that is to say, of nearly one third of a mile in length.
In artillery, bronze has given place to wrought iron
and steel ; the 68 -pound shot, which was the heaviest
projectile fifty years ago, with its range of about 1,200
yards, is being replaced by a shot of nearly a quarter-
ton weight, with a range of nearly five miles ; and
the armour-plates of ships are daily obtaining new
developments.

But it is in railroads, steamers, and the electric
telegraph that the progress of mechanical science has
most strikingly contributed to the welfare of man.

As regards railways, the Stockton and Darlington
Railway was opened in 1825, but the Liverpool and
Manchester Railway, perhaps the first truly passenger
line, dates from 1830, while the present mileage of rail-
ways is over 200,000 miles, costing nearly 4,000,000,000^.
sterling. It was not until 1838 that the Sirius and
Great Western first steamed across the Atlantic. The
steamer, in fact, is an excellent epitome of the progress
of the half-century ; the paddle has been superseded by
the screw ; the compound has replaced the simple
engine ; wood has given place to iron, and iron in its
turn to steel. The saving in dead weight, by this
improvement alone, is from 10 to 16 per cent. The
speed has been increased from 9 knots to 15, or even
more. Lastly, the steam -pressure has been increased
from less than 5 Ibs. to 70 Ibs. per square inch, while
the consumption of coal has been brought down from
5 or 6 Ibs. per horse-power to less than 2. It is a

ECONOMIC SCIENCE. 85

remarkable fact that not only is our British shipping
rapidly on the increase, but it is increasing relatively
to that of the rest of the world. In 1860 our' tonnage
was 5,700,000 against 7,200,000; while it may now be
placed as 8,500,000 against 8,200,000; so that con-
siderably more than half the whole shipping of the
world belongs to this country.

If I say little with reference to economic science
and statistics it is because time, not materials, are
wanting.

I scarcely think that in the present state of the
question I can be accused of wandering into politics if
I observe that the establishment of the doctrine of free
trade as a scientific truth falls within the period under
review.

In education some progress has been made towards
a more rational system. When I was a boy, neither
science, nor modern languages, nor arithmetic formed
any part of the public school system of the country.
This is now happily changed. Much, however, still
remains to be done. Too little time is still devoted to
French and German, and it is much to be regretted that
even in some of our best schools they are taught as
dead languages. Lastly, with few exceptions, only one
or two hours a week on an average are devoted to
science. We have, I am sure, none of us any desire to
exclude, or discourage, literature. What we ask is
that, say, six hours a week each should be devoted to
mathematics, modern languages, and science — an ar-
rangement which would still leave twenty hours for
Latin and Greek. I admit the difficulties which school-

86 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

masters have to contend with ; nevertheless, when we
consider what science has done and is doing for us, we
cannot but consider that our present system of educa-
tion is, in the words of the Duke of Devonshire's Com-
mission, ' little less than a national misfortune.'

In Agriculture the changes which have occurred hi
the period since 1831 have been immense. The last
half- century has witnessed the introduction of the mo-
dern system of subsoil drainage founded on the experi-
ments of Smith of Deanston. The thrashing and
drilling machines were the most advanced forms of
machinery hi use in 1831. Since then there have been
introduced the steam-plough ; the mowing-machine ;
the reaping-machine, which not only cuts the corn but
binds it into sheaves ; while the steam-engine thrashes
out the grain and builds the ricks. Science has thus
greatly reduced the actual cost of labour, and yet it has
increased the wages of the labourer.

It was to the British Association, at Glasgow, in
1841, that Baron Liebig first communicated his work
1 On the Application of Chemistry to Vegetable Phy-
siology,' while we have also from time to tune received
accounts of the persevering and important experiments
which Mr. Lawes, with the assistance of Dr. Gilbert,
has now carried on for more than forty years at Eotham-
sted, and which have given so great an impulse to
agriculture by directing attention to the principles of
cropping, and by leading to the more philosophical
application of manures.

I feel that in quitting Section F so soon, I owe an
apology to our fellow-workers in that branch of science,
but I doubt not that my shortcomings will be more than

INTERCONNECTION OF THE SCIENCES. 87

made tip for by the address of their excellent President,
Mr. Grant- Duff, whose appointment to the Governor-
ship of Madras, while occasioning so sad a loss to his
friends, will unquestionably prove a great advantage to
India, and materially conduce to the progress of science
in that country.

Moreover, several other subjects of much importance,
which might have been referred to in connection with
these latter Sections, I have already dealt with under
their own more purely scientific aspect.

Indeed, one very marked feature in modern discovery
is the manner in which distinct branches of science
have thrown, and are throwing, light on one another.
Thus the study of geographical distribution of living
beings, to the knowledge of which our late general
secretary, Mr. Sclater, has so greatly contributed, has
done much to illustrate ancient geography. The exist-
ence of high northern forms in the Pyrenees and Alps
indicates the existence of a period of cold when Arctic
species occupied the whole of habitable Europe. Wal-
lace's line — as it has been justly named after that dis-
tinguished naturalist — points to the very ancient
separation between the Malayan and Australian re-
gions ; and the study of corals has thrown light upon
the nature and significance of atolls and barrier-reefs.

In studying the antiquity of man, the archaeologist
has to invoke the aid of the chemist, the geologist, the
physicist, and the mathematician. The recent progress
in astronomy is greatly due to physics and chemistry.
In geology the composition of rocks is a question of
chemistry and physics ; the determination of the boun-
daries of the different formations falls within the limits

88 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

of geography ; while palaeontology is the biology of the
past.

And now I must conclude. I fear I ought to apo-
logise to you for keeping you so long, but still more
strongly do I wish to express my regret that there are
almost innumerable researches of great interest and
importance which fall within the last fifty years (many
even among those with which our Association has been
connected) to which I have found it impossible to refer.
Such for instance are, in biology alone, Owen's memo-
rable report on the homologies of the vertebrate skeleton,
Carpenter's laborious researches on the microscopic
structure of shells, the reports on marine zoology by
Allman, Forbes, Jeffreys, Spence Bate, Norman, and
others ; on Kent's Cavern by Pengelly ; those by Dun-
can on corals ; Woodward on Crustacea ; Carruthers,
Williamson, and others on fossil botany, and many
more. Indeed no one who has not had occasion to
study the progress of science throughout its various
departments can have any idea how enormous — how
unprecedented — the advance has been.

Though it is difficult, indeed impossible, to measure
exactly the extent of the influence exercised by this
Association, no one can doubt that it has been very
considerable. For my own part, I must acknowledge
with gratitude how much the interest of my life has
been enhanced by the stimulus of our meetings, by the
lectures and memoirs to which I have had the advan-
tage of listening, and above all, by the many friend-
ships which I owe to this Association.

Summing up the principal results which have been
attained in the last half-century we may mention (over

SUMMARY. 89

and above the accumulation of facts), the theory of evo-
lution, the antiquity of man, and the far greater antiquity
of the world itself ; the correlation of physical forces
and the conservation of energy ; spectrum analysis and
its application to celestial physics ; the higher algebra
and the modern geometry ; lastly, the innumerable ap-
plications of science to practical life — as, for instance, in
photography, the locomotive engine, the electric tele-
graph, the spectroscope, and most recently the electric
light and the telephone.

To Science, again, we owe the idea of progress.
The ancients, says Bagehot, ' had no conception of pro-
gress ; they did not so much as reject the idea ; they
did not even entertain it.' It is not, I think, going too
far to say that the true test of the civilisation of a nation
must now be measured by its progress in science. It is
often said, however, that, great arid unexpected as the
recent discoveries have been, there are certain ultimate
problems which must ever remain unsolved. For my
part, I would prefer to abstain from laying down any
such limitations. When Park asked the Arabs what
became of the sun at night, and whether the sun was
always the same, or new each day, they replied that
such a question was childish, and entirely beyond the
reach of human investigation. I have already mentioned
that, even as lately as 1842, so high an authority as
Comte treated as obviously impossible and hopeless any
attempt to determine the chemical composition of the
heavenly bodies. Doubtless there are questions the
solution of which we do not as yet see our way even to
attempt ; nevertheless the experience of the past warns
us not to limit the possibilities of the future.

90 ADDRESS TO THE BRITISH ASSOCIATION, 1881.

But however this may be, though the progress made
has been so rapid, and though no similar period in the
world's history has been nearly so prolific of great re-
sults, yet, on the other hand, the prospects of the future
were never more encouraging. We must not, indeed,
shut our eyes to the possibility of failure : the tempta-
tion to military ambition ; the tendency to over-inter-
ference by the State ; the spirit of anarchy and
socialism ; these and other elements of danger may mar
the fair prospects of the future. That they will suc-
ceed in doing so, I cannot believe. I cannot but
feel confident that fifty years hence, when perhaps the
city of York may renew its hospitable invitation, my
successor in this chair — more competent, I trust, than I
have been to do justice to so grand a theme — will have
to record a series of discoveries even more unexpected
and more brilliant than those which I have, I fear so
imperfectly, attempted to bring before you this evening ;
for assuredly one great lesson of science is, how little
we yet know, and how much, we have still to learn.

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