_THE ADVANCE OF SCIENCE, 1881-1906_
I propose to give in the following pages an outline of the advance of
science in the past twenty-five years. It is necessary to distinguish
two main kinds of advancement, both of which are important. Francis
Bacon gave the title ‘Advancement of Learning’ to that book in
which he explained not merely the methods by which the increase of
knowledge was possible, but advocated the promotion of knowledge to
a new and influential position in the organization of human society.
His purpose, says Dean Church, was ‘to make knowledge really and
intelligently the interest, not of the school or the study or the
laboratory only, but of society at large.’ So that in surveying the
advancement of science in the past quarter of a century we should
ask not only what are the new facts discovered, the new ideas and
conceptions which have come into activity, but what progress has
science made in becoming really and intelligently the interest of
society at large. Is there evidence that there is an increase in
the influence of science on the lives of our fellow-citizens and
in the great affairs of the State? Is there an increased provision
for securing the progress of scientific investigation in proportion
to the urgency of its need or an increased disposition to secure
the employment of really competent men trained in scientific
investigation for the public service?
1. THE INCREASE OF KNOWLEDGE IN THE SEVERAL BRANCHES OF SCIENCE.
The boundaries of my own understanding and the practical
consideration of what is appropriate to a brief essay must limit my
attempt to give to the general reader some presentation of what has
been going on in the workshops of science in this last quarter of a
century. My point of view is essentially that of the naturalist, and
in my endeavour to speak of some of the new things and new properties
of things discovered in recent years I find it is impossible to give
any systematic or detailed account of what has been done in each
division of science. All that I shall attempt is to mention some of
the discoveries which have aroused my own interest and admiration.
I feel, indeed, that it is necessary to ask forbearance for my
presumption in daring to treat of so many subjects in which I cannot
claim to speak as an authority, but only as a younger brother full
of fraternal pride and sympathy in the glorious achievements of the
great experimentalists and discoverers of our day.
As one might expect, the progress of the Knowledge of Nature (for
it is to that rather than to the historical, moral and mental
sciences that English-speaking people refer when they use the word
‘science’) has consisted, in the last twenty-five years, in the
amplification and fuller verification of principles and theories
already accepted, and in the discovery of hitherto unknown things
which either have fallen into place in the existing scheme of each
science or have necessitated new views, some not very disturbing
to existing general conceptions, others of a more startling and,
at first sight, disconcerting character. Nevertheless I think I am
justified in saying that, exciting and of entrancing interest as
have been some of the discoveries of the past few years, there has
been nothing to lead us to conclude that we have been on the wrong
path--nothing which is really revolutionary; that is to say, nothing
which cannot be accepted by an intelligible modification of previous
conceptions. There is, in fact, continuity and healthy evolution in
the realm of science. Whilst some onlookers have declared to the
public that science is at an end, its possibilities exhausted, and
but little of the hopes it raised realised, others have asserted on
the contrary, that the new discoveries--such as those relating to the
X-rays and to radium--are so inconsistent with previous knowledge as
to shake the foundations of science, and to justify a belief in any
and every absurdity of an unrestrained fancy. These two reciprocally
destructive accusations are due to a class of persons who must be
described as the enemies of science. Whether their attitude is due
to ignorance or traditions of self-interest, such persons exist. It
is one of the objects of our scientific associations and societies
to combat those assertions and to demonstrate, by the discoveries
announced at their meetings and the consequent orderly building up of
the great fabric of ‘natural knowledge,’ that Science has not come
to the end of her work--has, indeed, only as yet given mankind a
foretaste of what she has in store for it--that her methods and her
accomplished results are sound and trustworthy, serving with perfect
adaptability for the increase of true discovery and the expansion and
development of those general conceptions of the processes of nature
at which she aims.
_New Chemical Elements._--There can be no doubt that the past quarter
of a century will stand out for ever in human history as that in
which new chemical elements, not of an ordinary type, but possessed
of truly astounding properties, were made known with extraordinary
rapidity and sureness of demonstration. Interesting as the others
are, it is the discovery of radio-activity and of the element radium
which so far exceeds all others in importance that we may well
account it a supreme privilege that it has fallen to our lot to live
in the days of this discovery. No single discovery ever made by
the searchers of nature even approaches that of radio-activity in
respect of the novelty of the properties of matter suddenly revealed
by it. A new conception of the structure of matter is necessitated
and demonstrated by it, and yet, so far from being destructive
and disconcerting, the new conception fits in with, grows out of,
and justifies the older schemes which our previous knowledge has
formulated.
Before saying more of radio-activity, which is apt to eclipse in
interest every other topic of discourse, I must recall to you
the discovery of the five inert gaseous elements by Rayleigh and
Ramsay, which belongs to the period on which we are looking back.
It was found that nitrogen obtained from the atmosphere invariably
differed in weight from nitrogen obtained from one of its chemical
combinations; and thus the conclusion was arrived at by Rayleigh
that a distinct gas is present in the atmosphere, to the extent
of 1 per cent., which had hitherto passed for nitrogen. This gas
was separated, and to it the name argon (the lazy one) was given,
on account of its incapacity to combine with any other element.
Subsequently this argon was found by Ramsay to be itself impure,
and from it he obtained three other gaseous elements equally inert:
namely neon, krypton, and xenon. These were all distinguished from
one another by the spectrum, the sign-manual of an element given by
the light emitted in each case by the gas when in an incandescent
condition. A fifth inert gaseous element was discovered by Ramsay as
a constituent of certain minerals which was proved by its spectrum
to be identical with an element discovered twenty-five years ago by
Sir Norman Lockyer in the atmosphere of the sun, where it exists in
enormous quantities. Lockyer had given the name ‘helium’ to this new
solar element, and Ramsay thus found it locked up in certain rare
minerals in the crust of the earth.
But by helium we are led back to radium, for it has been found only
two years ago by Ramsay and Soddy that helium is actually formed by
a gaseous emanation from radium. Astounding as the statement seems,
yet that is one of the many unprecedented facts which recent study
has brought to light. The alchemist’s dream is, if not realised, at
any rate justified. One element is actually under our eyes converted
into another; the element radium decays into a gas which changes into
another element, namely helium.
Radium, this wonder of wonders, was discovered owing to the study of
the remarkable phosphorescence, as it is called--the glowing without
heat--of glass vacuum-tubes through which electric currents are
made to pass. Crookes, Lenard, and Röntgen each played an important
part in this study, showing that peculiar rays or linear streams of
at least three distinct kinds are set up in such tubes--rays which
are themselves invisible, but have the property of making glass or
other bodies which they strike glow with phosphorescent light. The
celebrated Röntgen rays make ordinary glass give out a bright green
light; but they pass through it, and cause phosphorescence outside
in various substances, such as barium platino-cyanide, calcium
tungstate, and many other such salts; they also act on a photographic
plate and discharge an electrified body such as an electroscope. But
the most remarkable feature about them is their power of penetrating
substances opaque to ordinary light. They will pass through thin
metal plates or black paper or wood, but are stopped by more or
less dense material. Hence it has been possible to obtain ‘shadow
pictures’ or skiagraphs by allowing the invisible Röntgen rays to
pass through a limb or even a whole animal, the denser bone stopping
the rays, whilst the skin, flesh, and blood let them through. They
are allowed to fall (still invisible) on to a photographic plate,
when a picture like an ordinary permanent photograph is obtained
by their chemical action, or they may be made to exert their
phosphorescence-producing power on a glass plate covered with a thin
coating of a phosphorescent salt such as barium platino-cyanide, when
a temporary picture in light and shade is seen.
The rays discovered by Röntgen were known as the X-rays, because
their exact nature was unknown. Other rays studied in the electrified
vacuum-tubes are known as cathode rays or radiant corpuscles, and
others, again, as the Lenard rays.
It occurred to M. Henri Becquerel, as he himself tells us, to inquire
whether other phosphorescent bodies besides the glowing vacuum-tubes
of the electricians’ laboratory can emit penetrating rays like the
X-rays. I say ‘other phosphorescent bodies,’ for this power of
glowing without heat--of giving out, so to speak, cold light--is
known to be possessed by many mineral substances. It has become
familiar to the public in the form of ‘phosphorescent paint,’ which
contains sulphide of calcium, a substance which shines in the dark
after exposure to sunlight--that is to say, is phosphorescent. Other
sulphides and the minerals fluor-spar, apatite, some gems, and, in
fact, a whole list of substances have, under different conditions
of treatment, this power of phosphorescence or shining in the dark
without combustion or chemical change. All, however, require some
special treatment, such as exposure to sunlight or heat or pressure,
to elicit the phosphorescence, which is of short duration only.
Many of the compounds of a somewhat uncommon metallic element,
called uranium, used for giving a fine green colour to glass, are
phosphorescent substances, and it was, fortunately, one of them which
Henri Becquerel chose for experiment. Henri Becquerel is professor
in the Jardin des Plantes of Paris; his laboratory is a delightful
old-fashioned building, which had for me a special interest and
sanctity when, a few years ago, I visited him there, for, a hundred
years before, it was the dwelling-house of the great Cuvier. Here
Henri Becquerel’s father and grandfather--men renowned throughout
the world for their discoveries in mineralogy, electricity, and
light--had worked, and here he had himself gone almost daily from
his earliest childhood. Many an experiment bringing new knowledge
on the relations of light and electricity had Henri Becquerel
carried out in that quiet old-world place before the day on which,
about twelve years ago, he made the experimental inquiry, ‘Does
uranium give off penetrating rays like Röntgen rays?’ He wrapped a
photographic plate in black paper, and on it placed and left lying
there for twenty-four hours some uranium salt. He had placed a cross,
cut out in thin metallic copper, under the uranium powder, so as to
give some shape to the photographic print should one be produced.
It _was_ produced. Penetrating rays were given off by the uranium:
the black paper was penetrated, and the form of the copper cross was
printed on a dark ground (fig. 9). The copper was also penetrated to
some extent by the rays from the uranium, so that its image was not
left actually white. Only one step more remained before Becquerel
made his great discovery. It was known, as I stated just now, that
sulphide of calcium and similar substances _become_ phosphorescent
when exposed to sunlight, and lose this phosphorescence after a few
hours. Becquerel thought at first that perhaps the uranium salt
acquired its power similarly by exposure to light; but very soon,
by experimenting with uranium salt long kept in the dark, he found
that the emission of penetrating rays, giving photographic effects,
was produced spontaneously. The emission of rays by this particular
sample of uranium salt has shown no sign of diminution since this
discovery. The emission of penetrating rays by uranium was soon found
to be independent of its phosphorescence. Phosphorescent bodies,
as such, do not emit penetrating rays. Uranium compounds, whether
phosphorescent or not, emit and continue to emit, these penetrating
rays, capable of passing through black paper and in a less degree
through metallic copper. They do not derive this property from the
action of light or any other treatment. The emission of these rays
discovered by Becquerel is a new property of matter. It is called
‘radio-activity,’ and the rays are called Becquerel rays.
[Illustration: FIG. 9.--HENRI BECQUEREL’S DISCOVERY OF RADIO ACTIVITY.
Photographic print or skiagraph of a copper Maltese Cross
produced by uranium salt placed as a heap of powder on the
surface of black paper wrapped round a sensitive plate. Between
the paper and the uranium powder the flat copper cross was
interposed. The rays from the uranium salt have penetrated the
black paper, but have been intercepted to a large extent by the
copper cross--so that the sensitive silver plate is darkened all
about the cross--over an area corresponding to that of the heap
of uranium salt, but is left pale where the copper figure blocked
the path of the active rays given off by the uranium, partially
but not wholly. It was thus proved that the rays from the uranium
salt can pass through blackened paper and also though to a less
extent through a plate of copper.]
From this discovery by Becquerel to the detection and separation of
the new element radium is an easy step in thought, though one of
enormous labour and difficulty in practice. Professor Pierre Curie
(whose name I cannot mention without expressing the grief caused
to all men of science by the sad accident by which his life was
taken) and his wife, Madame Sklodowski Curie, incited by Becquerel’s
discovery, examined the ore called pitch-blende which is worked in
mines in Bohemia and is found also in Cornwall. It is the ore from
which all commercial uranium is extracted. The Curies found that
pitch-blende has a radio-activity four times more powerful than that
of metallic uranium itself. They at once conceived the idea that the
radio-activity of the uranium salts examined by Becquerel is due not
to the uranium itself, but to another element present with it in
variable quantities. This proved to be in part true. The refuse of
the first processes by which in the manufacturer’s works the uranium
is extracted from its ore, pitch-blende, was found to contain four
times more of the radio-active matter than does the pure uranium. By
a long series of fusions, solutions, and crystallizations the Curies
succeeded in ‘hunting down,’ as it were, the radio-active element.
The first step gave them a powder mixed with barium chloride, and
having 2,000 times the activity of the uranium in which Becquerel
first proved the existence of the new property--radio-activity. Then
step by step they purified it to a condition 10,000 times, then
to 100,000 times, and finally to the condition of a crystalline
salt having 1,800,000 times the activity of Becquerel’s sample of
uranium. The purification could go no further, but the extraordinary
minuteness of the quantity of the pure radio-active substance
obtained and the amount of labour and time expended in preparing it
may be judged of from the fact that of one ton of the pitch-blende
ore submitted to the process of purification only the hundredth of a
gram--the one-seventh of a grain--remained.
The amount of radium in pitch-blende is one ten-millionth per
cent.; rarer than gold in sea-water. The marvel of this story and
of all that follows consists largely in the skill and accuracy with
which our chemists and physicists have learnt to deal with such
infinitesimal quantities, and the gigantic theoretical results which
are securely posed on this pin-point of substantial matter.
The Curies at once determined that the minute quantity of colourless
crystals they had obtained was the chloride of a new metallic element
with the atomic weight 225, to which they gave the name radium. The
proof that radium is an element is given by its ‘sign-manual’--the
spectrum which it shows to the observer when in the incandescent
state. It consists of six bright lines and three fainter lines in the
visible part of the spectrum, and of three very intense lines in the
ultra-violet (invisible) part (fig. 10). A very minute quantity is
enough for this observation; the lines given by radium are caused by
no other known element in heaven or earth. They prove its title to be
entered on the roll-call of elements.
[Illustration: FIG. 10.
A diagram of the _visible_ lines of the spectrum of the elements
Radium and Helium--when rendered incandescent by electric
‘sparking’ in a glass tube: kindly prepared for this book by Mr.
Frederick Soddy of the University of Glasgow. The position of
the chief great lines of the solar spectrum are marked on the
lowest horizontal line. On the upper line the wave-lengths of
the rays occupying the position indicated, are given. The figure
72 means that the wave-length of the ray occupying this position
when refracted by the prism of the spectroscope is, as measured
from crest to crest of the undulation, seven hundred and twenty
millionths of a millimetre. It is generally written 720·0 µµ.
Lines exist at the ultra-violet end of the spectrum which can
be photographed but do not affect the eye--that is to say are
invisible. On the other hand the lines of the red end of the
spectrum do not produce a photographic effect. Consequently a
‘_photographed_’ spectrum such as that given in the next figure
(fig. 11) differs in the lines presented both at the red and the
violet ends from the _visible_ series of lines. The two (visible
and photographed spectra) agree only from wave-length 587·6 µµ to
wave-length 447·2 µµ.
The two spectra given in fig. 10 show how great is the difference
in the position and number of the bands of Radium and Helium--yet
as shown in the next figure (fig. 11) the ‘emanation’ from Radium
actually is transformed into Helium.]
The atomic weight was determined in the usual way by precipitating
the chlorine in a solution of radium chloride by means of silver.
None of the precious element was lost in the process, but the Curies
never had enough of it to venture on any attempt to prepare pure
metallic radium. This is a piece of extravagance no one has yet
dared to undertake. Altogether the Curies did not have more than
some four or five grains of chloride of radium to experiment with,
and the total amount prepared and now in the hands of scientific
men in various parts of the world probably does not amount to more
than sixty grains at most. When Professor Curie lectured on radium
four years ago at the Royal Institution in London he made use of a
small tube an inch long and of one-eighth bore, containing nearly
the whole of his precious store, wrenched by such determined labour
and consummate skill from tons of black shapeless pitch-blende. On
his return to Paris he was one day demonstrating in his lecture room
with this precious tube the properties of radium when it slipped from
his hands, broke, and scattered far and wide the most precious and
magical powder ever dreamed of by alchemist or artist of romance.
Every scrap of dust was immediately and carefully collected,
dissolved, and re-crystallized, and the disaster averted with a loss
of but a minute fraction of the invaluable product.
Thus, then, we have arrived at the discovery of radium--the
new element endowed in an intense form with the new property
‘radio-activity’ discovered by Becquerel. The wonder of this powder,
incessantly and without loss, under any and all conditions pouring
forth by virtue of its own intrinsic property powerful rays capable
of penetrating opaque bodies and of exciting phosphorescence and
acting on photographic plates, can perhaps be realized when we
reflect that it is as marvelous as though we should dig up a stone
which without external influence or change, continually poured forth
light or heat, manufacturing both in itself, and not only continuing
to do so without appreciable loss or change, but necessarily having
always done so for countless ages whilst sunk beyond the ken of man
in the bowels of the earth.
Wonderful as the story is, so far it is really simple and commonplace
compared with what yet remains to be told. I will only barely and
abruptly state the fact that radio-activity has been discovered
in other elements, some very rare, such as actinium and polonium;
others more abundant and already known, such as thorium and uranium,
though their radio-activity was not known until Becquerel’s
pioneer-discovery. It is a little strange and no doubt significant
that, after all, pure uranium is found to have a radio-activity of
its own and not to have been altogether usurping the rights of its
infinitesimal associate.
The wonders connected with radium really begin when the experimental
examination of the properties of a few grains is made. What I am
saying here is not a systematic, technical account of radium; so I
shall venture to relate some of the story as it impresses me.
Leaving aside for a moment what has been done in regard to the more
precise examination of the rays emitted by radium, the following
astonishing facts have been found out in regard to it: (1) If a glass
tube containing radium is much handled or kept in the waistcoat
pocket, it produces a destruction of the skin and flesh over a
small area--in fact, a sore place. (2) The smallest trace of radium
brought into a room where a charged electroscope is present, causes
the discharge of the electroscope. So powerful is this electrical
action of radium that a very sensitive electrometer can detect the
presence of a quantity of radium five hundred thousand times more
minute than that which can be detected by the spectroscope (that
is to say, by the spectroscopic examination of a flame in which
minute traces of radium are present). (3) Radium actually realizes
one of the properties of the hypothetical stone to which I compared
it, giving out light and heat. For it does give out heat which it
makes itself incessantly and without appreciable loss of substance
or energy (‘appreciable’ is here an important qualifying term). It
is also faintly self-luminous. Fairly sensitive thermometers show
that a few granules of radium salt have always a higher temperature
than that of surrounding bodies. Radium has been proved to give out
enough heat to melt rather more than its own weight of ice every
hour; enough heat in one hour to raise its own weight of water from
the freezing-point to the boiling-point. After a year and six weeks
a gram of radium has emitted enough heat to raise the temperature of
a thousand kilograms of water one degree. And this is always going
on. Even a small quantity of radium diffused through the earth will
suffice to keep up its temperature against all loss by radiation! If
the sun consists of a fraction of one per cent. of radium this will
account for and make good the heat that is annually lost by it.
This is a tremendous fact, upsetting all the calculations of
physicists as to the duration in past and future of the sun’s heat
and the temperature of the earth’s surface. The geologists and the
biologists have long contended that some thousand million years
must have passed during which the earth’s surface has presented
approximately the same conditions of temperature as at present,
in order to allow time for the evolution of living things and
the formation of the aqueous deposits of the earth’s crust. The
physicists, notably Professor Tait and Lord Kelvin, refused to allow
more than ten million years (which they subsequently increased to a
hundred million)--basing this estimate on the rate of cooling of a
sphere of the size and composition of the earth. They have assumed
that its material is self-cooling. But, as Huxley pointed out,
mathematics will not give a true result when applied to erroneous
data. It has now, within these last five years, become evident that
the earth’s material is _not_ self-cooling, but on the contrary
self-heating. And away go the restrictions imposed by physicists
on geological time. They now are willing to give us not merely a
thousand million years, but as many more as we want.
And now I have to mention the strangest of all the proceedings
of radium--a proceeding in which the other radio-active bodies,
actinium and thorium, resemble it. This proceeding has been entirely
Rutherford’s discovery in Canada, and his name must be always
associated with it. Radium (he discovered) is continually giving
off, apart from and in addition to the rectilinear darting rays of
Becquerel--an ‘emanation’--a gaseous ‘emanation.’ This ‘emanation’
is radio-active--that is, gives off Becquerel rays--and deposits
‘something’ upon bodies brought near the radium so that they become
radio-active, and remain so for a time after the radium is itself
removed. This emanation is always being formed by a radium salt, and
may be most easily collected by dissolving the salt in water, when
it comes away with a rush, as a gas. Sixty milligrams of bromide of
radium yielded to Ramsay and Soddy ·124 (or about one-eighth) of a
cubic millimetre of this gaseous emanation. What is it? It cannot be
destroyed or altered by heat or by chemical agents; it is a heavy
gas, having a molecular density of 100, and it can be condensed to
a liquid by exposing it to the great cold of liquid air. It gives
a peculiar spectrum of its own, and is probably a hitherto unknown
inert gas--a new element similar to argon. But this by no means
completes its history, even so far as experiments have as yet gone.
The radium emanation decays, changes its character altogether, and
loses half its radio-activity every four days. Precisely at the same
rate as it decays the specimen of radium salt from which it was
removed forms a new quantity of emanation, having just the amount of
radio-activity which has been lost by the old emanation. All is not
known about the decay of the emanation, but one thing is absolutely
certain, having first been discovered by Ramsay and Soddy and
subsequently confirmed by independent experiment by Madame Curie. It
is this: After being kept three or four days the emanation becomes,
in part at least, converted into helium--the light gas (second only
in the list of elements to hydrogen), the gas found twenty-five years
ago by Lockyer in the sun, and since obtained in some quantities from
rare radio-active minerals by Ramsay! The proof of the formation
of helium from the radium emanation is, of course, obtained by the
spectroscope, and its evidence is beyond assail (see fig. 11). Here,
then, is the partial conversion or decay of one element, radium,
through an intermediate stage into another. And not only that, but
if, as seems probable, the presence of helium indicates the previous
presence of radium, we have the evidence of enormous quantities of
radium in the sun, for we know helium is there in vast quantity. Not
only that, but inasmuch as helium has been discovered in most hot
springs and in various radio-active minerals in the earth, it may
be legitimately argued that no inconsiderable quantity of radium is
present in the earth. Indeed, it now seems probable that there is
enough radium in the sun to keep up its continual output of heat,
and enough in the earth to make good its loss of heat by radiation
into space, for an almost indefinite period. Other experiments of
a similar kind have rendered it practically certain that radium
itself is formed by a somewhat similar transformation of uranium, so
that our ideas as to the permanence and immutability on this globe
of the chemical elements are destroyed, and must give place to new
conceptions. It seems not improbable that the final product of the
radium emanation after the helium is removed is or becomes the metal
lead!
[Illustration: FIG. 11.
A { Tube containing
{ Helium gas derived
{ from the
{ mineral Clevelandite.
B { Tube of Radium
{ emanation, a
{ year old.
C { Tube of Hydrogen
{ gas for
{ comparison.
Photographs of the “spark” spectra of A, Helium as extracted
from the mineral Clevelandite of B, the Radium “emanation” after
a year’s enclosure in the tube used and of C of Hydrogen gas:
copied from the paper by Mr. F. Giesel in the _Berichte der
Deutschen Chemischen Gesellschaft_, vol. xxxix, part 10.
The three photographs are accurately super-imposed so as to show
the coincident lines.
The spectrum B of the tube containing radium emanation is the
one which we are comparing with the other two. When the radium
emanation was first enclosed there was only a small quantity of
helium developed in it, but after keeping for a year the quantity
has greatly increased. After five minutes “sparking” (passage of
the electric spark through the tube) the chief lines of helium
become evident but faint in intensity. The present photograph B
was obtained after forty minutes sparking, and one result of that
longer “sparking” has been that a minute quantity of water vapour
in the tube has been broken up--_so as to yield the hydrogen
spectrum_, which is accordingly seen accompanying the now strong
and brightly developed helium spectrum.
The lines of the spectrum B which correspond with those of
hydrogen are at once recognised by the juxtaposition (below)
of the pure Hydrogen spectrum from another tube--C: the lines
in B belonging to and indicating helium are also recognised
by comparison with the pure helium spectrum of the tube A
juxta-posed above. A very few of the lines in B must be due to
other minimal impurities as they are not present either in A or
C.
Thirteen lines of the helium spectrum are thus photographed and
recognised in the radium emanation.
The following lines are present in the photographic but invisible
spectrum of radium (not given in fig. 10), viz. at 381·47 µµ (the
strongest line in the radium spectrum) and at 364·96 (a strong
line).
In the photographic but invisible spectrum of helium there are
three very faint lines between wave-length 447·2 and 443·7
(appearing as two only in our photograph); a moderately strong
one at 438·8; others at 414·4, at 412·1, at 402·6, and 396·5;
a very strong one is present at 388·9, and a very faint one
at 381·9. All these are seen in the photograph A and also in
B. Special treatment and spectroscopes reveal four other very
faint lines in the helium spectrum--the one furthest in the
invisible direction (that is of highest refrangibility and lowest
wave-length) being placed at 318·6 (Soddy).]
It must be obvious from all the foregoing that radium is very slowly,
but none the less surely, destroying itself. There is a definite
loss of particles which, in the course of time, must lead to the
destruction of the radium, and it would seem that the large new
credit on the bank of time given to biologists in consequence of
its discovery has a definite, if remote, limit. With the quantities
of radium at present available for experiment, the amount of loss
of particles is so small, and the rate so slow, that it cannot be
weighed by the most delicate balance. Nevertheless it has been
calculated that radium will transform half of itself in about fifteen
hundred years, and unless it were being produced in some way all of
the radium now in existence would disappear much too soon to make
it an important geological factor in the maintenance of the earth’s
temperature. As a reply to this depreciatory statement we have the
discovery by Rutherford and others that radium is continually being
formed afresh, and from that particular element in connection with
which it was discovered--namely, uranium. Hypotheses and experiments
as to the details of this process are at this moment in full swing,
and results of a momentous kind, involving the building-up of an
element with high atomic weight by the interaction of elements with
a lower atomic weight, are thought by some physicists to be not
improbable in the immediate future.
The delicate electric test for radio-activity has been largely
applied in the last few years to all sorts and conditions of matter.
As a result it appears that the radium emanation is always present in
our atmosphere; that the air in caves is especially rich in it, as
are underground waters. Tin-foil, glass, silver, zinc, lead, copper,
platinum and aluminium are, all of them, slightly radio-active. The
question has been raised whether this widespread radio-activity
is due to the wide dissemination of infinitesimal quantities of
strong radio-active elements, or whether it is the natural intrinsic
property of all matter to emit Becquerel rays. This is the immediate
subject of research.
Over and above the more simply appreciable facts which I have thus
narrated, there comes the necessary and difficult inquiry, What does
it all mean? What _are_ the Becquerel rays of radio-activity? What
must we conceive to be the structure and mechanism of the atoms of
radium and allied elements, which can not only pour forth ceaseless
streams of intrinsic energy from their own isolated substance, but
are perpetually, though in infinitesimal proportions, changing their
elemental nature spontaneously, so as to give rise to other atoms
which we recognise as other elements?
I cannot venture as an expositor into this field. It belongs to that
wonderful group of men, the modern physicists, who with an almost
weird power of visual imagination combine the great instrument of
exact statement and mental manipulation called mathematics, and
possess an ingenuity and delicacy in appropriate experiment which
must fill all who even partially follow their triumphant handling of
Nature with reverence and admiration. Such men now or recently among
us are Kelvin, Clerk Maxwell, Crookes, Rayleigh, and J. J. Thomson.
Becquerel showed early in his study of the rays emitted by radium
that some of them could be bent out of their straight path by making
them pass between the poles of a powerful electro-magnet. In this
way have finally been distinguished three classes of rays given off
by radium: (1) the _alpha_ rays, which are only slightly bent, and
have little penetrative power; (2) the _beta_ rays, easily bent in
a direction opposite to that in which the alpha rays bend, and of
considerable penetrative power; (3) the _gamma_ rays, which are
absolutely unbendable by the strongest magnetic force, and have an
extraordinary penetrative power, producing a photographic effect
through a foot thickness of solid iron.
The _alpha_ rays are shown to be streams of tiny bodies positively
electrified, such as are given off by gas flames and red-hot metals.
The particles have about twice the mass of a hydrogen atom, and they
fly off with a velocity of 20,000 miles a second; that is, 40,000
times greater than that of a rifle bullet. The heat produced by
radium is ascribed to the impact of these particles of the alpha
rays.
The _beta_ rays are streams of corpuscles similar to those given
off by the cathode in a vacuum tube. They are charged with negative
electricity and travel at the velocity of 100,000 miles a second.
They are far more minute than the alpha particles. Their mass is
equal to the one-thousandth of a hydrogen atom. They produce the
major part of the photographic and phosphorescent effects of the
radium rays.
The _gamma_ rays are apparently the same, or nearly the same, thing
as the X-rays of Röntgen. They are probably not particles at all,
but pulses or waves in the ether set up during the ejection of the
corpuscles which constitute the beta rays. They produce the same
effects in a much smaller degree as do the beta rays, but are more
penetrating.
The kind of conceptions to which these and like discoveries have led
the modern physicist in regard to the character of that supposed
unbreakable body--the chemical atom--the simple and unaffected
friend of our youth--are truly astounding. Nevertheless, they are
not destructive of our previous conceptions, but rather elaborations
and developments of the simpler views, introducing the notion of
structure and mechanism, agitated and whirling with tremendous force,
into what we formerly conceived of as homogeneous or simply built-up
particles, the earlier conception being not so much a positive
assertion of simplicity as a non-committal expectant formula awaiting
the progress of knowledge and the revelations which are now in our
hands.
As I have already stated, the attempt to show in detail how the
marvellous properties of radium and radio-activity in general are
thus capable of a pictorial or structural representation is beyond
the limits of the present essay; but the fact that such speculations
furnish a scheme into which the observed phenomena can be fitted is
what we may take on the authority of the physicists and chemists of
our day.
Intimately connected with all the work which has been done in the
past twenty-five years in the nature and possible transformations
of atoms is the great series of investigations and speculations on
astral chemistry and the development of the chemical elements which
we owe to the unremitting labour during this period of Sir Norman
Lockyer.
_Wireless telegraphy._--Of great importance has been the whole
progress in the theory and practical handling of electrical
phenomena of late years. The discovery of the Hertzian waves and
their application to wireless telegraphy is a feature of this
period, though I may remind some of those who have been impressed
by these discoveries that the mere fact of electrical action at a
distance is that which hundreds of years ago gave to electricity
its name. The power which we have gained of making an instrument
oscillate in accordance with a predetermined code of signalling,
although detached and a thousand miles distant, does not really
lend any new support[15] to the notion that the old-time beliefs of
thought-transference and second sight are more than illusions based
on incomplete observation and imperfect reasoning. For the important
factors in such human intercourse--namely, a signalling-instrument
and a code of signals--have not been discovered, as yet in the
structure of the human body, and have to be consciously devised and
manufactured by man in the only examples of thought-transference
over long distances at present discovered or laid bare to experiment
and observation.
_High and low temperatures._--The past quarter of a century has
witnessed a great development and application of the methods of
producing both very low and very high temperatures. Sir James Dewar,
by improved apparatus, has produced liquid hydrogen and a fall of
temperature probably reaching to the absolute zero. A number of
applications of extremely low temperatures to research in various
directions has been rendered possible by the facility with which
they may now be produced. Similarly high temperatures have been
employed in continuation of the earlier work of Deville, and others
by Moissan, the distinguished French chemist.
_Progress in Chemistry._--In chemistry generally the theoretical
tendency guiding a great deal of work has been the completion and
verification of the ‘periodic law’ of Mendeléeff; and, on the other
hand, the search by physical agents such as light and electricity for
evidence as to the arrangement of atoms in the molecules of the most
diverse chemical compounds. The study of ‘valency’ and its outcome,
stereo-chemistry, have been the special lines in which chemistry has
advanced. As a matter of course hundreds, if not thousands, of new
chemical bodies have been produced in the laboratory of greater or
less theoretical interest. The discovery of the greatest practical
and industrial importance in this connection is the production of
indigo by synthetical processes, first by laboratory and then by
factory methods, so as to compete successfully with the natural
product. Von Baeyer and Heumann are the names associated with this
remarkable achievement, which has necessarily dislocated a large
industry which derived its raw material from British India.
[Illustration: FIG. 12.
This figure should be examined with a magnifying glass. It is
a direct reproduction of a photograph of a detached nebula
and surrounding stars in Cygnus by Dr. Max Wolf of Heidelberg
(reproduced by permission from the Monthly Notices of the Royal
Astronomical Society, vol. lxiv, Plate 18, p. 839, q.v.). The
exposure was four hours on July 10th, 1904, with a camera the
lenses of which have a diameter of sixteen inches. The picture is
enlarged so that the apparent diameter of the Sun or Moon would
be about 1⅓ inch on the same scale (one minute, or sixtieth of a
degree, equals one millimetre).
The “apparent diameter” of the sun or moon is about one in 115:
that is to say that a covering disc of any size you like can be
made exactly to coincide with and “cover” the disc of the sun
or moon provided that you place it at a distance from the eye
equal to 115 times its own diameter--thus a disc of an inch in
diameter (say a halfpenny) will just “cover” the sun or moon if
placed at a distance from the eye of a little less than ten feet,
a threepenny piece will cover it at about six feet, and a disc of
somewhat less than half that size when held at arm’s length.
The nebula (on the horizontal A A) is seen surrounded by a dark
space--at the end of a long dark lane or “rift” which reminds us
of the track left by a snowball rolled along in the snow. Has the
nebula in some mysterious way swept up the stars in its journey
through space? We cannot at present either affirm or deny such
interpretations.
One or two of the brightest of the surrounding stars _might_ just
be seen by an acute eye unaided by a telescope--but no more. The
best existing telescopes would show _only_ the large nebular
body on the line A A, and the larger white spots; the finest
dust-like particles are stars of which the existence is only
demonstrated by prolonged photographic exposures such as this,
with a lens which focuses its image on to the _dry_ plate. The
old “wet-plate” would not remain wet sufficiently long to “take”
the picture.
It should be borne in mind in looking at this picture that each
of the minutest white spots is probably of at least the same size
as our own sun: further, that each is probably surrounded by a
planetary system similar to our own.]
_Astronomy._--A biologist may well refuse to offer any remarks on
his own authority in regard to this earliest and grandest of all the
sciences. I will therefore at once say that my friend the Savilian
Professor of Astronomy in Oxford has turned my thoughts in the right
direction in regard to this subject. There is no doubt that there has
been an immense ‘revival’ in astronomy since 1881; it has developed
in every direction. The invention of the ‘dry plate,’ which has
made it possible to apply photography freely in all astronomical
work, is the chief cause of its great expansion. Photography was
applied to astronomical work before 1881, but only with difficulty
and haltingly. It was the dry-plate (see Fig. 12) which made long
exposures possible, and thus enabled astronomers to obtain regular
records of faintly luminous objects such as nebulæ and star-spectra.
Roughly speaking, the number of stars visible to the naked eye may
be stated as eight thousand: this is raised by the use of our best
telescopes to some hundred million. But the number which can be
photographed is indefinite and depends on length of exposure: some
thousands of millions can certainly be so recorded.
The serious practical proposal to ‘chart the sky’ by means of
photography certainly dates from this side of 1881. The Paris
Conference of 1887, which made an international scheme for sharing
the sky among eighteen observatories (still busy with the work, and
producing excellent results), originated with photographs of the
comet of 1882, taken at the Cape Observatory.
Professor Pickering, of Harvard, did not join this co-operative
scheme, but has gradually devised methods of charting the sky very
rapidly, so that he has at Harvard records of the whole sky many
times over, and when new objects are discovered he can trace their
history _backwards_ for more than a dozen years by reference to his
plates. This is a wonderful new method, a mode of keeping record of
present movements and changes which promises much for the future of
astronomy. By the photographic method hundreds of new variable stars
and other interesting objects have been discovered. New planets have
been detected by the hundred. Up to 1881 two hundred and twenty were
known. In 1881 only one was found; namely, Stephania, being No. 220,
discovered on May 19. Now a score at least are discovered every year.
Over 500 are now known. One of these--Eros--(No. 433) is particularly
interesting, since it is nearer to the sun than is Mars, and gives
a splendid opportunity for fixing with increased accuracy the sun’s
distance from the earth. Two new satellites to Saturn and two to
Jupiter have been discovered by photography (besides one to Jupiter
in 1892 by the visual telescope of the Lick Observatory). One of the
new satellites of Saturn goes round that planet the _wrong way_, thus
calling for a fundamental revision of our ideas of the origin of the
solar system.
The introduction of photography has made an immense difference in
spectroscopic work. The spectra of the stars have been readily mapped
out and classified, and now the motions in the line of sight of
faint stars can be determined. This ‘motion in the line of sight,’
which was discernible but scarcely measurable with accuracy before,
now provides one of the most refined methods in astronomy for
ascertaining the dimensions and motions of the universe. It gives us
velocities in miles per second instead of in an angular unit to be
interpreted by a very imperfect knowledge of the star’s distance.
The method, initiated practically by Huggins thirteen years before,
was in 1881 regarded by many astronomers as a curiosity. Visual
observations were begun at Greenwich in 1875, but were found to be
affected by instrumental errors. The introduction of dry plates, and
their application by Vogel in 1887, was the beginning of general
use of the method, and line-of-sight work is now a vast department
of astronomical industry. Among other by-products of the method are
the ‘spectroscopic doubles,’ stars which we know to be double, and
of which we can determine the period of revolution, though we cannot
separate them visually by the greatest telescope.
Work on the sun has been entirely revolutionised by the use
of photography. The last decade has seen the invention of the
spectro-heliograph--which simply means that astronomers can now study
_in detail_ portions of the sun of which they could previously only
get a bare indication.
More of the same story could be related, but enough has been said to
show how full of life and progress is this most ancient and imposing
of all sciences.
A minor though very important influence in the progress of astronomy
has been the provision, by the expenditure of great wealth in
America, of great telescopes and equipments.
In 1877 Sir George Darwin started a line of mathematical research
which has been very fruitful and is of great future promise for
astronomy. As recently as last April, at the Royal Astronomical
Society, two important papers were read--one by Mr. Cowell and the
other by Mr. Stratton--which have their roots in Sir George Darwin’s
work. The former was led to suggest that the day is lengthening ten
times as rapidly as had been supposed, and the latter showed that in
all probability the planets had all turned upside down since their
birth.
And yet M. Brunetière and his friends wish us to believe that science
is bankrupt and has no new things in store for humanity.
_Geology._--In the field of geological research the main feature
in the past twenty-five years has been the increasing acceptance
of the evolutionary as contrasted with the uniformitarian view of
geological phenomena. The great work of Suess, ‘Das Antlitz der
Erde,’ is undoubtedly the most important contribution to physical
geology within the period. The first volume appeared in 1885, and the
impetus which it has given to the science may be judged of by the
epithet applied to the views for which Suess is responsible--‘the
New Geology.’ Suess attempts to trace the orderly sequence of the
principal changes in the earth’s crust since it first began to form.
He strongly opposes the old theory of elevation, and accounts for the
movements as due to differential collapse of the crust, accompanied
by folding due to tangential stress. Among special results gained by
geologists in the period we survey may be cited new views as to the
origin of the crystalline schists, favouring a return to something
like the hypogene origin advocated by Lyell; the facts as to deep-sea
deposits, now in course of formation, embodied in the ‘Challenger’
reports on that subject: the increasing discrimination and tracking
of those minor divisions of strata called ‘zones’; the assignment of
the Olenellus fauna of Cambrian age to a position earlier than that
of the Paradoxides fauna; the discovery of Radiolaria in palæozoic
rocks by special methods of examination, and the recognition of
Graptolites as indices of geological horizons in lower palæozoic
beds. Glacially eroded rocks in boulder-clays of permo-carboniferous
age have been recognised in many parts of the world (_e.g._,
Australia and South Africa), and thus the view put forward by W. T.
Blanford as to the occurrence of the same phenomena in conglomerates
of this age in India is confirmed. Eozoon is finally abandoned as
owing its structure to an organism. The oldest fossiliferous beds
known to us are still far from the beginning of life. They contain
a highly developed and varied animal fauna--and something like the
whole of the older moiety of rocks of aqueous origin have failed as
yet to present us with any remains of the animals or plants which
must have inhabited the seas which deposited them. The boring of a
coral reef initiated by Professor Sollas at the Nottingham meeting
of the British Association in 1893 was successfully carried out,
and a depth of 1,114½ feet reached. Information of great value to
geologists was thus obtained.
[Illustration: FIG. 13.
The Freshwater Jelly-fish of Regent’s Park (_Limnocodium
Sowerbii_) magnified five times linear.
It was discovered in the tropical lily tank of the Botanical
Gardens in June, 1880, and swarmed in great numbers year after
year--then suddenly disappeared. It has since been found in
similar tanks in Sheffield, Lyons, and Munich. Only male
specimens were discovered, and the native home of the wonderful
visitor is still unknown.]
[Illustration: FIG. 14.
The minute polyp attached to the rootlets of water-plants--from
which the Jelly-fish _Limnocodium_ was found to be ‘budded off.’]
[Illustration: FIG. 15.
One of the peculiar sense-organs from the edge of the swimming
disc of _Limnocodium_. C, cavity of capsule; EC, ectoderm; EN,
endoderm. Sense-organs of identical structure are found in
the Freshwater Jelly-fish of Lake Tanganyika and in no other
jelly-fish.]
_Animal and Vegetable Morphography._--Were I to attempt to give an
account of the new kinds of animals and plants discovered since 1881,
I should have to offer a bare catalogue, for space would not allow
me to explain the interest attaching to each. Explorers have been
busy in all parts of the world--in Central Africa, in the Antarctic,
in remote parts of China, in Patagonia and Australia, and on the
floor of the ocean as well as in caverns, on mountain tops, and
in great lakes and rivers. We have learnt much that is new as to
distribution; countless new forms have been discovered, and careful
anatomical and microscopical study conducted on specimens sent home
to our laboratories. I cannot refrain from calling to mind the
discovery of the eggs of the Australian duck-mole and hedgehog; the
freshwater jelly-fish (figs. 13, 14, and 15) of Regent’s Park, the
African lakes (fig. 16) and the Delaware River; the marsupial mole of
Central Australia; the okapi (figs. 17, 18, and 19); the breeding and
transformations of the common eel (fig. 20); the young and adult of
the mud-fishes of Australia, Africa, and South America; the fishes of
the Nile and Congo; the gill-bearing earth-worms and mud-worms; the
various forms of the caterpillar-like _Peripatus_; strange deep-sea
fishes, polyps and sponges.
[Illustration: FIG. 16.
The Freshwater Jelly-fish of Lake Tanganyika (_Limnocnida
Tanganyicae_), magnified five times linear. Since its discovery
in Tanganyika it has been found also in the Lake Victoria Nyanza
and in pools in the Upper Niger basin.]
[Illustration: FIG. 17.
The Giraffe-like animal called the Okapi, discovered by Sir Harry
Johnston in the Congo Forest. Photograph of the skin of a female
sent home by him in 1901, and now mounted and exhibited in the
Natural History Museum.]
[Illustration: FIG. 18.
Two “bandoliers” cut by the natives from the striped part of
the skin (the haunches) and at first supposed to be bits of the
hide of a new kind of Zebra. These were sent home by Sir Harry
Johnston in 1900.]
The main result of a good deal of such investigation is measured by
our increased knowledge of the pedigree of organisms, what used to
be called ‘classification.’ The anatomical study by the Australian
professors, Hill and Wilson, of the teeth and the fœtus of the
Australian group of pouched mammals--the marsupials--has entirely
upset previous notions, to the effect that these are a primitive
group, and has shown that their possession of only one replacing
tooth is a retention of one out of many such teeth (the germs of
which are present), as in placental mammals; and further that many of
these marsupials have the nourishing outgrowth of the fœtus called
the placenta fairly well developed, so that they must be regarded
as a degenerate side-branch of the placental mammals, and not as
primitive forerunners of that dominant series.
[Illustration: FIG. 19.
Photograph of the skull of a male Okapi--showing the paired boney
horn-cores--similar to those of the Giraffe, but connected with
the frontal bones and not with the parietals as the horn-cores of
Giraffes are.]
[Illustration: FIG. 20.
Drawings by Professor Grassi, of Rome, of the young of the common
Eel and its metamorphosis. All of the natural size. The uppermost
figure represents a transparent glass-like creature--which was
known as a rare “find” to marine naturalists, and received the
name _Leptocephalus_. Really it lives in vast numbers in great
depths of the sea--five hundred fathoms and more. It is hatched
here from the eggs of the common Eel which descends from the
ponds, lakes, and rivers of Europe in order to breed in these
great depths. The gradual change of the _Leptocephalus_ into a
young Eel or “Elver” is shown, and was discovered by Grassi. The
young Eels leave the great depth of the ocean and ascend the
rivers in immense shoals of many hundred thousand individuals,
and wriggle their way up banks and rocks into the small streams
and pools of the continent.
The above figures were published by Professor Grassi in November
1896, in the _Quarterly Journal of Microscopical Science_, edited
by E. Ray Lankester and published by Churchill & Sons.]
Speculations as to the ancestral connection of the great group of
vertebrates with other great groups have been varied and ingenious;
but most naturalists are now inclined to the view that it is a
mistake to assume any such connection in the case of vertebrates of
a more definite character than we admit in the case of starfishes,
shell-fish, and insects. All these groups are ultimately connected
by very simple, remote, and not by proximate ancestors, with one
another and with the ancestors of vertebrates.
[Illustration: FIG. 21.
The unicellular parasite _Benedenia_, from the gut of the
common Poulp or Octopus. 1 is the normal male individual; 2 and
3 show stages in the production of spermatozoa on its surface
by budding; 4, 5 and 6 show a female parasite with spermatozoa
approaching it.]
[Illustration: FIG. 22.
Production of spermatozoa on the surface of the unicellular
parasite _Coccidium oviforme_, from the Rabbit’s intestines.]
The origin of the limbs of vertebrates is now generally agreed to be
correctly indicated in the Thatcher-Mivart-Balfour theory to the
effect that they are derived from a pair of continuous lateral fins,
in fish-like ancestors, similar in every way to the continuous median
dorsal fin of fishes.
[Illustration: FIG. 23.
Spermatozoa (often called “microgametes”) of the unicellular
parasite _Echinospora_ found in the gut of the small Centipede
_Lithobius mutabilis_.]
The discovery of the formation of true spermatozoa by simple
unicellular animals of the group Protozoa is a startling thing, for
it had always been supposed that these peculiar reproductive elements
were only formed by multicellular organisms (figs. 21, 22, and 23).
They have been discovered in some of the gregarina-like animalcules,
the _Coccidia_, and also in the blood-parasites.
Among plants one of the most important discoveries relates to these
same reproductive elements, the spermatozoa, which by botanists are
called antherozoids. A great difference between the whole higher
series of plants, the flowering plants or phanerogams, and the
cryptogams or lower plants, including ferns, mosses, and algae,
was held to be that the latter produce vibratile spermatozoa like
those of animals which swim in liquid and fertilise the motionless
egg-cell of the plant. Two Japanese botanists (and the origin of this
discovery from Japan, from the University of Tokio, in itself marks
an era in the history of science), Hirase and Ikeno, astonished the
botanical world fifteen years ago by showing that motile antherozoids
or spermatozoa are produced by two gymnosperms, the ging-ko tree (or
_Salisburya_) and the cycads (fig. 24). The pollen-tube, which is
the fertilising agent in all other phanerogams, develops in these
cone-bearing trees, beautiful motile spermatozoa, which swim in a
cup of liquid provided for them in connection with the ovules. Thus
a great distinction between phanerogams and cryptogams was broken
down, and the actual nature of the pollen-tube as a potential parent
of spermatozoids demonstrated.
[Illustration: FIG. 24.
Spermatozoa (antherozoids) of _Cycas revoluta_, seen from the
side and from above. The spermatozoon is spherical, carrying a
spiral band of minute vibratile hairs (_cilia_) by which it is
propelled.]
When we come to the results of the digging out and study of extinct
plants and animals, the most remarkable results of all in regard
to the affinities and pedigree of organisms have been obtained.
Among plants the transition between cryptogams and phanerogams
has been practically bridged over by the discovery that certain
fern-like plants of the Coal Measures--the _Cycadofilices_, supposed
to be true ferns, are really seed-bearing plants and not ferns at
all, but phanerogams of a primitive type, allied to the cycads
and gymnosperms. They have been re-christened _Pteridosperms_ by
Scott, who, together with F. Oliver and Seward, has been the chief
discoverer in this most interesting field.
[Illustration: FIG. 25.
The gigantic three-horned Reptile, _Triceratops_, as large as an
Elephant, found in Jurassic strata in North America. A model of
the skeleton may be seen in the Natural History Museum in London.]
By their fossil remains whole series of new genera of extinct mammals
have been traced through the tertiary strata of North America and
their genetic connections established; and from yet older strata of
the same prolific source we have almost complete knowledge of several
genera of huge extinct _Dinosauria_ of great variety of form and
habit (fig. 25).
[Illustration: FIG. 26.
Photograph of the skeleton of a large carnivorous Reptile
from Triassic strata in North Russia, discovered by Professor
Amalitzky and named by him, _Inostransevia_. The head alone is
two feet in length.]
[Illustration: FIG. 27.
Photographs of completed models of the Devonian fish
_Drepanaspis_, from Devonian slates of North Germany, worked out
by Professor Traquair. The models are in the Natural History
Museum, London.]
[Illustration: FIG. 28.
The oldest fossil fish known--discovered in the Upper Silurian
strata of Scotland, and named _Birkenia_ by Professor Traquair.]
The discoveries by Seeley at the Cape, and by Amalitzky in
North Russia of identical genera of Triassic reptiles, which in
many respects resemble the Mammalia and constitute the group
_Theromorpha_, is also a prominent feature in the palæontology
of the past twenty-five years (fig. 26). Nor must we forget the
extraordinary Devonian and Silurian fishes discovered and described
by Professor Traquair (figs. 27 and 28). The most important discovery
of the kind of late years has been that of the Upper Eocene and
Miocene Mammals of the Egyptian Fayum, excavated by the Egyptian
Geological Survey and by Dr. Andrews of the Natural History Museum,
who has described and figured the remains. They include a huge
four-horned animal as big as a rhinoceros, but quite peculiar in
its characters--the _Arisinoïtherium_--and the ancestors of the
elephants, a group which was abundant in Miocene and Pliocene times
in Europe and Asia, and in still later times in America, and
survives at the present day in its representatives the African
and Indian elephant. One of the European extinct elephants--the
_Tetrabelodon_--had, we have long known, an immensely long lower
jaw with large chisel-shaped terminal teeth. It had been suggested
by me that the modern elephant’s trunk must have been derived
from the soft upper jaw and nasal area, which rested on this
elongated lower jaw, by the shortening (in the course of natural
selection and modification by descent) of this long lower jaw, to
the present small dimensions of the elephant’s lower jaw, and the
consequent down-dropping of the unshortened upper jaw and lips,
which thus become the proboscis. Dr. Andrews has described from
Egypt and placed in the Museum in London specimens of two new
genera--one _Palæomastodon_, in which there is a long, powerful
jaw, an elongated face, and an increased number of molar teeth (see
figs. 29 and 30); the second, _Meritherium_ (fig. 31), an animal
with a hippopotamus-like head, comparatively minute tusks, and a
well-developed complement of incisor, canine, and molar teeth, like a
typical ungulate mammal. Undoubtedly we have in these two forms the
indications of the steps by which the elephants have been evolved
from ordinary-looking pig-like creatures of moderate size, devoid of
trunk or tusks. Other remains belonging to this great mid-African
Eocene fauna indicate that not only the Elephants but the Sirenia
(the Dugong and Manatee) took their origin in this area. Amongst them
are also gigantic forms of Hyrax, like the little Syrian coney and
many other new mammals and reptiles.
[Illustration: FIG. 29.
Photograph of a complete model of the skull and lower jaw of the
ancestral elephant, _Palæomastodon_, discovered by Dr. Andrews
in the Upper Eocene of the Fayum Desert, Egypt, and modelled
and restored under his direction in the Natural History Museum,
London. The comparatively short trunk or snout rested on the
broad front teeth of the long lower jaw. The face is elongated,
and the cheek-teeth are numerous.]
[Illustration: FIG. 30.
Photograph of the lower face of the skull of a specimen of
_Palæomastodon_ brought from Egypt in April, 1906, by Dr.
Andrews, and now in the Natural History Museum, London. The
six characteristic cheek-teeth on each side, and the pair of
sabre-like tusks in front, are well seen.]
[Illustration: FIG. 31.
Drawing of the skull and lower jaw of the _Meritherium_,
discovered by Dr. Andrews in the Upper Eocene of the Fayum
Desert. The shape of the skull and proportions of face and jaw
are like those of an ordinary hoofed mammal such as the pig;
but the cheek-teeth are similar to those of the _Mastodon_, and
whilst the full complement of teeth is present in the front of
the upper jaw, we can distinguish the big tusk-like incisor which
alone survives on each side in _Palæomastodon_, _Mastodon_, and
the elephants, as the great pair of tusks.]
Another great area of exploration and source of new things has been
the southern part of Argentina and Patagonia, where Ameghino, Moreno,
and Scott of Princeton have brought to light a wonderful series of
extinct ant-eaters, armadilloes, huge sloths, and strange ungulates,
reaching back into early Tertiary times. But most remarkable has
been the discovery in this area of remains which indicate a former
connection with the Australian land surface. This connection is
suggested by the discovery in the Santa Cruz strata, considered to be
of early Tertiary date, of remains of a huge horned tortoise which is
generically identical with one found fossil in the Australian area of
later date, and known as _Miolania_. In the same wonderful area we
have the discovery in a cave of the fresh bones, hairy skin, and dung
of animals supposed to be extinct, viz., the giant sloth, _Mylodon_,
and the peculiar horse, _Onohippidium_. These remains seem to belong
to survivors from the last submergence of this strangely mobile
land-surface, and it is not improbable that some individuals of this
‘extinct’ fauna are still living in Patagonia. The region is still
unexplored and those who set out to examine it have, by some strange
fatality, hitherto failed to carry out the professed purpose of their
expeditions.
I cannot quit this immense field of gathered fact and growing
generalisation without alluding to the study of animal embryology
and the germ-layer theory, which has to some extent been superseded
by the study of embryonic cell-lineage, so well pursued by some
American microscopists. The great generalisation of the study
of the germ-layers and their formation seems to be now firmly
established--namely, that the earliest multicellular animals were
possessed of one structural cavity, the enteron, surrounded by a
double layer of cells, the ectoderm and endoderm. These _Enterocœla_
or _Cœlentera_ gave rise to forms having a second great body-cavity,
the cœlom, which originated not as a split between the two layers, as
was supposed twenty-five years ago by Haeckel and Gegenbaur and their
pupils, but by a pouching of the enteron to form one or more cavities
in which the reproductive cells should develop--pouchings which
became nipped off from the cavity of their origin, and formed thus
the independent cœlom. The animals so provided are the _Cœlomocœla_
(as opposed to the _Enterocœla_), and comprise all animals above
the polyps, jelly-fish, corals, and sea-anemones. It has been
established in these twenty-five years that the cœlom is a definite
structural unit of the higher groups, and that outgrowths from it to
the exterior (cœlomoducts) form the genital passages, and may become
renal excretory organs also. The vascular system has not, as it was
formerly supposed to have, any connection of origin with the cœlom,
but is independent of it, in origin and development, as also are
the primitive and superficial renal tubes known as nephridia. These
general statements seem to me to cover the most important advance
in the general morphology of animals which we owe to embryological
research in the past quarter of a century.[16]
Before leaving the subject of animal morphology I must apologise
for my inability to give space and time to a consideration of the
growing and important science of anthropology, which ranges from
the history of human institutions and language to the earliest
prehistoric bones and implements. Let me therefore note here the
discovery of the cranial dome of _Pithecanthropus_ in a river gravel
in Java--undoubtedly the most ape-like of human remains, and of great
age (see figs. 1 and 2); and, further, the Eoliths of Prestwich (see
figs. 3 and 4), in the human authorship of which I am inclined to
believe, though I should be sorry to say the same of all the broken
flints to which the name ‘Eolith’ has been applied. The systematic
investigation and record of savage races have taken on a new and
scientific character. Such work as Baldwin Spencer’s and Haddon’s in
Australasia furnish examples of what is being done in this way.
[Illustration: FIG. 32.