Sept. 2, 1886] 
NATURE 
425 
Now as these facts in the distribution of organic forms are 
generally considered by biological experts to rank anong the 
weightiest evidences in favour of the origin of species by a 
process of evolution, it seems natural, in this case as in the 
other, to view existing elements not as primordial but as the 
gradual outcome of a process of development, possibly even of a 
“struggle for existence.” Bodies not in harmony with the 
present general conditions have disappeared or perhaps have 
never existed. Others—the asteroids among the elements— 
have come into being and have survived, but only on a limited 
scale; whilst a third class are abundant because surrounding 
conditions have been favourable to their formation and pre- 
servation. 
The analogy here suggested between elements and organ- 
isms is, indeed, not the closest, and must not be pushed too 
far. From the nature of the case there cannot occur in the 
elements a difference corresponding to the difference between 
living and fossil organic forms. The ‘‘great stone book” can 
tell us nothing of extinct elements. Nor would I for a moment 
suggest that any one of our present elements, however rare, is 
like a rare animal or plant in process of extinction ; that any new 
element is in the course of formation, or that the properties of ex- 
isting elements are gradually undergoing modification. All such 
changes must have been confined to that period so remote as 
not to be grasped by the imagination, when our earth, or rather 
the matter of which it consists, was in a state very different from 
its present condition. The epoch of elemental development is 
decidedly over, and I may observe that in the opinion of not a 
few biologists the epoch of organic development is verging upon 
its close. 
Making, however, every allowance for these distinctions, if 
evolution be a cosmic law, manifest in heavenly bodies, in 
organic individuals, and in organic species, we shall in all 
probability recognise it, though under especial aspects, ia 
those elements of which stars and organisms are in the last 
resort composed. 
Is there then, in the first place, any direct evidence of the 
transmutation of any supposed ‘‘element”’ of our existing list 
into another, or of its resolution into anything simpler ? 
To this question I am obliged to reply in the negative. 
I doubt whether any chemist here present could suggest a 
process which would hold out a reasonable prospect of dissociat- 
ing any of our accepted simple bodies. The highest tempera- 
tures and the most powerful electric currents at our disposal 
have been tried, and tried in vain. At one time there seemed a 
possibility at least that the interesting researches of Prof. Victor 
Meyer might show the two higher members of the halogen 
group, bromine and iodine, as entering upon the path of dis- 
sociation. These hopes have not been fulfilled. It may be 
said, in the general opinion of the most eminent and judicious 
chemists, that none of the phenomena thus elicited prove that 
even an approach has been made to the object in view. 
Even if we leave our artificial laboratories and seek an escape 
from the difficulty by observing the processes of the great 
laboratories of Nature, we feel no sufficiently firm ground. 
We find ourselves thus driven to indirect evidence—to that 
which we may glean from the mutual relations of the elementary 
bodies. Such evidence of great value is by no means lacking, 
and to this I now beg to direct attention. First, we may 
consider the conclusion arrived at by Herschel, and pursued by 
Clerk-Maxwell, that atoms bear the impress of manufactured 
articles. Let us look a little more closely at this view. A 
manufactured article may well be supposed to involve a manu- 
facturer. But it does something more: it implies certainly a raw 
material, and probably, though not certainly, the existence of 
by-products, residues, paraleipomena. What or where is here 
the raw material? Can we detect any form of matter which 
bears to the chemical elements a relation like that of a raw 
material to the finished product, like that, say, of coal-tar to 
alizarin? Or can we recognise any elementary bodies which 
seem like waste or refuse? Or are all the elements, according 
to the common view, co-equals? To these questions no direct 
answer is as yet forthcoming.$ 
And this leads us up to an hypothesis which, if capable of full 
demonstration, would show us that the accepted elements are 
not co-equal, but have been formed by a process of expansion or 
evolution. I refer to the well-known hypothesis of Prout, which 
regards the atomic weights of the elements as multiples, by a 
series of whole numbers, of unity = the atomic weight of 
hydrogen. Every one is aware that the recent more accurate 
determinations of the atomic weights of different elements do 
not by any means bring them into close harmony with the values 
which Prout’s law would require. Still, in no small number of 
cases the actual atomic weights approach so closely to those 
which the hypothesis demands, that we can scarcely regard the 
coincidence as accidental. Accordingly, not a few chemists of 
admitted eminence consider that we have here an expression of 
the truth, masked by some residual or collateral phenomena 
which we have not yet succeeded in eliminating. 
The original calculations on which the most accurate numbers 
for the atomic weights are founded, have recently been re- 
calculated by Mr. F. W. Clarke. In his concluding remarks, 
speaking of Prout’s law, Mr. Clarke says that ‘‘none of the 
seeming exceptions are inexplicable. In short, admitting half- 
multiples as legitimate, it is more probable that the few ap- 
parent exceptions are due to undetected constant errors than 
that the great number of close agreements should be merely 
accidental. I began this re-calculation of the atomic weights 
with a strong prejudice against Prout’s hypothesis, but the facts 
as they came before me have forced me to give it a very respect- 
ful consideration.”’ 
But if the evidence in favour of Prout’s hypothesis in its 
original guise is deemed insufficient, may not Mr. Clarke's sug- 
gestion of half-multiples place it upon an entirely new basis ? 
Suppose that the unit ofthe scale, the body whose atomic weight 
if multiplied by a series of whole numbers gives the atomic 
weights of the remaining elements, is not hydrogen, but some 
element of still lower atomic weight? We are here at once 
reminded of helium—an element purely hypothetical as far as 
our earth is concerned, but supposed by many authorities, on the 
faith of spectroscopic observations, to exist in the sun and in other 
stellar bodies. Most solar eruptions present merely the charac- 
teristic lines of hydrogen, C, F, and H, and along with them 
one particular line which at first was classed in the sodium 
group, but which is a little more refrangible, and is designated 
by the symbol D3. According to Mr. Norman Lockyer and the 
late Father Secchi, this ray undergoes modifications not compar- 
able to those affecting other rays of the chromosphere. In the 
corresponding region of the spectrum no dark ray has been 
observed. That the accompanying lines, C, F, and H, pertain 
to hydrogen is evident ; and as D, has never been obtained in 
any other spectrum it is supposed to belong to a body foreign to 
our earth, though existing in abundance in the chromosphere 
of the sun. To this hypothetical body the name helium is 
assigned. 
In an able memoir on this subject read before the Academy of 
Brussels, the Abbé E. Spée shows that, if helium exists, it 
enjoys two very remarkable properties. Its spectrum consists of 
a single ray, and its vapour possesses no absorbent power. The 
simple single ray, though I believe unexampled, is by no means 
an impossible phenomenon, and indicates a remarkable simplicity 
of molecular constitution. The non-absorbent property of its 
vapour seems to be aserious objection to a general physical law. 
Prof. Tyndall has demonstrated that the absorptive power in- 
creases with the complexity of molecular structure, and hence he 
draws the conclusion that the simpler the molecule the feebler 
the absorption. This conclusion the Abbé Spce regards as 
perfectly legitimate ; but it neither explains nor even necessitates 
the absence of a// absorptive power. 
Granting that helium exists, all analogy points to its atomic 
weight being below that of hydrogen. Here, then, we may have 
the very element with atomic weight half that of hydrogen, re- 
quired by Mr. Clarke as the basis of Prout’s law. 
But a more important piece of evidence for the compound 
nature of the chemical elements has yet to be considered. Many 
chemists must have been struck with certain peculiarities in the 
occurrence of the elements in the earth’s crust; it is a stale 
remark that we do not find them evenly distributed throughout 
the globe. Nor are they associated in accordance with their 
specific gravities; the lighter elements placed on or near the 
surface, and the heavier ones following serially deeper and 
deeper. Neither can we trace any distinct relation between local 
climate and mineral distribution. And by no means can we say 
that elements are always or chiefly associated in Nature in the 
order of their so-called chemical affinities ; those which have a 
strong tendency to form with each other definite chemical com- 
binations being found together, whilst those which have little or 
no such tendency exist apart. We certainly find calcium as 
