June 1, 1899] 
NARORE 
105 
bryonic development present a remarkable uniformity 
throughout the whole of the zoological series; and 
although knowledge is still limited, some authorities hold 
that there is the closest possible connection between the 
development of the individual and the development of 
the whole series of animal life. There are others, how- 
ever, who do not regard the argument derived from 
embryology as a very convincing one. However this may 
be, if we study the embryos of the tortoise, fowl, dog and 
man, we find that there is a wonderful similarity between 
them ata certainstage. Ata further stage of development 
the similarity is still borne out. This does not mean 
that a vertebrate animal during its development first of 
all becomes a tortoise, and then the various animals 
which are represented by these embryos; it simply 
means that they are all related inasmuch as there is 
continuity. 
After these references to plants and animals it should 
be clear what organic evolution really is, and therefore 
what evolution is generally. I wish next to bring before 
you some considerations having relation to the strati- 
graphical record. 
The question for us now is—Is there any equivalent to 
this in the inorganic world? or, to put it in another way, 
in those facts which have been revealed to us by the 
presence of the various chemical forms in the stellar 
strata represented by stars of varying temperatures? 
That is the question. 
When I referred in my last course of Lectures here 
to cosmical evolution, I said that there we dealt with a 
continuity of effects accompanied by considerable changes 
of temperature; from the gradual coming together of 
meteoritic swarms until eventually we had a mass of 
matter cold and dark in space. The various stars which 
represent the different changes have been got out and 
have, in fact, been arranged along a so-called temperature 
curve. As we ascend one branch of this curve the stars 
get gradually hotter and hotter till ultimately at the top 
we find the hottest stars that we know of. Then on the 
descending branch are represented the cooling bodies, 
and finally they come down in temperature until we reach 
that of a dark world like the companion of Sirius, of our 
own moon, and the planet in which we dwell. 
We can now deal with all these bodies in relation to 
their chemistry. We find that in the hottest stars we get 
a very small number of chemical elements ; as we come 
down from the hottest star to the cooler ones the number 
of spectral lines increases, and with the number of lines of 
course the number of chemical elements. I will only refer 
to the known substances, it looks as if at present we have 
still many unknowns to battle with. In the hottest stars 
of all, we deal with a form of hydrogen which we do not 
know anything about here (but which we suppose to be 
due to the presence of a very high temperature), hydro- 
gen as we know it, the cleveite gases, and magnesium 
and calcium in forms which are difficult to get here ; we 
think we get them by using the highest temperatures 
available in our laboratories. In the stars of the next 
lower temperature we find the existence of these things 
continued in addition to the introduction of oxygen, 
nitrogen and carbon. In the next cooler stars we get 
silicium added; in the next we get the forms of iron, 
titanium, copper and manganese which we can produce 
at the very highest temperatures in our laboratories; and 
it is only when we come to stars much cooler that we find 
the ordinary indications of iron, calcium and manganese 
and other metals. All these, therefore, seem to be forms 
produced by the running down of temperature. As 
certain new forms are introduced at each stage, so certain 
old forms disappear. In order to connect this work with 
the stratigraphical work, to which I have referred, I have 
recently tried to define these various star-stages by means 
NO. 1544, VOL. 60] 
of their chemical forms which they reveal to us; so that 
we may treat these stellar strata, so to speak, as the 
equivalent of the geological strata to which I have already 
called your attention. 
From the hottest to the coldest stars I have found ten 
groups so distinct from each other chemically that they 
require to be dealt with separately as completely as do 
the Cambrian and the Silurian formations. Imitating 
the geologist, I have given the following names to these 
groups or genera beginning with the hottest, that is the 
oldest dealing with the running down of temperature :— 
Argonian, Alnitamian, Achernian, Algolian, Markabian 
[a “break in strata”], Sirian, Procyonian, Arcturian 
(solar), Piscian. 
I have gone further, and defined the chemical nature 
of these stellar genera as the biologist defines the nature 
of any of his organic genera ; we can say, for instance, 
that the Achernian stars contain chiefly hydrogen, 
nitrogen, oxygen and carbon, and to a certain less extent 
they contain proto-magnesium, proto-calcium, silicium 
and sodium,! and possibly chlorine and lithium ; so that 
at last, by means of this recent development of spectrum 
analysis, we have been able really to do for the various 
stars what the biologist a good many years ago did for 
the geological strata. 
Now, considering this inorganic evolution from the 
chemical point of view, there are several matters which 
merit consideration. We shall not get much help by 
thinking along several obvious lines, for the reason that 
in the stars we are dealing with transcendental tem- 
peratures ; for instance, we must not make too much of 
the difference between gases and solids, because, at high 
temperatures all the chemical elements known to us as 
solids are just as gaseous as the gases themselves ; that 
is to say, they exist as gases; at a high temperature, 
everything, of course, will put on the nature of gas. 
Those substances with the lowest melting points, such 
as lithium and sodium, will, of course, under our present 
conditions put on the gaseous condition very much 
more readily than other substances like iron and 
platinum, but those are considerations which need not 
be taken into account in relation to very high stellar 
temperatures ; of course, there would be no solids at a 
temperature of 10,000" C. 
Then with regard to metals and non-metals. Here 
again we really are not greatly helped by this distinc- 
tion. The general conception of a metal is that it is a 
solid, and that therefore a thing that is not a solid is not 
a metal; but the chemical evidence for the metallic 
nature of hydrogen has been enlarged upon by several 
very distinguished chemists. With regard to non- 
metals, there are certainly very many. Carbon is sup- 
posed to be a non-metal, and it is remarkable that, so 
far as the stellar evidence which I have brought before 
you has gone, carbon seems to be the only certain 
representative of that group. I want to point out 
specially that the table of the chemical definitions of the 
various stellar genera which I show you, which contains 
nothing but hard facts, is perhaps, like the geological 
record, more important on account of what it indicates 
as to the presence of the chemical elements in the stars 
than it is for what it omits. 
There are a great many reasons why some of the 
substances which may exist in these stars should not 
make their appearance. I wish to enlarge upon the 
fact that, seeing the very small range of our photo- 
graphs of stellar spectra, and seeing that it does not at 
all follow that the particular crucial lines of the various 
chemical substances will reveal themselves in that 
particular part of the spectrum which we can photo- 
graph, that the negative evidence is of very much less 
importance than the positive evidence. I think it is 
very likely, for instance, that we must add lithium to 
1 Campbell, ‘* Astronomy and Astro-physics,” 1894, Xili. p- 395. 
