SEPTEMBER 1, 1899.] 
vibrations are simple and unitary in nature. 
Lockyer’s most recent work, following up 
the line of his ‘ Working Hypothesis’ of 
twenty years ago, is very suggestive and 
may lead to important results (Chemistry 
of the Hottest Stars, Roy. Soe. Proc., LXI., 
148 ; On the Order of Appearance of Chem- 
ical Substances at Different Temperatures, 
Chem. News, 79, 145). Still too much must 
be assumed yet for such work to be very 
conclusive. He writes of ‘ proto-magnesium 
and proto-calcium,’ and Pickering discusses 
a ‘new hydrogen,’ all with an assurance 
and confidence which proves at least how 
deeply these changes in the spectra have 
impressed some of those who have most 
deeply studied them. 
But a more important method of indi- 
rectly testing the question is through a 
comparison of the properties of the atoms. 
Such a comparison has been made as to the 
atomic weights. In other words, the idea 
of the composite nature of the elements fol- 
lowed very close upon the adoption of a 
stricter definition of them as simple bodies. 
Dalton, Prout, Dobereiner, Dumas, Cooke 
and many others have aided in developing 
the idea, sometimes faultily and harmfully, 
at other times helpfully. Some fell into the 
common error of going too far, but all were 
struck by the fact that when these com- 
bining numbers, or atomic weights, were 
compared strange and interesting sym- 
metries appeared. The times were not ripe 
for an explanation of their meaning, and 
such crude assumptions as that of Prout, 
that the elements were composed of hydro- 
gen, or that of Low, that they were made 
up of carbon and hydrogen, were too base- 
less to command much genuine support or 
to withstand much careful analysis. The 
important feature of agreement between 
such theories was the belief that the ele- 
ments were composite and had one or more 
common constituents. 
From the comparison of one property, 
- SCIENCE. 
279 
the atomic weights, the nextstep was to the 
comparison of all the properties. This com- 
parison is brought out clearest and best for 
us in the Periodic System. Here all the 
properties are very carefully tabulated for 
us. The study of the system leads indis- 
putably to the conviction that this is not an 
arbitrary, but a natural arrangement, ex- 
ceedingly simple in its groundwork, but 
embodying most fascinating symmetries, 
which hint of great underlying laws. He 
who looks upon it as a mere table of atomic 
weights has lost its meaning. It tells, with 
no uncertain note, of the kinship of the ele- 
ments and leads to a search after the secret 
of this interdependence and of their common 
factor or factors. There is so much which 
is made clearer if we assume a composite 
nature for the elements that many do not 
hesitate to make the assumption. 
Still another indirect method of approach- 
ing that problem is by analogy with bodies 
whose nature and cemposition are known. 
A very striking symmetry is observed be- 
tween the hydrocarbons, and these in the 
form of compound radicals show a strong 
resemblance to certain of the elements. 
This analogy need not be dwelt upon here. 
It has been recognized for a long time and 
tables of hydrocarbons have been con- 
-structed after the manner of the Periodic 
System. Now these bodies are simply built 
up of carbon and hydrogen in varying pro- 
portions, and in any one homologous series 
the increments areregular. We know that 
they are composite and that they have but 
two common factors, carbon and hydrogen. 
Again, the fact that certain groups of as- 
sociated atoms behave as one element and 
closely resemble known elements may be 
taken as a clue to the nature of the ele- 
ments. Thus carbon and nitrogen, in the 
form of cyanogen, behave very much like © 
the halogens ; and nitrogen and hydrogen 
in the form of ammonia so closely resemble 
the group of elements known as the alkalies 
