14 THE PRESIDENTIAL ADDRESS. 
negative electricity whose mass is only 1/1800 of that of an atom of 
hydrogen, and the other a particle of positive electricity whose mass is 
practically identical with that of the same atom—the outcome, in short, 
of the collective work of Soddy, Rutherford, J. J. Thomson, Collie, 
Moseley, and others—are pregnant facts which have completely altered 
the fundamental aspects of the science. Chemical philosophy has, in 
fact, now definitely entered on a new phase. 
Looking back over the past, some indications of the coming change 
might have been perceived wholly unconnected, of course, with the 
recent experimental work which has served to ratify it. In a short 
paper entitled ‘ Speculative Ideas respecting the Constitution of 
Matter,’ originally published in 1863, Graham conceived that the 
various kinds of matter, now recognised as different elementary sub- 
stances, may possess one and the same ultimate or atomic molecule 
existing in different conditions of movement. ‘This idea, in its essence, 
may be said to be as old as the time of Leucippus. To Graham as to 
Leucippus ‘ the action of the atom as one substance taking various 
forms by combinations unlimited, was enough to account for all the 
phenomena of the world. By separation and union with constant 
motion all things could be done.” But Graham developed the concep- 
tion by independent thought, and in the light of experimentally ascer- 
tained knowledge which the world owes to his labours. He might have 
been cognisant of the speculations of the Greeks, but there is no evi- 
dence that he was knowingly influenced by them. In his paper Graham 
uses the terms atom and molecule if not exactly in the same sense that 
modern teaching demands, yet very different from that hitherto required 
by the limitations of contemporary chemical doctrine. He conceives 
of a lower order of atoms than the chemical atom of Dalton, and founds 
on his conception an explanation of chemical combination based upon 
a fixed combining measure, which he terms the metron, its relative 
weight being one for hydrogen, sixteen for oxygen, and so on with the 
other so-called ‘elements.’ Graham, in fact, like Davy before him, 
never committed himself to a belief in the indiyisibility of the Daltonian 
atom. The original atom may, he thought, be far down. 
The idea of a primordial ylé, or of the essential unity of matter, has 
persisted throughout the ages, and, in spite of much experimental work, 
some of it of the highest order, which was thought to have demolished 
it, it has survived, revivified and supported by analogies and arguments 
drawn from every field of natural inquiry. This idea of course was at 
the basis of the hypothesis of Prout, but which, even as modified by 
Dumas, was held to be refuted by the monumental work of Stas. But, as 
pointed out by Marignac and Dumas, anyone who will impartially look 
at the facts can hardly escape the feeling that there must be some reason 
for the frequent recurrence of atomic weights differing by so little 
