258 



SCIENCE 



[N. S. Vol. LIV. No. 1395 



tion : " What is the inner mechanism of the 

 atom?" 



If the properties and affections of matter 

 are dependent upon the inner mechanism of 

 the atom, an atomic theory, to be valid, 

 must comprehend and explain the all. There 

 can not be one kind of atom for the physicist 

 and another for the chemist. The nature of 

 chemical affinity and of valency, the modes 

 of their action, the difference in characteris- 

 tics of the chemical elements, even their 

 number, internal constitution, periodic posi- 

 tion, and possible isotopic rearrangements 

 must be accounted for and explained by it. 

 Fifty years ago chemists, for the most part, 

 rested in the comfortable belief of the exist- 

 ence of atoms in the restricted sense in which 

 Dalton, as a legacy from N^ewton, had im- 

 agined them. Lord Kelvin, unlike the chem- 

 ists, had never been in the habit of " evading 

 questions as to the hardness or indivisibility 

 of atoms by virtually assuming them to be 

 infinitely small and infinitely numerous." 

 IN'or, on the other hand, did he realize, with 

 Boscovich, the atom " as a mystic point en- 

 dowed with inertia and the attribute of at- 

 tracting or repelling other such centers." 

 Science advances not so much by funda- 

 mental alterations in its beliefs as by addi- 

 tions to them. Dalton would equally have 

 regarded the atom " as a piece of matter of 

 measurable dimensions, with shape, motion, 

 and laws of action, intelligible subjects of 

 scientific investigation." 



In spite of the fact that the atomic theory, 

 as formulated by Dalton, has been generally 

 accepted for nearly a century, it is only with- 

 in the last few years that physicists have ar- 

 rived at a conception of the structure of the 

 atom sufficiently precise to be of service to 

 chemists in connection with the relation be- 

 tween the properties of elements of different 

 kinds, and in throwing light on the mechan- 

 ism of chemical combination. 



This further investigation of the " superla- 

 tively grand question — the inner mechanism 

 of the atom," — has profoundly modified the 

 basic conceptions of chemistry. It has led to 

 a great extension of our views concerning the 



real nature of the chemical elements. The 

 discovery of the electron, the production of 

 helium in the radioactive disintegration of 

 atoms, the recognition of the existence of 

 isotopes, the possibility that all elementary 

 atoms are composed either of helium atoms or 

 of atoms of hydrogen and helium, and that 

 these atoms, in their turn, are built up of two 

 constituents, one of which is the electron, a 

 particle of negative electricity whose mass is 

 only 1/1800 of that of an atom of hydrogen, 

 and the other a particle of positive electi'icity 

 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 definite- 

 ly entered on a new phase. 



Looking back over the past, some indica- 

 tions 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 constitu- 

 tion of matter," originally published in 1863, 

 Graham conceived that the various kinds of 

 matter, now recognized as different elementary 

 substances, may possess one and the same 

 ultimate or atomic molecule existing in differ- 

 ent conditions of movement. This idea, in 

 its essence, may be said to be as old as the 

 time of Leucippus. To Graham as to Leucip- 

 pus " the action of the atom as one substance 

 taking various forms by combinations un- 

 limited, 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 con- 

 ception by independent thought, and in the 

 light of experimentally ascertained knowl- 

 edge which the world owes to his labors. 

 He might have been cognizant of the 

 speculations of the Greeks, but there is 

 no evidence that he was knowingly influ- 

 enced by them. In his paper Graham uses 

 the terms atom and molecule if not exactly 

 in the same sense that modern teaching de- 



