18 PRESIDENT’S ADDRESS. 
Berkeley’s logical jibes against the Newtonian ideas of fluxions 
and limiting ratios cannot be adequately appeased in the rigorous 
mathematical conscience until our apparent continuities are re- 
solved mentally into discrete aggregates which we only partially 
apprehend. The irresistible impulse to atomise everything thus 
proves to be not merely a disease of the physicist: a deeper 
origin, in the nature of knowledge itself, is suggested.’ 
One very valid excuse for this prevalent attitude is the astonishing 
progress that has been made in actually seeing, or almost seeing, the 
molecules, and studying their arrangement and distribution. 
The laws of gases have been found to apply to emulsions and to 
fine powders in suspension, of which the Brownian movement has 
long been known. This movement is caused by the orthodox mole- 
cular bombardment, and its average amplitude exactly represents the 
theoretical mean free path calculated from the ‘ molecular weight ’ of 
the relatively gigantic particles. The behaviour of these microscopi- 
cally visible masses corresponds closely and quantitatively with what 
could be predicted for them as fearfully heavy atoms, on the kinetic 
theory of gases; they may indeed be said to constitute a gas with a 
gram-molecule as high as 200,000 tons; and, what is rather important 
as well as interesting, they tend visibly to verify the law of equiparti- 
tion of energy even in so extreme a case, when that law is properly 
stated and applied. 
Still more remarkable—the application of X-rays to display the 
arrangement of molecules in crystals, and ultimately the arrangement 
of atoms in molecules, as initiated by Professor Laue with Drs. 
Friedrich and Knipping, and continued by Professor Bragg and his 
son and by Dr. Tutton, constitute a series of researches of high interest 
and promise. By this means many of the theoretical anticipations of 
our countryman, Mr. William Barlow, and—working with him—Pro- 
fessor Pope, as well as of those distinguished crystallographers yon 
Groth and von Fedorow, have been confirmed in a striking way. 
These brilliant researches, which seem likely to constitute a branch of 
Physics in themselves, and which are being continued by Messrs. 
Moseley and C. G. Darwin, and by Mr. Keene and others, may be 
called an apotheosis of the atomic theory of matter. 
One other controversial topic I shall touch upon in the domain 
of physics, though I shall touch upon it lightly, for it is not a matter 
for easy reference as yet. If the ‘ Principle of Relativity’ in an 
extreme sense establishes itself, it seems as if even Time would become 
discontinuous and be supplied in atoms, as money is doled out in 
pence or centimes instead of continuously ;—in which case our cus- 
tomary existence will turn out to be no more really continuous than 
