10 PRESIDENT’S ADDRESS. 
It has usually been the practice of the President of this Association 
to give some account of the progress made in the last few years in the 
branch of science which he has the honour to represent. 
I propose this evening to follow that precedent and to attempt to 
give a very short account of some of the more recent developments of 
physics, and the new conceptions of physical processes to which they 
have led. 
The period which has elapsed since the Association last met in Canada 
has been one of almost unparalleled activity in many branches of physics, 
and many new and unsuspected properties of matter and electricity have 
been discovered. The history of this period affords a remarkable illustra- 
tion of the effect which may be produced by a single discovery ; for it is, I 
think, to the discovery of the Réntgen rays that we owe the rapidity of the 
progress which has recently been made in physics. A striking discovery 
like that of the Réntgen rays acts much like the discovery of gold in a 
sparsely populated country ; it attracts workers who come in the first place 
for the gold, but who may find that the country has other products, other 
charms, perhaps even more valuable than the gold itself. The country 
in which the gold was discovered in the case of the Réntgen rays was the 
department of physics dealing with the discharge of electricity through 
zases, a subject which, almost from the beginning of electrical science, 
had attracted a few enthusiastic workers, who felt convinced that the key 
to unlock the secret of electricity was to be found in a vacuum tube. 
Rontgen, in 1895, showed that when electricity passed through such a 
tube, the tube emitted rays which could pass through bodies opaque 
to ordinary light; which could, for example, pass through the flesh of 
the body and throw a shadow of the bones on a suitable screen. The 
fascination of this discovery attracted many workers to the subject of 
the discharge of electricity through gases, and led to great improvements 
in the instruments used in this type of research. It is not, however, to 
the power of probing dark places, important though this is, that the 
influence of Réntgen rays on the progress of science has mainly been due; 
it is rather because these rays make gases, and, indeed, solids and liquids, 
through which they pass conductors of electricity. It is true that before 
the discovery of these rays other methods of making gases conductors 
were known, but none of these was so convenient for the purposes of 
accurate measurement. 
The study of gases exposed to Réntgen rays has revealed in such gases 
the presence of particles charged with electricity ; some of these particles 
are charged with positive, others with negative electricity. 
‘The properties of these particles have been investigated; we know 
the charge they carry, the speed with which they move under an electric 
force, the rate at which the oppositely charged ones recombine, and these 
investigations have thrown a new light not only on electricity, but also 
on the structure of matter. 
