1909] 



SCIENCE 



2H3 



think this is in anj^ way inconsistent with 

 the policy of an open door from one uni- 

 versity to every other in the empire. 



It has usually been the practise 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 honor 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 con- 

 ceptions of physical processes to M'hich 

 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 his- 

 tory of this period affords a remarkable 

 illu.stration of the effect which may be pro- 

 duced by a single discovery; for it is, I 

 think, to the discovery of the Rontgen rays 

 that we owe the rapidity of the progress 

 which has recently been made in physics. 

 A striking discovery like that of the Ront- 

 gen 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 Rontgen rays 

 was the department of physics dealing with 

 the discharge of electricity through gases, 

 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 elec- 

 tricity was to be found in a vacuum tube. 

 Rontgen, in 1S95, showed that when elec- 

 tricity 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 fascina- 

 tion of this discovery attracted many work- 

 ers to the subject of the discharge of elec- 

 tricity through gases, and led to great im- 

 provements in the instruments used in this 

 type of research. It is not, however, to 

 the power of probing dark places, impor- 

 tant though this is, that the influence of 

 Rontgen 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 conduc- 

 tors 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 Rontgen 

 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. 



We know from these investigations that 

 electricity, like matter, is molecular in 

 structure, that just as a quantity of hydro- 

 gen is a collection of an immense number 

 of small particles called molecules, so a 

 charge of electricity is made up of a great 

 number of small charges, each of a per- 

 fectly definite and known amount. 



Ilelmholtz said in 1880 that in his opin- 

 ion the evidence in favor of the molecular 

 constitution of electricity was even stronger 

 than that in favor of the molecular consti- 



