August 26, 1909] 



NA TURE 



251 



of students between the universities in the Mother Country 

 and those in the Colonies. 



I am quite sure that many of our English students, 

 especially those destined for public life, could have no 

 more valuable experience than to spend a year in one or 

 other of vour universities, and I hope some of your students 

 might profit by a visit to ours. 



1 can think of nothing more likely to lead to a better 

 understanding of the feelings, the sympathies, and, what 

 is not less important, the prejudices, of one country by 

 another, than by the youths of those countries spending 

 a part of their student life together. Undergraduates as 

 a rule do not wear a mask either of politeness or any 

 other material, and have probably a better knowledge of 

 each other's opinions and points of view — in fact, know 

 each other. better than do people of riper age. To bring 

 this communion of students about there must be coopera- 

 tion between the universities throughout the Empire ; 

 there must be recognition of each other's examinations, 

 residence, and degrees. Before this can be accomplished 

 there must, as my friend Mr. E. B. Sargant pointed out 

 in a lecture given at the McGill University, be coopera- 

 tion and recognition between the universities in each part 

 of the Empire. I do not mean for a moment that all 

 universities in a country should be under one government. 

 I am a strong believer in the individuality of universities, 

 but I do not think this is in any way inconsistent with 

 the policy of an open door from one university to every 

 other in the Empire. 



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 concep- 

 tions 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 un- 

 suspected properties of matter and electricity have been 

 discovered. The history of this period affords a remark- 

 able illustration of the effect which mav be produced 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. \ striking 

 discovery like that of the Rontgen 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 

 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 manv 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 Rontgen rays on the progress of science has mainlv 

 been due ; it is rather because these ravs make gases, 

 and, indeed, solids and liquids, through which they pass 

 conductors of electricity. It is true that before the dis- 

 covery of these rays other methods of making gases con- 

 ductors were known, but none of these was so convenient 

 for the purposes of accurate measurement. 



The study of gases exposed to Rontgen ravs has revealed 

 in such gases the presence of particles charged with elec- 

 tricity ; 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 



NO. 2078, VOL. 81] 



they move under an electric force, the rate at which the 

 oppositely charged ones recombine, and these investiga- 

 tions 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 hydrogen 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 perfectly definite and known amount. 



Helmholtz said in 1880 that in his opinion the evidence 

 in favour of the molecular constitution of electricity was 

 even stronger than that in favour of the molecular con- 

 stitution of matter. How much stronger is that evidence 

 now, when we have measured the charge on the unit and 

 found it to be the same from whatever source the electricity 

 is obtained. Nay, further, the molecular theory of matter 

 is indebted to the molecular theory of electricity for the 

 most accurate determination of its fundamental quantity, 

 the number of molecules in any given quantity of an 

 elementary substance. 



The great advantage of the electrical methods for the 

 study of the properties of matter is due to the fact that 

 whenever a particle is electrified it is very easily identified, 

 whereas an uncharged molecule is most elusive ; and it is 

 only when these are present in immense numbers that we 

 are able to detect them. .A very simple calculation will 

 illustrate the difference in our power of detecting electrified 

 and unelectrified molecules. The smallest quantity of un- 

 electrified matter ever detected is probably that of neon, 

 one of the inert gases of the atmosphere. Prof. Strutt 

 has shown that the amount of neon in i/20th of a cubic 

 centimetre of the air at ordinary pressures can be detected 

 by the spectroscope ; Sir William Ramsay estimates that 

 the neon in the air only amounts to one part of neon in 

 100,000 parts of air, so that the neon in i/20th of a cubic 

 centimetre of air would only occupy at atmospheric pressure 

 a volume of half a millionth of a cubic centimetre. When 

 stated in this form the quantity seems exceedingly small, 

 but in this small volume there are about ten million million 

 molecules. Now the population of the earth is estimated 

 at about fifteen hundred millions, so that the smallest 

 number of molecules of neon we can identify is about 7,000 

 times the population of the earth. In other words, if we 

 had no better test for the existence of a man than we 

 have for that of an unelectrified molecule we should come 

 to the conclusion that the earth is uninhabited. Contrast 

 this with our power of detecting electrified molecules. We 

 can bv the electrical method, even better by the cloud 

 method of C. T. R. Wilson, detect the presence of three 

 or four charged particles in a cubic centimetre. Ruther- 

 ford has shown that we can detect the presence of a single 

 a particle. Now the a particle is a charged atom of 

 helium ; if this atom had been uncharged we should have 

 required more than a million million of them, instead of 

 one, before we should have been able to detect them. 



We may, I think, conclude, since electrified particles 

 can be studied with so much greater ease than unelectrified 

 ones, that we shall obtain a knowledge of the ultimate 

 structure of electricitv before we arrive at a corresponding 

 degree of certainty with regard to the structure of matter. 



We have already made considerable progress in the task 

 of discovering what the structure of electricity is. We 

 have known for some time that of one kind of electricity 

 — the negative — and a very interesting one it is. We 

 know that negative electricity is made up of units all of 

 which are of the same kind ; that these units are exceed- 

 inglv small compared with even the smallest atom, for 

 the mass of the unit is only 1/ 1700th part of the mass of 

 an atom of hydrogen; that its radius is only 10-" centi- 

 metre, and that these units, " corpuscles " as thev have 

 been called, can be obtained from all substances. The size 

 of these corpuscles is on an altogether different scale from 

 that of atoms ; the volume of a corpuscle bears to that 

 of the atom about the same relation as that of a speck 

 of dust to the volume of this room. Under suitable con- 

 ditions thev move at enormous speeds, which approach in 

 some instances the velocity of light. 



The discovery of these corpuscles is an interesting ex- 

 ample of the way Nature responds to the demands; rnade 

 upon her by mathematicians. Some years before the dis- 



