8- INAUGURAL ADDRESS. 



coiistniction which was vagTjely thought of a few years ago, but has 

 only now acquired some degree of precision. The idea has recently 

 received further support from the remarkable experiments of J. J. 

 Thomson on positive rays. It seems that these rays, when formed in 

 the vacuum tube, consist of atoms of helium and atoms of hydrogen, 

 ifo matter what other materials the tube contains, and even if hydro- 

 gen aiid helium have been carefully excluded in the manufacture of the 

 tube. This suggests that helium, as before, and now hydrogen also, 

 are building materials used in the construction of atoms. But we 

 cannot g:o much further as yet; if we tiy to do so we find ourselves in 

 the midst of great uncertainties. We see that the alpha particle 

 appears to be a frequent subdivision of the atom ; and we know 

 further that every atom contains electrons ; but the number of the 

 latter is doubtful, and is indeed greatly debated at the present time. 

 On the one hand J. J. Thomson concludes that the number is nearly 

 the same as the atomic weight; on the other it is said that this esti- 

 mate must be thousands of times too small. When the atom is put 

 together it has a certain mass ; the uncertainty arises principally from 

 ignorance as to how to allow for this rnass. It is possible to explain 

 mass as an electrical phenomenon, every negative electron has so much 

 mass of this kind. Is this, then, the only source of atomic mass? If 

 so the electrons must be many. But perhaps there may be mass which 

 is not an electrical phenomenon, as we always used to think vaguely; 

 then a smaller number of electrons will be necessary. It seems un- 

 likely, however, that there should be two sources of mass, one electric 

 and one not. Or, again, the positive electricity in the atom may also 

 be responsible for some of the mass in the same way as the negative 

 electrons : but it is well known that electrical charges must be con- 

 densed into extremely minute centres before they can show '" electrical " 

 mass : and there is a general tendency at present to suppose that the 

 positive electricity in the atom is not condensed into centres so small 

 as is the negative electricity, but is probably much more diffused. 



It is, indeed, one of the greatest puzzles of the subject that so 

 little should be known of the positively charged constituents of the 

 atpni. Tlie negative electron is comparatively a familiar acquaint- 

 ance. Tlie cathode rays of the vacuum tube, the beta raj^s of radium, 

 the delta rays which issue froto all atoms under the influence of any 

 oi"" the radiations we are discussing, are all negative electrons exactly 

 like each other, but endowed with different velocities. For years the 

 negative electrons have been handled and investigated with ease. But 

 no one has succeeded in handling the positive electron, if it exist, in 

 the same manner. It is perhaps instructive to consider to AA-hat causes 



