24 THE 1896 ANNUAL ADDEESS. 



have failed. This, however, does not prove that the vibra- 

 tions are normal, for the peculiar properties of the X rays 

 shut us out, or at least almost completely shut us out, from 

 the ordinary means of obtaining polarisation. There is, how- 

 ever, one paper in the Comptes ReMclus, by Prince Galitzine 

 and M. de Karnojitsky, in which the authors profess to have 

 obtained by a special method undoubted indications of polar- 

 isation. No reasonable doubt can remain as to the abstract 

 capacity of these rays for polarisation after what has been 

 done by another physicist. I wish I had time to go into the 

 experiments that have been made by M. H. Becquerel in the 

 direction of polarisation ; but I have already kept you too 

 long. He had more particularly studied a very remarkable 

 phenomenon, viz. : that certain phosphorescent bodies, such 

 as sulphide of calcium for instance, and salts of uranium, on 

 exposure to ordinary sunlight give out rays of some kind 

 which pass through bodies opaque to light and are able to 

 affect a photographic plate beneath them. So far thesa 

 agree in their properties with the X rays which are ob- 

 tained from a Crookes tube, Avhich they far more closely 

 resemble than they do rays of ordinary light ; but the rays 

 thus obtained were found by Becquerel to admit of polarisa- 

 tion by means of tourmalines in a manner altogether un- 

 mistakable. I think therefore that we may take it as 

 established that the Rontgen rays are due to some kind of 

 transversal disturbance propagated in the ether. 



The non-exhibition of the ordinary phenomena of diffrac- 

 tion and interference is explicable on the supposition that the 

 vibrations in the X rays are of an excessively high order 

 of frequency. I am not sure that a different sort of explana- 

 tion might not, perhaps, be possible which I have in my 

 mind, though I have not matured it ; but, save the possibility 

 of that, one is led to regard them as consisting of transverse 

 vibrations of excessively high frequency. This opens out 

 some points of considerable interest in the theory of light ;; 

 but I am afraid it would keep you too long if I were to 

 attempt to go further into this matter. I will merely remark 

 that taking the way in which these rays are most commonly 

 produced, viz. : as coming from a point where the cathodic 

 discharge in the Crookes tube falls on the opposite wall, we 

 may undei'stand how it is that vibrations of excessively 

 unusual frequency may be produced. These highly charged 

 molecules, charged with electricity, coming suddenly against 

 the wall, may produce vibrations of a degree of frequency 



