22 INAUGURAL ADDRESS. 



positive countei-part. The former is the secondaiy cathode ray, and 

 perhaps is responsible for all the action in the gas by which we trace 

 the progress of the X rays. The latter we may suppose to remain in 

 the atom where the break-up of the pair has occurred. It is too light 

 to assume an independent existence. 



Simple as this conception is, it correlates the facts in a remarkably 

 effective way. Moreover, it has led to new discoveries, as I will now 

 explain. 



I have said that the radiations which are known to be material 

 are capable of being scattered or deflected in passing through the 

 atoms. It is most easy to examine the effect in the case of the beta 

 vays. The flying electron which passes close to a centre of force within 

 the atom is only deflected through a large angle when tlie degi'ee of 

 approach is very close indeed. Since close approaches are relatively 

 rare, if a stream of electrons passes through a sheet of material so 

 thin that any one electron is not likely to experience more than one 

 deflection or so, then we find that the number of electrons which are 

 only slightly deflected, and, therefore, appear on the further side of 

 the plate, is much greater than the number wdiich are so much de- 

 flected as to be tunaed right back and emerge again on the side of the 

 plate at which the original stream entered. The fact might be antici- 

 pated : but it has actually been shown very clearly by Dr. Madsen in 

 some experiments of which the account is to be read at this meeting. 



Now a certain proportion of a stream of X rays or gamma rays 

 is scattered in passing through a plate; and the aether pulse theory 

 has hitherto been held to show that there should be equality on the 

 two sides of the plate in respect to the proportions scattered. Thus the 

 two tlieories lead to different conclusions in this respect. 



Wlien the experiment is made it is found that the X rays and 

 the gamma rtxya behave like the material beta rays, and not in the 

 manner to be expected on a pulse theoiy. Madsen has recently shown 

 that when gamma rays are passed through a plate, the scattered rays 

 on the far side of the plate are sometimes five or six times as important 

 as those which are to be found on the near side, that at which the 

 oi-iginal stream enters. I liave myself foimd the effect to be clearly 

 showni by X raA'-s, though to a smaller degree. 



And, again, when the gamma rays are replaced Ij}' beta rays the 

 experiments of Madsen and myself show that the latter nnist at first 

 travel straight on in the original direction of the former. This is 

 easilv imderstood on the neutral pair theory, since we may suppose the 

 removal of the positive from tlie pair to be effected without seriously 



