must be symmetrical also if the ether-pulse theory is cor- 

 rect, and therefore the tertiaries and so on. Nor is it neces- 

 sary to consider whether the secondary radiations are )3 rays 

 or scattered y rays. Also, it must be remembered that the 

 secondary radiations which enter the chamber have their 

 origin almost entirely in a very few millimetres of material 

 bordering on the chamber. Therefore, the y rays are in 

 almost exactly the same condition, both as to quality and as 

 to quantity, when they excite secondary radiations from the 

 top plate as they enter the chamber, and secondary radia- 

 tions from the bottom plate as they leave. 



The details of the experiment may be varied greatly ; but 

 in all the cases we have tried the want of symmetry is obvious. 

 In fig. 3 are shown the details of one other case, in which 

 carbon and lead were the materials used, and the form of the 





^2 ) " ,. ^ o^dL n> i^U^ai^Ici = 'S^ /^. 



(3 ) CU o^ O), ^n^ ^^^ :?<S!cZ<a^a^ ti can^rru ^ ^^ S' 



Fig. 3. 



chamber was different. It seems unnecessary to give more, 

 because, in the first place, the experiments are easy to re- 

 peat ; and in the second place, the complete quantitative 

 analysis of the figures depends on several factors, the influ- 

 ence of which is imperfectly understood, such as the previous 

 screening of the rays, the form of the chamber, and the re- 

 spective parts played by the original y rays, cathode rays, and 

 secondary y rays, if any such exist. The experiments, as they 

 stand, show how far away is that symmetry w^iich the ether- 

 pulse theory demands. It seems to us that there is no escape 

 from the conclusion that the y rays are not ether pulses. 



Let us, therefore, proceed to consider the hypothesis that 



the y rays are material. In the paper already mentioned, it 



was argued that they might well consist of neutral pairs, 



liable to be broken up on encountering atoms or parts of 



a2 



