RADIOACTIVITY 41 



before them or as if the ft rays to some extent took the place 

 of the 7 rays which have been absorbed in the plate. The 

 dissymmetry is most marked in the case of the penetrating 

 7 rays and is much less in the case of the X rays. 



Just as in the case of the ft rays in relation to the secondary 

 or scattered ft rays, so now we must try to settle one point 

 before we go further. Whence comes the energy of these 

 ft rays which the 7 rays produced? It is a most important 

 question ; the whole argument that follows depends on the 

 answer we give to it. Shall we suppose the energy to come 

 from the atom, so that the 7 ray, so to speak, merely pulls the 

 trigger and the ft ray results from some intra-atomic con- 

 vulsion which was on the point of happening and is now 

 precipitated ? Or shall we suppose the 7 ray to provide the 

 energy for the ft ray and the atom to play no higher a part 

 than that of energy transformer? The reasons in favour of 

 the one or the other of these alternatives are practically the 

 same as those which were before us in the corresponding case 

 of the ft ray. The whole argument seems to me to be now as 

 then in favour of the latter of the two. It becomes easy to 

 understand why the speed of the ft ray and the direction of 

 its motion are so closely connected with the 7 ray from which 

 it draws its energy : and why the atom itself, where the change 

 takes place, is so unimportant an agent. It seems unnatural to 

 suppose that the atom contains, as it were, an infinite number 

 of guns pointing in all directions and that when the 7 ray 

 enters it fires off just that gun which gives a muzzle-velocity 

 characteristic of that 7 ray and which happens to point more or 

 less in the direction in which the 7 ray has been moving. On the 

 other hand, it is not so difficult to picture the 7 ray as carrying 

 with it into the atom a certain amount of energy and momentum, 

 and handing them on to an electron, which then proceeds from 

 the atom as a ft ray. 



Supposing then that we are satisfied as to the answer we 

 give to this fundamental question, we proceed to take into the 

 argument another experimental fact. It is found that the speed 

 of the ft ray does not depend on the distance between the 

 radium which is the source of the 7 rays and the atom where 

 the ft ray comes into existence. No matter how far the 7 ray 

 has gone away from its origin, it hands over to the ft ray exactly 

 the same amount of energy. 



