RADIOACTIVITY 43 



measurement. Now there are great difficulties in the way 

 of supposing that several cathode rays act together to make one 

 X ray and that several X rays act together to make one cathode 

 ray 'again. It would be like supposing that no injury was 

 caused to person or thing by the bullets from the fort spoken 

 of above, until several bullets had hit in the same place and 

 that then the effect of all the bullets was added together. So the 

 only thing left to us to suppose is that one cathode ray makes 

 one X ray at the anticathode, giving to it most of its energy. 

 The X ray passes out of the tube and through many atoms, 

 until at last it meets its fate : it disappears and now we have 

 a cathode ray again, inheriting the energy of the X ray and 

 continuing its motion. It is a case of transformation and 

 retransformation ; and the thing that is transformed is the 

 projectile that carries a definite quantity of energy. We are 

 strongly tempted to speak of it as one thing throughout; just 

 as we may think of the Australian mail as one thing though 

 at one time the bags are carried by a train and at another by 

 a steamer. It all depends what we fix our ideas upon. 



It is when we try to be more definite as to the nature of the 

 corpuscle of the 7 or X ray that we find a difficult task before 

 us and disagreement as to the course to be adopted. It is 

 not that we must know whether it is material or immaterial ; 

 the point is rather, does the stream of corpuscles behave like 

 a radiation working under Maxwell's laws of electromagnetism ? 

 If it does, it is rather a surprise to find such a thing to be 

 possible ; and our ideas of the radiation of light would be 

 altered. We should, I think, come to the conclusion that we 

 had been putting unnecessary and false details into our mental 

 picture of it : forcing it to look to our minds like waves moving 

 over the sea or through the air when we ought not to have 

 given in to our cravings for complete models. We should be 

 compelled also to admit that we were farther from a com- 

 prehension of the processes of interference and diffraction than 

 we had hoped ; and that, though we still had mathematical 

 equations which drew all the phenomena together, we could 

 not form a mental picture what the terms of the equations 

 stood for. There are many physicists nevertheless who are 

 willing to move in this direction, being reluctant to let the 7 

 and X rays stand outside a scheme which shall link them up 

 to electromagnetic radiations and to light; and they point 



