Manchester Memoirs, Vol. xli, (1897), No. 15. 15 



According to the view here pat forward, the Rontgen 

 emanation consists of a vast succession of independent 

 pulses, starting respectively from the points and at the 

 times at which the individual charged molecules pro- 

 jected from the cathode impinge on the target. At 

 first sight it might appear as if mere pulses would be 

 inadequate to account for the effects produced, seeing 

 that in the case of light we have to deal with series 

 consisting each of a very great number of consecutive 

 undulations. But we must bear in mind how vast, 

 according to our theoretical views, must be the number 

 of molecules contained in the smallest quantity of 

 ponderable matter of which we can take cognisance by 

 our senses. Hence, small as is the quantity of matter 

 projected in a given short time from the cathode, it may 

 yet be sufficient to give rise to pulses the number of 

 which is inconceivably great. It remains to consider in 

 what way this conception may enable us to explain the 

 most striking properties of the Rontgen rays in relation 

 to the contrasts which they offer to rays of light. 



The most elementary difference, as being one which 

 has relation only to propagation in the ether, consists 

 in the absence, or, at any rate, almost complete absence, 

 of diffraction. As the different pulses are by hypothesis 

 quite independent of one another, we have to explain 

 this phenomenon for a single pulse. 



In the figure let C B be a portion of a spherical 

 pulse spreading outwards from the centre of disturbance 



