62 ".V" RAYS 



act for a determined period on a sensitive plate, 

 whilst this source is subjected to the action of 

 " N " rays, and then repeating the experiment 

 for the same interval of time and under the 

 same conditions, save that the " N " rays 

 are suppressed. The impression produced is 

 notably more intense in the first case than in 

 the second. As an example of the application 

 of this method, I gave at the time two photo- 

 engravings, whose comparison shows that 

 water, even when used in very thin films, 

 arrests " N " rays issuing from an Auer 

 burner (see page 16). Since then I have 

 extended the experiments to the registration 

 of actions produced by " N " rays from 

 various sources, and I have perfected the pro- 

 cess, as will be shown. 



A small, luminous spark is the most ap- 

 propriate luminous source for this kind of 

 investigation : for, on the one hand, it is very 

 actinic, and, on the other, it can be maintained 

 as long as necessary at the same intensity. 

 Although it is impossible to obtain absolute 

 steadiness of glow in the spark, since these 

 variations are not produced systematically, 



