52 Dr. E. H. Cook on Experiments 



of the point and not at some distance from it. The visible 

 divergence of the brush does not start exactly from the point 

 but at some little distance in front of it. It would seem 

 therefore that the point of the emanation of these rays does 

 not coincide with that of the visible part of the brush-dis- 

 charge. 



The next step was to find if the effect could be produced 

 after reflexion. This was shown with the following apparatus. 

 A cardboard box was made of the shape shown in sketch. 



i§- 



A B is a mirror, the positive terminal of the machine, D an 

 object, and E the photographic plate. Internal reflexion was 

 carefully prevented and the experiment made in the dark 

 room. The point was about 20 centims. from the mirror and the 

 mirror about the same distance from the plate. The object, 

 which was a piece of sheet-zinc, was from 1 to 5 centims. from 

 the plate. When the machine was worked, and no mirror in 

 position, it was found that the exposed plate was unaffected, 

 the rays we may imagine being absorbed by the sides of the 

 box. This experiment also shows that the fogging of the 

 plate is not caused by any ozone which may accompany the 

 discharge. When, however, the mirror is in position a dis- 

 tinct image is formed upon the plate after a slight exposure 

 (5 minutes was usually given). Supposing the effects to be 

 caused by the emission of electrified particles from the terminal 

 it might be imagined that these would be reflected from the 

 mirror and so turned from their course as to impinge upon 

 the plate. In order to discover if this explanation be correct, 

 the mirror A B (which was of glass in the first experiment) 

 was replaced by a sheet of metal. Xow, if electrified particles 

 fall upon this and it be earth-connected, their electricity will 



