KORN'S SELENIUM RECEIVER 



37 



The shadow of the galvanometer foil is cast 

 upon a triangular aperture in a diaphragm E 

 (Fig. 1 6), being magnified up a good many 

 times by the lens T which is fitted into one pole 

 of the electro -magnet. This shadow prevents 

 the light from the lamp N reaching the small 

 lens O which concentrates a real image of the 

 aperture (when illuminated) upon the photo- 

 graphic film ; this revolves on the drum D, the 



*o 



FIG. 16. 



drum being fitted into a small light-tight wooden 

 box. Now if the shutter is displaced, the shadow 

 moves to one side, and light immediately passes 

 through the aperture at E and exposes the film. 

 The more the shadow moves towards the base of 

 the triangular hole, the greater is the light which 

 reaches the film ; by using a triangular instead of a 

 square hole the effect of movement of the shutter 

 on the light transmitted to the film is obviously 

 amplified, and this amplification* is necessary 

 because the ratio of illumination to resistance of 



