318 M7' Gamphell, Discontinuities in Light Emission. 



made an angle of approximately 45° with the direction of the light. 

 The resulting two beams were suitably reflected by mirrors and 

 brought to a focus on the surface of the alloy in the photo-electric 

 cells by lenses similar to that previously mentioned. The angle of 

 incidence of the light on the surface of the alloy was approxi- 

 mately 65°. 



In order to adjust the currents through the two photo-electric 

 cells to equality, a shutter moved by a fine screw was inserted in 

 front of one of the cells. The light acting on the cells in the 

 absence of the shutter was first adjusted as closely as possible to 

 give equal currents, and the final adjustment made by means of 



The figure shows only one cell ; the 

 second cell was exactly similar and 

 lay beneath the plane of the paper. 



the shutter. The primary adjustment was made by varying the 

 distance of the lamps from the cells, when two independent lamps 

 were used : by moving the front mirror across the path of the 

 beam, when the light from a single lamp was split by two full 

 mirrors : and by altering the inclination of the half-silvered mirror 

 to the path of the light, when the splitting was effected by the 

 half-silvered mirror. 



§ 12. As photo-electric cells an attempt was first made to use 



