402 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



With a large capacity the number of discharges occurring during the 



half-cycle is small. In Figure 6, Plate II (C=.117 microfarads, 



V— 15,000 volts), only one, or sometimes two, discharges occur during 



the half-cycle of the transformer. In this picture the whole of the 



mercury-vapor bulb together with the bright surfaces of the electrodes 



Figure VIII. 



are shown, while the legs of the interrupter, of course, make no impres- 

 sion on the film. The images are arranged in the form of a spiral on 

 the film. Both electrodes are bright, for several oscillations occur 

 during each discharge. 



By keeping the voltage of the transformer the same and reducing the 

 capacity about thirty-fold, Figure 7, Plate II was obtained. In taking 

 this photograph, to prevent confusion, the greater part of the bulb was 



