and the Intensities of Lights of different Colors. 11 



face in the circuit, the discharge lasts ^tli of a second and is 

 formed of over 120 separate sparks ; but as the striking dis- 

 tance is increased the discharge is formed of fewer and fewer 

 components, till at a striking distance between 1 and 2 cms the 

 discharge is reduced to a single flash. In the following experi- 

 ments the striking distance is 8 cms , and a single flash was given, 

 whose duration we may safely assume was less than T,o"o""D","oTnr 

 of a second. 



In a dark room, at night, the flash of this machine gave 

 vivid contrast-colors. The gray ring appearing bright pink on 

 an emerald green ground, and of a bright yellow on an ultra- 

 marine ground. The after images of these effects lasted about 

 £ of a second. 



A rod was placed in front of a white cardboard and the 

 shadow of the rod was formed on the screen by a candle. The 

 distance of the candle was such that the white cardboard 

 appeared equally brilliant when illuminated only by the candle, 

 or, only by the electric flash. At the moment of the flash the 

 appearance presented was very remarkable. From the shadow 

 of the candle appeared suddenly to shoot a dark screen, which 

 had superposed the shadow of the candle, and which shot to 

 the side of the shadow and appeared of a bright golden orange, 

 while the apparently uncovered shadow of the candle appeared 

 of a brilliant cobalt 

 blue ; t o my eye 

 exactly a s though 

 a n opaque screen 

 had been suddenly 

 removed from a slit- 

 in the shutter of a 

 darkened room, 

 which slit was cov- 

 ered by a piece of cobalt glass. 



A square of thin green glass, 4 cms by 6 cms , was placed on a 

 piece of thin silvered glass, 4 cms by 12 cm8 , so that the edges of 

 the green glass and of the silvered glass coincided. This 

 arrangement gave a surface, half of silvered mirror, half of 

 green glass. This apparatus was so placed that the electrodes 

 of the machine and the flash were reflected from it to the eye. 

 The room was dark. At the moment of the flash its reflection 

 appeared as in fig. 12. On the mirror the line of the discharge 

 was white ; W in the figure. The continuation of this line on 

 the surface of the green glass appeared red (R in figure), 

 though really white. In front of and parallel to this line was 

 a green line, G, produced by the light of the flash reflected 

 from the surface of the silvered mirror, and having traversed 



Fisr.12. 



