212 The Photophone, April, 
it to cool slowly for 60 hours. With conducive selenium 
thus prepared he constructed his photophonic cell for receiv- 
ing the transmitted light. 
Fig. i represents this device, which combines a low resist- 
ance of the selenium with a large receptive surface. It 
consists of a number of round disks or “ washers ” of brass, 
about 2 inches in diameter, arranged side by side on axles, 
T T, but separated from each other by disks of mica of 
slightly less diameter. These are clamped together in close 
Fig. i. — The Selenium Receiver. 
t e 3 4. y e r 0 9 10 
Fig. 2. — DIACRAM 5H0WIIIC THE ACTION OF THE 
SELENIUM RECEIVER 
file, and the grooves formed between the edges of the mica 
and brass are filled up with melted selenium, s, which is 
then annealed in the manner described, and the surface of 
the whole turned smooth in a lathe. The alternate brass 
disks are connected together, the first to the third and fifth, 
the second to the fourth and sixth, and so on, in the way 
shown in Fig. 2 at M and N, so as to give a circuit through 
the selenium surface, the battery, p, and a receiving tele- 
phone, T. A double cell of this construction is then placed 
