Tainter and Bell— Production of Sound by Lnght. 815 
number of cells of different forms. Time will only admit of 
my showing you two typical forms. One of these is shown in 
plan in fig. 1, and in section in i 2. 
This cell consists of two brass plates insulated from one 
another by a sheet of mica. The upper plate has numerous 
perforations and brass pins attached to the lower plate, pass 
through these orifices so tha 3 
their ends without touching 
the up per ‘plate are flush with 
its surface 
The paeaiie spaces between 
the pins and the plate are filled 
with selenium. The whole ar- 
rangement forms part of a gal- 
vanic circuit, and it will be 
observed that the current can 
only pass from the plate to 
the through the selenium 
rin 
4 will also be seen that ow- 
ing to the conical shape of the 
perforations the points of clos- 
est approximation between the 
pins and the plate are on the 
upper surface. As the effect produced by light upon selenium 
is chiefly a surface action, this arrangement is found to be of 
great pe butions 
