316 Tainter and Bell—Production of Sound by Light. 
The second typical cell is cylindrical in form, for the purpose 
of being used with a concave reflector instead of with a lens 
(see fig. 3.) 
This cell is composed of a large number of ee ce 
separated by dises of mica sli ightly smaller in diamet 
spaces between the brass discs over the mica are filled with 
ae and the alternate brass discs aes il ed con- 
ecte e arrangement practically consists of a num- 
hee of annular selenium cells united in qeatple are. 
The mode of applying the selenium is as follows: 
The cell is heated, and when hot enough a stick of selenium 
is rubbed over the surface. 
In order to acquire conductivity and ser cine the sele- 
nium must next undergo a process of ann 
The method we first adopted was the si 
The selenium cell was placed with a thermometer in the inte- 
rior of the cylindrical annealing chamber shown i 
This was inserted in a 
pot of linseed oil, and the 
latter stood upon glass 
supports within another 
similar pot containing 
linseed oil. The whole 
arrangement was then 
placed over a gas stove 
and heated to a temper- 
ature of about 214° C., 
which was found to be the 
temperature of maximum 
conductivity for the sele- 
nium used. 
This temperature was 
ee retained for about twenty- 
B=battery; Sh=shunt; G=galvanometer. ‘four hours, and the pots, 
with their contents, were 
then packed in a box so arranged as to retard radiation of heat. 
The selenium took ca forty to sixty hours to cool down to 
the temperature of the a 
A powerful battery ect was passed through the selenium 
during the whole process of heating and cooling, in accord- 
ance with our theory that the current, exerted a powerful i influ- 
ence in causing a set of the selenium molecules, and in retain- 
ing them in position until fixed by ery stallization. 
A shunted galvanometer was introduced into the circuit for 
the purpose of observing the changes of conductivity. We 
malesbeeate found this tedious process to be unnecessary, as 
during the course of our experiments we discovered a meth 
of preparing sensitive selenium in a very few minutes. 
