246 
[April, 
The Phonograph. 
is turned a spiral groove, the pitch of which is the same as 
that of the screw on the horizontal shaft, so that if a fixed 
pointer were to be set in the groove at any portion of its 
length it would remain in it as the cylinder was rotated until 
it worked out at either end. 
In front of the cylinder and directed to its axis is fixed a 
thin metallic diaphragm, carried by an arm attached to the 
