46 
Proceedings of Royal Society of Edinburgh. [sess. 
Note on Mr Alfred Graham’s Method of producing 
Sound by an Electrical Arrangement. By John G. 
M‘Kendrick, M.D., Professor of Physiology in the Univer- 
sity of Glasgow. 
(Read February 17, 1896.) 
During the past year I have had many opportunities, in connec- 
tion with a research on the phonograph, of observing the efficacy 
of Mr Graham’s method of electrically producing sound, and as it 
is not generally known, a short explanation may be useful. 
Two or more cells are connected to a mass of granular carbon 
whose resistance can be varied by vibration, and the circuit is then 
completed through the coils of an electro-magnet. In front of the 
electro-magnet is a diaphragm sensitive to the variations of current 
flowing through the electro-magnet. This diaphragm is so placed 
relatively to the circuit of variable resistance, that any vibration 
imparted to it is transmitted through a column of air to the circuit 
of the variable resistance or its diaphragm. The granular carbon, 
similar to that in telephonic transmitters, is contained in a box or 
chamber closed at one end by a diaphragm of carbon, with 
which the granular carbon is in electrical contact. The carbon 
resistance box is so placed that its diaphragm is acted on by the 
vibrations set up by the diaphragm of the electro-magnet. To 
effect this, a flexible tube passes from the front of the diaphragm of 
the transmitter to the front of the diaphragm of the electro-magnet. 
Thus, when the various parts of the apparatus are connected, 
as seen in the figure, and when the circuit is completed by closing 
a key, the vibrations set up in the telephone diaphragm are caused 
to act upon the circuit of variable resistance, which, in turn, again 
acts upon the telephone or receiver diaphragm. A continuous 
musical sound is then emitted. 
The receiving or telephonic element of the apparatus consists of 
a powerful permanent magnet carrying upon its poles spools wound 
with low resistance coils. This acts on an iron diaphragm of 
considerable area, about 90 mm. in diameter, and of minimum 
