Fig. 21.
Fig. 22.
Fig. 23.
[Fig. 22] shows the form of apparatus that I was then employing for producing undulatory currents of electricity for the purposes of multiple telegraphy. A steel reed A was clamped firmly by one extremity to the uncovered leg h of an electro-magnet E, and the free end of the reed projected above the covered leg. When the reed A was vibrated in any mechanical way, the battery current was thrown into waves, and electrical undulations traversed the circuit B E W E´, throwing into vibration the corresponding reed A´ at the other end of the circuit. I immediately proceeded to put my new idea to the test of practical experiment, and for this purpose I attached the reed A ([fig. 23]) loosely by one extremity to the uncovered pole h of the magnet, and fastened the other extremity to the centre of a stretched membrane of goldbeaters’ skin n. I presumed that upon speaking in the neighbourhood of the membrane n it would be thrown into vibration and cause the steel reed A to move in a similar manner, occasioning undulations in the electrical current that would correspond to the changes in the density of the air during the production of the sound; and I further thought that the change of the intensity of the current at the receiving end would cause the magnet there to attract the reed A´ in such a manner that it should copy the motion of the reed A, in which case its movements would occasion a sound from the membrane n´ similar in timbre to that which had occasioned the original vibration.