The popular impression has been, concerning the telephone, that the sound was in some way conveyed over the wire. It will be obvious to every one who may read this, that such is very far from being the case. The fact is, it is a beautiful example of the convertibility of forces from one form to another. There is first the initial vibratory mechanical motion of the air, which is imparted to the membrane carrying the iron. This motion is converted into electricity in the coil of wire surrounding the electro-magnet, and at the receiving-end is first effective as magnetism, which is again converted into vibratory motion of the iron armature, which motion is imparted to the air, and so becomes again a sound-wave in air like the original one.
This was the first speaking-telephone that was ever constructed, so far as the writer is aware, but it was not a practicable instrument. Many sounds were not reproduced at all, and, according to the report of the judges at the Philadelphia Exposition, one needed to shout himself hoarse in order that he might be heard at all.
THE AUTHOR'S TELEPHONE.
For several years past my regularly recurring duties have taken me over the various subjects treated of in this book, and each one has been extensively illustrated in an experimental way, and a considerable number of new pieces of apparatus and new experiments to exhibit their phenomena have been devised by me.
Among these, I would mention the following:—
1. Measurement of the elongation of a magnetized bar.
2. A magneto-electric telegraph.
3. An electro-magnetic instrument for demonstrating the rotation of the earth.
4. The permanent magnetism of the magnetic phantom.
5. The convertibility of sound into electricity.