sensitive a transfer of motion to the lower head of the drum as there would be transferred to the kite by the movement of the hand holding the kite cord. Reis’ plan resembled the broken drum beats, and Bell’s the kite cord, which always preserved a certain amount of tension. Bell accomplished his object by the means shown in Figs. 56 and 57, in which Fig. 56 represents his first patent of March 7, 1876, and Fig. 57 his second patent of January 30, 1877. In both cases the current was a continuously closed one, and was not alternately made and broken as by the separating contacts of Reis. Prof. Bell caused the vocal air vibrations to undulate or oscillate the continuously closed circuit by the principle of magnetic induction as follows (see Fig. 56): He caused diaphragm _a_, when spoken against, to vibrate the armature _c_ in front of the electro-magnet _b_, but without touching it, and as the armature approached and receded from the electro-magnet it induced an undulating but never broken current in the helix of this electro-magnet and along the line to and through the helix of the electro-magnet _f_ at the distant receiver, and this undulating current, influencing the armature _h_, which touched the diaphragm _i_ but not the electro-magnet, produced in the attractive influence of the magnet on this armature and diaphragm, vibrations of the same rapidity, range, and quality as those vocal vibrations that acted upon the first diaphragm _a_. In other words, the sequence of transference was air vibrations in A, mechanical vibrations of diaphragm _a_, electrical undulations traversing the line, induced vibrations in armature _h_ and diaphragm _i_, and air vibrations again resolved back into sounds of articulate speech, the same as those spoken into A. It will be perceived that in the Bell telephone both transmitter and receiver were of identical construction. This is better shown in Fig. 57 of his later patent, in which the horizontal line below the electro-magnet on one side represents a metal transmitting diaphragm, and the horizontal line under the electro-magnet at the other side was the receiving diaphragm. Not only were the sounds thus reproduced, but as the circuit was continuous and never broken by any separating contacts, the extreme sensitiveness of the electric vibrations set up by magnetic induction was such that the discordant and irregular quality of the vibrations of articulate speech were transferred and reproduced with exact fidelity, as well as the musical tones, and this rendered the speaking telephone a success. In later telephones the current is actually transmitted through the contacting points, but this only became practicable after the carbon microphone transmitter was invented, in which the essential undulations of the electric current were produced in another way, _i. e._, by the application of the important discovery that the varying of the pressure on carbon, by vibration, varied its conductivity, and in this way