The transmission of musical harmonies telegraphically, while in itself of great scientific interest, was of no practical use, but it led to other inventions, of which it is the base, that are transcendently useful in every-day life. The transmission of harmonic sounds by electricity underlies the principle of the telephone. There is a vast difference, in principle, between the transmission of simple melody, which is a combination of musical tones transmitted successively--one tone following another--and the transmission of harmony, which involves the transmission of two or more tones simultaneously. The former can be transmitted by a make-and-break current. In the latter case one tone has to be superposed upon another and must be transmitted with a varying but a continuously closed current. I make a distinction between a closed circuit and a closed current. In the case of the arc-light the circuit is open (that is, broken), technically speaking, but the current is still flowing. The reason why the Reiss and other metallic contact telephone transmitters cannot successfully be used for telephone purposes is that metal points will not allow of sufficient separation of the transmitting points without breaking the current as well as the circuit. Carbon contacts admit of a much wider separation without actually stopping the flow of the current, which latter is a necessity for perfect telephonic transmission, and it was the use of carbon that made that form of transmitter a success. There are other forms, or at least one other form that does not depend upon the length of the voltaic arc formed when the electrodes are separated. Of this we will speak another time. Now let us go back to the domestic incident referred to above.