Dr. Guthe Makes Arc Light Talk Or Sing At Pleasure

An arc light that talks, the kind of an arc light that you see on the street corner, has been designed by a professor in the physical laboratory of the University. Arc lights as musical instruments and telephones are the late methods of utilizing the electric current with which Dr. Karl E. Guthe, assistant professor of physics, has been amusing and instructing students in his department. In one of these experiments he played upon the are as if it had been a piano, using a regular keyboard on which he picked out "yankee Doodle" and other airs. In another the tones and words of the human voice were reproduced as in a telephone, but much louder so that they were audible throughout a large lecture room seating 150 persons. The sounds as reproduced also lacked the harsh, metallic character of telephonic utterances and so responsive was the arc light receiver that it reproduced with remarkable fidelity the tones of a violin, every person in the large lecture room being able to hear distinctly.

The "singing arc"  and the "talking arc," as Dr. Guthe calls them, though apparently so similar in results, work on different principles and require a different adjustment of current and apparatus, one creating the sound and the other reproducing sounds that have been produced before a telephone transmitter located some distance away. In the "speaking arc" an ordinary Berliner transmitter is so connected with the feed wires of an are light that vibrations set up by sounds uttered into the transmitter cause corresponding variations in the surrent passing through the arc. This increases and decreases with the volume of incandescent vapor between the carbons of the arc, setting up corresponding vibrations in the surrounding air and causing the sounds to be produced with great fidelity. For this experiment a steady, long arc was required and large solid carbons were used. Their points were separated about four inches and a rather large current of 15 amperes was employed. In the "singing arc" on the other hand a current of less than one ampere, but of rather high coltage was used.

The same principle is involved as that which produces the hissing and spitting which the common are light on the street corners is forever doing.