### Note on a humming telephone

F. Gill
1902 Journal of the Institution of Electrical Engineers
of the humming telephone, as I hope to show it, is new and has not been published hitherto. This note is merely a record of a few experiments carried out at odd times since the effect was first noticed by me two years ago. The ordinary humming telephone is, of course, well known, and was first noticed by A. S. Hibbard, of the United States, in 1890. 1 We have Hall effect and Ferranti effect, why not Hibbard effect ? In Hibbard's experiment a telephone is held against or near to the diaphragm of
more » ... to the diaphragm of the microphone, and a hum or whistle is set up and continues. A rough explanation of the experiment is that in the first place some slight noise is taken up by the microphone, and the sound is, in the usual way, given out by the telephone ; but, because the latter is near the microphone, the sound waves set up by the telephone affect the microphone, which in turn again acts upon the telephone, and thus the reaction is maintained. The connections in this case are those ordinarily used in telephony, where the microphone is in scries with the battery and with the primary of the induction coil; the telephone in series with the secondary of the induction coil is short-circuited. The feature which I believe to be new is that, if the wires leading to the telephone be reversed while the instrument is humming the note at once changes in a striking degree, and if the hum is stopped it will recommence again, high or low, according to the side the reversing switch is set. It is also to be noted that the high note starts more easily and is altogether more vigorous than the low note. Of course, reversing the current in the primary circuit also produces the same change in pitch, and if the primary and secondary circuits be each reversed simultaneously no change is observed. Returning to the ordinary humming, the exact conditions which determine the note given by the telephone appear to be most complex, apparently every portion of the circuit and instruments has a share in 1