and delicacy of contact," and there is a "jolting or shaking motion,"
and it does not seem possible that there can be any "pressure of one
carbon against another."

I repeat the question I asked at the beginning of this communication,
and hope that it may elicit from you, or some of our scientific men, an
explanation of the theory of the action of this form of microphone.

W.C. BARNEY.

* * * * *




THE DEMBINSKI MICROPHONIC TELEPHONE TRANSMITTER.


This apparatus, which is shown by Figs. 1, 2, and 3, consists of a
wooden case, A, of oblong shape, closed by a lid fixed by hinges to the
top or one side of the case. The lid is actually a frame for holding a
piece of wire gauze, L L, through which the sound waves from the voice
can pass. In the case a flat shallow box, E F (or several boxes), is
placed, on the lid of which the carbon microphone, D C (Figs. 1 and 3),
which is of the ordinary construction, is placed. The box is of thin
wood, coated inside with petroleum lamp black, for the purpose of
increasing the resonance. It is secured in two lateral slides, fixed to
the case. The bottom of the box is pierced with two openings, resembling
those in a violin (Fig. 2). Lengthwise across the bottom are stretched a
series of brass spiral springs, G G G, which are tuned to a chromatic