metallic support, B. To another support. A, is loosely hinged a frame,
which at its further extremity carries a little coil of German silver
wire, C, which by its weight rests upon the center of the gauze plate,
G; and in contact therewith, and to increase the pressure of contact, a
little bar weight is laid within the convolutions of the core. The
two electrodes, the gauze, and the coil are connected, as shown, to a
receiving telephone, T. Upon the application of heat, as from the flame
of a spirit lamp placed below, a thermo-electric current is set up
throughout the circuit; in this condition the apparatus becomes a very
perfect microphone, and when the pressure between the electrodes is
properly adjusted it is a very efficient telephonic transmitter,
transmitting articulate speech and musical sounds with remarkable
clearness and fidelity.

[Illustration: FIG. 5]

Mr. Munro is, with the aid of Mr. Warwick's manipulative skill,
extending this portion of his investigation further by experimenting
with gauzes and coils of various metals forming other couples in
the thermo-electric series, as well as with iron and other gauzes
electrotyped with bismuth and other metals, and we hope in due time to
lay the results of those experiments before our readers.

Mr. Munro has, moreover, observed that if two pieces of gauze of
identical material and in microphonic contact be heated, a peculiar
sighing sound is heard in a telephone connected with them and with a
battery, and he attributes this phenomenon to the electrical discharge
between the gauze plates being facilitated and increased by the
action of heat, but we are rather inclined to trace the effect to the
mechanical action of the one gauze moving over the other under the