impact, no sort of diaphragm or equivalent device is necessary, and none
is employed.

[Illustration: FIG. 1.]

A convenient form of this apparatus is shown in Fig. 1, and to which the
name of "The Lyre Telephone" has been given from its resemblance to that
impossible musical instrument. In this apparatus, G is a plate of iron
wire gauze stretched vertically between two horizontal wires attached to
a lyre-shaped framework of mahogany; against the plate rests the smaller
plate, G squared, the normal pressure between them being regulated by an
adjustable spring acting in opposition to a weighted lever, W. The two
plates are connected respectively with the attachment screws, X and
Y, by which the instrument is placed in a circuit with a battery and
telephonic circuit.

[Illustration: FIG. 2.]

A modification of this apparatus is shown in the diagram sketch, Fig.
2, which will probably be a more practical form. In this instrument the
electrodes consist of two circular disks of iron wire gauze of different
diameters, the larger disk, G, which is fixed, being pierced with holes
of smaller diameter than the smaller disk, G squared. In the diagram the two
disks are shown separated for the purpose of explanation, but in reality
they rest the one against the other; the smaller and movable disk,
G squared, is held up against G with greater or less pressure by the spiral
spring, S, the tension of which can be adjusted by a screw or other
suitable device at N. This form of the apparatus is more suitable for
inclosure in a wall box with or without a mouthpiece, but it does not
require the employment of any kind of diaphragm or tympan. Mr. Munro