.]

The sounds to be transmitted, of whatever sort they may be, are to be
made on the side P, Fig. 16; and likewise, when the instrument is used
as a receiver, the ear is to be applied at the same place. A tube about
two inches in diameter may be made fast to the front of the board, in a
line with the centre of the plate; this will aid somewhat in hearing.
When two or three persons are to sing, it will be best to have each one
supplied with a tube to sing through; one end of the tube to be placed
close to the front of the plate. The sound of musical instruments, such
as the flute and the cornet, will be reproduced much louder, if the
front of such instrument be allowed to rest upon the rim of the hole in
the board, just in front of the plate.

It is noticeable that low talking can be heard more distinctly than when
a great effort is made; but the sounds though distinct are not strong at
any time, and other sounds seriously interfere with hearing. It is
probable that some way will hereafter be devised for increasing the
usefulness of the invention by increasing the volume of sound. On
account of the weakness of the sound it becomes necessary to provide a
call to attract the attention of one in the room. This may be
accomplished by having a small electric bell worked by a one or two cell
battery. Another way which I have found to be quite as efficient is to
have a rod of iron or steel about a foot long, and half an inch in
diameter, bent into a U form. When this is held by the bend, and struck
upon the floor or with a stick, it vibrates powerfully; and if one of
its prongs be permitted to strike against the plate P, Fig. 16, the
sound will be reproduced loud enough to hear over a large room. I have
never failed to call with this when any one was in the same room with
the telephone.

Wherever a telephone circuit has been made upon telegraph poles having
other wires upon them, the inductive actions of the currents upon the
other wires has been found to seriously interfere with the action of the
telephones, inasmuch as the latter reproduce every other message. One
skilled in reading by sound in the ordinary way can read through the
telephone what message is travelling in a neighboring wire. Messages may
be thus read upon wires as far distant as ten feet from the telephone
circuit. It there fore seems to be essential that each telephone circuit
should be isolated from every other one, else there can be no secrecy in
messag