urge through the secondary
coil the pressure or potentiality of the current finally causes it to
leap across the small space separating the filings and, as it were, it
welds together their edges so that a current freely passes. The
bringing together of the particles, under these conditions, is called
cohering.

Fig. 75 shows the simplest form of coherer. The posts (A) are firmly
affixed to the base (B), each post having an adjusting screw (C) in its
upper end, and these screw downwardly against and serve to bind a pair
of horizontal rods (D), the inner ends of which closely approach each
other. These may be adjusted so as to be as near together or as far
apart as desired. E is a glass tube in which the ends of the rods (D)
rest, and between the separated ends of the rods (D) the iron filings
(F) are placed.

THE DECOHERERS.--For the purpose of causing the metal filings to fall
apart, or decohere, the tube is tapped lightly, and this is done by a
little object like the clapper of an electric bell.

In practice, the coils and the parts directly connected with it are put
together on one base.

THE SENDING APPARATUS.--Fig. 76 shows a section of a coil with its
connection in the sending station. The spark gap rods (A) may be swung
so as to bring them closer together or farther apart, but they must not
at any time contact with each other.

The induction coil has one terminal of the primary coil connected up by
a wire (B) with one post of a telegraph key, and the other post of the
key has a wire connection (C), with one side of a storage battery. The
other side of the battery has a wire (D) running to the other terminal
of the primary.

[Illustration: _Fig. 76._ WIRELESS SENDING APPARATUS]

The secondary coil has one of its terminals connected with a binding
post (E). This binding post has an adjustable rod with a knob (F) on its
end, and the other binding post (G), which is connected up with the
other terminal of the secondary coil, carries a similar adjusting rod
with a knob (H).

From the post (E) is a wire (I), which extends upwardly, and is called
the aerial wire, or wire for the antennae, and this wire also connects
with one side of the condenser by a conductor (J). The ground wire (K)
connects with the other binding post (G), and a branch wire (L) also
connects the ground wire (K) with one end of the condenser.

[Illustration: _Fig. 77._ WIRELESS RECEIVING APPARATUS]

THE RECEIVING APPARATUS.--The receiving