Chapter XVII: Section 19: Conveying Messages

Messages can be conveyed by--

=1. Speaking tube;= for distances up to say 300 feet, ³⁄₄″ to 1″ bore
tubes.

=2. Telephone;= any distance.

=3. Telegraph;= any distance.

=4. By signals=--(a) Wire or cord and bell; (b) sight signals, such as
the semaphore, lamps, heliograph, flags, and other devices; (c) by
sound, such as a bell, trumpet, siren, whistle, &c. See Section 105.

=5. By pneumatic despatch:= that is, by forcing a piston carriage
containing the message or small parcel through a tube by compressed
air.

=6. Carrier pigeons.=

=368. Signalling dials= and =bevel gearing.=