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.