Lodge, Signalling across Space without Wires (3rd ed.
Between 1858 and 1868 he was employed in home waters on a variety of special services, chiefly connected with gunnery, signalling and the tactical characteristics and capacities of steam warships.
A complete system of signalling by night and day on the Morse system is worked by the police.
It possesses depots for artillery and mines, a meteorological observatory and a signalling station.
In this manner Trowbridge showed that signalling might be carried on over considerable distances by electric conduction through the earth or water between places not metallically connected.