The description of this arrangement proceeds thus :-
General Chazal combined the employment of electricity with that of a "camera obscura" in a very ingenious way for the defence of the Escaut by torpedoes.
Under a tent protected by fortifications he arranged the battery, or induction apparatus, from which the spark is produced. All the wires which electrically united the lines of the torpedoes with the apparatus ended separately in the tent, and each of them was numbered so as to render all error impossible. On the table was a plan of the harbour, where the positions of the lines of the torpedoes were indicated, and which was nothing else but the reproduction of the optical projection of the river by the apparatus of the camera obscura placed at the top of the tent.
Let us suppose that an enemy's ship is seen coming up the river; the officer watching and commanding could follow minute by minute the position which it occupies, relative to the lines of immersion of the torpedoes.
At an opportune moment he would give the order to the sailor in charge of the electrical apparatus, and tell him the number of the wire in which he must close the circuit.
Credit :
From Amedee Guillemin's book "Electricity and Magnetism", MacMillans 1891
