CHAP. VI 11-] 



THE ELECTRIC LIGHT. 



699 



Beneath a tent protected by earthworks, the pile or indu3tion appa- 

 ratus which produces the spark is arranged. Here all the wires which 

 unite electrically the lines of torpedoes with the apparatus end sepa- 

 rately, and each of them is numbered, so as to render any mistake 

 impossible. 



On a table is placed a plan of the Scheldt, where the positions 



FIG. 453. Explosion of torpedoes by electricity ; General Chazal's system of defence 

 for ports and coasts. 



of the lines of torpedoes are marked, and which is simply the repro- 

 duction of the optical projection of the river by the dark-chamber 

 apparatus placed on the top of the tent. Suppose a hostile ship 

 should be perceived coming up the river. The officer charged with 

 the superintendence and command can follow from minute to minute 

 the position it occupies relatively to the lines of immersion of the 

 torpedoes. At the opportune moment he gives the order to the marine 

 in charge of the electrical apparatus and indicates the number of the 



