698 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



is, employed not only to explode mines, but to kindle at a distance 

 any dangerous machines or gaseous matters such as fire-damp, or even 

 simply to light gas-jets to serve as signals. A naval officer, M. Treve, 

 has proposed the adoption in the fleet of a nautical telegraph, to 

 displace the night signals which are now made, as is known, by means 

 of lanterns. These lanterns consist of lamps provided with Fresnel 

 lenses similar to those of lighthouses, which are hoisted on one or 

 two halliards on the most elevated part of the ship. The lighting of 

 these lanterns and the movements necessary to 

 put them in place occupy considerable time. 

 M. Treve has proposed to render this kind of 

 communication more prompt by replacing the 

 candles of the lamps by gas. 



The setting fire to explosive matters at a dis- 

 tance by electricity, serves again for the protection 

 of ports and the neighbourhood of fortified places. 

 Every one has heard of those formidable engines 

 called torpedoes, the explosion of which is so 

 terrible that a single one (if made on purpose) 

 could sink the greatest navy. Torpedoes played 

 an important part in the War of Secession in 

 the United States : a considerable number of ships 

 owe to them their destruction. The American 

 torpedo is arranged in the following way : 



The engine in question is a tin box of a 

 capacity of forty-five or fifty litres, divided into 

 two parts by a transverse partition : one of these 

 parts receives the charge of powder, the other is the air chamber. 

 An iron rod, buried in the powder and capped by a capsule, receives 

 a blow from a hammer when a ship, in passing above the point where 

 the torpedo lies submerged touches a float provided with a cord in 

 communication with a catch upon the hammer. 



The explosion is not therefore produced directly by electricity. But 

 the advantages that might result from exploding it from a dis- 

 tance, according to the wish of the authorities charged with the defence 

 were soon perceived. The Belgian ex-minister of war, General Chazal, 

 has very ingeniously combined the employment of electricity with 

 that of the camera obscura for the defence of the Scheldt by torpedoes. 



FIG. 452. Trevc's lantern 

 for night telegraphy in 

 the navy. 



