MECHANICS AND USEFUL ARTS. 89 



raine light on the stereograph, is, in many cases, very striking, 

 but, for common use, the simple form is preferable." 



PRACTICAL APPLICATION OF SENSITIVE FLAMES. 



An apparatus has been invented by Barrett for making practi- 

 cal use of sensitive flames. It consists of two perpendicular cop- 

 per rods, one of which, on its upper end, holds a metallic ribbon, 

 which is composed of thin leaves of gold, silver, or platinum, 

 welded together. Such a ribbon expands unequally under the 

 influence of heat ; it bends toward one side, and, in doing so, 

 comes in contact with a fine platinum wire attached to a galvanic 

 battery. As soon as the poles of the battery are closed, a bell 

 begins to ring. The working of the apparatus is as follows : — 



"A sensitive flame is lighted about 10 inches from the metallic 

 ribbon. This burns quietly so long as there is no noise, but a 

 shrill whistle, or any unusual disturbance, will cause it to dimin- 

 ish one half in length, and to spread out wide in the middle, like 

 the wings of a bird. It thus heats the metallic ribbon, which 

 expands unequally, and occasions the contact of the poles of the 

 battery, which rings a bell." 



Such a light as this in a banking-house would betray to the 

 watchman the noise of robbery, and the inventor proposes to use 

 it as a species of burglar alarm. As sound can be transmitted in 

 water 4 times as rapidly as in the air, it is also suggested to em- 

 ploy this method on shipboard, to make known the apiDroach of a 

 vessel in time of a fog. 



There is probably the germ of curious applications of sensitive 

 flames in Barrett's invention, and it would not be surprising to 

 bear of its use in war, to warn a sentinel of the approach of the 

 enemy, or of its application to a new species of telegraphy. 



ELECTRIC BEACONS. 



Thomas Stevenson, C.E., Edinburgh, recently conducted an 

 experiment at Granton, with the view of showing the practica- 

 bility of illuminating beacons and buoys at sea with the electric 

 light produced by means of a battery on shore. A submarine 

 cable, fully half a mile in length, was laid between the east 

 breakwater of Granton Harbor and the cliair pier at Trinity, The 

 operator occupied a station near the centre of the breakwater, and 

 the light was shown at the point of the pier in front of an ordi- 

 nary light-house reflector, producing a most brilliant flash. The 

 flashes were emitted with groat rapidity ; as many as 500 can be 

 transmitted in a minute, but the machine can be regulated so as to 

 send one every second, or at any other desired interval. The ex- 

 periment gave entire satisAiction. 



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