320 SEC. 10. ELECTRICITY. 



GENERAL TELEGRAPHIC APPARATUS. 



1667. Apparatus specially intended to illustrate the 

 Morse System of Telegraphy in primary and secondary 

 schools. J> Cauderay, Lausanne. 



For the clockwork is substituted a small crank, which can be turned by hand. 

 This apparatus works by means of a single Bunsen cell, of small size. Its 

 low price, 40 frs., including the manipulator, places it within the reach of 

 every school. 



1669. Submarine Telegraphic Cables. Geminiano Zanni. 



In the above specimens the conductor (consisting of one or more copper 

 wires) is enclosed within a series of soft iron wires, which unite to form a 

 strand or core by passing the combined series of wires through a bath of 

 molten tin, or any other comparatively soft metal. The core thus combined 

 into a solid body is protected from corrosion. It is then coated with gutta 

 percha, or any insulating materials, over which tin, or other metal foil, is 

 wrapped to exclude moisture. A band of hemp (immersed in tar) is wound 

 round the core to protect the metal foil from injury or corrosion. 



1670. Ward's Dead Beat Telegraph. 



William Sykes Ward. 



Two delicate coils of fine wire are suspended on points around the poles of 

 powerful permanent magnets ; .the motions are limited so as to give distinct 

 indications without tremulous vibrations. Patented in 1847. 



1671. Signalling Key for Telegraphy, to send into a line 

 positive or negative currents. Elliott Brothers. 



1672. Patent Safety Indicator, for the more ready detection 

 of fire. Invented by A. C. Bagot, Esq., of Pembroke College, 

 Cambridge. Alfred App>> % 



This instrument detects fire instantly on board ships, in ricks, warehouses, 

 &c., gas in coal mines also, and rise or depression of temperature in conser- 

 vatories, &c. 



The invention, as applied to vessels at sea, may be thus described. 



There are placed in any one or more compartments, or even intermixed with 

 the cargo, ordinary metallic thermometers and metallic aneroid barometers, a 

 pair of each ; in some other portion of the vessel is placed a " Leclanche " or 

 other battery, and in the captain's cabin, or other special locality, there are 

 fixed an electrical indicator and bell, or other alarum. 



The pole of the battery is always in direct communication with the indicator 

 and bell. The other pole of the battery is similarly connected with a fixed 

 portion of each of the thermometrical and barometrical instruments at a dis- 

 tance somewhat removed from the sensitive metallic motors of these instruments 

 when in their normal state. 



Thus it will be seen that where there is no undue pressure or heat in any one 

 compartment of the vessel, the electric circuit with the battery is incomplete 

 or broken at the points separated by the termination of the conducting wires 

 from the battery and the sensitive metallic motors of the instruments before- 

 mentioned ; but in the event of any one or more of the compartments in which 

 the instruments are placed becoming heated or surcharged with gas so as to 

 become subject to an undue pressure, then the sensitive metallic motors of the 



