328 ELECTRO-IXDUCTIOX. SECT. XXXII. 



In telegraphs on land the intensity of the battery or magnets 

 is increased by induction on the same principle. It is by intensity 

 that the electric current is enabled to pass through the wires, and 

 that is augmented by increasing the number of coils round the 

 cylinder : however, it is only advantageous when the distance 

 between the stations is great, for then the resistance in the addi- 

 tional coils bears a small proportion to the resistance offered by 

 very long wires, but a very great proportion to that opposed in 

 very short ones. The nice adjustment for each case has been 

 determined by the experiments of eminent electricians, and all 

 the arrangements have been brought to great perfection in this 

 wonderful triumph of science, which is due to Volta, who called 

 into existence the fiery stream, and to Faraday, who has given it 

 the energy of the lightning. 



When the length of the wire in the helices of an electro-magnet 

 is very great, it offers increasing resistance to the passage of the 

 electricity, so that the cessation of magnetism is not instantaneous 

 when the contact with the Voltaic battery is broken. To remedy 

 that defect an instrument has been invented which instanta- 

 neously deprives the apparatus of the remaining electricity. A 

 great length of fine wire gives the severest shocks, while a shorter 

 and thicker wire gives the longest sparks and ignites the greatest 

 quantity of platinum wire. 



Kuhmkorff's electro-inductive apparatus has either been im- 

 proved, or new machines constructed, by Messrs. Grove, Gassiot, 

 and Joule, of intense energy. Indeed, so great is the energy of 

 electro-induction, that hopes were entertained of its superseding 

 steam as a motive power. For the current of electricity from an 

 electro-magnet can be made to flow in opposite directions, so as 

 to produce alternate attractions and repulsions, and consequently 

 a continued motion, which might be applied as a motive force 

 to machinery. However, Mr. Joule has proved that the power 

 developed by one pound of coal in combustion is to that produced 

 by one pound of zinc consumed in Mr. Grove's powerful electro- 

 magnetic apparatus as nine to one, so that, even if zinc were as 

 cheap as coal, and a Voltaic battery as easily kept in order as an 

 engine-furnace, electricity will not supersede steam as a motive 

 power. 



A current of electricity traversing a conductor gives out a 

 quantity of heat determined by fixed laws, the amount of which 

 is invariable as long as the machine to which it is applied remains 



