CHAP, ix.] ELECTRO-PLATING. 701 



CHAPTER IX. 



ELECTKO-PLATItftt. 



I. HISTORICAL SKETCH. 



WE have seen that electricity transmits to a distance, with a pro- 

 digious rapidity and under very varied forms, the signals made with 

 telegraphic apparatus, sometimes limited to simple oscillatory motions 

 of the needles of a galvanometer, sometimes writing or even printing 

 in known characters the letters of a message, and sometimes repro- 

 ducing with a surprising fidelity the fac-simile of the writing or 

 drawing which forms the message to be sent. Telegraphy then is a 

 mechanical application of electricity, or rather of electro-magnetism, 

 since the principle is the reciprocal action of galvanic currents and 

 magnets, It is by using the repulsions and attractions of electro- 

 magnets too that electric horology, chronographs, automatic registers 

 of physical phenomena, electric engines, and a crowd of apparatus 

 now used in the most varied branches of art and manufactures, have 

 V>een invented. 



But electricity does not only produce motion, it heats bodies, 

 jind that in so energetic a manner that it melts and volatilizes 

 metals and other refractory substances, and kindles at a distance the 

 fuses of mines, and the protecting torpedoes of ports and coasts. The 

 brilliant light which is given out between the two carbon points 

 rivals in intensity even the rays of the sun. By means of a 

 mechanism whose motion is regulated by the variations of the 

 intensity of the current, and by the combustion itself, the light of 

 the voltaic arc can also be used for many purposes. It pierces, too, 

 the mists in the darkest nights, and the lighthouses which Fresnel's 



