PART III. ELECTRIC LAMPS. 



IN order to obtain a continuous action from the carbons 

 used for the electric light, these carbons must, in proportion 

 to their consumption, be brought near each other, so that the 

 intensity of the current may be kept as constant as possible. 

 Now in order to obtain this result, arrangements have been 

 contrived which effect it automatically, and these form what 

 are called regulators of the electric light, or simply electric 

 lamps. Of course the construction of these apparatus varies 

 according as the light is produced by the voltaic arc or by 

 incandescence. 



VOLTAIC ARC LAMPS. 



Electric lamps are of an earlier date than is generally 

 supposed. In 1840 they consisted of a kind of Lannes 

 exciter, the balls of which were replaced by sticks of carbon, 

 which were pushed forward by hand as they were consumed, 

 and the apparatus had the form represented in Fig. i. A 

 little later an attempt was made to render the forward move- 

 ment of the carbons automatic by placing the holders under 

 the control of clockwork, or of electro-magnetic effects, which 

 could act as a balance, that is to say, on the least variation 

 in the intensity of the current. Then the idea was conceived 

 of arranging the, carbons so as to burn like a candle, and it 

 is to this last plan that recourse has been had in the attempts 

 at electric lighting of the streets, which so astonished visitors 

 during the whole period of the Exhibition of 1878. 



