VOLTAIC ARC LAMPS. 189 



Girouard's lamp, which is a clockwork regulator somewhat re- 

 sembling that of Foucault or Serrin,but acting under the power 

 of a kind of relay-regulator, and therefore capable of being 

 controlled from a distance. The system consists, therefore, 

 of two apparatus: i. An electro-magnetic coil with thick wire, 

 through which the current of the generator passes, and which 

 acts on a double contact ; 2. A lamp with a double clock- 

 work motion, on which act two electro-magnets with fine wires, 

 excited by the current of a battery of very feeble intensity. 

 The current of the generator, after having traversed the 

 electro-magnet of the relay-regulator, passes directly, there- 

 fore, through the carbons of the lamp, and their distance 

 apart is regulated by an independent system which works by 

 the influence of the two contacts of the relay-regulator. 

 When the current has its full intensity, the mechanism con- 

 trolling the separation of the carbons is set in motion, and 

 when on the contrary the current is too much enfeebled, the 

 .second clockwork mechanism is liberated, and this brings 

 the carbons nearer together. In order to obtain this double 

 action in opposite directions, Girouard used a spring barrel 

 with a double movement. The complete description of this 

 system may be found in vol. V. of my Expose des applica- 

 tions de V clectridte, p. 495. 



In order to increase the duration of the carbons, circular 

 carbons have been used. Indeed, the first electric lamp was 

 made by Thomas Wright on this system. Subsequently, in 

 1849, Lemolt, taking up Wright's idea, constructed a better 

 apparatus, in which the two discs of carbon, supported by 

 two curved and jointed levers, were set in motion by a 

 double system of pulleys driven by the clockwork mechanism. 

 A spiral spring connecting the two curved levers, pressed 

 the two carbon discs against each other, and these were 

 separated at very short intervals by the action of an eccen- 

 tric put in motion by clockwork. The result was a series of 

 sparks succeeding each other rapidly enough to impress the 

 sight as a continuous light. After this system came that of 



