VOLTAIC ARC LAMPS. 191 



organs, they have liquids which act either by communicating 

 vessels, or by serving as the medium of discharge under 

 certain conditions, or by producing an effect like that of the 

 moderator lamps. The principal forms in this class are those 

 of Lacassagne and Thiers, Pascal of Lyons, Margais and 

 Duboscq, and Way. 



In Lacassagne and Thiers' apparatus, invented in 1856, 

 only the lower carbon is movable, and it is directed by a float 

 fitted in a long cylinder filled with mercury, which is placed 

 in communication, by a tube, with a reservoir of the same 

 liquid, and this last is fixed on the column that supports 

 the upper carbon-holder. The tube that establishes the 

 communication between the two vessels is bent across one 

 of the poles of a powerful electro-magnet so as to present 

 its curvature beneath the armature, and from this arrange- 

 ment it results that the armature/pressing on the part of the 

 tube when the current has its whole intensity, plays the part 

 of a stopper, So long, therefore, as the current keeps all its 

 power, the level remains the same in the two vessels, and 

 the lower carbon continues motionless ; but when the current 

 becomes feeble by the increase of the length of the arc, the 

 tube is then liberated a little, and a small quantity of the 

 liquid passes from the reservoir into the tube, and this causes 

 the carbon to rise until the current, having resumed its 

 original intensity, has again occasioned the obstruction of 

 the tube. The action of the spring antagonistic to the 

 electro-magnet is regulated by a second electro-magnet placed 

 in a very resisting derivation of the circuit, and which acts 

 in the same direction as it would on the armature of the 

 large electro-magnet, which is for this purpose prolonged 

 beyond its pivot. 



Margais and Duboscq's regulator is a kind of moderator 

 lamp, the rack of which acts on the two carbon-holders by 

 means of a double pinion, and in which the movement of the 

 piston depends on the more or less rapid flow of the oil 

 below it. For this purpose, the upper and lower parts of the 



