VOLTAIC ARC LAMPS, 



173 



as the current is more or less energetic, there is motion or 

 rest in these carbon-holders. In the pattern shown in Fig. 

 43, this result is obtained by means of a large wheel R, which 

 carries on its axle the pulley c, on which is wound the chain 

 supporting the lower 

 carbon -holder. The 

 axle of the wheel rests 

 on a piece of iron A A 

 fixed to a jointed paral- 

 lelogram, and serving 

 as the armature of an 

 electro-magnet E con- 

 nected with the light 

 circuit. A spring 

 break F presses on the 

 circumference of this 

 wheel, and is suffi- 

 ciently bent to prevent 

 the wheel from turn- 

 ing when the latter is 

 at the proper height, 

 that is to say, when the 

 armature A is at its 

 greatest approximation 

 to the electro-magnet 

 E ; but when, in conse- 

 quence of the weaken- 

 ing of the current, this 

 armature is at a greater 

 distance, the wheel, by 

 dropping with the ar- 

 mature, withdraws from the break and is then able to turn by 

 the effect of the weight of the lower carbon (or of a spring 

 barrel attached to this carbon-holder), acting through the 

 chain which is wound about the pulley c. Thereupon the 

 lower carbon-holder rises, and the current, resuming its 



FIG. 43. 



