CHAP, viii.l THE ELECT RIU LIGHT. G75 



are sufficiently near together. The contact then rests on the horizontal 

 arm of the bent lever L, movable about F'. The vertical arm L of 

 this lever, by the intervention of a shorter lever Im, stops a toothed 

 wheel, which carries the regulating " fly " g of the wheel-work. The 

 motion of the wheel-work is then arrested as long as contact continues. 



The wearing away of the carbons, and their consequent too great 

 separation, enfeebles the current, the antagonistic spring s carries away 

 and separates the armature from the poles of the electro-magnet, and 

 the wheel-work is set free. The wheels pp' are then put in motion, 

 and the two racked rods sand T move in opposite directions; the 

 carbons c and c are drawn together, the current and the luminous arc 

 recover their original intensity, which causes a fresh contact of the 

 armature and stoppage of the wheel-work, and so on. The toothed 

 wheel which drives the rack T has a radius double of that of the 

 wheel which brings down the rack s. In this way the positive 

 carbon moves twice as far as the negative carbon, and the luminous 

 arc remains at a constant height. 



We must pass on now to Foucault's and Serrin's regulators, both 

 used in the industrial applications of the electric light. Fig. 442 

 represents the first of these apparatus. 



The racks H and D which carry the carbons are arranged pretty 

 nearly as they are in Duboscq's regulator ; only the toothed wheels 

 that move them can turn in two opposite directions, because they are 

 connected with a double clockwork movement, one part of which is 

 stopped, while the other goes. On this account the carbon cones are 

 able either to approach each other, or, on the contrary, to separate. 

 The automatic recoil of the carbons dispenses with their being put in 

 position by the hand, and prevents their accidental contact, from which 

 would result an extinction of the luminous arc. 



The two wheel-work arrangements are provided with two fly- 

 wheels or star-shaped regulators o o', on each of which the head t of 

 the lever T, acts alternately, obtaining its motion from the armature of 

 the electro-magnet E. When the " fly " o is caught, the correspond- 

 ing wheel-work is stopped, but then o is set free, and its wheel-work 

 is put in action ; an inverse motion of the armature and the lever T 

 produces the contrary effect. We will now explain under what 

 circumstances, and by what mechanism, these contrary motions are 

 produced. 



x x 2 



