676 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



F is the armature which the poles of the electro-magnet E draws 

 into contact/ provided that the intensity of the current depending on 

 the distance of the carbons is sufficient to overcome the power of the 

 antagonistic spring K. This latter does not act directly on the branch 

 p of the lever F, but on a lever situated above, and movable at x. 

 When the current lias its normal intensity, the rod T is vertical, and 

 the two trains of wheels, both stopped, are immovable. When 

 the current grows weaker F leaves the poles, the branch T inclines 

 towards the right, stopping the fly-wheel o', and the wheel-work to 

 the left of the figure, which draws the carbons together, is put in 

 motion. The current gradually regains its strength, the lever moves 

 in the opposite direction, and if the intensity increases beyond a 

 certain limit, that is to say, if the carbons approach each other more 

 than is necessary, . the wheel-work producing a recoil is put in 

 motion, while the other is stopped. By the aid of a screw, which 

 acts on a lever R, the tension of the spring can be suitably regulated 

 to the intensity of the current employed. Finally, by modifying one 

 of the parts of the mechanism, we can make the velocities of the 

 two points equal, or make the positive carbon move twice as fast 

 as the other. This regulator can therefore work just as well with 

 a battery as with a magneto-electric machine. 



The lever x, which acts on the branch p of the armature, has its 

 under surface slightly curved, so that the point where the lever acts 

 changes in position; the action of the spring is therefore also variable, 

 and varies according to the intensity of the current. Since the 

 curvature in question is very slight, the resulting oscillatory motions 

 of the armature are themselves very small, so that the approach and 

 separation of the carbons takes place by almost insensible gradations, 

 and there is a remarkable constancy in the light. 



In Serrin's regulator (Fig. 443) the upper carbon-holder A B has a 

 rack which works into the toothed wheel F ; it tends to descend by 

 its own weight, and to make the carbon c descend, and also to turn 

 the toothed wheel. On the axis of the latter is fixed a pulley G, 

 which by means of a chain arid a turning pulley J communicates an 

 ascending motion to the rod K K, which carries the lower carbon. 

 This motion takes place so long as no current passes, and thus draws 

 the carbons into contact. When, however, the circuit is closed and 

 the current is introduced into the apparatus, the electro-magnet E 



