DETAILS OF CONSTRUCTION. 



of the current upon these magnets are so regulated that it is 

 established upon each of them at the moment one of the bars of 



soft iron a is approaching it, and it is suspended at the moment 

 the bar begins to depart from it. Thus the attraction accelerates 

 the motion of the drum upon the approach of the piece a towards 

 the magnet b, and ceases to act when the piece a arrives in front 

 of b. The action of each of the six impelling forces upon each of the 

 eight bars of soft iron attached to the drum is thus intermitting. 

 During each revolution of the drum, each of the eight bars a 

 receives six impulses, and therefore the drum itself receives forty- 

 eight impulses. If we suppose the drum to make one revolution 

 in four seconds, it will therefore receive a succession of impulses 

 at intervals of the twelfth part of a second, which is prac- 

 tically equivalent to a continuous force. 



The intervals of intermission of the current are regulated by 

 a, simple and ingenious apparatus. A metallic disc c is fixed upon 

 the axis of rotation. Its surface consists of sixteen equal divisions, 

 the alternate divisions being coated with non-conducting matter, 

 A metallic roller 7i, which carries the current, presses constantly 

 on the surface of this disc, to which it imparts the current. Three 

 other metallic rollers e, f, g press against the edge of the disc, and, 

 as the disc revolves, come alternately into contact with the con- 

 ducting and non-conducting divisions of it. When they touch 



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