ELECTRICAL INVENTIONS 235 



see p. 238.) On the other side of the rectangle the current is 

 moving down instead of up, and consequently will be attracted 

 by the south pole. The curved wire loses contact with the wire 

 of the open square as the rectangle turns, but the momentum 

 of the rectangle carries it on around until contact is again made 

 and the process just described is repeated. 



FIG. ioo. Diagram of a commercial electric motor, skeleton view. (After 

 Trevert.) 



The commercial motor (Fig. ioo) is made up of a number of 

 such simple rectangular units, each consisting of many turns of 

 wire instead of a few. .These units may be so mounted that they 

 have a common axis, which is also the axis of an iron cylinder. 

 The tops and the bottoms of the rectangles are, therefore, diam- 

 eters of the ends of the cylinder. The sides of the rectangles 

 lie in the surface of the cylinder, separated from each other by a 

 few degrees of space. This structure is mounted on an axle 

 coincident with the axis of the cylinder. The ends of the wire 

 of each unit are both brought to the same end of the rectangle 



