312 



LESSONS IN ELECTRICITY. 



FIG. 30. 



dicnlar to the straw, and from half an 

 inch to three quarters of an incli long. 

 It is easy, by means of a bit of cork or 

 sealing-wax, to. fix the wire so that the 

 little bent arms shall point not upward or 

 downward, but sideways, when the cross 

 is horizontal. The points of sewing 

 needles may also be employed for the bent 

 arms. A little bit of straw stuck into the 

 cross at the centre forms a cap. This 

 slips over a sewing needle, N, supported 

 by a stick of sealing-wax, A. Connect 

 the sewing needle with the electric 

 machine, and turn. A wind of a certain 

 force is discharged from every point, and 

 the cross is urged round with the same 

 force in the opposite direction. 



Place your left hand on the prime con- 

 ductor of your machine. Let the hand) 



You 



of course, so 



arrange the points that the wind from 

 some of them would neutralize the wind 

 from others. But the little pointed arms 

 are lo be so bent that the reaction in 

 every case shall not oppose but add itself 

 to the others. 



The following experiments will yield 

 you important information regarding the 

 action of points. Stand, as you have so 

 often done before, upon a board support- 

 ed by four warm tumblers. Hold a small 

 sewing needle, with its point defended 

 by the forefinger of your right hand, 

 toward your Dutch metal electroscope. 



31. 



be turned by a friend or an assistant : tho 

 leaves of the electroscope open out a lit- 

 tle. Uncover the needle point by the re- 

 moval of your finger ; the leaves at once 

 fly violently apart. 



Mount a stout wire upright on the con- 

 ductor, c, fig. 30, of your machine ; or 

 sapport the wire by sealing-wax, gutta- 



