KI.KrTRICITY. 



Lesson III. 



itself when the two kind* of electricity are uncombined, but al.-o \\-\u-n 

 they are combinc-d ; and tlu re tore wlu-n an rleetric body is placed neur 

 to a body in a natural condition, disturbance takes place. This is 

 easily demonstrated [Experiment 6]. Here is an insulated nu-tal 

 hook, with a metallic ring attached to it. and two fine metallic threads, 

 having pith-balls at their extremities. Now when I bring this roll of 

 resin (a), which has been rendered electric by friction, near to the 

 ring, the two balls will be repelled, although the resin is at a considerable distance 

 from them ; and the nearer it is brought the more the balls diverge; but immediately 

 the resin is removed the balls will fall together. [Removes the resin, and the balls 

 are seen as represented by the black balls in Fig. 6]. Now all this depends upon the 

 separation of the electricities which were combined in the metallic ring and pendulums 

 before the resin was placed near to them ; and the reason is this, the electricity 

 is repelled towards the balls, whilst the + electricity is attracted to the ring. 



When a body charged with one kind of electricity is placed near to other bodies, 

 but not in contact, it communicates the opposite kind of electricity to them. Let us 

 see that such is the case. Here is some apparatus of a simple kind that you may 

 construct for yourselves.* 



* I 



Fig. 7. Fig. 8. Fig. 9. Fig. 10. 



Fig. 10 represents the prime conductor of an electrifying machine ; Figs. 8 and 9 

 are two insulated metallic cylinders, placed end to end, but not in contact with each 

 other or the conductor. Fig. 7 , is an insulated brass ball, with a pith-ball (') sus- 

 pended to it, [Experiment 7]. Now if I turn the electrifying machine, the surface 

 of Fig. 10 is positively electrified, and acts upon the insulated cylinder Fig. 9, so as 

 to make the end r negatively electric, and the end v positively electric. This is by 

 induction, and we observe that the central part c is neutral, and that the adjoining 

 cylinder (Fig. 8) is also rendered negatively and positively electric at either end, as in 

 the other case; and further, that the brass ball (Fig. 7) is rendered negatively 

 electric on one side, and positively electric on the opposite side, so as to repel the 

 pith-ball (a'). 



QUESTIONS. 



27. T. What is meant by induction? 



P. It is the excitement exerted by a 

 body already electrified upon all sur- 

 rounding substances, and is exerted at 

 very sensible and considerable distances, 

 producing a state opposite to its own in 



the proximate parts, and a similar one 

 in the remote parts. [See Experiment 7]. 



28. T. Does the intensify of the elec- 

 trical disturbance depend upon the prox- 

 imity of the bodies? 



P. Yes, it diminishes with the distance 



* For the method of constructing various kinds of Philosophical, Chemical, Electrical, and other 

 apparatus, see the papers now publishing in the new eries of the Family Friend, on " Practical 

 Science." 



