300 



BKNJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 353. Apparatus to show that extending the 



Surface diminishes the Quantity of 

 Electricity. This instrument (Fig. 353) 

 consists of a series of metallic plates, 

 increasing in size from the top, and sus- 

 pended from each other by metallic 

 threads, the upper one having a handle 

 of glass, or a silk cord being attached to 

 the upper plate. Let the plates rest on 

 each other, and placing the whole toge- 

 ther upon the top of a gold-leaf elec- 

 troscope, electrify them so that the gold 

 leaves diverge ; then gradually draw 

 them up by the silk thread at tli3 top, 

 when the diverging will diminish in 

 proportion, and again increase when let down as at first. 



Price, $2.00. 



- 354 - 



been 



Insulated Conductor for showing 

 d Electricity In/ Induction. (Fig, 

 354.) This is formed of a cylinder 

 of brass or tin, with well rounded 

 ends, and supported on a glass 

 stand, and furnished with a pith 

 ball electroscope, and let e be an 

 excited glass tube. On approach- 

 ing this tube within about six inches 

 distant from d, the pith balls will 

 instantly separate, indicating the 

 presence of free electricity. Now, 

 in this case the electric, e, has not 

 sufficiently near to the conducting body to 



brought 



communicate to it a portion of electricity, and the moment 

 that it is removed to a considerable distance the balls fall 

 together, and appear unelectrified ; on approaching e to d 

 the balls again diverge, and so on. The fact is, this is a 

 case of what is termed induction, the positive electricity of 

 e decomposes the neutral and latent combination in d a c, 

 attracting the negative towards d, and repelling the positive 

 towards e, and the balls consequently diverge, being posi- 

 tively electrified. On removing e the force which separated 

 the two electricities in c? a c is removed, the separated ele- 

 ments re-unite, neutrality is restored, and the pith balls fall 



