Lesson III. 



li V. 





from the charged body (d Fig 10); and 

 if it is entirely removed, all the disturb- 

 ance ceases, thus demonstrating that the 

 nent was only temporary or in- 

 duced. 



'29. T. Suppose that one end of an 

 insulated cylinder (Fit/. 9) is made to 

 communicate with the ground by means 

 of a conducting medium, what would be 

 the el": 



VI, I,- the electric body (d Fig. 10) 

 still acred by induction, all the repelled 

 electricity would be carried off by the 

 earth, and the i;isuhted conductor re- 

 main charged only with the electricity of 

 iucting b.>dv. If we remove the 

 communicating nudium with the 

 and the inducting body, the insulated 

 conductor will be. charged throughout 

 with the same electricity. 

 30. 7'. What is an e'lectroscope? 



\n instrument for 

 shoeing t! 



of electrical excitement. 

 It may be constructed of 

 two pith-balls (/ 

 or two strips of gold leaf, 

 enclosed in a glass vessel, 

 to prevent the action of 

 current* of air, &c., upon 

 11) Some- 



times t <^>pe is 



tarnished with a gnu 

 duated arc, in which case 

 it acts as an nu-usurcr of 



i_-iy. 



/'.How is the electroscope used? 

 /' lfw wish to examine what is tin- 

 nature of the electricity of a body, we 

 charge the electroscope with a kind of 

 ve know; for example, by 

 .: a roll of shell-lac over the disc, and 

 finger, so as 

 to carry <>tf all th- 

 ai In w th*- other to be * 1 accu- 

 Now obft'-rve, 

 ids a roll of shell-lac 

 ctmtcope, which is i 



with f 



ivi-s is observed], when I rcaOTC 



. 



"i leavm will di- 

 i-.rs pa rate. 



as in /',.>. II]. Now it is erid 

 nt is charged wi 



tit of the shell-lac. 



To render this plainer, we have only to 

 say that if we want a negative charge 

 M ruS a glass rod with silk, and use 

 that, because it is + electric. 



/'.How do you account for the 

 action <.f electric bodies upon the elec- 

 trosco; 



/'. By the laws of electrical induction. 



33. 7'. What apparatus do we require 

 to develop friction*! e ectric 



/'. The apparatus is very extensive, 

 because we also require some for collecting 

 the electricity, as well as developing it. It 

 will be better to describe each s-pa 



34. 7'. H>w do you usually excite and 



I\ By an electrical machine, which is 

 generally a hollow cylinder, or a circular 

 plate of pl.isv All frictional electrifying 

 machines consist, 1st, of the electric body 

 to be excited; 2ndly, of a rubber or ex- 

 citer; and 3rdly. of an insulated conductor 

 for collecting the electricity. 



35. T. Then it is not necessary to have 

 a glass electrifying machine. 



P. Certainly not, any electric body will 

 answer. In the (lrc.it I'.xlnlrtion there 

 was a gutta-percha machine. (C. 10, No. 

 444). 



36. T. Explain the construction of the 

 cylindrical machine. 



Fif. I). 



/' I- <>MMtg of a hollow cylinder of 

 gltM (CO), which in c< 

 volves i ) 

 pillars of glass (i 



