Lesson III. 





133 



be ni; v olec- 



jt is r . s positively 



electric when ruhbM wiih wool or silk, 

 i with fur. 



II. 1 >: bodies influenced by 



circumstances ? 



P. \ \r. arrangement of the 



moleci . iture, and the surface 



of the bcid-L-s produce different effects 

 from those usually observed : for ex- 

 ample, a blacl; silk riband will be ren- 

 dered nejra'ivi'iy electric if rubbed with a 



/". How is electricity communi- 



/'. When free it may pass from one 



. eith.-r by in: 



contact, or by traversing a distance of 

 more or less" extent between the body 

 communicating and the body conveying 

 it. It may h. communicated by ; 

 from one body to another withou' 



and then we ohs. rve what is 

 o .IK-d an electric spark. [Experiment 5.] 

 a metal rod, and VMI will observe 

 that when it is brought rear to the con- 

 ductor of the electrifying machine, that a 

 vivid spark is produced, and also a snap- 

 ping noise. [Does so, and the effect is 

 observed.] If I placed my k:. 

 near a rubbed glass or shell- lac rod, the 

 effect would be the same, only much 



! it possible to draw . 

 sparks from the human bo-: 



. n stand upon a stool 

 with glass Ifgt, and bring the body into 

 contact wit! tor of an electrical 



turned, 

 1 a peculiar creeping K 



If I get upon 



snlated Mool, and place my knuckles near 

 any j . p, a spark will be 



1, and a shock gm n in pr< 

 to the distance the electricity has tra- 

 VMMd 



/'. How is electricity dulri 1 



/'. According to the amount of sur- 

 faces on passing from one insulated con- 

 ductor to another. Suppose that a charged 

 1 conductor is brought in contact 

 i'h the ground, it will lose all its elec- 

 tricity, because it is distributed over so 

 large a surface. And further suppose two 

 ic halls, both the same size and 

 iusula-ed ; the one on the right being 

 . d and the other not. When these 

 re brought in contact, the 

 electrified one will lose exactly half its 

 elcctn- 



T.' What are the best insulating 

 substances ? 



/'.The vitreous and resinous non- 

 condiuvors (see Q. 7), such as shell-lac, 

 sulphur, dry glass, and also silk. 



26. 7". Wo know that there are two 

 kinds of electricity, because it has been 

 demonstrated by experiment. I wish to 

 know if one kind only can be developed 



/'.Certainly not. One kind of elec- 

 tricity cannot be developed without the 

 oiher, any more than one kind of mag- 

 netism. If a body is rubbed, the body 

 and the rubber assume opposite states; 

 the one is positively and the other nega- 

 tively electrified. "(See Q. 19.) 



x n 

 > respecting 



ny reason to doubt the 

 <>!<! th ory tii fluid? 



in we excite equal degrees of po- 

 ;id lu-LMtiv at the same 



>ns of friction? 



>n the same body have opposite 

 States if ler:rieity (i- 



5. In what manner H y com- 







6 Is it possibk >sitive elcc- 



uthout developing negative eke- 



LKs>n\ in. 



have already seen that the opposite states :> attract one another, 



and, like states, repel e . Now this attraction n > show* 



