134 



ELECTRICITY. 



Lesson II 



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LESSON II. 



ELECTRICITY, according to Franklin, signifies a single imponderable fluid, which 

 produces the phenomena of positive and negative electricity, by its relative excess or 

 deficiency. Dufay and Symmer consider it to be two imponderable fluids, similar in 

 their properties, but diametrically opposed in their mutual relations. The hitter theory 

 has been more generally adopted as a means of explaining electrical phenomena, and 

 it has been considered that when these two fluids are united in one body, and they 

 mutually neutralize each other in that body, it is in its natural condition"; and when 

 the two electricities are decomposed in a body, if the vitreous electricity predominates, 

 it will become positively electric; but negatively, if the resinous electricity predo- 

 minates. A difference has always beeu made between the electric and magnetic fluids. 

 Very recently, however (Feb., 1852), Mr. Groves demonstrated before the members 

 of the Royal Institution that electricity is not a fluid, but merely a quality of djnaniu.- 

 relations between molecules. We will perform his experiment 

 for ourselves. [Experiment 3.] Here is a bar of wood suit- 

 ported at both ends, and having six small balls of ivory sus- 

 pended from it (a bed ef) by silk cords. Now let us imagine 

 that the line of balls represents the particles of a bar or wire 

 through which the electricity is to he transmitted. If we 

 remove thetball a, and allow it to impinge or strike against tin- 

 ball b, the whole line will not move forwards, but will appear t<> 

 act only on the ball/ at the other end of the row, causing it first to separate from tin 

 the rest and to be moved in the same direction as the ball which communicated tin 

 motion, viz., from the position of /to/'. The ball/' will, in turn, impinge on tin 

 ball e, and cause the ball a to be separated to the distance a', which is not quite s<> 

 great as that of/' from its original position/. From this experiment, Mr. Grove* 

 concludes, that as the transmission of a force without motion, except at the extremities 

 is very evident, that electricity or the transmission of what is calK-d the electric cur- 

 rent, may be referred to a parallel agency. Mr. Groves cited as an example of 

 the molecular disturbance of conductors when electricity is transmitted through them, 

 the -well-known expansion of a platinum wire when voltaic electricity is passed 

 through it, and the appearance of little globules all along the wire when electric 

 fusion was employed. 



[The pupil should read Catechisms I. and III., particularly pages 12, 14, and 70.] 



QUESTIONS. 

 19. T. If + electricity be given off 



/ ed c b a 

 Fig. 4. 





by friction in a body, does it not follow 

 that electricity must be given off in an 

 equal degree ? 



P. Yes ; and I will prove it to you by 

 a simple experiment. [Experiment 4.] 

 Here are two discs insulated by glass 

 rods. The upper one, which I hold in 

 my right hand, is made of glass, and the 

 lower one of wood covered with leather, 

 which has been rubbed over with amal- 

 gam. Now, when I rub these two discs 



together, you will not observe 

 any traces of electricity as long 

 as they are in contact; but im- 

 mediately that 1 separate them, 

 the one becomes positively elec- 

 trified, and the other negatively. 

 [Does so, and the result is as 

 anticipated.] 



20. T. Do you imagine thru 

 bodies show a preference for 

 either kind of ekcrrieity ? 



P. No ; the same body may 



