.ELECTRICITY. 



own in the remote part. Hence the neu- 

 trality of the second body is destroyed by 

 the action of the first ; and the adjacent 

 parts of the two bodies, having now 

 opposite electricities, will attract each 

 other. It thus appears, that the attrac- 

 tion which is observed to take place 

 between electrified bodies and those 

 that are unelectrified, is merely a con- 

 sequence of the altered state of those 

 bodies, resulting directly from the law 

 of induction ; and that it is by no 

 means itself an original law, or primary 

 fact in the science. 



(39.) The effects of induction will 

 be in proportion to the facility with 

 which changes in the distribution of 

 electricity among the different parts of 

 a body can be effected, a facility which 

 corresponds with the conducting power 

 of the body. Hence the attraction ex- 

 erted by an electrified body upon ano- 

 ther body previously neutral, will be 

 much more energetic if the latter be a 

 conductor, than if it be an electric, in 

 which these changes can take place 

 only to a very small extent. This is 

 confirmed by the following experi- 

 ment : suspend by fine silk threads of 

 equal length, two small balls of equal 

 dimensions, both made of gum-lac, 

 but one having its surface covered 

 with gold leaf. Place these two pen- 

 dulums, as they may be called, at a 

 little distance from one another, so as 

 to admit of a comparison of their mo- 

 tions ; and then present to them an 

 excited electric, which may be either a 

 tube of glass, or a cylinder of sealing- 

 wax. It will at once be seen that the 

 ball, with a metallic covering, which 

 readily admits of the transfer of elec- 

 tricity from one side to the other, will 

 be much more readily and powerfully 

 attracted, than the other ball which 

 allows of no motion in its electricity. 

 The latter ball will, by slow degrees, 

 however, assume electrical states of the 

 same kind as the gilt ball, and will be 

 feebly attracted. As this change is very 

 slowly effected, so it is more permanent 

 when once produced ; and the plain 

 ball adheres for a considerable time to 

 the electric which has attracted it. The 

 gilt ball, on the contrary, is sooner re- 

 pelled, by its readily receiving the 

 charge of electricity imparted to it by 

 the electric. A degree of permanent 

 electricity, however, is also induced on 

 this ball, in consequence of its gradual 

 penetration into the substance of the 

 gum-lac. 



CHAPTER II. 



Theories of Electricity. 



(40.) It is impossible to arrive at the 

 full comprehension of the multifarious 

 facts relating to any of the physical 

 sciences without the aid of some lead- 

 ing principles, or modes of viewing 

 them, by which their connexions can 

 be represented to the mind, so as to 

 combine them into an intelligible system. 

 We begin by classing the different 

 agents in nature, designating them by 

 specific names ; we next endeavour to 

 conceive these agents as possessed of 

 certain pow r ers or qualities adapted to 

 the production of the observed effects. 

 In the case of light, for example, we 

 may conceive the phenomena to result 

 from the action of material particles, 

 emanating in all directions from the lu- 

 minous body, and obeying certain laws 

 in their course ; or we may adopt ano- 

 ther hypothesis, namely, that they pro- 

 ceed from the undulations of an elastic 

 medium pervading space. By employ- 

 ing either the one^or the other of these 

 hypotheses, we acquire great facility in 

 tracing the connexions of the pheno- 

 mena of optics, and retaining them in 

 our minds. This advantage is not im- 

 mediately dependent on the truth of the 

 particular hypothesis we employ for 

 that purpose : for, in the example before 

 us, it is evident they cannot both be 

 true, and yet they both answer this 

 end. But, of course, the utility of an 

 hypothesis will be proportionate to the 

 degree of exactness with which it ac- 

 cords with the phenomena. No incon- 

 venience can arise from its adoption, as 

 long as we bear in mind that our rea- 

 sonings are founded on a mere hypo- 

 thesis, and as long as we hold our- 

 selves in readiness'to abandon it, the 

 moment we meet with facts with which 

 it is decidedly inconsistent. 



(41.) The hypothesis .which naturally 

 suggests itself for the explanation of 

 electrical phenomena is that of a very 

 subtile and highly elastic fluid, pervad- 

 ing the earth and all other material 

 bodies, but itself devoid of any sensible 

 gravity. We must suppose this fluid 

 to be capable of moving, with various 

 degrees of facility, through the pores, or 

 actual substance of different kinds of 

 matter. In some, as in those we call 

 conductors, or non- electrics, such as 

 the metals, it moves without any per- 

 ceivable obstruction : but, in glass, 

 resin, and, in general, in all bodies 





