FRICTIONAL ELECTRICITY. 203 



When a body is electrified, it gives up a part of one of the fluids 

 and gains an equal amount of the other. The change is wholly in 

 the kind ; not at all in the quantity. The body which has an excess 

 of + electricity is positively electrified. This involves an excess of 

 electricity in some other body which is negatively electrified at 

 the same instant. Hence the electricity of the rubber must be of 

 the kind opposite to that of the body rubbed. Experiment confirms 

 the deduction. 



336. Electric and Magnetic Fluids Compared. 



These two sets of imaginary fluids have many obvious points of 

 resemblance, but they have one marked difference. Neither mag- 

 netic fluid can leave the molecule to which it originally pertained ; 

 either one of the electric fluids may leave its molecule and be 

 replaced by a like amount of its opposite. 



337. Induction. From several of the preceding 

 experiments we see that actual contact with an electrified 

 body is not necessary for the manifestation of electric 

 action in an unelectrified body. When an electrified body 

 C, is brought near an insulated unelectrified conductor B, 

 the neutral fluid of the latter is decomposed by the influ- 

 ence of the former. The electricity of (7, repels one con- 

 stituent of the neutral fluid in B and attracts the other, 

 thus separating them. The second body, B, is then said to 



be polarized. The same fluids of 

 B, each of which a moment ago 

 rendered the other powerless, are 

 still there in full quantity, but 

 they have been separated and each 

 clothed with its proper power. 

 This effect is due to the mere 



presence of the electrified body (7, which is said to decom- 

 pose the neutral fluid of B by induction. When C is 

 removed, the separated fluids of B again mingle and neu- 

 tralize each other. 



