LESSORS IN ELECTRICITY. 35 



flannel, the electricity of the body is negative ; if it repel, or is re- 

 pelled by, glass, rubbed with silk, its electricity is positive. Du Fay 

 had the sagacity to propose this mode of testing quality. 



Apply this test to the strips of foolscap paper excited by the In- 

 dia-rubber. Bring a rubbed gutta-percha tube near the electrified 

 strips, you have strong attraction. Bring a rubbed glass tube be- 

 tween the strips, you have strong repulsion and augmented diver- 

 gence. Hence, the electricity, being repelled by the positive glass, is 

 itself positive. 



Sec. 11. Double or " Polar'''' Character of the Electric Force. We 

 have examined the action of each kind of electricity upon itself, and 

 upon the other kind ; but hitherto we have kept the rubber out of 

 view. One of the questions which inevitably occur to the inquiring 

 scientific mind would be, How is the rubber affected by the act of 

 friction ? Here, as elsewhere, you must examine the subject for your- 

 self, and base your conclusions on the facts you establish. 



Test your rubbei-, then, by your balanced lath. The lath is attract- 

 ed by the flaunel, which has rubbed against gutta-percha ; and it is 

 attracted by the silk, which has rubbed against glass. 



Regarding the quality of the electricity of the flannel or of the 

 silk, the attraction of the lath teaches you nothing. But, suspend 

 your rubbed glass tube, and bring the flannel rubber near it: repul- 

 sion follows. The silk rubber, on the contrary, attracts the glass 

 tube. Suspend your rubbed gutta-percha tube, and bring the silk 

 rubber near it : repulsion follows. The flannel, on the contrary, at- 

 tracts the tube. 



The conclusion is obvious : the electricity of the flannel is posi- 

 tive, that of the silk is negative. 



But the flannel is the rubber of the gutta-percha, whose electrici- 

 ty is negative ; and the silk is the rubber of the glass, whose elec- 

 tricity is positive. Consequently, we have not only proved the rub- 

 ber to be electrified by the friction, but also proved the electricity 

 of the rubber to be opposite in quality to that of the body rubbed. 



Sec. 12. What is Electricity? Thus far we have proceeded from 

 fact to fact, acquiring knowledge of a very valuable kind. But facts 

 alone cannot satisfy us. We seek a knowledge of the principles 

 which lie behind the facts, and which are to be discerned by the mind 

 alone. Thus, having spoken, as we have done, of electricity passing 

 hither and thither, and of its being prevented from passing, hardly 

 any thoughtful boy or girl can avoid asking, What is it that thus 

 passes ? what is electricity ? Boyle and Newton betrayed their 

 need of an answer to this question when the one imagined his unc- 

 tuous threads issuing from and returning to the electrified body, and 

 when the other imagined that an elastic fluid existed which penetrated 

 bis rubbed glass. 



When I say " imagined " I do not intend to represent the notions 



