ELECTRICITY. 



On positive 

 nd negative 

 electricity, 



PLATE 



(I XI, III. 

 Fig. 1. 



Two tiiffe- 

 rcrit kind* 



ty procured 

 luidrr dilic- 



u-- 

 CUIDSUUCtS. 



The eutaUncfe in die above list which are marked 

 in italic^, are evidently such aa cannot be excited by fric- 

 tion; but they ar. in the tal)le, from their pps- 



sCMing, like the other < mother property, which 



we shall soon have occasion to notice. All bod> 

 Contained in the preceding enumeration, cannot be con- 

 sidered as non-clei tries. Those only are properly en- 

 titled to that name, which have been found incapable 

 of electrical excitation. A lUt of them will be intro- 

 duced with more propriety under another head. 



SECT. II. On Positive and Negative Electricity. 



IN whatever manner, and by whatever bodies, clcc- 

 tricity is produced, its general effects are always the 

 game. Electric attraction, and electric light, are both 

 produced, whether we make the experiment with exci- 

 ted glass, or excited amber. The electricities, however, 

 generated from these two substances, have different cha- 

 racters, which manifest themselves by an attentive exa- 

 mination of their effects. If two small balls, turned 

 from the pi'.h of elder, are suspended by silver wires, 

 or fine threads, a- is represented in Plate CCXLIII. Fig. 

 1. they will remain in contact. But as soon as a tul>e 

 of !jl;'S!i, excited by friction, is presented to them, the 

 'nails diverge, and separate from each other, as in the 

 figure. The same divergence is produced, by presenting 

 1 amber or wax to the pith balls. Bnt if, when 

 the pith balls are in a state of divergence by the ap- 

 plication of excited glass, we present also to them a 

 stick of excited wax, the electricity will disappear, and 

 the balls will collap'se. If, on the contrary, when the di- 

 vergencv of the balls has been produced by the applica- 

 tion of excited wax. we present to rhevn a tube of exci- 

 ted glass, the balls will collapse as before. If the exci- 

 tcd wax, and the excited glass tube, are presented to- 

 gether to the pith balls, no divergency will take place. 

 Here then we have an unequivocal indication of two 

 different kinds of electricity, viz. that of the glass and 

 of the scaling- wax, the one always counteracting the 

 effect of the other. These two kinds of electricity were 

 denominated the vitreous and the resinous electricities, 

 from the bodies by which they were produced ; but as 





r been found, that resinous electricity can be 

 obtained by the excitation of glass, and vitr 

 tricity from the excitation of resinous bo:'.ic-, the terms 

 of vitreous and resinous can no longer be admitted. The 

 ti nns jtitxitiff and nrgiitirr, or /)///.? ar.il mums, have 

 therefore been universally employed to denote the vi- 

 treous ami rc-mous electricities. 



The substitution of these new terms will appear -till 

 more appropriate, when we consider tliat. in every case, myaiive 

 where a body is excited, both |>ositive and negative el 

 electricity are simultaneously produced, and in almost jj 1 

 every case can be rendered visible by the application of ,,,, t j me> 

 the pith balls. This truth admits of a very simple proof, 

 by exciting sealing-wax with dry flannel, nnd applying 

 them together anrt separately to the pith balls. When 

 they are applied separately, the flannel will indicate .1 

 positive electricity, like a tube of glass excited with silk, 

 while the wax will indicate negative electricity. When 

 re prcvntcd together to the pith balls, no effect 

 whatever will take place, so that the positive electricity 

 of the flannel is in equilibrium with, or equal in effect 

 to, the negative electricity of the wax. In the .same 

 manner, when the black ribbon is separated from tin- 

 white ribbon, after being excited in the manner already 

 described, the black ribbon will be found negatively, 

 and the white ribbon positively electrified. 



But the positive and negative electricities are rot 

 only simultaneous phenomena ; any electric can be 

 made to exhibit either of the electricities, according to 

 the nature of the substance with which it is excited, Or 

 the state of the surface of the electric itself. This im- 

 portant discovery we owe to MrC'anton, who establish- 

 ed it by numerous experiments. Polished glass, for ex- 

 ample, is positively electrified when rubbed with flan- 

 nel, but negatively electrified when rubbed with the 

 back of a cat ; while rough glass acquires positive elec- 

 tricity by the friction of dry oiled silk, and negative 

 electricity by the friction of flannel. 



The results of the numerous experiments which 

 have been made on this subject, are contained in the 

 following Table, altered and greatly enlarged from th:' 

 Table drawn up by the late Mr Cavallo, from the expe- 

 riments of various electricians. 



^ T tfM,^/c.or 

 Suhttuncei ruMica. , 



Back of a living cat 



Smooth glass . . 



Rough glass . . 



Tourmalin . . . 



Hare-skin . . . 



White ilk . . . 



Black silk . . . 



Positive 

 Positive 

 Negative 



t Positive 



(_ Negative 



Positive 

 Negative 

 'Positive 

 Negative 

 Positive 

 Negative 

 Positive 



Negative 



Substantrs vith tiV. tlie Electrics are excited. 



Every substance which has hitherto been tried. 



Kvery substance which has hitherto been tried, except the back of a cat 



and mercury. 



The back of a cat, and sometimes caoutchouc. " 



Dry oiled silk, sulphur, metals, white wax, sealing-wax, or any resinous 

 matter; every substance being considered resinous which is inflammable, 

 nnd soluble in oils, alcohol, and ether. + 

 Woollen cloth, quills, wood, paper, the human hand, and the back of a 



cat. 



Amber, blast of air from bellows. 

 Diamonds and the human hand. 



Metals, silk, loadstone, leather, human hand, paper, and baked wood. 

 Other finer furs. 



Black silk, metals, and black cloth. 

 Pa]>er, human hand, hair, weasel's skin. 

 Sealing wax. 



f Hares, weaselg, and ferrets skin, loadstone, brass, silver, iron, human 

 I hand, white silk. 



De Luc found, that when glass And caoutchouc were rubbed together, the electricity wa on some days positive, and on ot'icr days ne- 

 .gauvc. See A'icAalMm'i Journal, voL uriii. p. 1 1. 



r The effect of wax and retinous bodies it here given on the authority of Litres, 

 ricitr to rough glass. 



Cavallo states, that they communicate negative 



