ELECTRICITY. 



431 



ariam 



Substances viui 



the Elttbics use sictied. 



Woollen cloth . 



Sealing wax. t 



Baked wood 



Sulphur . . 

 Resinous bodies 



they exhibit, 

 Positive 



Negative 



f Positive 

 (_ Negative 



Positive 



Xegative 

 ' Positive 



Negative 

 'Positive 



Negative 



Descriptive 

 Electricity. 



Ziiu 1 strong, silver, bismuth strong, copper, lead, oligist iron. 

 Platina, gold, tin, antimony, gray copper strong, sulphuretted copper 

 strong, pyritous copper strong, sulphuretted lead, tellurium of naygag 

 strong, antimonial silver, sulphuretted silver strong, nickel, gray cobalt, 

 arsenical cobalt, sulphuretted antimony, sulphuretted iron, oxydulous 

 iron. 



r White wax, rough glass, sulphur, and all the metals that have been tried, 

 J except iron, steel, plumbago, lead, and bismuth. Caoutchouc, according 

 to De Luc. 



Hares, weasels, and ferrets skin, human liand, leather, smooth glass, flan- 

 nel, quills, wood, paper, iron, steel, plumbago, lead, and bismuth. 

 Brass, according to De Luc. 

 r Silk, rough glass, paper, sealing wax, white wax, lead, sulphur, and the 



metals. 



"Flannel, smooth glass, quills, hare-skin. 

 All the metals except lead. 



Lead, and all other substances that have beer* hitherto tried. 

 Resinous substances. 

 All bodies except resinous ones. 



In the repetition of some of the preceding experi- 

 ments, the minutest attention must be paid to the state 

 of the bodies- which are rubbed together, and to the 

 manner in which the friction is applied. When a stick 

 of sealing wax is rubbed with an iron chain, the elec- 

 tricity of the wax will be positive when its own sur- 

 face is scratched, and negative when it is smooth. When 

 a silk ribbon is drawn lengthwise over a part of another 

 ribbon of the same length, the ribbon which has been 

 mbbed along its whole length becomes positively and 

 the other negatively electrified. In like manner, when 

 the whole length of the bow of a violin is drawn over 

 a limited p.\rt of the string, the hairs of the bow exhibit 

 a positive, and the string a negative electricity, the 

 body whose excited portion is of the least extent being 

 generally negatively electrifued. Some other examples 

 of a similar kind have been given in our historical ac- 

 count of the experiments of Cigna. 



In exciting metals with woollen cloth, similar ano- 

 malies have been observed by Hauy ; the same piece of 

 metal, even when placed in similar circumstances, some- 

 times acquiring positive and sometimes negative elec- 

 tricity. M. De Luc has observed a similar irregularity 

 in the friction of glass and caoutchouc. This anomaly, 

 however, is seen in a most beautiful manner in the mi- 

 of neral commonly called cyanite, which was first descri- 

 bed by the younger Saussure, under the name of sap- 

 pare. Some of the crystals of this mineral acquire po- 

 sitive electricity by friction, while others acquire ne- 

 gative electricity ; and in some of them the one species 

 of electricity is found on one face, and the opposite 

 cpecies on the other face, although neither the eye nor 

 the touch could discover any difference cither in the 

 lustre or the polish of the two faces. I'rotn this pro- 

 perty Hauy has called the mineral disthrne, which sig- 

 nifies having two virtues. 



The effect of minute circumstances in the simultane- 



ous production of positive and negative electricity, is Cavallo's 



excellently illustrated by the experiments of Mr Ca- "Pf 6 ^* 



. -. / i . on the fnc- 



vallo, on the electricity of glass tubes containing mercu- tion O f i ;lss 



ry, and hermetically sealed. These tubes were about tu bcs with 

 31 inches long, less than half an inch in diameter, and mercury. . 

 half an inch thick. Having put about three-fourths 

 of an ounce of mercury into the tube, he boiled it, and, 

 when the air was rarefied, the tube was hermetically 

 sealed. After cleaning and warming the tube, he 

 brought it into a horizontal position, and excited it 

 by the friction of the mercury, which took place in ele- 

 vating and depressing either end alternately. When 

 the tube after this kind of excitation was brought into 

 a vertical position, the end containing the mercury was 

 electrified positively, and all the rest of the tube nega- 

 tively. When the positive end was raised, the mercu- 

 ry flowed to the negative end, but the end where the 

 mercury now stood acquired a positive electricity, and 

 the rest of the tube a negative one. When the positive 

 end where the mercury first stood, was elevated without 

 touching it with the hand, it exhibited only a very 

 slight degree of negative electricity ; and if trie mercu- 

 ry was made to flow back to it, and again retire from it, 

 its electricity was positive, while by 'elevating it with 

 the finger it always became strongly negative. 



SECT. III. On the Communication of Electricity. 



IN the few simple experiments of which we have On the com. 

 given an account, the reader must already have seen, munication 

 that electricity is capable of being communicated to ot electri " 

 other bodies. The pith balls obviously diverge, in con- dtjr ' 

 sequence of the electricity which they receive from the 

 rxriti-d glass or ro.-in, and retain it for a considerable 

 time. If we touch any of the pith balls, when in a state 

 of divergence, with a piece of gla^s free from moisture, 

 or with a dry stick of sealing-wax or sulphur, the di 



The preceding experiments on the electricities produced hy the friction of the metals upon woollen cloth were made by M. Hauy. lie 

 nsuU'.cd the fragment of metal which he wished to try at the extremity of a stick of gum lac, or sealing wax, and then holding the stick 

 in hii hand, he made the metallic fragment pass several times over a piece of cloth. Alter rubbing it five or six times, he touched with 

 th metallic fragment the knob of Volta's condensing electrometer, which we have represented in Plate CCXLIX. Fig. 15. and found the 

 kind of electricity in the common manner. Sec Annalen du Mvxrum <THut. Katun-tic, No. IT. 



fr M. Libes found that sealing-wax, when rubbed with insulated discs of copper, zinc, and silver, was always electrified negatively. 



J Mr Cavxllo having inserted metals among the list of substances that rendered sealinp wax positively t-lcctrilicil, Mr Singer ra- 

 fcated the experiments with great care, and obtained the results given above. Sec Singer's flemcnti of Elcrtricity, p, 33. 



See Singer's Elaunti of Electricity, p. 34. 



