ELECTRICITY. 



COftsidered the production of phosphoreal light without 

 attraction, as tin- excitation ot electricity without the ac- 

 cumulation ot' it. When a tube was excited w ith a 

 woollen cloth, with white wax or oil upon it, it ejected 

 flames, each ot which seemed to issue t'roin a little fiery 

 protulx-rancc. He found, that when sparks were pro- 

 duced between two lulls, (except when both the balls 

 were metallic,) the light formed a cone, the ba-c of 

 which was always on the body positively electrified, and 

 the vertex on the out- negatively electrified, a criterion 

 which he considers as sufficient for discriminating the 

 two electricities. When a point not electrified i.s oppo- 

 sed to a positively electrified point, the luminous cones, 

 which in other circumstances would have been seen 

 upon both of them, are not in this case visible ; but if 

 a positive cone be opposed to a negative cone, they both 

 retain their characteristic properties. 



Kesearche* ^' e come now * ' a X before our readers on account of 

 of JBpinus the labours of .'Epinus, who may be considered as the 

 tirst person who employed geometry and analysis in ex- 

 tending the science of electricity. He performed a series 

 of exi--riments, similar to those of Mr Wilke, on melted 

 sulphur. \\ lien the sulphur was poured into metallic 

 cups and cooled, the cup and the sulphur together shew- 

 ed no signs of electricity till they were separated, when 

 the electricity was very strong ; the electrical effects al- 

 ways disappearing when the sulphur was put back in- 

 to the cup, and re-appearing when the separation was 

 repeated. The electricity of the cup was always nega- 

 tive, and that of the sulphur positive; but if either of 

 the two had been deprived of its electricity when they 

 were separate, they both exhibited, when united, the 

 electricity which had not been taken away, and which 

 was always on the surface of the .sulphur. Upon pres- 

 sing together two plates of looking-glass, one of them 

 exhibited after separation a strung negative, and the 

 other a strong positive electricity. When they were 

 again joined, the electricity of both disappeared; but 

 ii'oiic of them had its electricity taken off when sepa- 

 rate, then the two, when reunited, had the electricity 

 of the other plate. He made the same experiments with 

 glass and sulphur, with several other electrics, and with 

 an electric and a piece of metal. JFpimis and Wilke 

 happening to be resident at the same time at Berlin, 

 pursued in company their experiments on electric at- 

 mospheres, and were led to the discovery of a beautiful 

 method of charging a plate of air, in the same manner 

 as the charge had been communicated to plates of glass. 

 Having found that the negative state of one of the bo- 

 dies depended on the opposite state of the other, which 

 was precisely the case with a charged pane of glass, they 

 therefore tried to give an electric shock by means of air, 

 which they effected, by suspending large wooden boards 

 coated with tin, having their flat surfaces parallel, and 

 some inches distant. When one of the boards was elec- 

 trified positively, the other possessed a negative elec- 

 tricity, and when a person touched one of the plates 

 with one hand, and the other plate with his other hand, 

 he received a shock exactly as in the Leyden jar. Tlie 

 opposite electricities of the two boards occasioned a 

 strong attraction, which it was necessary to counteract 

 by means of strings, which prevented the approach of 

 the boards. Sometimes the electricity of both the boards 

 was discharged by a strong spark between them, in the 

 game manner us when n pane of glass bursts with an 



overcharge. A shock was experienced when tlu- iii - n 

 charge wan effected by the intervention of the linger, '*""V i ' 

 and when there w s any nniiu-iu < on either of the p' 

 tlie spontaneous di-char ;< always passvd through it, 

 and a pointed body fixed at I pri -\elited the 



boards trom being charged. Wilke and -Kpimis con- 

 sidered the two boards as representing the earth and the 

 cloud- electrified in an opposite manner, and the phe- 

 nomenon of lightning as the bursting of the plate of 

 nir by a spontaneous discharge, which is always made 

 through eminence*. M. .V.pinu perfon -ome 



interesting experiments on the tourmalin, which he 

 published in the Memoirs of the Academy of Berlin 

 for 175ti. 



Notwithstanding the value of these experiments, the Thtirr of 

 greatest service which .'Epinus did to electricity, was *pinu> 

 in connecting together all ti ed phenomena- by an 1 "*- 



ingenious and plausible theory, of which he has given 

 a full account in his Teittamen Thcoriw E/ulriciliitit et 

 Ma^m-liiini, published at St PeU-rshuruh in 1759. This 

 theory is founded on the following simple principles: 

 1. That tlie molecules of the electric fluid mutually re- 

 pel each other, even at considerable dilute-, and with 

 a force decreasing as the distance increases. 2. The 

 particles of the electric fluid attract the particles of all 

 known bodies, and are attracted by them in their turn, 

 with a force following the same law. 3. The electric 

 fluid exists in the pores of bodies, moving without any 

 perceptible obstruction in non-electrics, such as the 

 metals, inner, ivc. but with extreme difficulty in the 

 pores of electrics, such as ylam, rosin, cvc. 4. Tlie phe- 

 nomena of electricity arise from two causes, 1st, From 

 the transference of the fluid from a body containing 

 more, to another containing less of it; and.'-id, From its 

 attraction and repulsion, where no transference takes 

 place. These simple principles are managed with great 

 address, in explaining even the most singular pheno- 

 mena of electricity, and enable us to predict, with the 

 utmost exactness, the result of any proposed experiment. 



The work of ^Fpimis is, perhaps, too mathematical 

 for ordinary readers, but it has been rendered ai 

 sible to those who have no mathematical knowledge, by 

 the labours of the Abbe Hauy, in his work entitled 

 E.cpofilidH rtiiarmin'-f <ic lit '1'hniric d<- I' i'.lci ,'riciti- et du 

 M(ii!>n'lixie apres les Principet de -M. JEpimts. Pari., 

 1787, 8vo. * 



The labours of our countryman, Dr Priestley, were Labours ot 

 not confined to the composition of his laborious work Or Priest- 

 on the history of electricity, which appeared in the year ' 

 1767, and which contains a full and instructive ac- 

 count of all the disco', erics in electricity which had been 

 made either in Kurope or America. At the end of this 

 work, he has given us an account of a number of original 

 experiments, and he afterwards published several papers 

 on electricity in the Transactions of the Royal Society. 

 In attempting to ascertain the electrical qualities of me- 

 phitic air, Dr Priestley was led to make experiments on. 

 charcoal, as it was from that substance that he procured 

 the gas in the greatest quantity. He found that char- 

 coal, whatever was its state with regard to heat or cold, 

 was nearly as good a conductor of electricity as the me- 

 tals; a result which overturned the established notion, 

 that all other bodies but water and the metals are non- 

 conductors. Different pieces of wood charcoal h;u! dif- 

 ferent degrees of conducting power ; but the most per- 



Born 1T3S. 

 Died 18114k 



* Such of our readers an are prevented from consulting the original work of .tftyinus, will find an admirable view of liii theory in Dr 

 Ftubison's System uf Mechanical PkUowi'hy, vol. iv. which w now in the press. We have been induced to make this reference, <u> in the 

 lot lowing article we propose to girc a dtuulid account of tlie more perfect theory of Cavendish, which comprehends tliat uf Jtylnus. 





