ELECTRICITY. 



425 



History. 



Labours of 

 B'-'r^ tian. 

 Born 1735. 

 Dial 1781. 



Labours of 

 Mr Kin. 

 aenley. 



M. JaUa. 

 bet 



Labours of 

 iMr Wilkc. 

 Born 

 Died 1796. 



1757. 



upon separation, they were electrified as before. Hence 

 he endeavours to explain the nonexcitation of a globe 

 or tube, from which the air is exhausted. 



The celebrated chemist, Torbern Bergman, of Up- 

 sal, made a few experiments on electricity. He found, 

 what had already been discovered by Beccaria, that a 

 small quantity of water was not capable of conducting 

 the electric fluid, but that more was transmitted as the 

 quantity of water was increased. He obtained a simi- 

 lar result from ice, and concluded that ice is a worse 

 conductor than water. It was ascertained by later ex- 

 periments, that ice l>ecame a non-conductor when 

 cooled down to 13 of Fahrenheit. 



To Mr Kinnersley, the friend and associate of Dr 

 Franklin, electricity owes considerable obligations. Mr 

 Kinnersley first distinguished himself by discovering 

 the two opposite electricities of glass and sulphur, in 

 which, however, he had been anticipated by Dufay ; 

 but he immediately saw that Dufay did not imagine 

 that these two electricities were the same as the positive 

 and negative electricities of Dr Franklin. He found 

 that a coated flask, containing boiling water, could 

 not be charged, as the electricity passed oft' with the 

 steam ; l.ut as soon as the water was cold, the flask 

 was readily charged. He found, that if a person insu- 

 lated, and negatively electrified, should hold out in the 

 dark a long sharp needle, pointing upwards, a light 

 would be observed on the point of it, the electricity 

 being in this case drawn from the air. Upon sending 

 the charge of a case of 35 bottles through a piece of 

 brass wire about 24 inches long, with a pound weight 

 at the lower end, the whole wire became red hot, and 

 was an inch longer than before. By means of a second 

 charge, the wire was melted. It was drawn asunder 

 near the middle, and when the two ends were put to- 

 gether, it measured four inches longer than before. * 



M. .lallabert, Professor of Philosophy and Mathe- 

 matics at Geneva, found that a coating of pitch did not 

 prevent the conductor from being electrified ; from 

 which it followed, that the electric fluid entered the 

 fobttance of ntttll* ; and he likewise showed that ice 

 conducted electricity by performing the J.eyden experi- 

 ment in a jar in which water was fro/en. He appears 

 also to have been the first who observed that a body, 

 pointed at one end, and round at another, produced 

 different electrical appearances upon the same body, 

 according as the round or the pointed end wa ) 'reput- 

 ed to it. He was also the author of a theorv of elec- 

 tricity, in which he supposes that a very rare and elas- 

 tic fluid fills the universe and the pores of all bodies, 

 tending always to an equilibrium, by filling up any va- 

 cuities that may be occasioned He affirms, liki 

 that the density of this fluid is not the same in all bo- 

 dio. and that it i.s most rare in dense bodies, and most 

 dense in rare bodies. A full account of this theory is 

 contained in his work, entitled, Ki peril nccx uir /'/ 

 tricile avec que/ques cnnject i' ri's . nr la cause de sex effels, 

 fieneva, 1748. M. Jallabert performed a singular cure 

 by means of electricity in 1747, and was thus led to 

 publish, in 17.50, his work entitled, Ex/icrinu-iila Elec- 

 trica Lhi/jus Medici* ."jrj^^-nln 



One of the most successful cultivators of the science 

 of electricity was Mr Wilke of R'.-tock, in Lower Sax- 

 ony, whoha> published an account of his labours in his 

 celebrated work, entitled Di'putatio /'', //.t; <n cxperimen- 

 talit Je Eleclricitalibiif, Rostock, 175", 4to. His re- 

 searches respecting spontaneous electricity, a name 



which he gives to the electricity produced by the melt- 

 ing of electric substances, have contributed most essen- 

 tially to the progress of the science. He found, that 

 sulphur melted in an earthen vessel, which he placed 

 upon conductors, was strongly electrical when taken out 

 al'ter it was cold, but it exhibited no indications of elec- 

 tricity when it was cooled upon electric substances. 

 When melted in vessels of glass, the sulphur acquired 

 a strong electricity, whether the vessels were placed upon 

 glass vessels or not ; but it was always stronger when 

 they were not placed on electrics, and strongest of all 

 when the glass vessel had a metallic coating. The elec- 

 tricity of the glass was, in these cases, constantly posi- 

 tive,andthat of thesulphur negative; and, what was very 

 singular, the electricity of the sulphur did not develope 

 itself till it began to cool and contract, and reached its 

 maximum at the poinT of greatest contraction. The 

 electricity of the glass was then the lenst, and was strong- 

 est of all when the sulphur was shaken out of it, before 

 its contraction commenced. Melted sealing-wax he al- 

 so found to acquire negative electricity when poured 

 into glass, and positive electricity when poured into 

 sulphur. Seal*ig-wax poured into baked wooci was ne- 

 gative, and the wood positive. Sulphur poured into 

 wood became negative, but when poured into sulphur, 

 or rough glass, it acquired no rk ttririty. Mr Wilke's 

 experiments on the friction of bodies are also interesting. 

 When sulphur and glass were rubUed together, the glass 

 was strongly positive, and the sulphur strongly nega- 

 tive. Wood excited with cloth w;is r'lwjrys negative. 

 Wood rubbed against smooth glass is negative, but 

 positive when rubbed against rough glass. Sulphur ex- 

 hibited positive electricity only in the case when it 

 wris rubbed against metals. Lead, however, formed an 

 exception ; for sulphur became negative when rubbed 

 against it, and the metal itself positive ; from which 

 Wilke concludes, that lead is not such a good conduc- 

 tor as the other metais. In the following catalogue 

 given by Mr Wilke, the substances are arranged in the 

 order in which they are disposed to acquire positive or 

 negative electricity, any one of the bodies acquiring po- 

 sitive electricity when rublx-d by any that follow it in 

 the catalogue, and a negative electricity when rubbed 

 with any that go before it: 



History. 



Smooth gliiss. 

 Woolltu cloth. 

 Quills. 

 Wood. 



Paper. 



Sealing-wax. 

 White wax. 

 Rough glass. 



Lead. 



Sulphur. 



Metals. 



Mr Wilke believed, that smooth glass gives in all cases 

 a positive electricity ; but Mr Canton had discovered 

 thnt the smoothest glass may be negatively electrified 

 when drawn over the back of a cat. 



The experiments of Dr Franklin and Mr Canton on 

 electric atmospheres, were verified and extended by Mr 

 Wilke, who concluded, that parts of non-electrics im- 

 merged in electric atmospheres, acquire an opposite 

 electricity to that of theatmosphere itself. The subject of 

 electric light received also considerable illustration from 

 the labours of this ingenious electrician. When two 

 pieces of glass were nibbed together, he noticed a vivid 

 phosphoreal Hght, which threw out rays, but adhered 

 to the place where it was produced, and emitted a strong 

 phosphoreal smell. As it was accompanied with no at- 

 traction or repulsion, he concluded that friction was not 

 able of itself to produce electricity, but that it was ne- 

 cessary to have the bodies of different kinds ; and he 



See FranUiti's LelUn, and Phil. Traiu. 1763, voU ML p. 84. 



