THE VOLTAIC PILE. 481 



statical electricity, and finally settled that question; he 

 also discovered the laws of electric distribution on sur- 

 faces. In 1786 and 1787, by the help of the same 

 balance, and the method of oscillation, he discovered 

 the law of variation of magnetism according to distance. 

 Bennet also, in 1786, by employing his electroscope, dis- 

 covered the production of electricity by the sifting of 

 powders. In 1788, Cavallo invented his ' condenser.' In 

 1789, Cuthbertson invented his guarded gold points ; and 

 in 1801, Wollaston, by using a similar contrivance, was 

 enabled to decompose water by means of frictional elec- 

 tricity. About the year 1803, Dyckhoff first obtained 

 electricity from a ' dry column.' In 1820, Bohnenberger 

 invented his gold-leaf dry-pile electroscope, which enabled 

 him to distinguish between the two kinds of electricity, 

 even when in very minute amounts. It was by means of 

 his e exploring wires ' that Crosse, in 1836, was enabled to 

 collect atmospheric electricity in a more convenient man- 

 ner than by the aid of a kite, and to gain additional new 

 knowledge respecting it, More recently also Sir William 

 Thomson, by the invention of his reflecting quadrant and 

 absolute electrometers, facilitated the discovery of addi- 

 tional new truths in electrical science. 



It was by the use of very fine gold wires immersed in 

 water, and passing electric sparks between them, that 

 Paetz and Van Troostwik, in the year 1790, first decom- 

 posed water into its constituent gases. Nicholson invented 

 his rotating electric condenser in the year 1797, and it 

 was by its aid that he and Carlisle discovered the nature 

 of the free electricity at each end of the voltaic couple. 

 By the invention and use of his pile, in the year 1799, 

 Volta laid the foundation of chemical electricity. 'He 

 procured a number (say fifty) of pieces of zinc, about the 

 size of a crown-piece, and as many pieces of copper, and 



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