fcXAMiNATiotf of Volga's experiments, &c. 289 



di (covered by Volla in 1780*, and uf'ed for atmofpheric elec- 

 tricity and in the grand difcovery of the electricity produced 

 by chemical changes, it was applied very early by Cavallo in 

 the compound form; that is to fay, by charging a fmaller in- 

 liniment with the contents of a larger. Mr. Bennet before 

 1787 f, added the condenfer to his electrometer, and invented 

 the method called - oubling, which had before been ufed with 

 the eleftrophore by Lichtenberg % and Klinoock §. Our elec- 

 tricians, particularly Mr. Cavallo and Mr. Bennet, were at 

 this time fully aware of the fpontaneous electricity of the 

 doubler, and the evils to be apprehended from the varnifh and 

 the actual contacts. I think it was Mr. Cavallo who fubfti- 

 tuted fmall knobs of fealing wax Mead of varniih, which I 

 faw adopted in a mechanical doubler by Dr. Darwin in 1787 ^ 

 and in the year 1788 I communicated to the Royal Society |f 

 the revolving doubler, in which the plates approach and re- 

 cede without touching ; and foon afterwards I made the fpin- 

 ning inftrument, confiding of a condenfer and anelectrical well. 

 In the fame year Mr. Cavallo publifhed ** his colle&or of elec- 

 tricity, which is a condenfer having two uninfulated plates, 

 which feparate like plate a, fig. 2, on each fide of b, without 

 contact; and in the third vol. of his " Complete Treatife on 

 " Electricity/' 1795, he defcribes his multiplier, which confifts 

 of two condenfers, equally perfect; one of which is made to 

 charge the other by repeated alternations of the compen fating 

 plate. 



The above fliort (ketch will enable the reader to afcertain to 

 what extent the ingenious contrivers of the inftruments in 

 plate XV. have availed themfelves of the labours of former 

 operators. 



* Journal de Phyfique for May and Auguft 1783, and Phil, 

 Tranf. LXXII. p. 237. 



f Phik Tranf. LXXII. p. 32. 

 % Journal dePhyf. Jan. 1780, p. 20. 

 § Phil. Tranf. LXVIII. p. 1029. 

 II Phil. Tranf. LXXVIII. 

 ** Phil. Tranf. LXXVIII. 



Vol. IL— August, 1802. U XV, QbfervatioT* 



