LAWS OF ELECTRIC PHENOMENA. 13 



the same time, arrived at the same conclusions, 

 which he expresses by saying that the electricity of 

 A was more rare, and that of B more dense, than 

 it naturally would have been 4 . But that which 

 gave the main importance to this doctrine was its 

 application to some remarkable experiments, of 

 which we must now speak. 



Electric action is accompanied, in many cases, 

 by light and a crackling sound. Otto Guericke 5 ob- 

 serves that his sulphur-globe, when rubbed in a 

 dark place, gave faint flashes, such as take place 

 when sugar is crushed. And shortly after, a light 

 was observed at the surface of the mercury in the 

 barometer, when shaken, which was explained at 

 first by Bernoulli, on the then prevalent Cartesian 

 principles ; but, afterwards, more truly by Hawkes- 

 bee, as an electrical phenomenon. Wall, in 1708, 

 found sparks produced by rubbing amber, and 

 Hawkesbee observed the light and the snapping, as 

 he calls it, under various modifications. But the 

 electric spark from a living body, which, as Priest- 

 ley says 6 , " makes a principal part of the diversion 

 of gentlemen and ladies who come to see experi- 

 ments in electricity," was first observed by Dufay 

 and the Abbe Nollet. Nollet says 7 he " shall never 

 forget the surprize which the first electric spark 

 ever drawn from the human body excited, both in 



4 Priestley, p. 115. 



5 Experimenta Magdcburgica, 1672, lib. iv. cap. 15. 6 P. p. 47. 

 7 Priestley, p. 47 Nollet, Lcgons de Physique, vol. vi. p. 408. 



