ELECTRICITY FROM THALES TO FARADAY. 249 



of electricity, and Franklin charged a Ley den jar from the key, thus 

 achieving the actual storage of " lightning." 



He continued his investigations in atmospheric electricity, and 

 discovered that the electrification of the clouds (or of the upper 

 atmosphere) was sometimes positive and sometimes negative. The in- 

 vention of the lightning rod is due to him. 



Franklin sided with AVatson in his belief in the single nature of 

 the electric fluid. 



As intimated above, atmospheric electricity appears to have been 

 collected independently about the same time in Europe, and certain 

 very daring and dangerous experiments were performed there. One 

 sad occurrence, as a result, was the death of Professor Richman, in 

 St. Petersburg, in 1753. Richman, in company with a friend, Soko- 

 low, was taking observations on an electroscope connected with an 

 iron rod which terminated in the apartment and extended in the 

 other direction above the roof of the building. During the progress 

 of their experiments a violent peal of thunder was heard in the neigh- 

 borhood, and Richman bent to examine the instrument. In doing 

 so he approached his head to within a foot of the end of the rod, 

 and Sokolow saw a ball of fire " about the size of a man's fist " shoot 

 from it to Richman's head with a terrific report. The stroke was, of 

 course, immediately fatal, and what we now know as the return shock 

 •stupefied and benumbed Sokolow. The unfortunate event served as 

 a warning to other daring experimenters. 



Canton, another j^rominent worker in this field, discovered that 

 the so-called vitreous electricity was not necessarily always developed 

 by the friction of glass, as had hitherto been believed to be invariably 

 the case. By applying different rubbers to glass he obtained either 

 positive or negative at pleasure. This at once disposed of the idea 

 that one kind of electricity resided in certain bodies and its opposite 

 in others. Canton also made the interesting discovery that glass, 

 amber, rock crystal, etc., when taken out of mercury, were all elec- 

 trified positively. He was thus enabled to make the improvement in 

 the electrical machine of coating its rubber with an amalgam rich in 

 mercury, which greatly enhanced. its powers. 



Among the numerous names now coming into prominence must 

 be mentioned those of Beccaria, Symmer, Delaval, "Wilson, Kinners- 

 ley, Wilcke, and Priestley. 



The first named. Father Beccaria, was a celebrated Italian physi- 

 cist who did most valuable work in connection with atmospheric elec- 

 tricity, and who published several classical works on that and allied 

 subjects. Among these may be mentioned his Lettre del Elettri- 

 citd, 1758, and Experimenta, 1772. He ascertained that water is 

 not by any means a good conductor, as it had previously been sup- 



