ELECTRICITY. 



59 



set, after which it diminishes, and con- 

 tinues feeble during the night. In cloudy 

 weather the electrical state is much more 

 uncertain ; and when there are several 

 strata of clouds, moving in diiferent 

 directions, it is subject to great and 

 rapid variations, changing sometimes 

 from positive to negative, and back 

 again, in the course of a few minutes. 

 On the first appearance of fog, rain, 

 snow, hail, or sleet, the electricity of the 

 air is generally negative, and often 

 highly so ; but it afterwards undergoes 

 frequent transitions to opposite states. 

 On the approach of a thunder-storm 

 these alternations of the electric condition 

 of the air succeed one another with re- 

 markable rapidity. Strong sparks are 

 sent out, in great abundance, from the 

 conductor ; and it becomes dangerous to 

 prosecute experiments with it in its in- 

 sulated state. 



(219.) The analogy between the elec- 

 tric spark, and more especially of the 

 explosive discharge of the Leyden jar, 

 with atmospheric lightning and thunder, 

 is too obvious to have escaped notice, 

 even in the early periods of electrical 

 research. It had been observed by Dr. 

 Wall and by Gray, and still more point* 

 edly remarked by the Abbe Nollet. Dr. 

 Franklin was so impressed with the 

 many points of resemblance between 

 lightning and electricity, that he was 

 convinced of their identity, and deter- 

 mined to ascertain by direct experiment 

 the truth of his bold conjecture. A 

 spire which was erecting at Philadel- 

 phia he conceived might assist him in 

 this inquiry ; but, while waiting for its 

 completion, the sight of a boy's kite, 

 which had been raised for amusement, 

 immediately suggested to him a more 

 ready method of attaining his object. 

 Having constructed a kite by stretching 

 a large silk handkerchief over two sticks 

 in the form of a cross, on the first ap- 



Searance of an approaching storm, in 

 ime 17.V2, he went out into a field, 

 accompanied by his son, to whom alone 

 lie had imparted his design. Having 

 raised his kite, and attached a key to the 

 lower end of the hempen string, he in- 

 sulated it by fastening it to a post, by 

 means of silk, and waited with intense 

 anxiety for the result. A considerable 

 time elapsed without the apparatus 

 giving any sign of electricity, even al- 

 though adenss cloud, apparently charg- 

 ed with lightning, had passed over the 

 spot on which they stood. Franklin was 

 just beginning to despair of success, 

 when his attention was caught by the 



bristling up of some loose fibres on the 

 hempen cord ; he immediately presented 

 his knuckle to the key, and received an 

 electric spark. Overcome with the emo- 

 tion inspired by this decisive evidence of 

 the great discovery he had achieved, he 

 heaved a deep sigh, and conscious of an 

 immortal name, felt that he could have 

 been content if that moment had been 

 his last. The rain now fell in torrents, 

 and wetting the string, rendered it con- 

 ducting in its whole length ; so that 

 electric sparks were now collected from 

 it in great abundance. 



It should be noticed, however, that 

 about a month before Franklin had made 

 these successful trials, some philoso- 

 phers, in particular Dalibard and De 

 Lors, had obtained similar results in 

 France, by following the plan recom- 

 mended by Franklin. But the glory of 

 the discovery is universally given to 

 Franklin, as it was from his suggestions 

 that the methods of attaining it were 

 originally derived. 



(220.) This important discovery was 

 prosecuted with great ardour by philo- 

 sophers in every part of Europe. The 

 first experimenters incurred consider- 

 able risk in their attempts to draw down 

 electricity from the clouds, as was soon 

 proved by the fatal catastrophe, which, 

 on the 6th of August, 1753, befel 

 Professor Richman, of Petersburg, 

 whose name has already been before us, 

 ($ 123.) He had constructed an appa- 

 ratus for observations on atmospherical 

 electricity, and was attending a meeting 

 of the Academy of Sciences, when the 

 sound of distant thunder caught his ear. 

 He immediately hastened home, taking 

 with him his engraver, Sokolow, in 

 order that he might delineate the ap- 

 pearances that should present them- 

 selves. While intent upon examining 

 the electrometer, a large globe of fire 

 flashed from the conducting rod, which 

 was insulated, to the head of Richman, 

 and passing through his body, instantly 

 deprived him of life. A red spot was 

 found on his forehead, where the elec- 

 tricity had entered, his shoe was burst 

 open, and part of his clothes singed. 

 His companion was struck down, and 

 remained senseless for some time ;' the 

 door-case of the room was split, and the 

 door itself torn off its hinges. 



(221.) The protection of buildings 

 from the effects of lightning, is the most 

 important practical application of the 

 theory of electricity. We have only 

 room for a few observations on the 

 principles on which conductors for this 



