LESSONS IN ELECTRICITY. 337 



by warm tumblers. Hold in your right hand a sheet of vulcanized 

 India-rubber, and clasp, with it between you, the left hand of a friend. 

 Place your left hand ou the conductor of the machine, aud let it be 

 worked. You and your friend soon feel a crackling and a tickling of 

 the hands, due to the heightening attraction of the opposite electrici- 

 ties across the India-rubber. The hand-jar is then charged. To dis- 

 charge it you have only to bring your other hands together: the 

 shock of the Leyden-jar is felt. 



By the discharge of the hand-jar you can fire gunpowder. But this 

 will be referred to more particularly further on. 



Sec. 20. Physiological Effects of the Shock. The physiological 

 effect of the shock was variously studied. Graham caused a number 

 of persons to lay hold of the same metal plate, which was connected 

 with the outer coating of a charged Leyden-jar, and also to lay hold 

 of a rod by which the jar was discharged. The shock divided itself 

 equally among them. 



The Abbe Xollet formed a line of one hundred and eighty guards- 

 men, and sent the discharge through them all. He also killed sparrows 

 and fishes by the shock. The analogy of these effects with those pro- 

 duced by thunder and lightning could not escape attention, nor fail 

 to stimulate inquiry. 



Indeed, as experimental knowledge increased, men's thoughts be- 

 came more definite and exact as regards the relation of electrical 

 effects to thunder and lightning. The Abbe Nollet thus quaintly ex- 

 presses himself: " If any one should take upon him to prove, from a 

 well-connected comparison of phenomena, that thunder is, in the hands 

 of Nature, what electricity is in ours, and that the wonders which we 

 now exhibit at our pleasure are little imitations of those great effects 

 which frighten us, I avow that this idea, if it was well supported, 

 would give me a great deal of pleasure." He then points out the 

 analogies between both, and continues thus : " All those points of 

 analogy, which I have been some time meditating, begin to make me 

 believe that one might, by taking electricity as the model, form to 

 one's self, in relation to thunder and lightning, more perfect and more 

 probable ideas than what have been offered hitherto. 1 " 



These views were prevalent at this time, and out of them grew 

 the experimental proof by the great physical philosopher, Franklin, 

 of the substantial identity of the lightning-flash and the electric 

 spark. 



Franklin was twice struck senseless by the shock. He afterward 

 sent the discharge of two large jars through six robust men ; they fell 

 to the ground and got up again without knowing what had happened ; 

 they neither heard nor felt the discharge. Priestley, who made many 

 valuable contributions to electricity, received the charge of two jars, 

 but did not find it painful. 



1 Priestley's " History of Electricity," pp. 151, 152. 

 VOL. ix. 22 



