57P THE INTELLECTUAL RISE IN ELECTRICITY. 



and afterwards the seeker for such allusions will find a 

 harvest of them which space does not permit me to gather 

 here. 



By the end of the seventeenth century the explanation 

 of lightning which prevailed up to Franklin's time was 

 fully formulated. Dr. Wallis believed it to be due to the 

 detonation of a mixture of nitrous and sulphurous vapors 

 in the air the conditions being similar to those occurring 

 during the explosion of gunpowder, in which substantially 

 the same elements are present. Later opinions differed as 

 to the nature of the exploding gases and their mode of 

 generation in the atmosphere; but the general consensus 

 regarded the lightning and the thunder as the celestial 

 artillery the explosion and the report occurring in the 

 same way as in earthly fire-arms. 1 



Early in the eighteenth century Hauksbee compared 

 the flickering lights in his globe to the lightning flash, 

 and Dr. Wall saw in the cracklings and sparks of rubbed 

 amber a resemblance, in some degree, to thunder and 

 lightning; and Gray, following the same thought, con- 

 ceived the electric fire and lightning to be "of the same 

 nature." But these were the merest conjectures. That 

 of Wall is equally true of the discharge of a fire-arm. 

 Gray's conception that the electric fire is "of the same 

 nature" as the lightning is consonant with the common 

 belief that fire is an element, and therefore the same 

 everywhere; so that his assertion amounts to nothing 



1 To show how a precisely similar idea is often reached by entirely 

 different paths, it may here be noted that Dr. Dionysius Lardner, writing 

 in 1844 (see Manual of Electricity, ii., 165), after noting the many in- 

 stances collected by Arago of the sulphurous odor following a lightning 

 stroke, and the detection by Liebig of nitric acid in rain water, says "it 

 would be a curious and interesting result of scientific investigation to de- 

 monstrate that the thunder of heaven elaborates in the clouds the chief 

 ingredients of the counterfeit thunders which man has invented for the 

 destruction of his fellows." 





