86 Sheet Lightning. 



lowing fact, which I extract from the works of Boyle. *' In 

 July 1681, a thunder storm produced a great deal of damage 

 near to Cape Cod, upon the English ship the Albemarle. A 

 flash of lightning was followed hy the fall of a hurning bitu- 

 minous matter into the boat hanging at the stern, which gave 

 out an odour similar to that of gunpowder. This substance 

 was consumed on the spot, and it was in vain tlmt they at- 

 tempted to extinguish it with water, and to sweep it overboard 

 with a broom.'* 



Sheet Lightmr,g. 



We may now inquire what is the nature oi eclairs de chalenr^^' 

 or the lightning which occurs in the course of serene nights. 

 " In the calmest nights," says Seneca, " with the stars shining 

 bright, you may see lightnings flash, but doubt not, he adds, 

 that, in the direction of the lightnings there will be found 

 clouds which the spherical form of the earth hides from our 

 view. The flash ascends on high, and appears in the bright 

 and serene sky, being withal elaborated in some obscure and 

 dark cloud." (Quest. Nat. v. ii. § 26.) In his dissertation 

 upon thunder, to which L Academic de Bourdeaucc awarded its 

 prize of the year 1726, Lozeran de Fesc also did not regard 

 the^Q eclairs de chaleur as primordial. According to him, they 

 are the reverberation upon the more or less elevated atmospheric 

 strata, of common lightning, having its origin in a storm, of 

 which the direct view is obstructed by the rotundity of the 

 globe. This explanation is very simple, and has been adopted 

 by the majority of natural philosophers. What, more natural, 

 they allege, than to endow the atmosphere with a certain re- 

 flecting power ? Is it not to it we owe the crepuscular light 

 which we enjoy so long before the sun rises, and after it has 

 set.? 



Some doubts as to the conclusiveness of this reasoning might 

 be urged in relation to the subject of quantity. Might it not 

 happen, it may be said, that the atmosphere, though possessing 

 a reflecting quality sufficient to transmit the crepuscular light 

 of the sun, can produce no sensible reverberation on receiving 



* The term " eclairs de chaleur ^'^ corresponds to our slieet, sinnmer, or silent 

 lightning.— Edit. 



