148 Mayow 



there would be no second flash. And indeed the 

 flash would continue for some time ; but the opposite 

 is the case. 



Should any one here say that the sulphureous ex- 

 halations, which are imprisoned here and there among 

 the clouds, are separately kindled in consequence 

 of their being violently agitated, and that the flash of 

 lightning is due to the wide expansion of their light ;: 

 I reply that it is scarcely probable that a fire so im- 

 mense as to be capable of propagating light to such 

 vast distances, is produced by a succession of separate 

 flashes, for it is to be noted that lightning is not 

 only seen at a distance, but reaches to the eye of the 

 spectator. Further, if lightning were nothing else 

 than rays of light, how does it happen that it not in- 

 frequently sets fire to things which it meets ? For this 

 is never done, even by the solar rays, except when 

 collected by a burning-glass. And from what source 

 finally should the power come, which is required for 

 the effects usually produced by lightning, if it consisted 

 merely of light ? 



I confess for my part that sulphureous exhalations 

 disseminated through the air are not infrequently 

 kindled by lightning, but the flame produced by their 

 burning is quite diff"erent from a flash of lightning, 

 and is propagated hither and thither in a skirmishing 

 way, as it is led by the exhalations, and it also lasts 

 for some time. Such a flame is sometimes seen in a 

 very intense flash. 



But that it may be understood what I think about 

 lightning, it is allowable for us to assume that thunder- 

 storms are caused by this, that the clouds high up 

 in the atmosphere, when condensed and frozen, descend 

 on those beneath with a violent crash, as has been 

 shown by the very ingenious Descartes. Further,. 



