244 STUDIES OF NATURE. 



reckoning, our batteries of cannon ought to be- 

 come glaciers in the midft of a battle, for a world 

 of nitre is kindled into flame on fuch occafions ; 

 they are under the neceffity, however, of cooling 

 the cannon with vinegar ; for, after having been 

 fired off twenty times, in quick fucceffion, it is- 

 impoffible to apply your hand to the piece. The 

 flame of the nitre, though infl:antaneous, power- 

 fully penetrates the metal, notwithftanding it's 

 thicknefs and folidity. 



The heat, it is true, may likewife be occafioned 

 by the interior vibration of the parts. Whatever 

 may be in this, the cooling of the air, after a 

 thunder-ftorm, proceeds, in my opinion, from that 

 ftratum of frozen air which furrounds us, to the 

 height of from twelve to fifteen hundred fathoms; 

 and which, being divided and dilated at it's bafe, 

 by the fire of the fl:ormy clouds, flows haftily into 

 our Atmofphere. It's motion determines the fire of 

 the thunder, to dired itfelf, contrary to it's nature, 

 toward the Earth. It produces ftill farther efFeds, 

 which neither time nor place permit me at prefent 

 to unfold. • 



It was affirmed, in the lad age, that the Earth 

 was drawn out at the Poles ; and we are now po- 

 fitively told, that it is flattened there. 1 fhall not 

 at prefent enter into an examinatio» of the prin- 

 ciples 



