STUDY IX. 



243 



î havefeen, for example, the formation of thun- 

 der explained, in highly celebrated phyfical rradls. 

 Some demonftrate to you, that it is produced by 

 the coliifion of two clouds, as if clouds, or foggy 

 vapours, ever could produce a coliifion ! Others 

 gravely tell you, that it is the effeél of the air di- 

 lated by the fudden inflammation of the fulphur 

 and of the nitre which float in the air. But, in 

 order to it's being capable of producing it's tre- 

 mendous explofions, we are under the neceffity of 

 fuppofing, that the air was confined in a body 

 which made fome refiftance. If you fet fire to a 

 great mafs of gun-powder in an unconfined fitua- 

 tion, no explofion follows. I know very well that 

 the detonation of thunder has been imitated, in 

 the experiment of fulminating powder ; but the 

 ipaterials employed in the compoficion of it have a 

 fort of tenacity. They undergo, on the part of the 

 iron ladle which contains them, a refiftance againft: 

 which they fometimes ad with fo much violence 

 as to perforate it. After all, to imitate a pheno- 

 menon is not to explain it. The other effefts of 

 thunder are explained with fimilar levity. As the 

 air is found to be cooler after a thunder-ftorm, the 

 nitre, we are told, which is diffufed through the 

 Atmofphere, is the caufe of it -, but was not that 

 nitre there before the explofion, when we were al- 

 moft fuffocated with heat ? Does nitre cool only 

 when it is fet en fire ? According to this mode of 

 R 2 reckoning, 



