ARTIFICIAL RAINS. 493 



Third, It is known by chemical principles, that the 

 caloric of elasticity given out during the condensation of 

 this vapor, would be equal to about 20,000 tons of anthra- 

 cite coal burnt on each square mile over which the cloud 

 extended. 



Fourth, I have shown by experiment, (see Saturday 

 Courier, March 18, 1837,) that this caloric of elasticity 

 would prevent the air from cooling only about half as much 

 as it would, if it had no vapor in it, or about 45 at the height 

 assumed ; which would cause the air in the cloud to be, at 

 that height, about 45 warmer than the air on the outside 

 of the cloud at the same height. I have shown from these 

 principles, (see Journal of the Franklin Institute for 1836,) 

 that the barometer would fall under the cloud thus formed, 

 in favorable circumstances, a quantity as great as it is known 

 to fall sometimes under the middle of a dense and lofty 

 cloud, and that consequently the air would rush in on all 

 sides towards the centre of the cloud and upwards in the 

 middle, and thus continue the condensation of the vapor 

 and the formation of cloud and the generation of rain. 

 (See also Journal of the Franklin Institute for September 

 and October, 1838, and for January, February and March, 

 and subsequent, 1839.) 



Fifth, I have shown also in the volumes quoted above, 

 that the air does move inwards on all sides towards the cen- 

 tre of the space or region where a great rain is falling, and 

 of course upwards, after it comes in under the cloud, which 

 is so much lighter than the surrounding air ; at least, that 

 it does so in all storms which have been investigated, which 

 now amount to sixteen, besides several tornadoes, in all of 

 which the trees were thrown with their tops inwards. 



From the principles here established by experiment, and 

 afterwards confirmed by observation, it follows, that if a 

 large body of air is made to ascend in a column, a large 

 cloud will be generated, and that that cloud will contain in 



