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CHAP. V. 



Of Precipitations from the Atmofphere. 



There are five fubftances conftantly contained in the atmof- 

 phere, or at leaft in its lower ftrata, with which we are principally 

 concerned; namely, oxygen, mephite, moifture, caloric, and elec- 

 tron, otherwife called the elei^ric fluid, if this be not (which 

 neverthelefs I fufped it to be) a modification of caloric* As, 

 however, its efFeds are very different from thofe ufually afcribed 

 to caloric, it may and ought, like ice and water, to be diftinguifh- 

 by a different appellation. Befides thefe, heavy inflammable air 

 and other miafmata are frequently found in it, and the lighter in- 

 flammable air in its fuperior flrata ; but thefe mixtures are contin- 

 gent, and therefore form no part of the prefent general inquiry. 



Oxygen is frequently precipitated through its aflinity to terreitrial 

 fubftances in certain ftates, as combuftion, putrefadion, &c. Ef- 



feds 



* By modification I here mean a different fituation of caloric, namely, on the ex- 

 ternal furfaces of bodies, and not in their minutcft internal cavities. Light I take 

 to be another modification of caloric, namely, an homogeneous arrangement of fome 

 or all its conftituent particles, which, when thus arranged, and then only, become 

 vifible. 



