4i6 EXPERIMENTS on 



In a former memoir which I had the honour to read be- 

 fore this fociety, I paid particular attention to the atmof- 

 phere over the ocean, rivers and neighbouring land, and 

 hope that my experiments have been of fome fervice to- 

 wards the eftablifhment of truth ; in the prefent eflay I in- 

 tend giving an account of fome experiments w^hich 1 per- 

 formed at different times on the air over marfhes. 



A few general remarks refpe<5ting the common ftate of 

 our atmofphere, perhaps become neceflary for the fake of 

 future comparifons. 



We no longer believe, for experiments have taught us 

 the contrary, that our atmofphere is an homogeneous ele- 

 ment : the prefent ingenious dodtrines of heat have thrown 

 much light upon thefubjedl ; and with much reafon fome 

 phiiofophers are induced to believe " that the aeriform ftate 

 is a modification of bodies, dependent on the degree of 

 temperature, and on the prefl'ure which thefe bodies under- 

 go !"* This opinion has been extended fo far as to induce 

 fome to fay, " Perhaps alfo metals are contained in the at- 

 mofphere. "f Thefe fentiment^ do not appear to be merely 

 conjectural, for Chaptal has precipitated mercury from ox- 

 ygen gas (which was obtained from red precipitate) by 

 means of ice; and the family ot Achard, fuifered ptyalifm 

 from breathing in an atmol'phere where mercury had been 

 cxpofed for fome time in a faucer. 



The above opinions, if true (and I think them highly pro- 

 bable) prepare us to meet many difficulties in the analyfis of the 

 atmofphere. But all I expeft to do is to open the paflage, 

 and I lliall leave others to render it more certain ; for nume- 

 rous experiments, and thofe often repeated, are the only 

 means whereby we can afcertain truth ; and I fear the la- 

 bours of one man are infufficient to perform this tafk. 



I am 



* Lavoifier's Elements of Chemiftry, p. 59. 

 f Gritauner's Antiphlogiftiche Chemie, p. 58. 



