ON LAND AND SEA AIR. 26^; — 



houfz and others ; the fubje(n; is not exhaufted, and an ex- 

 tenfive field continues open for him who wiflies to en- 

 gage in this intricate branch of Pneumatic Philofophy. 



The purity of the air is not interefting to us merely 

 as an object of curiosity, but demands our attention as 

 phyficians and phiiofophers. In proportion to the num- 

 ber of afcertained fa<3:s, the certainty of inference is in- 

 creafed. The fliort life of any one individual, together 

 with his local fituation, will prevent him from completing 

 this department of fcience. It is merely from repeated 

 experiments made under different circumftances, that we 

 can exped to arrive at truth. The more we multiply 

 fadts the more decided may we be in our conclufions. 

 Such are the refledtions, which Induced me to engage 

 in a feries of experiments, which fhall be related in the 

 following pages. 



Our atmofphere having been fo fuccefsfully analyzed 

 by the celebrated Lavoifier, and being found to confift of 

 fluids pofleffing very different and oppofite qualities ; 

 chemifts foon began to enquire whether its ingredients 

 might not be in various proportions in different fitua- 

 tions ; and, particularly, whether it differed in point of 

 purity in different fituations on land and on the ocean. 



Mofl of the experiments of which we have an ac- 

 count were made on land : The Memoir of Dr. Ingen- 

 houfz publifhed in the 70th volume of the Philofophical 

 Tranfadlions is the only effay I have {ccn containing 

 experiments made at fea : but his traverfc was fo fhort, 

 that he had not an opportunity of examining the air in 

 different latitudes. He, however is of opinion that fea 

 air is, ceteris paribus, purer than land air ; but he ap- 

 pears to have found fome feeming contradidlions of his - 

 general inference. He fays, page 364, that air taken from 

 the middle of the channel was of an inferior quality to 

 that at the mouth of the Thames ; and that air near the 

 L 1 2 fea 



