SECT. V. 



Experiments on the Contents of the 

 A I R. 



Cef* une erreur de croire, q'une experience aveugle, 

 et une habitude mechanique, tiennent lieu de prin- 

 cipes furs, et de maximes fondees fur un folide 

 raifonnement. 



BeecariA Traduft. d'un difcours fur la Commerce. 



NOTHING is more evident than that our 

 atmofphere abounds with a great variety 

 of fubftances, if we confider the various exhala- 

 tions conftantly emitted from all vegetables; 

 in prodigious quantities from all animal bodies 

 and the great variety of foffil matters that are 

 inceffantly rifing in the atmofphere (j). 



To inveftigate the nature of all thefe is im- 

 poffible in very few cafes can we find the exha- 

 lation of one kind only *, and many of them are 

 of little confequence ; for if we confider the 

 quantity that is conftantly exhaling, and the 

 powers many of them might have in acting upon 

 the human body, we fhould expect the effects to 

 appear every moment to a considerable degree, 

 which we find very far from being the cafe : 

 there are certainly fome means by which they are 

 obviated : thele exhalations are no doubt more or 

 lefs diffufed into the higher regions of the air - 9 



(y) This was publiflied before the author became ac- 

 quainted with the obfervations on different kinds of air by 

 the learned Dr. Prieftley, and as this inquiiitive philofopher 

 is ftil! purfuing his enquiries, it is thought fufficient to re- 

 fer the reader to the original experiments, in the lait volume 

 of the Philofophical Tranfactions. 



and 



