F'kal Air in the Atmvfpherc. oJSv 



very long time may become fufHciently fenfiule to make the 

 proportion of the vital air of the atniofphere experience a 

 progreflive or periodical increafc or diminution ? The expe- 

 riments which I have hitherto made are not fiifficicnt to 

 enable nie to afcertain whether there be fach a difference of - 

 feme thoiifandth parts, and this <;ould not be known even 

 by employing more confidcrable portions of common air and 

 very long tubes. Obfervation, indeed, ihows that fulphuret 

 may contain, int^rpofed between its particles, a certain portion 

 of mephitic air, and we do not know whether it may not vary 

 fome fniall part ; befides, the particles of the water, which are 

 more or lefs adhefive to the inner furface of the tube, what- 

 ever care may be taken, difference of temperature and other 

 caufes united, though they can be fo fur avoided as not to 

 have in the refuft of the operation the error of a hundredth 

 part, are capable of occafioning, fomctimes, others lefs con- 

 lidcrable, fuch as of a thoufandth part, unlefs a degree of 

 attention of which few perfons arc capable be employed. 



Though we may confider, as exact, in general, the ana- 

 lyfis of natural produ6lions carried to that degree of perfec- 

 tion yielded bv eudiometric proofs; yet it is not impofli- 

 ble, for feveral reafons, that greater exa(Jl;nefs might be at- 

 tained to refolve the propofed queftion. Thofe would cer- 

 tainly be in an error who fhould calculate the lofs of vittd 

 air produced in the atniofphere from the cauics of its dc- 

 ibu6lion already known : they would certainly lind ifim- 

 poflible that many years could elapfe without its becoming 

 perceptible; the quantity which animals confume being 

 very great, as well as that conlumed by combuftible bodies^; 

 with which it. combines during the acl of combultion. Con- 

 fequently, pofierity would be 'forced to refpire an air inore 

 charged with mephitic gas than that which we breathe at 

 prefent. But we are not entirely ignorant of the means 

 wViicl* the Divine Providence employs for refioring that 

 adive fluid to the common receptacle, via. plants a<Sted upon 

 by the rays of the fun. It is not, however, poiTible to calculate 

 the quantity of the vital air which the atmofphere recovers, 

 from that quarter. We have reafon to expccl that the ob- 

 servers pf; ^atvire, will difcover other caufes of the additioa o£ 

 . " vital 



