PROPERTIES OF PURE AIR. 231 



It is, however, always to be remembered, 

 that variations of considerable extent may take 

 place in these results ; but these do not affect 

 this table, representing, as it does, the average 

 composition of the atmosphere, deduced from 

 an extensive series of carefully-performed experi- 

 ments. 



Professor Schmid, of the University of Jena, 

 has recently calculated the entire weight of the 

 atmosphere, omitting its watery vapour and 

 carburetted hydrogen, and he places it at 

 1,371977,266659,000,000 Ibs. Of this sum the 

 relative proportions of nitrogen, oxygen, and car- 

 bon, in pounds, are stated as follows : 



1,057245,681687,000,000 Ibs. nitrogen. 

 313634,003159,000,000 oxygen. 

 1097,581813,000,000 carbonic acid. 



Total . . 1,371977,266659,000,000 Ibs. 



In reality the weight of the air must considerably 

 exceed this. 



From this it is apparent that the air which 

 floats around us, and in which we live and 

 breathe, is by no means a simple fluid. In its 

 regular constitution we find there are no less 

 than five different ingredients, oxygen and 

 nitrogen, however, infinitely predominating 

 above the rest. It is only the light of science 

 that has detected this fact. The evidence of 



