25 
lated the weight of the vapour to be to that of perfectly dry- 
air as 10 to 23.5. From these circumstances, without doubt, 
the something wanted to complete the compound of the at- 
mosphere is aqueous vapour ; and from the data they afford, 
we compute the proportions of a cubic foot of atmospheric 
air to be as follows, viz : — 
Cubic inches, 
Oxygen gas 366 
Nitrogen gas 1334 
Carbonic acid gas 2 
Aqueous vapour ... 26 
MR. MURKAY, 
Cubic inches. Weight in Parts. 
363. ... 23.32 
1339.1 ... 75.55 
1.4 ... .1 
24.5 ... 1.03 
1728 j 1728. 100. 
And the specific gravity of this compound, we find to agree 
with that of atmospheric air, as determined by Mr. Kirwan 
in nearly the same temperature. 
Having noticed the mixture and proportions of the gases 
constituting the atmosphere, at a medium temperature, let 
us now inquire into the cause of the very obvious difference 
in its effect on the Blast Furnace during the seasons of sum- 
mer and winter. This variation follows so uniformly the 
heat or coolness of the weather, that we formerly were led 
to conclude it originated entirely from some different modifi- 
cation of the atmosphere, by the presence or absence of 
caloric : that either the oxygen gas being more dilatable 
by heat than the other gases, became in summer considerably 
rarer, and consequently less in its proportional quantity : or 
that the oxygen gas was subject to a partial spontaneous 
combustion, somewhat similar to that of phosphorus, at a 
lower heat than that of our summer's day ; by which the 
purity of the atmosphere might be much diminished. These 
notions, however, upon a closer investigation, we found alto- 
* These numbers of measure and weight were gathered from a Lecture by 
Mr. Murray, from fifteen to twenty years ago, and are inserted here merely for 
the sake of comparison. 
