27 
kind of geometrical progression to the arithmetical increase 
of the degrees of temperature. 
Thus 1728 inches, or a cubic foot of any of the gases, 
expand uniformly by 67° of heat (the difference from 13° to 
80% which we have made choice of, as being about the two 
extremes of temperature in summer and winter) into 1972 
inches, or in the ratio of 100 to 114, while the expansion in 
aqueous vapour, generated from water of 13° and 80° temper- 
ature, is found to be 0.1 and 1.0, or in the ratio of I to 10. 
The expansion of vapour at 55° is found to be .45 ; here, 
then, we have data to calculate the quantity of moisture in 
the atmosphere, supposing the same to be saturated there- 
with, (though we know it seldom is completely) and taking 
it for granted that the quantity is always proportional to the 
expansive force. 
For if the atmosphere at 55" temperature, when the ex- 
pansive force is 0.45, contains 26 cubic inches of vapour per 
foot, it must, at the temperatures of 13° and 80°, or with 
expansive forces of 0.1 and 1.0, contain respectively 5.8 and 
58 inches of vapour per cubic foot of air. From the conclu- 
sions of General Roy and Mr. Schmidt, a much larger pro- 
portion of moisture is held in the air at those temperatures ; 
but they seem to have been led into considerable errors, by 
attempting to establish mean rates of expansion from differ- 
ent points of the thermometric scale. x\dmitting, therefore, 
the above results, v/hich are calculated after the later and 
much more accurate experiments of Mr. Dalton, we have 
two very distinct effects of heat on the atmosphere, — the pro- 
portional expansion of the gases, and the progressional ac- 
cumulation of aqueous vapour. 
First, supposing the air to be perfectly dry, we find that a 
cubic foot of it in winter, at the temperature of 13° will 
contain about 370 inches of oxygen gas ; but this gas, by the 
summer heat of 80°, will expand into 422 inches : hence it 
is evident that a foot of dry air in winter contains l-7th more 
