Ou Respiration and Animal Heat, 29 
yamifications of the air-vessels of the lungs, 
surrounded by moist membranes, must, in a 
moment, be nearly saturated with vapour; we 
shall have, therefore, an increase of the force 
of vapour from that inspired, .30 to that ex- 
pired of 1,74 inches of mercury, being an 
increase of 1,44 inch, But by reason of the 
less specific gravity of vapour than air, in pro- 
portion as 7 to 10, vapour of the above force 
will only be equal in weight to air of 1 inch 
of force. Hence the weight of aqueous vapour 
exhaled at any time must be nearly equal to 
3, of the weight of the whole mass of elastic 
fluids expired. We have then +£:5 =1,55 lbs. 
troy for the weight of aqueous vapour expired 
in a day, on the supposition that 464 lbs. of 
air, &c. are expired, and that the air so ex- 
pired is saturated with vapour, or contains as 
much as any gas can do in the temperature. 
The real quantity expired can not exceed that 
stated above; nor is it probable that it can 
fall much short of it. 
It is worthy of remark, that Dr. Hales, who 
was one of the earliest to investigate the 
quantity of water exhaled, should have ap- 
proximated nearest to the truth; and that he 
should rather have exceeded the truth in con- 
sequence of his alkali extracting, not only 
the additional vapour acquired in the lungs, 
