31& Description of a Ventilator 
in each stroke, and 600 strokes to be made in a minute. 
Then 8 gallons discharged at a stroke^ 
multiplied by 60, the number of strokes, 
amounts to 480 gallons fier minute ; 
which multiplied by 60, the minutes in an hour, produces 
— — — 28800 gallons in that time ; 
and that, divided by 252 ; 28800(~1 14.3 tons. (The number of gal- 
lons in a ton, both wine and ship measure) quotes 114 tons in an 
hour. 
« 
Then, suppose the area of the hold of a ship to be — 
120 tons, and, when freighted, the interstices between the 
grains, together with the area between the surface of the 
corn and the underside of the deck m 5 tons rz to the 
quantity of mephitic air confined ; such being the lightest 
fluid, the major part of it would, soon after the commence- 
ment of the operation, be forced, by the atmospheric air, 
to vent itself at the holes provided for that purpose ; and 
the remainder of the hour being employed in the like 
ventilation, five tons of fresh air would pass above twenty 
times repeatedly amidst the grains, to cool, refresh, and 
sweeten the cargo. A purification thus administered once 
in eight- and- forty hours, would, I conceive, be amply 
sufficient to preserve the corn from taint or injury, be the 
voyage ever so tedious ; and unless it should by neglect 
have overheated and grown together, or settled too close, 
the labour would be that of a boy onjy ; for the dairy-girl 
at her churn works harder than he otherwise need to do 
at this. 
My air-\^ssel is, for the sake of cheapness, confined to 
the narrow diameter of ten inches ; but, as the contents 
of circles are proportionate to the square of their diame- 
ters, by enlarging that, you increase their power accor- 
dingly ; wherefore, by extending the diameter to four- 
teen inches, the contents will be nearly doubled ; and, 
by adding ten inches more to the length of the stroke, 
you almost treble the discharge of No. 1, and obtain a 
