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become brown; in less than two minutes the inside of the glass was clouded 
with a vapour, and in half an hour drops of water began to trickle down its 
inside, in various places. This experiment was repeated several times with 
the same success. That X might accurately estimate the quantity, thus raised, 
in any certain portion of time, I measured the area of the mouth of the glass, 
and found it to be twenty square inches: there are 1206 square inches in a 
square yard, and 4840 square yards in a statute acre 5 hence, if we can find 
the means of measuring the quantity of vapour raised from twenty square 
inches of earth, suppose in one quarter of an hour, it will be an easy matter 
to calculate the quantity which would be raised with the same degree of heat, 
from an acre in twelve hours. The method X took to measure the quantity 
of vapour, was not perhaps the most accurate which might be thought of, but 
it was simple and easy to be practised: when the glass had stood on the grass- 
plat one quarter of an hour, and had collected a quantity of vapour, I wiped 
its inside with a piece of muslin, the weight of which had been previously 
taken; as soon as the glass was wiped dry, the muslin was weighed again, 
its increase of weight shewed the quantity of vapour which had been col¬ 
lected. The medium increase of weight, from several experiments made on 
the same day, between twelve and three o’clock, was six grains collected in 
one quarter of an hour, from twenty square inches of earth. If the reader 
takes the trouble to make the calculation, he will find that above 1600 gal¬ 
lons, reckoning eight pints to a gallon, and estimating the weight of a pint 
of water at one pound avoirdupois, or 7000 grains troy weight, would be 
raised, at the rate here mentioned, from an acre of ground in 24 hours. 
The immense quantity of exhalation from the seas surrounding our globe 
is still more astonishing. Dr. Hally, by observing the quantity evaporated 
from a vessel full of water of the same degree of saltness with that of the 
ocean, calculated, that the quantity exhaled from the Mediterranean Sea alone, 
in one summer’s day, there being little wind, amounted to 5 , 280 , 000,000 
tons of water. 
SECOND EXPERIMENT. 
It may easily be conceived, that the quantity thus elevated will be greater 
when the ground has been well soaked with rain, provided the heat be the 
