183 
same; I did not happen to mark the heat of the ground when I made the 
fore-mentioned experiment; the two following are more circumstantial: the 
ground had been wetted the day before I made them by a thunder-shower, 
the heat of the earth, at the time of making them, estimated by a thermome¬ 
ter laid on the grass, was ninety-six degrees; one experiment gave 19/3 
gallons from an acre in twelve hours, the other gave 1905 . Another expe¬ 
riment made, when there had been no rain for a week, and the heat of the 
earth was 110 degrees, gave after the rate of 2800 gallons from an acre in 
twelve hours. 
The quantity of water which was condensed on the inside of the glass, I 
found to be accurately proportionable to the time during which it stood on 
the grass; for in one experiment six grains were collected in ten minutes, 
and in another fifteen grains were collected in twenty-five minutes; now the 
proportion of six to ten is the same as that of fifteen to twenty-five. 
In order to see whether the copious vapour collected by the glass was 
owing to the natural perspiration of the grass, or to a kind of mechanical 
distillation from the body of the earth, I put the glass upon a footpath which 
was dry, and had no grass growing upon it, the vapour rose from the foot¬ 
path as well as from the grass, but not so abundantly. 
THIRD EXPERIMENT. 
Upon the same grass-plat, and contiguous to the glass used in these expe¬ 
riments, I placed a silver cup, with its mouth downwards, of a shape similar 
to that of the glass, and nearly of the same dimensions; but I could never 
observe that its inside had collected the least particle of vapour, though I 
frequently let it stand on the grass for half an hour or more. 
FOURTH EXPERIMENT. 
By means of a little bees wax, I fastened an half crown very near, but not 
quite contiguous, to the side of the glass, and setting the glass, with its mouth 
downwards, on the grass, it presently became covered with vapour, except 
that part of it which was near to the half crown. Not only the half crown 
itself was free from vapour, but it had hindered any from settling on the glass 
