370 On Rain, Evaporation, Se 
ated ;| whence we may conclude that 9 inches 
nearly had ascended and been evaporated. This 
evidently shews, that earth ts capable of holding 
ai.very great proportion of water, that in sum- 
mer the water ascends, to supply the exigences 
at the surface, and that earth far under tie point 
of saturation, with moisture is still fit to support 
vegetation. 7 
This observation suggested the following 
question—How much water is there in a given 
depth of earth when the soil is at the point of 
saturation, or in that state when it begins to 
yield water from the lower pipe of the evapora. 
ting gage? 
To determine this I took a quantity of gar- 
den soil that had been soaked with rain a day 
before, and pressed it into a crucible; in this 
state 2 found’ its specific gravity to that of 
water as § to 3+ It was then exposed to a mo- 
derate heat till it appeared, as near as I could 
judge, of the same moisture as garden soil two 
inches deep in dry summer weather ; afterwards 
it was exposed almost to a red heat till it be- 
came a perfectly dry powder; in the former case 
it Jost» of its weight, and in the latter £— 
When it had lost 4, it did not appear too dry 
tO support vegetation. When it had lost 4, 
it appeared like the top soil in summer.— 
Hence it follows, that every foot of earth 
