174 6N RAIN, EVAPORATION, &C 



ply the exigencies at the furface, and that earth far under the 

 point of faturation with moiflure is ftill fit to fupport vegeta- 

 tion. 

 Queftion. How This obfervation fuggefted the following queftion — How 



wnteineTfn fa- mU ° h WateF lS there in a S iven de P th °* earth when tne fciIis 

 turated ground, at the point of faturation, or in that ftate when it begins to 



yield water from the lower pipe of the evaporating gage ? 

 Experiment, i To determine this I took a quantity of garden foil that had 

 earth contains 7 k een ^ oa ^ e( ^ w * tn raul a day before, and prefled it into a cru- 

 jnches water, cible ; in this ftate I found its fpecific gravity to that of water 



l n Vt T y ^ a& five t0 three - ^ was then expofed to a moderate heat till 

 half before it is . * 



toodry forvege-it appeared, as near as I could judge, of the fame moifture 

 tation. as g arc Jen foil two inches deep in dry fummer weather ; after- 



wards it was expofed almoft to a red heat till it became a per- 

 fectly dry powder ; in the former cafe it loft j~ of its weight, 

 and in the latter, j-. — When it had loft \ t it did not appear too 

 dry to fupport vegetation. When it had loft ■§•, it appeared 

 like the top foil in fummer. — Hence it follows, that every foot 

 of earth in depth, fo faturated, contains feven inches of water, 

 and that it may part with one quarter of its water, or even 

 one half, and not be too dry for fupporling vegetation. 

 Brick clay naarly Clay, juft dug out for the purpofe of making bricks, was 

 tried in the fame manner : It gave the fame fpecific gravity as 

 the earth, and yielded not much lefs water. 

 De la Hire's Thefe experiments and obfervations prove, that M. de la 



conclufions er- Hire's conclufions, drawn from the vegetation of plants in a 

 roneous. . . - * .. *w . . 



given quantity of foil, precluded from any communication 



with the earth at large, are erroneous, or at leaft unwarranted : 

 As it does not thence appear that the evaporation for the whole 

 year exceeds the rain in the year, whatever it may do for a 

 month or two in fummer. 

 Swings are The origin of fprings may ftill therefore be attributed to rain, 



therefore fup- till fome more decifive experiments appear to the contrary : 

 plied by the . . . „ r •« . 



rains. and lt: becomes unnecellary to controvert the other two opi- 



nions refpecting this fubject. 

 Springs are Upon the whole it fliould feem, that at the commencement 



thence defi- f fp r i n g the ground is nearly faturated with water for five 

 caent in fummer* r ° . ° J 



or fix feet in depth, as the rains and dews in autumn and 



winter far exceed the evaporation : There are then five or fix 



inches of water at leaft to be raifed up again to the furface in 



cafe 



