54 Vegetable Stanch. 



of a foot diameter ; and circles being as the 

 fquares of their diameters 10 pounds -\- 2 

 ounces, will in 21 days be evaporated from 

 the hemifphere of 30 inches diameter, which 

 the Sunflower's root occupies : Which with 

 the 29 pounds drawn off by the Plant in 

 the fame time, makes 39 pounds, that is 9 

 pounds and % out of every cubick foot of 

 earth, the Plant's roots occupying more than 

 4 cubick feet •> but this is a much greater de- 

 gree of drynefs than the furface of the earth 

 ever fuffers for 1 5 inches depth, even in the 

 dryefl feafons in this country. 



In a long dry feafon, therefore, efpeciaily 

 within the Tropicks, we muft have recourfe 

 for fufficient moifture (to keep Plants and 

 Trees alive) to the moift ftrata of earth, 

 which lay next below that in which the 

 roots are. Now moift bodies always com- 

 municate of their moifture to more dry 

 adjoyning bodies 5 but this flow motion of 

 the afcent of moifture is much accelerated 

 by the Sun's heat to considerable depths in 

 the earth, as is probable from the following 

 20th experiment. 



Now 1 So grains of Dew falling in one 

 night, on a circle of a foot diameter, =z 



113 fquare 



