Vegetable Staticks . 89 
the tranfverfe cut of the branch was co- 
vered with innumerable little hemifpheres of 
air, and many air bubbles iffued out of the 
fap veffels, which air did in part fill the 
tube e r, as the water was drawn out of it ; 
fo that the height of the mercury could 
only be proportionable to the excefs of the 
quantity of water drawn off, above the quan- 
tity of air which iffued out of the wood. 
And if the quantity of air, which iffued 
from the wood into the tube, had been equal 
to the quantity of water imbibed, then the 
mercury would not rife at all ; becaufe there 
would be no room for it in the tube. 
But if 9 parts in 12 of the water be im- 
bibed by the branch, and in the mean time 
but three fuch parts of air iffue into the tube, 
then the mercury muft needs rife near 6 
inches, and fo proportionably in different 
cafes. 
I obferved in this, and mod of the follow- 
ing experiments of this fort, that the mer- 
cury rofe higheft, when the fun was very 
clear and warm; and towards evening it 
would fubfide 3 or 4 inches, and rife again 
the next day as it grew warm, but feldom 
to the fame height it did at firft. For I have 
always found the fap veffcls grow every day, 
after 
