Vegetable Statickf. iij 
In very hot weather many air bubbles 
would rife, fo as to make a froth an inch 
deep, on the top of the fap in the tube. 
I fix’d a fmall air Pump to the top of a 
long tube, which had 12 feet height of fap 
in it ; when I pumped great plenty of bub- 
bles arofe, tho’ the fap did not rife, but fall 
a little, after I had done pumping. 
In Experiment 34- (where a tube was 
fixed to a very fhort flump of a Vine, with- 
out any lateral branches) we find the fap 
rofc all day, and fafteft of all in thegreatefl: 
heat of the day : But by many obfervations 
under the 37th and this 38th Experiments, 
we find the fap in the tubes conftantly fub- 
fided as the warmth came on towards the 
middle of the day, and fafteft in the greateft 
heat of the day. Whence we may reafon- 
ably conclude (confidering the great perfpi- 
rations of trees, Ihewn in the firft chapter) 
that the fall of the fap in thefe fap gages* 
in the middle of the day, efpccially in the 
warmer days, is owing to the then greater 
perfpiration of the branches, which perfpi- 
ration decreafes, as the heat decreafes to- 
wards evening, and probably wholly ceafes 
when the dews fall. 
But 
