DR. HALES’ EXPERIMENTS. 55 
be able to measure this force. A little water 
must be poured into the tube; and taking care 
that it does not run out, by placing the finger 
on the open end, it must then be plunged into 
a basin containing a little quicksilver. The ac- 
companying cut will represent the method of 
arranging this apparatus.. In a quarter of an 
hour the heavy quicksilver will be seen to have 
risen up into the tube, and 
will rise until it actually 
touches the end of the 
branch. The great Dr. Hales 
made some most beautiful ex- 
periments on this subject, and 
found a branch of a nonpareil 
apple-tree, with twenty apples 
on it, actually sucked up a 
column of mercury a foot 
high in seven minutes. ‘The 
result of his experiments 
shewed that, in some instances, #7 eee eck oF. 
the power which moves the sap CIRCULATION. 
in plants is five times stronger than that which 
drives the blood through the artery in the horse’s 
leg. 
