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" About 4 or 5 o'clock in the afternoon ; when the sun went off the vine, the sap 

 began to push afresh into the gages, so as to make the mercury rise in the open legs ; but 

 it always rose fastest from sun-rise till 9 or 10 in the morning. 



HALES'S METHOD OF MEASURING THE FORCE OF THE ASCENT OF THE SAP IN THE VINE. 



" The sap in b (the oldest stem) played the most freely to and fro, and was therefore 

 soonest affected with the changes from hot to cool, or from wet to dry, and vice 

 versd. 



" And April 20, towards the end of the bleeding season, b began first to suck 

 up the mercury from 6 to 5, so as to be 4 inches higher in that leg than the other. But 

 April 24, after a night's rain, b pushed the mercury 4 inches up the other leg, a did not 

 Ijegin to suck till April 29, viz., 9 days after b ; c did not begin to suck till May 3, viz., 

 13 days after b, and 4 days after a. May 5th at 7 a.m. a pushed 1 inch, c 1 + J, but 

 towards noon they all three sucked. I have frequently observed the same difference 

 in other vines, where the like gages have been fixed at the same time, to old and young- 

 branches of the same vine, viz., the oldest began first to suck. 



" In this experiment we see the great force of the sap, at 44 feet 3 inches distance 

 from the root, equal to the force of a column of water 30 feet +11 inches + ^ high. 



" From this experiment we see, too, that this force is not from the root only, but 

 must also proceed from some power, in the stem and branches : For the branch b was 

 much sooner influenced by changes from warm to cool, or dry to wet, and vice vnrsii, 

 than the other two branches a or c and b was in an imbibing state, 9 days before a, which 

 was all that time in a state of pushing sap; and c pushed 13 days after 6 had ceased 

 pushing, and was in an imbibing state. Which imbibing state vines and apple-trees 

 continue in all the summer, in every branch, as I have found by fixing the like gages to 

 them in July." 



Hales 's method of placing a vertical tube in an artery is still the 

 most striking method of bringing home some of the facts of blood 

 pressure to students. His experiments mark a great and specific 

 advance in this subject and carry one on from Borelli to Poiseuille 

 and Ludwig, who used a mercury manometer instead of a long straight 

 tube lead us, in fact, to the kymograph of Ludwig, and, indeed, 

 indirectly to the graphic method as now used in physiology. 



" AN ACCOUNT OF SOME HYDRAULICK AND HYDROSTATICAL EXPERIMENTS MADE ON 



THE BLOOD AND BLOOD-VESSELS OF ANIMALS." EXPERIMENT I. 



" In December I caused a mare to be tied down alive on her back ; she was fourteen 

 hands high, and about fourteen years of age, had a fistula on her withers, was neither 



