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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. 



HALESS METHOD OF MEASCRIXO 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 

 begin 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 +£, 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 versd, 

 than the other two branches aorc; 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 b 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 ox 

 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 



