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He fixed an apple-branch, three feet long, half-inch in diameter, 

 full of leaves and lateral shoots, to a tube seven feet long, and five- 

 eighths of an inch in diameter. He filled the tube with water, 

 arid then immersed the whole branch up to the lower end of the 

 tube, in a vessel full of water. The water was driven into the 

 branch by the pressure of the column of water in the tube, which 

 Subsided fourteen and a quarter inches in two days. 



On the third day he removed the branch and tube out of the 

 water, and hung it up in the open air ; the water in the tube fell 

 now twenty-seven inches in twelve hours. 



To determine the comparative force with which the water is 

 driven through the vessels of the ligneous body by pressure alone, 

 and by pressure and exhalation combined, Hales joined a leafy ap- 

 ple branch to a tube nine feet long filled with water. In conse- 

 quence of the pressure of the column of water and of the exha- 

 lation taking place from the surface of the leaves and twigs, the 

 water in the tube (fortieth experiment) sank 36 inches in an hour. 

 He then cut off the branch 13 inches below the glass tube, and 

 placed the cut portion (with leaves and twigs) upright in a vessel 

 with water. It was found to imbibe 18 ozs. of water in 30 hours ; 

 in which time only 6 ozs. of water had passed through the 13 

 inches of the stem connected with the tube, and that too under 

 the pressure of a column of water 7 feet high. 



In three other experiments, Hales shows that though the sap- 

 vessels of plants will imbibe water plentifully by capillary attrac- 

 tion in branches severed from the trunk, as well as in those left in 

 connection with the uninjured roots, they have very little power 

 to protrude sap out at their extremities, and make it rise in a tube 

 fixed to them. 



The motion of the sap, Hales concludes, is to be attributed to 

 the exhalation from the surface alone, and he proves that it pro- 

 ceeds in an equal degree from the trunk, branches, leaves, flower 

 and fruit, and that the effect of the exhalation bears a certain def- 

 inite ratio to the temperature and moisture of the air. When the 

 atmosphere was charged with humidity little water was imbibed, 

 and on rainy days the absorption was barely perceptible. Hales 

 opens this second chapter of his statics with the following intro- 

 troductory remarks : 



' Having in the first chapter seen many proofs of the great 

 quantity of liquid imbibed and perspired by vegetables, I propose 

 in this to inquire with what force they do imbibe moisture. 



' Though vegetables (which are inanimate) have not an engine 

 which by its alternate dilatations and contractions does in animals 

 forcibly drive the blood through the arteries and veins, yet has 

 nature wonderfully contrived other means, most powerfully to 

 raise and keep in motion the sap.' 



In his twenty-first experiment he laid bare one of the chief 

 roots of a thriving pear-tree at a depth of 2* feet, cut off the end 



15 



