128 STEPHEN HALES 



goes on to call it nutation^ which must be the locus 

 classicus for the term used in this sense. 



An experiment^ that I do not remember to have 

 seen quoted elsewhere is worth describing. It is 

 incidentally of interest as showing the generous 

 scale on which his work was planned. An apple 

 bough five feet long was fixed to a vertical glass tube 

 nine feet long. The tube being above and the 

 branch hanging below, the pressure of the column 

 of water would act in concert with the suck of the 

 transpiring leaves, instead of in opposition to this 

 force. He then cut the bare stem of his branch in 

 two, placing the apical half of the specimen (bearing 

 side branches and leaves) with its cut end in a glass 

 vessel of water ; the basal and leafless half of the 

 branch remained attached to the vertical tube of 

 water. In the next 30 hours only 6 ounces dripped 

 through the leafless branch, whereas the leafy 

 branch absorbed 18 ounces. This, as he saj'-s, 

 shows the great power of perspiration. And though 

 he does not pursue the experiment, it is worthy of 

 note as an attempt, like those of Janse^ and others, 

 to correlate the flow of water under pressure with 

 the flow due to transpiration. 



It is interesting to find that Hales used the three 

 methods of estimating transpiration which have 

 been employed in modern times — namely, (i) 

 weighing, (ii) a rough sort of potometer, (iii) en- 

 closing a branch in a glass balloon and collecting 



' Vegetable Staticks, p. 41. 



^ Janse in Prittgsheim's Jahrb. xviii. p. 38. The later literature 

 is given by Dixon in Progressus Ret Bot. III., 1909, p. 58. 



