354 PHILOSOPHICAL TRANSACTIONS. [aNNO 166q, 



except that in cylinders, the edge of the tool is parallel to the axis, but here 

 inclined. 



Therefore it is to be observed, that the species of the hyperbola is varied ac- 

 cording to the inclination of the angle G A O ; consequently, it may be so 

 easily fitted to a given hyperbola, that there is no need of farther demonstration. 

 But if, the angle continuing the same, the generating line approach nearer the 

 centre, there will arise a less hyperbola, but quite similar to the former. 



Experiments on the Motion of the Sap in Trees. By Mr. JFjllughby* 

 and Mr. Ray,-^ Fellows of the Royal Society. N" 48, p, 963. 



In birch trees, the sap issues out of the least twigs of branches, and fibres of 

 roots, in proportion to their size. 



From branches that bend downward, there issues a great deal more sap, than 

 from others of the same size in a more erect posture. 



Branches and young trees cut quite off when full of sap, and held perpendi- 

 cularly, will bleed. And if you cut off their tops, and invert them, they will 

 bleed also at the small ends. 



Roots of birch and sycamore cut asunder will bleed both ways, that is, from 

 that part remaining to the tree, and from the part separated ; but a great deal 

 faster from the part remaining to the tree. But in a cold snowy day the root of 

 one sycamore, we had bared, bled faster from the part separated, and ten times 

 faster than it did before in warm weather. 



In birches, the sap does not issue out of the bark, be it ever so thick; but as 

 soon as you have cut the bark quite through, then it first begins to bleed. 



The bark being quite pared off above a hand's breadth round, about several 



* Francis Willughbyj Esq. the amiable and learned author of several ingenious papers relative to 

 natural history published in the Philosophicar Transactions, and particularly distinguished by his 

 Ornithology and Ichtliyology, published after his deatli, by his friend Mr. Ray, was born in the 

 year l635, and was the only son of Sir Francis Willughby, Knight. He travelled into France, 

 Spain, Italy, Germany, and tlie Low Countries, accompanied by Mr. Ray, collecting and describ- 

 ing with great attention and exactness the various species of animals which occasionally presented 

 themselves. He died in l672, aged 37 ; to the great regret of tlie republic of letters, and more 

 especially of the Royal Society, of which he was an eminent and estimable member. His principal 

 works are his Ornithology and his Ichthyology, both published after his death, under the care of 

 Mr. Ray, who revised the MSS. and added such species as were not described by Mr. Willughby 

 from the works of other autliors, viz. Gesner, Aldrovandus, Clusius, Piso, &c. Mr. Ray assures 

 us that what rendered Mr. Willughby most commendable was his eminent virtue. *' I cannot say 

 " that I ever observed such a confluence of excellent qualities in one person." Mr. Ray also informs 

 us, that Mr. Willughby had meditated a voyage to the new world> in order to investigate the na- 

 tural history of that portion of the globe. 



f A biographical account of Mr. Ray will be given hereafter. 



lib 



