^ CIRCULATION t»F THE SAT. 



VI. 



On the inverted Jcfion of the alburnous Vessels of Trees. By 

 Thomas Andrew Knight, Esq, F.R.S. From the Phi- 

 losophical Transactions, 1806. 



Theory Ac- Jj^ HAVE endeavoured to prove, in several Memoirs* which 



facts, by tlie 7^^ have done me the konour to lay before the Royal Society, 



author: that (hat the fluid by which the various parts (that are annually 



Lt'ertLou^h' ^^^^^ ^o trees, and herbaceous plants whose organization is 



'.he leaves and similar to that of trees), are generated, has previously circu- 



^j^J*-'"^^ lated through their leaves f either in the same, or preceding 



fcark.'' 



hyperbolic curvature, in the speculum ; and that the latter will be 



most correctly formed by a polisher, whose area is nearly circular. 

 For, in order to make the speculum hyperbolic, the longest dia- 

 meter of the oval polisher must be considerably greater than the 

 shortest one, i. e. than the breadth of the mirror : as will be evi- 

 dent, from a consideration of the circumstances I have endea-t 

 Toured to explain. And, as the mirror must be carried, by the 

 strokes in polishing, to the extreme verge of the polisher; so, 

 when it is to traverse it, in the direction of its longest diameter, it 

 will have its center or vertex removed too far from that of the po- 

 lisher, to acquire from it a true conoidal figure. Either, therefore, 

 the face of the polisher should be round ; or, if it be oval, it 

 ought to be rendered a less eccentric ellipse, by having its shortest 

 diameter greater than that ©f the mirror, which will allow the ex- 

 tent of the polisher to be reduced, by contracting proportionablr 

 its tranverse diameter ; i. e. it must be brought nearer to a circular 

 figure. For the objection, mentioned by Mr. Edwards, to « 

 round shape of the polisher, when it is to be considerably larger 

 than the mirror, viz. " that it makes the latter perpetually into a 

 " segment of a larger sphere, and by no means of good figure," I 

 apprehend to have chiefly arisen, from an omission, in those who 

 tried it, to make furrows in the pitch, in the proper tract, on the 

 surface of the polisher; which, if it had been done, would have 

 produced, not a spherical, but a canoidal figure. 



* In the Phil. Trans, for 1801, 18o3, 1804, and 1805. 



-f During the circulation of the sap through the leaves, a 

 transparent fluid is emitted, in the night, from pores situated 

 ©n their edges ; and on evaporating this liquid obtained from 

 v«ry luxuriant plants of the vine, I found a very large residuum 



