RoT/al Society of London. 181 



even be carried beyond that point by an apparatus strong 

 enouch to compress the steam : this, however, can seldom 

 be warned. At first it was objected to this construction, 

 that the expansion of the pipes, when heated, might da- 

 mage the building : but experience has proved, that the 

 expansion occasioned by the heat of steam is quite in- 

 sensil)le. 



The memorialist thinks it would be improper, in ad- 

 dressing so intelligent a body as the Society of Arts, &c. 

 to expatiate on the various oeconomical purposes to which 

 the principle, which he has been able but imperfectly to 

 unfold, may be applied. In abler hands it may be found 

 susceptible of improvement, which he cannot anticipate. 



Neil Snodgrass. 



XXX. Proceed'mgs of Learned Societies. 



ROYAL SOCIETV OF LONDON. 



Feb. 26. The right honourable the carl of Morton, vice- 

 president, in the chair.— Continuation of Mr. Knight's pa- " 

 per on the bark of trees. This philosopher, after many ex- 

 periments and observations during several years, has come 

 to the following conclusion : that there is a juice in trees 

 distinct from that which is elaborated by the leaves or con- 

 veyed by the alburnum ; that this juice gradually exudes, 

 and, like all vegetable matter, naturally assumes a regular 

 form, which at first resembles a honey-comb, and afterwards 

 unites itself with the alburnum to form vessels fit to convey 

 the true sap either from the roots to the leaves, or from the 

 leaves to the roots, and in this manner is finally incorpo- 

 rated with the wood of the tree. The author was led to this 

 conclusion chiefly from having observed that the bark of 

 grafted trees gradually unites and forms an uniform mass, 

 and that bark on the trunks of trees is speedily regenerated 

 where ttie leaves are, perhaps, at a distance of nearly 200 

 feet. The theories of Malpighi and Hales he considered 

 very inadequate \o the explanation of these phenomena. 



M 4 March 



