440 On the Nautical Almanac for 1830. 
be cleft asunder in silence. The oak timber of England is 
also much more frequently rifted than that of the north of Eu- 
rope. ‘The force with which the cellular substance of timber 
expands, is fully equal to produce the preceding effects. I have 
often seen it overcome the pressure of many tons ; it is therefore 
greatly more than equal to give the impulse to the sap, which 
was observed by Hale; and as it is obviously in action in the 
living tree, I must retain the opinion which 1 formerly gave, that 
it is the agent by which motion is given to the ascending fluid. 
How it immediately acts upon the passages through which that 
fluid ascends, and whether that fluid passes through the cells 
themselves, or through the intercellular passages described in the 
elaborate work of Dr. Kieser*, I confess myself to be wholly ig- 
~ norant; and the slow motion of the fluid, the excessive minute- 
ness of the passages, and the varieties of directions in which it is 
often moving at one and the same time, will ever render this a 
question of extremely didicult soiution, 
There is another kind of contraction in timber whilst drying, 
and of expansion when subsequently wetted or moistened, which 
is observable only in lifeless wood ; and whieh has apparently ho 
connexion with the power by which the sap is raised in the 
living tree. The interior and older layers of wood are much 
more solid and specifically heavy than the external layers in the 
same tree; and the latter, consequently, contract more lengitu- 
dinally in drying than the former, and the edge of every board 
(that has been cut with surfaces nearly parallel with the line of 
the convergent cellular processes) which Jay nearest the medulla 
in the tree, will therefore in drying become convex, whilst the 
opposite edge will become concave. The ill effects of this are 
often felt when oak timber is employed to form, joists, part of 
these in drying always rising above, and others Sinking below the 
first and proper position. The cause of some musical and other 
instruments being put out of order by changes of weather, whilst 
others, apparently similarly coustricted, are free from such de- 
fects, may probably be traced to one of the sources above men- 
tioned. I am, my dear Sir, &c. 
Downton, April 26, 1817. T. A. Knieet. 
The Right Hon. Sir Joseph Banks, Bt. G.C.B.P.R.S. 
——— 
LXXIV. On the Nautical Almanac for 1820. 
Zo Mr, Tilloch. ; 
December 20, 1817. 
I HAVE just seen the Nautical Almanac for the year 1820; and 
am happy to find that the attention of the Commissioners of the 
* Mcmoire surl’Organization des Plantes. 
Board 
