Jrom an Increase of Temperature. 357 
inches and a half. In order to get the wood as well seasoned as 
possible, I selected it from the best of the oak beams got in the 
old houses lately pulled down in forwarding the improvements of 
Edinburgh ; and from the number of coats of size-paint which 
covered three sides of it, there could be no doubt that it had 
been long in an open situation. After it was worked to the pro- 
per shape, it was allowed to stand for some weeks, as it is some- 
times said that, to remove the surface from timber, will cause it 
to warp, however well it may have been seasoned beforehand. 
The stand for this instrument, however, did not alter; and even 
smaller pieces of the same tree, and of another tree from the 
same place, which were accurately worked into other parts con- 
nected with the experiments, have not altered in the least de- 
gree. I therefore concluded that the wood had been very long 
kept in a dry situation. To the oak stand A, which was 42 feet 
long, all the other parts of the instrument were attached. B is a 
double metal case containing the specimen C under experiment. 
The bottom of the case B rests in a strong brass plate, which is 
fixed on the top of a block of oak 8 inches broad and 11 long, 
and the block is strongly hooped and bolted with iron to the stand. 
The upper part of the case B is fixed to the stand by a brass clamp. 
Fig. 2. is a cross section of the double case of the full size, and the 
part marked ss is the space through which the current of steam 
passes : so that the specimen C, placed within the inner case, can 
be heated by the steam, and yet kept quite dry. P, Fig. 1, is the 
pipe by which the steam is brought from the boiler and thrown 
into the bottom of the double case ; and DD are eduction-pipes, 
from the top and bottom of the case B, by which the steam is 
carried off and thrown into the chimney, to prevent the atmo- 
sphere of the room from being rendered damp from its escaping 
into it. On each of the eduction-pipes DD there is a stop-cock 
E, to regulate the quantity of steam which ought to pass off 
from the top and bottom of the double case, in order to keep the 
thermometers TT, which are inserted into the top and bottom 
of the inner case, at the same height; and by regulating the 
ZZz2 
