TIMBER. 
this is only during the advances of the tree 
to maturity ; for the strength of the dif- 
ferent circles approaches gradually to equa- 
lity during the tree’s healthy growth, and 
then it decays in these parts in a contrary 
order. Our tool-makers assert the same 
tiling with respect to beech ; yet a contrary 
opinion is very prevalent ; and wood with a 
fine, that is, a small grain, is frequently 
preferred. Perhaps no person has ever 
made the trial with such minuteness as 
M. Buffon, and much deference is thought 
to be due to his opinion. Column 3, is 
the number of pounds necessary for break- 
ing the tree in the course of a few minutes. 
Column 4, is the inches which it bent down 
before breaking. Column 5, is the time at 
which it broke. 
1 
2 
o 
4 
5 
5 60 
5350 
3.5 
29 
7 
1 36 
5275 
4.5 
22 
8 
5 68 
4600 
3.75 
15 
\ 63 
4500 
4.7 
13 
S 77 
4100 
4.85 
14 
9 
1 71 
3950 
5.5 
12 
10 
f 84 
3625 
5.83 
15 
1 82 
3600 
6.5 
15 
12 
f 100 
3050 
7. 
1 98 
2925 
8. 
Mr. George Smart, well known for his 
practical knowledge of mechanics, in al- 
most every department, says, that after 
making many experiments on timber, and 
comparing them with those of Belidore, 
Buffon, &c. : the diflferences were so great 
that it would be wasting time to enumerate 
them. He therefore mentions some useful 
observations necessary to be known by all 
those mechanics who use timber ; and points 
out some evident errors in a table of Beli- 
dore’s, supposed to be the result of the best 
set of experiments ever produced in 
transverse strains. He tells us, that a bar 
of wood, thirty-six inches long, and one 
inch square, supported at the ends by tvyo 
props, will break with a weight of 187 
pounds on the middle, if it is loose at the 
ends ; but if the ends are firmly fixed, it 
will require 283 pounds to break it. “ This 
appeared to me,” says Mr. Smart, “ so 
great an error, that I was induced to put lit- 
tle or no confidence in many of his' experi- 
ments ; and, in consequence, I made two 
laths of fir, of the same dimensions, one 
with a strong shoulder at each end, to pre'- 
vent its bending, which having firmly fixed 
in a frame, it carried a weight more than 
ten times greater than that which was 
loose.” 
The fibres of timber requiring so great a 
force to tear them asunder in a vertical di- 
rection, and being easily broken by a trans- 
verse strain, when compared to that of a 
rope carrying nearly an equal weight in all 
directions, opens a wide field for useful ex- 
periments. All timber trees have theii an- 
nual circles, or growths, which vary greatly 
according to the soil and exposure to the 
sun. The north east side of the trees (being 
much smaller in the grain than the other 
parts, which are more exposed to the sun) 
is strongest for any column that has a weight 
to support in a vertical direction ; because 
its hard circles, or tubes, are nearer each 
otlier, and the area contains a greater quan- 
tity of them ; nor are they so liable to be 
compressed by the weight, or to slide past 
each other, as when they are at a greater 
distance. On the other hand, this part of 
the tree is not fit for a transverse strain ; be- 
cause the nearer the hard circles are to 
each other, the easier the beam will break, 
there being so little space between them, 
that one forms a fulcrum to break the other 
upon ; but that part of a tree, the tubes of 
which are at a greater distance, or of larger 
grain, is more elastic, P.nd requires a greater 
force to break it; because the outside fibre 
on the convex side cannot snap till the next 
one is pressed upon it, which forms the ful- 
crum to break it on. It is generally ob- 
served in large timbers, such as masts, that 
the fracture is seldom on the convex, but 
usually on the concave side ; which is owing 
to the fibres on the concave side being more 
readily forced past each other, and those on 
the convex being so difficult to be torii 
asunder, that they cannot snap, in conse- 
quence of the largeness of the segment of 
the circle they describe when on the strain. 
The curve described by the in;er layers of 
the wood being so Brge, and indeed little 
less than a straight line, cannot form a ful- 
crum to break the outer ones upon ; and as 
the convex side, or that on which the fibres 
are extended, ought to be always free from 
any mortise or incision on the outside, the 
strength decreases as it approaches the 
centre. Mr. Smart has, iii a paper in the 
“ Repertory,” given directions how to cut 
and join timber so as to have the greatest 
