STK
470
STB
The cut next to the root was always found to be theheaviest, stiffest, and strongest; and from this invariablecoincidence of weight and strength, M. De Buffon recom-mends, as an unerring rule, to make choice of timber by itsweight. He finds, that this was always the case when tim-ber had grown vigorously, forming thick annual layers ; butobserves, that this is only during the advances of the tree tomaturity; for the strength of the different circles approachesgradually to an equality, during the healthy growth ofthe tree.
M. De Buffon also made experiments on other sizes oftimber of a square section. The medium of two pieces ofthe same length and section were taken; and the followingTable exhibits the results of those mediums. The lengthsare contained in the vertical column on the left hand, andthe dimensions of the section, or scantling, are expressed atthe top, in inches.
The experiments on the five-inch bars were considered, byM. De Buffon, as a standard, he having both extended theirnumber, and tried other pieces of the same length. He found,after repeated trials, that oak timber lost much of its strengthin seasoning, to secure uniformity; and therefore, he causedit all to be felled at the same time of the year, squared theday after, and tried on the third day ; which gave him anopportunity of observing a very curious phenomenon. Forwhen the weights were laid quickly, and were nearly uponthe point of breaking, a sensible smoke was observed toissue from the ends with a sharp hissing noise, whichcontinued while the beam was bending. This evidentlyshows, that it must have been compressed throughout itswhole length.
tie fi r9 “
preceding ; the lengths being contained in th a tvertical column, and the dimensions of the s eCtIthe top.
Table IV.
L.
4 In. sq.
5 In. sq.
6 In. sq.
7 In. sq.
8 In. sq-
7
28.777
44.965
64.750
88.131
115.11!
8
32.888
51.388
74.000
100.722
131.555
9
37.000
57.812
83.250
113.312
148.000
10
41.111
64.236
92.500
125.902
164.444
12
49.333
77.083
111.000
151.083
197.333
14
89.930
129.500
176.263
230.222
16
102.777
148.000
201.444
263.111
18
115.625
166.500
226.625
296.000
20
128.472
185.000
251.805
328 888
22
141.269
_
24
154.166
_
28
179.861
The numbers in the above Table, added to the P re0give the following, omitting the decimals.
difl&>
Table III.
L.
4 In.sq.
5 In.sq.
6In.sq.
7 In.sq.
8In.sq.
L.
4 In.sq.
5 In.sq
6 In.sq.
7 In sq.
7
5812
11525
18950
32200
47649
7
5340
11570
19014
32288
8
4550
9787 J
15525
26050
39750
8
4582
9838
15599
26150
9
4025
8308J
13150
22350
32800
9
4062
8365
13233
22463
10
3612
7125
11250
19475
27750
10
3653
7189
11342
19600
12
2987£
6075
9100
16175
23450
12
3036
6152
9211
16326
14
5300
7475
13225
19775
14
5389
7604
13401
16
4350
63624
11000
16375
16
4452
6510
11201
18
3700
5562J
9245
13200
18
3815
5728
9471
20
3225
4950
8375
114874
20
3353
5135
8626
22
2975
22
3116
24
2162J
24
2316
28
1775
28
1954
--
In the above Table, the weight of the beams is nottaken into the account ; therefore, to make a just comparisonwith the theory, it will be necessary to add half the weightof each beam to itself. The half-weights will be found inthe following Table, in the same manner as in the
Table V.
8 In.sq.
47764
39881
32948
27914
23647
20006
16638
13496
11815
to the Sve'rf.f! 1 ' 6 in the above Table, cerr^gg
may be calculated e >" gths , a . s a standard, the frllo#
in the recinroml ’ !-^ m f kw S the succeeding weigreciprocal ratio of their lengths.