704 
MR. FAIRBAIRN’S EXPERIMENTAL INQUIRY 
Resistance of planks of timber to the entrance of a ball, 3 inches diameter, the 
planks being laid upon props 12 inches asunder ; the object of the experiments being 
to burst them by pressing a pin, terminated by a hemispherical end, 3 inehes dia- 
meter, through the centre of the plank, as was done with the plates of iron. 
Table XIV. 
No. 
of 
exp. 
Description of plank. 
Weight 
laid on. 
Remarks. 
1 . 
English oak, very dry and good, Ilf inches 
broad, and 2^ inches deep. 
lbs. 
16,115 
17,235 
Indentation from hemisphere \ inch deep ; wood otherwise 
uninjured. 
Hole through the middle, 3 inches diameter nearly broke out, 
all the rest remaining sound. 
2. 
English oak, rather green, 8 inches broad, 
3 inches deep. 
18,941 
It bore 1 8,941 lbs. about ten minutes, and then exploded with 
violence, dividing into three parts, the middle one on which the 
pin rested being about an inch thick at the top, and ^ an inch at 
the bottom. With a ton less weight there was a crack under the 
plank in the centre, and an indentation by the pin inch deep on 
the upper side. Sap was driven out from the ends on the side 
nearest to the heart. 
3. 
English oak plank, and dimensions same as in 
last experiment. 
12,445 
16,925 
Sap driven out as in last experiment ; plank without crack ; in- 
dentation by the pressure about -J inch. 
The plank split with bearing the pressure about ten minutes. 
4. 
English oak from same plank as in experiment 
2 and 3 ; breadth 8 inches, depth inch. 
4,532 
The plank broke by splitting. 
5. 
English oak from same plank and same size 
as in the last experiment. 
4,280 
Broke by splitting diagonally. 
Taking the results of the four last experiments, which were on pieces from the 
same plank, we obtain — 
lbs. Mean. 
Strength from planks 3 inches thick 
Strength from planks 3 inches thick 
Strength from planks 1^ inch thick 
Strength from planks 1^ inch thick 
18,941 ■) 
16,925 J 
4,532-) 
4,280 J 
17,933 
4,406 
Here the strength to resist crushing follows the ratio of the square of the depth, as 
is found to be the case in the transverse fracture of rectangular bodies of constant 
breadth and span. 
If we compare the foregoing results with the experiments performed by Mr. Hodg- 
KiNSON on timber, it will be found that the strength of dry English oak to resist a 
crushing force is 4‘24 tons to the square inch, whereas wrought iron, according to 
Rondelet, requires a pressure of about 31 tons per square inch, and with this weight 
it is reduced about one-sixteenth of its length. The resistance of wrought iron to a 
crushing force is therefore about seven and a quarter times greater than that of oak : 
and according to the experiments in the preeeding Table, it appears that the resist- 
ance of wrought-iron plates to a force calculated to burst them, follows a different 
law to that of oak, the resistance of the former being directly as the depth and of the 
latter as the square of the depth. Reasoning from these facts, it may be interesting to 
know that in the use of timber, such as the oak sheathing of ships, the strength to ex- 
