5 2 
TIMBER AND TIMBER TREES. [chap. 
ing weight varied from 59 ® t° B®® 2 lbs., and from 753 f° 
1,005 lbs., the average results of one parcel being 
193-96 lbs., and of the other 209-21 lbs. on the square 
inch, the difference between the two being only 
15-25 lbs. 
Taking the mean of the figures in the Tables V. and 
VI., we have a deflection of 2-489 inches with 390 lbs.; 
but only '151 inch after the weight had been removed, 
the ultimate deflection at the time of breaking being 
7-166 inches, the breaking weight, 806-83 lbs., and the 
specific gravity 810. By applying the formulae used by 
Professor Barlow, viz., ^ an< ^ res P ec ^ ve ^ 
for elasticity and strength, we obtain the following result: 
E = 386400, S = 2116. 
It should be borne in mind that in determining the 
scantlings to be employed, there are to be taken into 
account the possible chance of a short or twisted grain, a 
spiral turn of the fibre, knots, faulty or otherwise, and the 
risk which the practical builder must always run of having 
some defects hidden beyond the possibility of detection 
in, perhaps, his best-looking pieces. It would, therefore 
be obviously unsafe to subject them to anything like the 
strain which the ascertained average strength of the 
specimens tested would seem to warrant charging them 
with. 
Considering the importance of this, it was determined 
to extend the experiments by testing a series of pieces 
taken from a longitudinal section cut through the centre 
breadth of a very fine-looking Oak tree. In setting out 
the specimens, the centre piece containing the pith and a 
very small heart-shake, was allowed to drop out as being 
of little or no value for the trial. 
The six pieces cut from one side of the centre or pith 
