52 TIMBER AND TIMBER TREES. [CHAP. 



ing weight varied from 590 to 1,002 Ibs., and from 753 to 

 1,005 Ibs., the average results of one parcel being 

 I93*961bs., and of the other 209' 21 Ibs. on the square 

 inch, the difference between the two being only 

 15-25 Ibs. 



Taking the mean of the figures in the Tables V. and 

 VI, we have a deflection of 2-489 inches with 390 Ibs. ; 

 but only * 1 5 1 inch after the weight had been removed, 

 the ultimate deflection at the time of breaking being 

 7-166 inches, the breaking weight, 806 '83 Ibs., and the 

 specific gravity 810. By applying the formulae used by 



Professor Barlow, viz., ^ w . ^ and ^- respectively 

 I o aa 3 o 4 aa 



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 



