ix.J BARLOW'S FORMULA. lOi 



the ultimate deflection at the time of breaking being 

 7" i66 inches, the breaking weight 8o6'83 lbs., and the 

 specific gravity 8io. Further results may be got by 

 applying the formulse used by Professor Barlow, viz., 



/ IJD 



E = — jt? ; /= length, a = width, ar= depth, and S = de- 



flection. 



* 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 any- 

 thing 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 of this tree, came out with a long, clean, straight 

 grain, as the appearance of the log had promised ; but 

 the six taken from the opposite side were not nearly so 

 good, the grain being in each a little waved or twisted, 



* It should be noted that Laslett gives the total length of his specimens, 

 instead of the length between supports, and consequently his results are not in 

 accordance with those of others. The reader should consult special works on 

 this part of the subject. {See p. 72.) 



