CHAPTER X. 



ON THE TENSILE STRENGTH, OR DIRECT COHESION, 

 AND VERTICAL STRENGTH OF BRITISH OAK. 



THE tensile experiments are somewhat difficult to carry 

 out, and therefore only specimens Nos. I to 6, Table VI I., 

 were tested from the log referred to at page 53. They 

 varied from 2,240 to 5,320 Ibs., giving a mean strength 

 f 3>837 Ibs. to the square inch, the wood next to the 

 pith or centre proving to be the strongest, as with the 

 transverse test. The gradations of strength, taking 

 No. I as unity or roo, give No. 2 as '82 ; No. 3, 785 ; 

 No. 4, '81; No. 5, -475; and No. 6, -42, the tensile 

 strength of the inner wood of this tree being therefore 

 about 58 per cent, greater than the outer. 



Instances of weakness, both transversely and tensilely, 

 similar to those which are given in Table VII., are not 

 unfrequent, and may occur, as before stated, in good- 

 looking specimens of any species of timber : and this, 

 again, serves to show that it would be unsafe to arrange 

 the various parts of any construction according to the 

 highest calculated strength of any timber to be 

 employed. 



Further tensile experiments were made on six speci- 

 mens of British Oak saved from the pieces experimented 

 upon, and referred to in Tables V. and VI. They appear 



