xxxiv.] YELLOW PINE. 281 



direct proportion existing between the specific gravity 

 and the strength, the densest wood having borne the 

 greatest strain before breaking. Instead, however, of 

 this point of density lying at the centre of the tree, as in 

 the specimens of Oak that were tested in a similar 

 manner, we find it, as is generally the case with other 

 woods, about midway between the pith and the outer 

 layers of duramen. 



The results, if compared with the mean of the first- 

 mentioned set of experiments on Yellow Pine (Table 

 CXLVIII.), which were upon pieces taken from several 

 trees, show that the tree from which the seven specimens 

 were obtained possessed a little less strength, and rather 

 less elasticity, than the former ; but then it must be borne 

 in mind that they were selected pieces, and probably did 

 not include the weaker wood of either the oldest or the 

 newest layers. 



Further experiments were tried on six out of seven 

 of the specimens, to ascertain their relative tensile 

 strength (Table CLXIX., column 9). The following 

 are the average results : 



The pieces I and i' s.g. 562 broke with 2,607 Ibs. on the square inch. 

 2 ,, 2' 584 2,800 



3 ,t 3' it 5 6 7 



. it 



The centre piece O was not tried for tensile strength, 

 as it was too much crippled under the transverse 

 strain to be of any further value for experimental pur- 

 poses. 



The denser layers 2 and 2', were not in this case 

 quite so strong as 3 and 3', which were of a less specific 

 gravity. 



