XXXIV.] 
YELLOW PLNE. 
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 lbs. on the square inch. 
,, 2 ,, 2' ,, 5S4 ,, 2,800 „ „ 
,, 3 „ 3' » 567 >i 2,870 „ 
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. 
