IO TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
You will observe that in the case of the first set, those with 
a small tensile area and a very large shear area, no less than 
three of them sheared at the head instead of breaking in fair 
tension, and you will notice how very low the shear strength 
per square inch is, as compared with the tensile strength, in 
these specimens. On the other hand, the tensile strength of 
those specimens which did give way in tension appears to be 
rather greater in the form of a flat specimen than in the form 
of a round specimen. 
From Table III., which gives the results of the bigger round 
specimens, you will see that they practically all went by shearing 
at the head, though one would have been inclined to believe 
(in view of the fact that the shearing area was so large), 
had one not made the experiment, that there was abundant 
strength in the head to prevent any action of this kind taking 
place. 
These few tests show then, first, that it is extremely difficult to 
get accurate and reliable tensile tests, and secondly, that in 
designing any part of a structure in which timber is subjected to 
a direct tension, the utmost care must be taken to see that it is 
strong enough in its various parts to resist the possible shear 
stresses which may be set up. 
Other experimenters have found exactly the same difficulty. 
Professor Lanza, who made a series of tension tests on large 
specimens, stated that, in his opinion, tie bars in constructional 
work will always give way in some other manner than by direct 
tearing, for instance, by tearing out the fastenings, by shearing, 
and by splitting the timber. 
Professor Johnson, in his research, meeting with the same 
difficulty, decided to abandon tensile tests, on the ground that 
timber would never fail in pure tension in practice. 
Bauschinger, in his research, found that the elastic limit in 
tension practically was of the same value as the ultimate breaking 
strength, that is to say, that there is no marked limit of elasticity 
in timber when tested in tension; and he also found that the 
influence of the time of felling upon the strength in tension very 
soon disappeared. 
I give in a Table some figures taken from Bauschinger’s first 
research, in order to show the great difference between the 
strength in tension of the living sap-wood and the dead heart- 
wood. The figures in the Table represent the mean of eight tests 
