STEENGTIi AND TESTING OF TIMBER 
313 
The results of compression tests are less variable than 
any other tests. 
So far as the engineer or architect is concerned, the 
tests which chiefly concern them are those for transverse, 
shearing, and crushing strength, since, long before the 
timber would give way in tensile strain, the bolts or con- 
nections would shear through the ends of the timber ; and 
it may here be stated that no bolts should be nearer than 
3 or 4 inches from the end of a timber having to bear 
tensile stress. Moreover, the tensile and transverse 
strength of timbers do not vary much. Mr. Julius found 
that with the Australian timber the tensile stress was about 
5 per cent, above the ultimate strength in cross breaking ; 
whilst in the case of Quebec pine beams tested by Mr. 
H. D. Smith, M.I.C.E., the ratio of transverse to tensile 
strength only varied between 0'82 and 1'31 in the same beam. 
In tensile tests on timber the experiments have generally 
been made upon small turned specimens of about 1 inch 
in diameter ; the centre portion of a piece of timber for 
about 6 inches long is turned down to a diameter of aboat 
1 inch, the thicker portions at the ends being secured 
in the grips of the testing machine ; there is difficulty, 
however, in holding them, and occasionally the enlarged 
ends draw through the grips, and the timber fails by 
shearing along the grain, and not in tension. 
Timber is not a satisfactory material for a tie bar ; the 
only case in which it is likely to be used in tension is in 
the tie beam of a roof where the strain it has to bear is 
generally small. 
In making calculations for the strength of beams or 
columns it is advisable to assume either the minimum results 
of tests, or thereabouts, as it is safe to assume that there 
would be no more care exercised in the selection of timber 
for actual work than there would be in tlie case of timber 
