AS APPLIED TO WORKS OF CONSTRUCTION. 267 
Compression.—The testing of specimens in compression in the 
University machine is comparatively a simple matter, as it is not 
necessary to make any provision for fixing the ends in clips, or to 
reduce the section as in the case of tensile specimens. 
The following tests were made :— 
resist- 
é ; Area of Section | Ultimate 
No. Size of specimen. Ann pPPsquare inch. 
Peas vin: Se. +04 thy 1°89: in: 3°67 square in, 8,719 
Sy. .. x 100.,,..% 189 4.| 32l Ss 9,034 
be Sa EOS su 5 ee 3°16 9,168 
2+ O38 10, OPO RH Pea o 10,000 
5 | 8°35 2805, “Ree as 2°7 5 9,074 
rupture was not affected by the size of the specimen, the average 
of the above results gives 9,199 lb. per square inca. 
Compressive Elasticity.—As in tensile elasticity the author has 
found that the modulus of elasticity is not constant, but decreases 
as the load increases. The modulus of compressive elasticity is a 
factor in Rankine’s formula for pile driving. Referring to figs. 5 
and 6, which show the compressions and loads producing them it 
is seen for a load of 1,869 lb. per square inch, see fig. 6, the 
compression produced was 0-00175 inches, from which £ ct 
25,630,000 Ib., while with a load of 4,979 lb. per square inch, 
producing a compression of 0-016 inches, E= 7,468,500. The 
author has not yet made experiments on the resistance to shearing 
along the grain, or across the grain. 
Although timber is being superseded in permanent works of 
construction by the use of iron and steel, there are many cases 1n 
which iron is entirely unsuitable, and where timber is the only 
hat 
appears, therefore, that timber will always be used to a consider- 
able extent in works of construction. Timber in yielding gives 
more warning than iron, so that an accident can generally I 
foreseen and prevented. The chief objections to the use of timher 
in this colony is its liability to decay from dry rot, and to the 
attacks of the white ant. Where timber is used in marine works 
it is liable to the attacks of the teredo. 
In the Wagga Wagga timber viaduct, which was thoroughly 
inspected by the Railway Bridges Inquiry Commission, it appears 
that, owing to the difficulty of obtaining ironbark timber for the 
