DEFECTS IN TIMBER AND GENEEAL NOTES 299 
It should be understood that when a tmiber is referred 
to as durable, or fairly durable, this is only a comparative 
term, and only applies to its use under conditions for which 
it is adapted and generally used, because although some 
classes of timber such as greenheart, jarrah, pitch pine, oak, 
and many hardwoods may be used in most situations and 
either for interior work or where exposed to the weather, 
and will have a fairly long hfe in either, yet with many 
other timbers it would be quite the contrary. For instance, 
sycamore, poplar, and other softwoods which last for very 
long periods if protected from the weather would not be at 
all durable if placed in situations where they would be 
alternately wet and dry, and no one would think of using 
them in Great Britain for, say, a timber quay, irrespective 
altogether of their want of strength. 
The durabihty or otherwise of timber in various situations 
is very variable ; the poorest timber may, in a dry protected 
situation, last for centuries; the best of timber in other situa- 
tions will decay in a few years. Some of the softer woods 
last longer as railway sleepers — and this is about the most 
severe test to which timber can be subjected, especially if 
placed in a cinder bahasted track — than some of the hard- 
woods, which in ordinary situations could not compare with 
them in point of longevity. Oak, as we have seen, will last 
in fairly good condition in some places for 2,000 years, but 
the best American oak, when used for railway sleepers, 
only lasts eight or ten years, and in some situations will 
decay in three years. In America, which is about the only 
country in the world where large quantities of untreated 
softwoods are used for railway sleepers, it has been found 
that the comparatively soft red cedar, the arbor vitae, and 
redwood resist decay best, as they are less affected by disease 
than most timbers ; treated hemlock will not last so long 
in some situations as untreated cedar ; some roads get a life 
