292 PRACTICAL ARBORICULTURE 
rear of the long train is acting with great force in a contrary course while in- 
termediate portions of the train jump from side to side with an incalculable 
momentum. It is not difficult to account for spreading of rails, broken rails 
and strained track which is not discovered until some fast express train finds 
the break and rolls into the ditch. 
If beneath the castings at the foundry there is a solid foundation the re- 
peated blows soon fracture the metal. But if there be an elastic cushion 
beneath, it may be pounded a year before it will yield. 
The old experiment of an athlete supporting an anvil on his chest while 
a comrade rains heavy blows upon the iron, is but another illustration of this 
subject. Bolt a hundred pound steel rail to an inflexible metal or concrete tie 
and something must give way under the frequent passage of heavy traffic. 
Bolts must give way as they do in frog crossings and constant repairs become 
necessary. 
The driving of a railway spike into a wooden tie pushes aside the fibers 
of the wood and forms an elastic cushion for each spike, while the wood 
itself forms an elastic foundation over which the traffic is borne in safety. 
Hard woods, as in some of the tropic growths 
where ties must be bored before spikes may be 
driven, are very much less flexible and are inelastic 
for want of this cushion. 
The slow process of removing bolts and replac- 
ing them, in case of accident or in change of track 
to the use of bolts as fastenings for cross ties. 
Iron and steel are rapidly corroded by oxidation 
when in the presence of moist earth, and while paint 
or an asphaltum coating may protect for a while, 
vet these substances are destroved by moisture and 
the acids ever present in soils, leaving the metal un- 
protected. The increasing use of electricity on rail- 
ways, even the quantity generated by engines for 
lighting. hastens this process of corrosion since 
there 1 
earth through rails and ties. If the latter be of metal, 
both bolts and metal ties must be rapidly weakened 
s a direct current between the trains and 
by this rusting process, yet hidden from view it 
may be after some serious accident that the discovery is made. 
On some European railways steel ties are in use, but conditions in Europe 
and America are very different. Scarcity of wood and high price of ties on 
account of transportation for great distances make it specially desirable that 
some substitute be adopted. Lower wages for labor encourage a greater use 
of metal. Straight tracks within minimum grade, more substantially con- 
structed roadbeds. shorter lines of roadway, dense population and lighter 
trafhc, with greater care in all operating departments, combine to discourage 
the use of wooden ties which must largely be brought from America, where 
