A living freight is far more liable than a dead freight to
move during the journey; and as the safety of all overhead lines depends
upon what is scientifically designated "unstable equilibrium," the
flexible girder tramway is not recommendable for passenger lines,
although it can, of course, be fitted for passenger traffic, a suitable
vehicle and ten or a dozen good stout workmen coming well within a
two-ton load, which can be readily carried.
[Illustration: BALL'S FLEXIBLE WIRE TRAMWAY.]
Rope traction or animal traction--practically speaking--is alone
available for wire tramways (that is to say, if the trains are each to be
propelled by its own locomotive--whether steam, springs, or
electricity--the cost of construction and maintenance becomes so serious
that overhead lines, however well designed, are no longer economic); and
experience gained with rope traction in numerous collieries in the North
of England and Lancashire districts--where it is highly appreciated--has
shown that, all circumstances considered, the endless rope is preferable.
The chief objection urged against wire tramways as hitherto constructed
has been that the "sag" of the rope has sometimes caused annoyance to
those using the property passed over, and has always added much to the
cost of traction, owing to the increased power required for moving the
load; this has also resulted in vastly increased wear and tear and the
rapid deterioration and destruction of the wire rope.
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