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. The flexible girder
system so reduces the "sag" that the maximum economy and durability are
obtained, and the gradients over which the load has to travel can be made
as easy and regular as those upon an ordinary railway. This advantage
will be the more readily appreciated when it is considered that with a
given load on a gradient of 1 in 30 the resistance due to gravity alone
is 200 per cent. greater than on a gradient of 1 in 150, and that the
retardation and wear and tear due to friction, greater curves, and
imperfections increase still more rapidly with increase of gradient, soon
rendering the old sagging wire line practically worthless.

To construct an entire line of flexible girders would be not only
unnecessary, but so costly as to neutralize any advantage which it may
possess, yet for surmounting occasional obstacles the claim made for
it--that it will sometimes permit of a line otherwise impracticable being
cheaply made--seems justified. One can readily imagine a light narrow
gauge line costing L1,000 per mile being laid, for example, between a
mine and the shipping place, and that a swamp, river, or valley would
cost more to bridge over than the whole line besides. If at this obstacle
the trucks or carriages could be lifted bodily, passed along the flexible
girder, and again placed on the line the other side of the obstacle, the
advantage to be derived