iable to get out of
order. The advantages of a large over a small wheel in reducing the
amount of resistance offered by rough roads have long been
recognised, and the limit of height was soon attained. In looking for
improvement in this direction, therefore, we must inquire what new
types of wheel may be suggested, and whether an intermediate plan
between the endless band, as already referred to, and the
old-fashioned large wheel may not find a useful place.

Let the wheel consist of a very small truck-wheel running on the
inside of a large, rigid steel hoop. The latter must be supported, to
keep it from falling to either side, by means of a steel semi-circular
framework rising from the sides of the vehicle and carrying small
wheels to prevent friction. We now have a kind of rail which conforms
to the condition already mentioned, namely, that of being capable of
being laid down in front of the wheel of the truck or vehicle, and of
being picked up again when the weight has passed over any particular
part. The hoop, in fact, constitutes a rolling railway, and the larger
it can with convenience be made, the nearer is the approach which it
presents to a straight railway track as regards the absence of
resistance to the passing of a loaded truck-wheel over it.

The method of applying the rolling hoop, more particularly as regards
the question whether two or four shall be used for a vehicle, will
depend upon the special work to be performed. Some vehicles, however,
will have only two hoops, one on each side, but several small
truck-wheels running on the inside of each. A vehicle of this pattern
is not to be classed with a two-wheeled buggy, because it will
maintain its equilibrium without being held in position by shafts or
other similar means. So far as contact with the road is concerned it
is two-wheeled; and yet, in its relation to the force of gravitation
upon which its statical stability depends, it is a four or six-wheeler
according to the number of the small truck-wheels with which it is
fitted.

Traction engines carrying hoops twenty feet in height, or at any rate
as high as may be found compatible with stability when referred to the
available width on the road, will be capable of transporting goods at
a cost much below that of horse traction. The limit of available
height may be increased by the bringing of the two hoops closer to
each other at the top than they are at the roadway, because the
application of the