ilway track is
difficult to maintain, and where, at any rate, there would hardly be
sufficient traffic to encourage expenditure in laying an iron road, a
very great boon would be a kind of motor which would lay its own rails
in front of its wheels and pick them up again as soon as they had
passed.

A carriage of this kind was worked for some time on the Landes in
France. The track was virtually a kind of endless band which ran round
the four wheels, bearing a close resemblance to the ramp upon which
the horse is made to tread in the "box" type of horse-gear. Several
somewhat similar devices have been brought out, and a gradual approach
seems to have been made towards a serviceable vehicle.

A large wheel offers less resistance to the traction of the weight
upon it than a small one. The principal reason for this is that its
outer periphery, being at any particular point comparatively straight,
does not dip down into every hollow of the road, but strikes an
average of the depressions and prominences which it meets. The
pneumatic tyre accomplishes the same object, although in a different
way, the weight being supported by an elastic surface which fits into
the contour of the ground beneath it; and the downward pressure being
balanced by the sum total of all the resistant forces offered by every
part of the tyre which touches the ground, whether resting on hollows
or on prominences.

Careful tests which have been made with pneumatic-tyred vehicles by
means of various types of dynamometer have proved that, altogether
apart from the question of comfort arising from absence of vibration,
there is a very true and real saving of actual power in the driving of
a vehicle on wheels fitted with inflated tubes, as compared with the
quantity that is required to propel the same vehicle when resting on
wheels having hard unyielding rims. So far as cycles and motor-cars
are concerned, this is the best solution of the problem of averaging
the inequalities of a road that has yet been presented; but when we
come to consider the making of provision for goods traffic carried by
traction engines along ordinary roadways, the difficulties which
present themselves militating against the adoption of the pneumatic
principle--at any rate so long as a cheap substitute for india-rubber
is undiscovered--are practically insurmountable.

Large cart wheels of the ordinary type are much more difficult to
construct than small ones, besides being more l