400 
Report on the Exhibition of Implements 
which is lowest receives more than its share of the load, and this 
additional weight is thrown upon it in a way which causes more 
strain upon the wlieel than if a much greater weight were merely 
placed in the cart, because when one wheel sinks the whole load 
gives a lurch sideways, and in descending into a deep hole or 
rut, acquires a certain velocitv which at the bottom is brought 
to a sudden stop, and thus exerts upon the wheel on that side a 
force which partakes of the nature of impact. It thus appears, 
that in addition to the vertical pressure produced by the weight 
of the load, a wheel is subjected to a succession of side thrusts, 
applied at the axle but resisted at the circumference or rim, 
which at the instant of any particular thrust may be considered 
stationary, and is so in point of fact, with reference to any lateral 
pressure. Having thus determined the nature and direction of 
the forces which a wheel is required to resist, it will be compara- 
tively easy to determine its proper form. If a wheel be flat, the 
outward thrust above described is only resisted by the strength 
of the joints by which the spokes are fixed into the felloes and 
nave. It is true that in wheels of this make these joints are 
square, and can be made truer and better fitted than those of any 
other shape, but, however good the joints, it is impossible for 
them to stand long when taken at so great a disadvantage. The 
joints in the felloes especially have the whole leverage of the 
spoke acting to force them out of their place. The rim resting 
on the ground is the fulcrum, the side thrust at the axle is the 
power which is here applied at right angles to the spoke which 
forms the lever, so that this lateral pressure acts at a great 
mechanical advantage in forcing the joints, and must soon destroy 
the wheel if put to rough work. If, however, the wheels be 
dished, the case is materially altered, as the outward thrust which 
has a tendency to flatten the wheel is resisted by the convex 
arrangement of the spokes, which imparts to it in some measure 
the strength of an arch, and the wheel cannot give w ay in this 
direction unless the material fail or the tire be forced asunder. It 
ought therefore to be considered an established rule in cart-build- 
ing that, unless for some special object, wheels should be mode- 
rately dished ; if carried to excess, however, the wheels will be un- 
able, from the slanting position of the spokes, to bear without injury 
the vertical pressure of the load. This may be obviated by using 
bent axles, and making the lower part of the w heel perpendicular 
whilst the upper part leans outwards ; but there are many ob- 
jections to this plan, and it is not at all required if the dishing 
be not extreme ; H-inch is found to answer well, and should not 
be much exceeded. 
Form of Axles, position of Wheels, and shape of Rim. — These 
three points are so closely connected that it will be more con- 
