WHEEL-CARRIAGE. 
-felloes of the wheels may be at top and bottom, 
while the greater distance at the top gives additional 
room for both carriage and load. In fact, it is to the 
want of a proper attention to the nature and true 
properties of the axle, that most, if not all, the faults 
said to attend well constructed dished wheels may 
be attributed. Undoubtedly the oblique action of 
conical wheels is unfavourable for easy motion; but, 
if the spokes in the under side of the wheels be at 
right angles to the truly horizontal under surface of 
the axle within the nave, the easy motion of the 
wheel would not be much injured by such a shape, 
if it were possible that the exterior surface of the 
iron-hoop could touch the rod at the lower point 
only. Now as this, though not perfectly true in bad 
roads, is nearly so in good ones, there seems to be 
little cause for the vituperation of dished wheels pro- 
perly made, which has been generally cast upon them 
by many. popular writers, who have not investigated 
their properties upon scientific principles. Indeed 
they offer several advantages which the other wheels 
do not, and a careful consideration of their properties 
can alone show their qualities. Any custom very 
generally adopted, frequently results from some valid 
reason of the inventor, which is often lost sight of by 
his successors, who continue, as they think, to follow 
the original plan, sometimes with improvements ; 
but having become ignorant of the motives and prin- 
ciples of the first constructors which should have 
guided them, they fall frequently into extremes, 
which are really injurious. In addition to the taper 
of the axle, a considerable bend, much more than is 
requisite for the purposes already pointed out, and 
consequently injudicious, is often given to it at the 
shoulder where it enters the nave, thus producing a 
very injurious action in the wheel, placing the 
spokes, or rather the plane of the spokes, too much 
in an inclined position towards each other at the 
bottom, unfavourable to strength, and diminishing 
the stability when the carriage is inclined on a bad 
road. All these ought to be particularly guarded 
against, although perhaps a slight degree of dishing 
more than the taper of the axle, depending on the 
amount of bend, may be given, especially when the 
wheels are narrow, as a slight inclination of the 
spokes outwards appears to be of use in keeping 
them more steady on their axles than if they were 
exactly vertical. By an inclination of the carriage, 
too, a greater proportion of the weight of the load 
is thrown on the lower wheel, and then its spokes, 
being in a vertical position, are able to exert all 
their strength with advantage. The dished form 
will be found on experience to render the wheels 
more lasting, because, from their slightly conical 
shape, the effect of the felloes, supported by the 
iron hoop, tends to bind them together, and pre- 
vents the spokes from working loose in the mortises 
of the naves. But when the spokes, as sometimes 
recommended, are at right angles to the axis, this 
property is lost, and the spokes are then chiefly pre- 
vented from working in the direction of the axis by 
the support of the nave only, and in time acquire a 
slight dishing in the opposite direction, or toward 
the cart, at the same time the tops of the wheels 
become closer than the bottom, which makes them 
look very unseemly. In some wheels each alternate 
spoke is made to have a different inclination, pro- 
ducing by that means greater stiffness and mutual 
support, by bearing against each other, and acting as 
braces in the direction of the axis, than when they 
have all the same degree of dishing. 
The next property to be considered is the stabi- 
lity of wheel carriages, or their tendency to resist 
oversetting when on an inclined road, and moving at 
a considerable velocity. This depends upon the 
position of the centre of gravity of the carriage and 
load together. ‘The lower it is, so much the more 
(13 
stable will the carriage be. A proper proportion 
between the height and breadth regulates this point. 
When carriages are narrow and high, the centre of 
gravity rises; and, on the contrary, when they are 
broad and low, under the same capacity, it de- 
scends; and a just proportion between these serves 
to assign its true and safe position, so as to fall 
within the wheels, even when the carriage is mode- 
rately inclined. It is obvious, then, that it depends 
in part on the proper position of the under part of 
the wheels, when the distance of their centres is 
given. By increasing the distance between the fel- 
loes at the bottom, the stability may be increased; 
and, by diminishing it, the stability will be lessened. 
But it is clear that a certain latitude only can be 
given to this variation of the inclination of the planes 
of the wheels, otherwise their strength and effi- 
ciency will be injured; and we shall now endea- 
vour to place the different varieties in one point of 
view, so that the relative properties with regard to 
stability also may become known. Let Fig. 6 bea 
Fig. 6. 
x B 
carriage supported on wheels, of which the spokes 
are perpendicular to the axis of the nave, as in Figs. 
1 and 4, formerly given, and moving on the inclined 
plane AB. Fig. 7, also corresponding to Fig. 5, and 
Fig. 8 to Fig. 3, already explained, and moving on 
Fig. 7. 
ZO 
