at the York Mcetinrj, 1 848, 
401 
venient to tro.it of the whole at once. The most common position 
of cart-wheels is th.it ahove descrihcd, in which the lower part of 
the wheel is perpendicular and the upper part leans outward, 
the wheels beings dished and the axles bent downwards. The 
consequence of this position of wheel is, that if the tire were flat, 
or, properly speaking, cylindrical, the wheel would run only on , 
its outer edge, and to obviate this diflicully the rim is made 
conical, the outer edge forming a smaller circle than the inner, 
so that the rim meets the ground in a horizontal position. This 
mode of construction combines so many mechanical disadvantages 
that it seems difficult to conceive why it should ever have been 
adopted, and the following is the only plausible reas-.on which 
the writer has ever heard adduced in its favour, viz., that, ad- 
mitting the superiority of dished wheels on account of their 
greater firmness and durability, it is desirable that the inclination 
of the spokes produced by the dishing should be corrected by the 
bent axle and conical rim above described, so that the spokes 
when they receive the weight of the cart should be perpendicular, 
i. e., in the position of greatest strength. This would be good rea- 
soning if the cart when at work preserved its horizontal position ; 
but, as has been previously shown, this is not the case, and the 
greatest strain which a wheel has to bear is when it sinks into a 
hole and has additional weight thrown suddenly upon it. When 
this occurs, in what position is the wheel placed whose lower spokes 
were perpendicular when on the level? Clearly the lower part 
of such a wheel is now too much under the cart, and receives its 
greatest pressure when in a slanting and therefore disadvantageous 
position. 
On the other hand, a dished wheel running on a straight 
axle, and, therefore, standing upright, has its spokes in a slant- 
ing position when on the level ; but the moment it sinks into 
a hollow its spokes become perpendicular, in which position 
they are not only able to bear the shock without injury, but have 
a direct tendency to check the swing of the load. I his is very 
observable with a top load of corn or hay where the centre of 
gravity lies high, and carts with upright dished wheels may pass 
with safety where those whose wheels lean much outwards will 
either be overturned or throw off part of their load. The most 
serious objection, however, to this mode of construction arises 
from its adding considerably to the draught. In order that carts, 
or indeed any kind of machinery, should work without waste of 
power, the two points to be especially guarded against are, un- 
necessary friction and a jerking, unsteady motion, both of which 
defects are the necessary consequence of using wheels with bent 
axles and conical rims : for when the axles are bent downwards 
the bushes into which they fit must necessarily have the same 
