374 
MINUTES OF PROCEEDINGS OF 
for tlie load; and one great disadvantage—namely, the bevelling of the 
sole of the wheel, which is brought about by the necessity, consequent 
upon the dish, of having to set the axletree-arm at an angle downwards. 
The bevelling makes the wheel conical in form, instead of cylindrical. 
Now a cone, we know, if set in motion on the level, will describe a 
circular path round its apex as centre; so the wheel, if set in motion 
and free, would describe a circular path round the point where the pro¬ 
longation of its sole would meet the prolongation of its axis—or, in 
other words, where the latter would meet the ground. On the carriage, 
the wheel is compelled to move straight forward, in a path unnatural to 
it; and consequently, instead of rolling it partly slides, thereby, as it 
were, giving a frictional surface between the ground and the body 
moved, and tending to defeat the primary object of using wheels. 
The dish of a wheel is measured practically by laying a straight¬ 
edge across the face of the wheel, just above the nave, and measuring 
the perpendicular distance from it to the foot of the spoke; which dis¬ 
tance should agree with the same calculated by similar triangles, or 
with a similar measurement on a wheel of the same nature whose dish 
is known to be correct. 
Ash, as a strong elastic wood, is used for felloes. The number of 
felloes in a wheel is fixed by the consideration that the length of each 
must not be so great as to necessitate the fibre of the wood being much 
cut across in shaping the felloe; and, at the same time, the fewer the 
felloes there are, the better for the strength of the wheel, as the 
junction between every two is a weak point. In the 5-ft. wheel six 
felloes is the approved number, each receiving two spokes. It is usual 
to cut felloes to a larger radius than that of the wheel for which they 
are intended, to prevent their extremities afterwards drooping ; and 
from this circumstance a new wheel does not form a perfect circle. 
With regard to the tire, which is of wrought-iron, its width to some 
extent depends upon the scantling of the felloes; but is mainly 
governed by the considerations that it ought to be at a maximum for 
passing over yielding ground, and at a minimum for lightness. With 
regard to the latter point, its thickness also should be at a minimum 
consistent with strength. Comparing the “ ring 33 tire with the 
“ streak 33 tire, we see that the former gives much better support to 
the other parts of the wheel; but in the case of a wooden nave, should 
the latter shrink, it cannot follow up the movement of the spokes men¬ 
tioned before, which the streak tire (there being a small space between 
the ends of the streaks, and the bolts holding it being capable of 
yielding a little), to a certain extent can, and thus diminish the play of 
the spokes. The streak tire also admits of readier repair, should a 
felloe be damaged ; but, on the other hand, on account of the number 
of bolts and rivets through the felloe, weakens the latter more than 
the ring tire, when one or at most two bolts are required. 
The considerations which govern the height, or diameter, of a wheel are 
the following :—It should be at a maximum, in order to carry out as com¬ 
pletely as possible the object and advantages in view of which wheels are 
used; but increase of diameter carries with it increase of weight and cost, 
and also decrease of stability, and entails, in the case of a gun-carriage 
wheel, greater inertia to recoil. There are cases, however—as with the 
