376 
MINUTES OF PROCEEDINGS OF 
It will be seen from the foregoing that the amount of hollow given 
depends entirely upon the dish of the wheel, together with the amount 
of strut it is desired to give. 
The hollow is expressed in parts of an inch, and measured as the 
perpendicular distance from a point A (Fig. 3), in the under edge of the 
arm, distant from the shoulder the length of the pipe-box, to a point B , 
in a line drawn parallel to the axis of the body, and touching the lowest 
point of the base of the arm. This manner of reckoning the hollow, 
though convenient, is not strictly correct, as it takes into account the 
amount of cone of the arm. Practically, the hollow may be measured 
with sufficient exactness by stretching a string from one linchpin-hole 
to the other, on the under side, and measuring the distance from the 
string to the base of the arm. The amount of the hollow is always such 
as to point the arm downwards, notwithstanding its conical form ; which 
has the effect of relieving the washer and linchpin of the pressure 
which the nave would otherwise ha ve against them, due to the tendency 
of the wheel to roll outwards. 
In addition to the ee hollow,” an inclination to the front, or “ lead,” 
is given to the axletree-arm, in order to place the front part of the 
wheel, as in revolving it approaches the ground, more in the direction 
in which the wheel is intended to travel, and from which the hollow of 
the arm, as well as the dish of the wheel, make it to deviate. The 
lead thus causes the wheel to meet any obstacle which opposes it more 
directly, as regards the spoke on which the stress due to the resistance 
of the obstacle happens mainly to fall; in fact, it does for that spoke 
what the hollow does for the lower spoke. Strictly speaking, the 
amount of the lead should be proportional to the dish of the wheel ; 
being, however, small, it has been empirically fixed at -fa in., and is 
measured in the same manner as the hollow (Fig. 4). 
Fig. 4. 
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1 
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It will be seen from the preceding remarks upon the wheel and 
axletree, that in planning the former, after its general dimensions have 
been fixed, the amount of “ dish ” and of “ strut ” have to be deter¬ 
mined ; from which follow the amount of “ hollow ” of the axletree-arm, 
and then from the latter the amount of bevel of the sole of the wheel. 
March, 1874. 
