MINUTES OF PKOCEEDINGS OF 
the less will be the amount of the friction developed between them. 
But, in opposition to this, there is the consideration that, should there 
be any cross action of the pipe-box on the arm, it should be allowed 
as little room for action as possible. To this latter, practically, 
attention is mainly directed, and only sufficient play is given to ensure 
freedom in working. The length of the pipe-box must be such as to 
give the wheel proper stability upon its arm, and also to furnish, besides 
enough grease recess, sufficient frictional bearings to prevent too rapid 
wear. A hard alloy, technically known as “ metal,” is now used as the 
material for pipe-boxes in preference to cast-iron, on account of the 
less development of friction between it and the iron arm. 
For the flanges of the naves of artillery wheels metal is also em¬ 
ployed, but of a softer nature than that used for pipe-boxes. In the 
naves of wheels for transport service the flanges are of wrought-iron, 
as being lighter, for the same strength, than metal. 
The position of the feet of the spokes in the nave is a point of 
importance. It must be such that, when the wheel is completed and 
on its carriage, the perpendicular from the centre of resistance, or 
centre of the bearing part of the tire on the ground, should pass within 
the cross-section of the lower or “ working ” spoke through the centre 
of pressure, in order that there may not be any cross action of the 
pipe-box on the axletree-arm. The centre of pressure is usually taken 
as represented by the central point of the axis of the pipe-box, though 
in reality it lies inside of this point. 
A defect in the wood nave, as compared with the metal or Madras 
pattern nave, deserves here to be mentioned. In the former, from the 
mode of manufacture, more or less vacant space is always left between 
the feet of the spokes and the pipe-box ; consequently, when the wood 
shrinks, the mortises enlarge, giving the spokes opportunity of en¬ 
tering further into them. When this is the case, as the wheel revolves 
and each spoke in succession becomes a working spoke, it will be 
pressed as far as it can go into the stock; while the spokes which for 
the time are upper, will be rather drawn out from the stock. Thus, as 
the wheel continuously rolls, the spokes will work in and out of the 
nave, and the wheel cannot last. 
Spokes, for strength, are made of oak; and to ensure the proper 
direction of the fibre, are cleft from the tree. From the latter circum¬ 
stance, they shew on their deeper sides that appearance of the fibre 
which is termed the “ felt.” The most severe stress to which spokes 
are subject, is from the lateral thrust brought to bear upon the nave 
when one wheel becomes lower than the other by dipping into a rut, &c. 
In order, therefore, to place them in a better position to resist this thrust, 
the wheel is “ dished,” or formed into a kind of dome ; and just as the 
dome or arch is strong, from its form, to resist pressure upon the crown 
tending to crush it in, so is the wheel made strong by the dish to resist 
the lateral thrust tending to force the nave outwards. In fact, not 
only do the spokes, sustained by the tire, yield mutual support to each 
other, but the lateral thrust upon each becomes partly converted into 
a compressing strain, which the wood has better power to resist. The 
greater the dish, the stronger the wheel will be to resist the lateral 
