The inclination outward of the spokes, when fastened in the nave.
10. What is the advantage of this obliquity of the spokes?
It gives elasticity to the wheel, and protects it from the effect of shocks, which would destroy it, if the spokes were in the same plane.
11. What is the object of giving dish to a wheel?
For the purpose of making the body of the carriage wider; to diminish the length of the axle-tree, thus increasing its strength; to throw the mud and water outside the wheels; and to keep the wheel close against the carriage, and prevent any tendency to run off the axle.
12. How are movable gun-carriages distinguished?
As field, mountain, and siege-carriages.
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13. What are the principal considerations to be kept in view in the construction of movable carriages?
In firing, the carriage should yield to the recoil. Were it fixed immovably, it would soon be destroyed, no matter how great its solidity. Its weight should be proportional to that of the piece. If too heavy it would soon be destroyed by the shocks of the piece. If too light, the recoil would be immoderate. Its weight should always be less than that of the piece. A heavy piece upon too light a carriage will perform better service than the reverse arrangement, since the effort exerted by a piece depends upon its mass multiplied into the square of the velocity.