In transporting the piece on its carriage for short distances, as from one front of a fort to another. [Sidenote: 135]] 51. Describe the chassis. It consists of two _rails_ and a _tongue_, joined by three transoms. The tongue is in the middle, and projects considerably beyond the rails, to the rear. At each end of the rails on top, a hard piece of wood is notched in, and bolted. They are called hurters and counter-hurters, and their use is to prevent the gun carriage from running off the chassis. Rail-plates of iron to protect the wooden rails are let in to the outside of the rails. At the rear end of the tongue, a swinging prop is placed to support the end of the tongue when the piece is run back. The lower side of the end of the tongue is notched out, and a manœuvering loop fixed there, with a bolt and screws, to assist in handling the chassis. On the under side of each rail, opposite the rear transom, a mortise is formed, for the reception of a socket of iron which receives the _handle_ of the traverse-wheel fork. Each of these forks receives a traverse-wheel, joined to it by an axle-bolt, and these support the rear end of the chassis. The front end is supported on a pintle-plate of iron; through which, and up into the middle of the front transom, passes a pintle or bolt, which serves as a pivot around which the whole system moves. 52. In permanent batteries, how are the pintle and traverse circle fixed? The pintle is fixed in a block of stone, and the traverse circle is an iron plate set also in stone. 53. In temporary batteries, how is the pintle attached? To a wooden bolster which is covered by a circular cast-iron plate, and attached by bolts to a wooden cross picketed firmly into the ground. 54. How may a temporary traverse circle be made? Of plank, pinned to sleepers, and fastened to pickets, or secured to string-pieces, which connect the traverse circle with the pintle-cross. [Sidenote: 136]] 55. What retains the traverse-wheels and their forks in their places? The weight of the carriage and gun, and the form of the socket and handle of the fork. 56. Where are the handspikes applied in traversing the carriage? To the pivot-bolts of the traverse-wheels, which project to the rear; or under the traverse-wheels. 57. Why does the chassis slope towards the front? In order to diminish the recoil, and aid in running the piece into battery. 58. Describe the _columbiad_ gun-carriage. It is a triangular frame-work, consisting on each side of an upright, a horizontal rail or tie, and a brace, firmly mortised and bolted together, forming the cheeks, which are joined by a transom at each end. These project below the lower surfaces of the ties, and fit in between the rails of the chassis, serving, like the flanges on the rollers in the other barbette-carriages, to prevent the gun-carriage from slipping sideways off the chassis.