44. How many forms of the barbette-carriage are in use in the service? Two: one for _iron guns_ and sea-coast howitzers (12, 18, 24, 32, 42-pdrs., and 8 and 10-in.); and one for the columbiads. [Sidenote: 133]] 45. Of how many parts are barbette-carriages composed? Of a _gun-carriage_ and a _chassis_. 46. Describe the gun-carriage. It is formed of two upright pieces of timber, nearly vertical, behind which are placed two inclined braces, mortised into the uprights, and designed to receive the force of the recoil, the whole forming the cheeks, which are firmly connected and braced by transoms and assembling bolts, thus forming a _triangular_ frame-work, _which_ is less liable than any other form to become deformed from the shocks of the gun. A horizontal piece (the transom and axle-tie) runs from front to rear between the cheeks, connecting the axle-body and rear transom. The trunnion-bed is at the top of the upright, where it is joined to the brace; and the breech of the gun is supported on an elevating screw, working into a screw-box placed in the rear end of the transom and axle-tie. The front transom is just under the gun; the middle transom is between the braces; and the rear transom is at the lower end of the braces, and under the transom and axle-tie, into which it is notched; the lower part of this transom is notched to receive the tongue of the chassis on which it slides. Between this transom and the transom and axle-tie, the end of a lunette is placed projecting to the rear, and fastened by a bolt for the purpose of attaching a limber to the carriage. [Sidenote: 134]] The feet of the uprights and front end of the transom and axle-tie are joined to an axle-body, in which an iron axle is placed. On the ends of the axle are fitted cast-iron rollers, which rest on the rails of the chassis, and support the front of the carriage. On the outside of the roller is placed an octagonal projection, on which the cast-iron nave of the wheel fits, secured by a washer and linch-pin. The spokes of the wheels are wood, inclosed within heavy iron tires. Manœuvring bolts are inserted in front of the feet of the uprights, and in the carriages, for pieces heavier than a 24-pdr., in rear of these feet also. These bolts and the spokes of the wheels form the points of application for the handspikes, in manœuvering the piece. Manœuvering staples are placed in front of the feet of the braces, for the purpose of using handspikes to raise the rear of the carriage from the tongue of the chassis in running to and from battery. 47. What pieces go on the same carriage? The 32-pound gun, and 8-inch howitzer. All other pieces have separate carriages. 48. How many sizes of rollers are used? Two: one for the carriages of the 12, 18, and 24-pounders; the other for the remaining carriages. 49. Are cap-squares used with these carriages? No. 50. What other purposes do the wheels subserve besides assisting in manœuvering the gun-carriage?