17. Describe these gun-carriages. They consist of two short cheeks of wood, bolted upon a stock and wooden axle-body, in a recess of which fits the iron axle on which the wheels are placed. The stock terminates in a _trail_ and _trail-plate_ which rests on the ground, and has on the end a strong ring called the _lunette_, which is placed on the pintle hook when the piece is limbered. In the stock is placed an elevating screw-box of bronze in which the elevating screw fits. [Sidenote: 126]] 18. Mention other parts of a field-carriage. Cap-squares, ear-plates, trunnion-plates, under-strap, elevating screw, wheel guard plate, axle-tree, trail-plate, trail-handles, prolong-hooks, pointing-rings, washer-hooks, lock-chain, sponge-chain, sponge and rammer stop, bolts, rings, bands, hooks, keys, straps, nuts, and nails. 19. What is the limber? It consists of a similar axle-body, axle, and two wheels, and on these rests a frame-work to receive the tongue. On top of the whole is an ammunition box, the top of which forms a seat for three cannoneers. In rear of the axle-tree is a _pintle-hook_ to receive the lunette of the trail. Connected with the frame-work in front, is a fixed _splinter-bar_ with four hooks, to which are attached the traces of the wheel-horses. At the extremity of the tongue are placed two pole-chains, by which the tongue or pole is held up, and a pole-yoke with two movable branches, to prevent, as much as possible, the pole from oscillating and striking the horses. 20. What is the use of the limber? To facilitate the movements of the carriage. By means of it a considerable portion of ammunition and stores may be conveyed for the immediate use of the piece, some of the cannoneers may be seated on the boxes, and by the simple manner in which it is attached to the carriage, the greatest facility is afforded for coming into action, or in retiring. [Sidenote: 127]] 21. Are there any other advantages from the manner in which the gun-carriage and limber are connected? These two parts thus possess all the advantages of a four-wheel carriage, and the _freedom_ of motion peculiar to each admits of their passing over ground uninjured, or without being overturned or strained, where any other four-wheel carriage would invariably fail. 22. Describe the _mountain artillery_ gun-carriage.