84. What is the use of the _hand-cart_? For the transportation of light stores in siege and garrison service. 85. Describe it. It consists of a light body with shafts, mounted on two wheels. The shafts are joined together at the ends, and supported immediately in front of the body by iron legs. [Sidenote: 146]] 86. What is the use of the _hand sling-cart_? It is used in siege and garrison service for transporting artillery short distances. 87. Describe it. It is a two-wheeled carriage made entirely of iron, except the pole, which is of oak. The axle-tree is arched to make it stronger, and connected with the pole by strong wrought iron straps and braces. In the rear of the axle a projection is welded to receive the end of a strong hook. The end of the pole terminates in a ferule and an eye. The eye is for the purpose of attaching to the cart when necessary, a limber or a horse. 88. How great weights can be transported by this cart? It should not be used with heavier weights than about 4000 lbs., but in case of necessity a 24 or 32-pd. gun may be transported on it. For heavier guns or material, the large _sling-cart_ drawn by horses or oxen should be used. 89. What is the _field and siege gin_ and its use? It consists, like all gins, of two legs and a pry-pole, a windlass, sheaves, pulleys, and a fall or rope, and is used for mounting or handling guns, or other heavy bodies, in the field or in the trenches of a siege. The legs are about 14½ feet long and the height of the gun about 12 feet. 90. How does the _garrison gin_ differ from the field and siege gun? It is heavier and stronger, as it is used for mounting heavier guns, and has not to be transported like the other with an army in the field. The legs are longer and the gin higher than the other. 91. Describe the _casemate gin_. It does not differ from the garrison gin except in its height (which is about that of the field and siege gin) and the thickness and strength of the parts. [Sidenote: 147]] PART XIII. PRACTICAL GUNNERY. 1. How may the velocity of a shot or shell be ascertained? Approximately by the empirical formula, ( _ac_ ) _V_ = 1600√(————— ). ( _w_ ) Where _V_ = initial velocity. _a_ = a coefficient, whose value depends on the windage. _c_ = charge } _w_ = weight of ball } in lbs. The values of _a_ are: Windage. Values of _a_. 0.175 3.6 0.125 4.4 0.090 5.0 2. Does a shot or shell continue at the same uniform velocity during its flight? The velocity decreases as the distance increases, in a proportion a little higher than the squares of the velocities throughout. 3. What causes a decrease in the velocity of a shot? The resistance of the air, which varies as the square of the velocity of the shot. [Sidenote: 148]]