COMPOUND MOTION. ■ 77 



According to the lawa which govern the motion of project- 

 ^Tbe'^a^med '^^^ ^^ '^ evident that f gun must be aimed, in order to hit 

 to hit an ob- an object, in a direction above that of the object, more or less, 

 distance'r^'^''^ according to the distance of the object and the force of the 

 charge. "With an aim directed, as in Fig. 49, at the object, 

 the ball, moving in a curved path, must necessarily fall below it. 



straight, or rectilinear path. A rifle sends a ball more accurately than a musket, bccanse 

 the ball is in more accurate contact with the sides of the barrel than in the case of a com- 

 mon musket The space produced by the difference of diameter between the ball and tho 

 bore of the gun, greatly diminishes the effuct of the powder, by allowing a part of tli« 

 elastic fluid to escape before the ball, and also permits the ball to deviate from a straight 

 line. The peculiarity and superiority of the new rifle, called the " Miniu rifle," is to be 

 found in the construction of the ball, which, by the act of firing, is made to fit completely 

 the barrel, or bore, of the gun. This is accomplished by making the ball of an oblong 

 shape and a conical point, with an opening in the base extending up for two thirds the 

 length of the ball. Into the opening of this internal cylinder there is placed a Bm;ill con- 

 cave section of iron, which the powder, at the moment of firing, forces into the leaden 

 ball with great power, spreading it open, and causing it to fit tightly to the cavity of tho 

 barrel in its course out, thus giving it a perfect direction. 



Cannon of different sizes are named according to the weight of the ball which they are 

 capable of discharging. Thus, we have 6S-pounders, 24-poundcrB, IS-pounders, and tha 

 lighter field-pieces, from 4 to 12-pounders. The quantity of powder generally used for 

 discharging common iron or brass cannon, is one third the weight of the ball. In gen- 

 eral warfare, the effective distance at which artillery can be used is from 500 to 600 yards, 

 or from a quarter to half a mile. At the battle of Waterloo, the brigades of artillery were 

 stationed about half a mile from each other. Cannon-balls and shells can be thrown 

 with effect to the distance of a mile and a half to two miles. 



The distance to which a ball may be thrown by a 24-pounder, with a quantity of powder 

 equal to two thirds the weight of the ball, is about four miles. Its effective range is, how- 

 ever, much less. Were the resistance of the air entirely removed, the same ball would 

 be thrown to about five times that distance, or twenty miles. 



It has been found that, by the firing of .in 18-pound shot into a butt, or target, made of 

 beams of oak, when the charges were C pounds of powder, 3 pounds, 2i pounds, aruL 1 

 ^und, the respective depths of the penetration vere 42 inches, 30 inches, 23 inches, and 

 15 inches; and the velocities at which the balls flew, were 1,600 feet in a stcond, 1,140 

 feet, l,02i feet, and 6,56 /ee(. 



When the cannon is so pointed that the ball goes perfectly straight toward the object 

 aimed at, the direction is said to be point-blank. Ricochet firing Is when the ball is dis- 

 charged in such a manner that it goes bounding aTul shipping along the surface of tho 

 ground. In this way a ball can be thrown moro effectively, and for a greater distance, 

 than in any other way. 



There are several substances known to chemists which possess a greater exploeivo 

 power than gunpowder. It has not, however, been considered possible to increase the 

 range and effect of a projectile fired from a gun, or cannon, by using any of them. Sup- 

 posing that the guns could be made indefinitely strong, and the gunpowder indefinitely 

 powerful, the point would soon be reached where the resistance which the air opposes to 

 a body moving very rapidly would balance the force derived from the explosive compound, 

 which drives the projectile forward. Beyond this point no increase of impulsive force 

 would urge the projectile farther ; and this limit is considerably within the range of 

 power that can be exercised by common gunpowder. Beside this, the strength of mate- 

 rials of which guns are made is limited. Practical experience has fully demonstrated that 

 the largest piece of ordnance which can be cast perfect, sound, and free from flaws, is a 

 mortar 13 inches diameter; and even this weighs five tons. The French, at the siege of 

 Antwerp, constructed a mortar having a bore of uo less than 20 inches diameter, but ik 

 burst on the uinth time of firing. 



