In modern warfare, the term cannon is applied to a shell-firing gun of a heavier calibre than a machine gun. They have a lower rate of fire, but are more destructive than machine guns. Before the Great War, all big guns which we would now refer to as howitzers and anti-tank guns etc were called cannons, irrespective of whether they were muzzle or breech loaded.
In older warfare, the term cannon was applied to a big gun or piece of ordnance. The precise period at which engines for projecting missiles by mechanical force (catapults, etc) were supplanted by those utilizing explosive materials is a matter of controversy, the invention of cannon being attributed to the Chinese, from whom the Saracens may have acquired the knowledge. A doubtful authority asserts their use at the siege of Belgrade in 1073; but they were certainly brought into use in France as early as 1338. At first they were made of wood, well secured by iron hoops, the earliest shape being somewhat conical, with wide muzzles, and afterwards cylindrical. They were then made of iron bars firmly bound together with iron hoops like casks, Mons Meg at Edinburgh being a good example.
The first cannons used in Britain appeared around 1335. Edward III used cannons at the Battle of Cressy. In the reign of Elizabeth I, the British cannon was a muzzle-loading gun with an 8-inch bore that fired a 60 lb projectile. Bronze was used in the second half of the 14th century, towards the close of which and during the 15th century cast-iron ordnance came into use. A form of breech-loading cannon was introduced in the 16th century.
Cannon formerly received the following distinctive names: cannon royal, or carthoun, carrying 48 pounds; culverin, 18; demi-culverin, 9; falcon, 6; basilisk, 48; siren, 60; etc. They were afterwards named from the weight of the balls which they carried: 6-pounders, 12-pounders, etc; but by 1900 were often, especially the large ones, designated by their weight, as a 25-ton gun, a 67-ton gun, an 80-ton gun, etc. Their calibre or diameter of bore was also used in designating them: a 6-inch gun, a 12-inch gun, etc.
Around the 19th century the classification of cannons into muzzle-loading and breech-loading came into use though all the guns of the improved types of the 19th century were breech-loading. Quick-firing guns and machine-guns were classes of introduced late in the 19th century.
Great improvements and changes in the manufacture of cannon were introduced in the late 19th century. Not long before they were all made of iron, brass, or gun-metal (a variety of bronze) by casting. The introduction of rifled small-arms led the way to that of rifled cannon, and the adoption of heavy armour for ships of war rendered guns of enormous power and magnitude necessary in order to penetrate their sides. For round balls projectiles of considerable length were substituted in the rifled ordnance; and the increased weight and inertia of the projectiles and their rapid rotation in these rifled guns try the piece so severely that cast-iron and bronze were superseded, and the old methods of making guns given up. Guns built up in different ways are now in general use, and the construction and connected mechanism is now somewhat complicated, so that to turn out a large gun of modern type is a long and expensive process. In Englandsteel and wrought-iron guns came in for all heavy artillery by 1900, and they were manufactured for foreign powers on a large scale, especially by the Elswick Ordnance Company.
The former heavy guns of the British service, made on the 'Woolwich' system, had a steel tube to form the bore, over which were shrunk coils of wrought-iron, increasing in thickness about the breech, This method of manufacture was first introduced by Sir William Armstrong about 1858. Such guns present the hard steel to meet the wear and tear on the bore of the gun, while great support is given by shrinking on the wrought-iron hoops, which contract with a tight grip upon the steel. Hoops of steel were later preferred to those of wrought-iron; and later still the guns were strengthened by flat steel wire or a narrow ribbon of steel coiled round it.
Steel guns of very high quality were long made by Krupp of Essen, and Sir J. Whitworth's guns also gained a high name. The Whitworth guns were made of mild steel of a special quality, massive hoops being forced over a central tube, and over one another, by shrinkage or by hydraulic pressure. These guns had comparatively small hexagonal bores, with a very rapid twist, and fire long projectiles, made to fit mechanically, with remarkable accuracy to a great range.
A dipping-needle or inclination compass is an instrument for showing the direction of one of the components of the earth's magnetism. In essentials the instrument consists of a light, magnetized steel bar supported on a horizontal axis which passes, as nearly as possible, through the centre of inertia of the bar. When a needle thus mounted is placed anywhere not in the magnetic equator, it dips or points downward; and if the vertical plane, in which it moves, coincides with the magnetic meridian the position of the needle shows at once the direction of the magnetic force. The intersection of two or more directions found by making the experiment at different places, indicates the place of the magnetic pole. Research Dipping-Needle
All bodies on the earth, by virtue of the attraction of gravitation, tend to the centre of the earth. A ball held in the hand presses downward; if dropped, it descends perpendicularly; if placed on an inclined plane, it rolls down, in doing which it presses the plane with a part of its weight. In the air bodies fall with unequal velocities, a piece of paper, for instance, more slowly than a ball of lead; and it was formerly thought that the velocity of the fall of bodies was in proportion to their weight.
This error was attacked by Galileo, who, experimenting with balls of different substances which he dropped from the tower of Pisa, was led to the conclusion that the resistance of the air acting on different extents of surface was the cause of the unequal velocities, and that in a vacuum all bodies would fall with the same velocity. The truth of this last proposition wag first demonstrated by Isaac Newton in his celebrated 'guinea-and-feather' experiment, where a guinea and feather are shown to fall side by side in the vacuum of the air-pump. This experiment proves that the force of gravitation in bodies is proportional to their inertia, that is to their mass. The laws of falling bodies, that is of bodies falling freely in a straight line and through a distance short in comparison with the earth's centre, are the following:
1. When a body falls from rest it acquires velocity at the rate of about 32.2 feet per second. This number, which represents the acceleration due to the force of gravity, varies slightly with the locality, increasing from the equator to the poles, and diminishing as we recede from the centre of the earth. At the end of five seconds, therefore, the body would be found to be moving at the rate of 5 x 32.2, that is 161 feet per second.
2. The space fallen through in the first second is half of 32.2, that is 16.1 feet; and the space fallen through in any given time is found by multiplying the square of the number of seconds by 16.1. Thus, in three seconds a body falls 9 x 16.1 feet, or 144.9 feet.
3. The square of the velocity acquired by falling through any number of feet is found by multiplying twice that number by 32.2. Thus if a body falls 9 feet, the square of the velocity acquired is 2 x 32 x 9, or 576 feet per second, 32 being used instead of 32.2; and taking the square root of 576, we find that a velocity of 24 feet is acquired in a fall of 9 feet.
4. When a body is projected vertically upward with a given velocity, it continues to rise during a number of seconds found by dividing the number that expresses the velocity of projection by 32.2; and it rises to a height found by dividing the square of that number by 2 x 32.2, or 64.4. Research Fall of Bodies
A fly-wheel is a heavy wheel whose inertia maintains a nearly uniform speed of rotation under variable load or driving force, and is thus used for the purpose of rendering the motion equable and regular by means of its momentum. The revolving fly-wheel is a reservoir of energy by virtue of its movement of inertia, and its effectiveness depends on the amount of energy which it absorbs or gives up for a given change of speed. Research Fly-wheel
A gyroscope is any rotating body that exhibits two fundamental properties: gyroscopic inertia, or rigidity in space, and precession, the tilting of the axis at right angles to any force tending to alter the plane of rotation. These properties are inherent in all rotating bodies, including the earth itself. The term gyroscope is commonly applied to spherical, wheel-shaped, or disk-shaped bodies that are universally mounted to be free to rotate in any direction; they are used to demonstrate these properties or to indicate movements in space. A gyroscope that is constrained from moving around one axis other than the axis of rotation is sometimes called a gyrostat. In nearly all its practical applications, the gyroscope is constrained or controlled this way, and the prefix gyro is customarily added to the name of the application, as, for instance, gyrocompass, gyrostabiliser, and gyropilot. Research Gyroscope
Gyroscopic inertia is the rigidity in space of a gyroscope. It is a consequence of Newton's first law of motion which states that a body tends to continue in its state of rest or uniform motion unless subject to outside forces. Thus, the wheel of a gyroscope, when started spinning, tends to continue to rotate in the same plane about the same axis in space. An example of this tendency is a spinning top, which has freedom about two axes in addition to the spinningaxis. Another example is a riflebullet that, because it spins or revolves in flight, exhibits gyroscopic inertia, tending to maintain a straighter line of flight than it would if not rotating. Rigidity in space can best be demonstrated, however, by a model gyroscope consisting of a flywheel supported in rings in such a way that the axle of the flywheel can assume any angle in space.
When the flywheel is spinning, the model can be moved about, tipped, or turned at the will of the demonstrator, but the flywheel will maintain its original plane of rotation as long as it continues to spin with sufficient velocity to overcome the friction with its supporting bearings. Gyroscopes constitute an important part of automatic-navigation or inertial-guidance systems in aircraft, spacecraft, guided missiles, rockets, and ships and submarines. In these systems, inertial-guidance instruments comprise gyroscopes and accelerometers that continuously calculate exact speed and direction of the craft in motion. These signals are fed into a computer, which records and compensates for course aberrations.
The most advanced research craft and missiles also obtain guidance from so-called laser gyros, which are not really inertial devices but instead measure changes in counter rotating beams of laser light caused by changes in craft direction. Another advanced system, called the electrically suspended gyro, uses a hollow berylliumsphere suspended in a magnetic cradle; fibre-optic systems are also being developed. Research Gyroscopic Inertia
Inertia is the property of a body that causes it to oppose any change in its velocity, even if the velocity is zero. An object at rest requires a force to make it move, and a moving object requires a force to make it slow down, accelerate, or change direction. Newton called this resistance to a change of velocity inertia. It has been found that the greater the mass of a body, the higher is its inertia. Research Inertia
Abbreviations
Research Dipping-Needle
