Page:The American Cyclopædia (1879) Volume III.djvu/717

 CANNON 707 burning match for the purpose of setting the powder on fire; but this practice was aban- doned for a time, owing to the rudeness of the methods, and the frequency of accidents result- ing ;herefrom. Means were however devised in 1334 for overcoming the difficulties which bad been encountered, and for perfecting the manufacture and use of mortars. They are now in use throughout the world, and owing to the great improvements which have been made in constructing armored ships and fortifi- cations, so as to render them proof against direct fire, mortars and mortar or vertical firing are attracting special attention from artillerists and engineers. In the time of Louis XIV. a great variety of mortars were used, some of which, called Comminges after their inventor, threw projectiles weighing as much as 550 Ibs. Du- ring our civil war, wooden mortars of the most primitive kind, made of logs bored or burnt out, and with very light charges at close range, were used effectually by the Union troops at Vicksburg, for throwing grenades and small shells into the enemy's lines. Thirteen-inch mortars of cast iron were used also in the siege of Fort Pulaski and the attack upon the forts below New Orleans, while those of a smaller calibre were used at the siege of Petersburg, under the direction of Gen. H. L. Abbott, in pursuance of an idea suggested by Maj. Gen. Bormann, of the Belgian service. He proposed to convert a 10-inch mortar shell into a spheri- cal case shot, by filling it with balls and a bursting charge sufficient to rupture the shell, the fuse to be so timed as to explode the charge about 50 ft. from the ground. The expedient was of great effect, and will doubtless be imi- tated in future wars. A light kind of mortar, called Coehorn after its inventor, and weighing about 160 Ibs., mounted upon wooden blocks furnished with handles, designed to throw 24- pound shells, is also an effective gun for use against rifle pits or light breastworks, and is again becoming popular. Early attempts were made to throw hollow projectiles from per- rieres and culverins; but great difficulties were experienced in loading them, and the accidents which resulted caused the practice to be aban- doned for a time. Subsequently, however, the effort was renewed, and, after the length of the piece was reduced so that the projectile could be placed in position by hand, became successful. These short cannon came rapidly into use, and, under the name of howitzers (Ger. Haubitzen), are now found in the artillery systems of all nations. The calibre of a can- non is the diameter of its bore, given in inches, or in the weight of the ball which it takes ; but since the introduction of rifled cannon and elongated shot, the calibre of a gun is generally expressed in the measure used in giving the diameter of the bore. Each nation has its own system of calibres, and no two have the same. Changes are continually being made, and im- provements are everywhere in progress. Du- ring the past 20 years many novelties have been introduced both in the construction and the use of cannon. In 1820 the heaviest gun mounted upon our seacoast was the 24-pdr. throwing a ball 5'82 inches in diameter. At pre- sent (1873) the heaviest is a cast-iron smooth- bored 20-inch gun, throwing a shell weighing 1,080 Ibs., with acharge of powder varying from 100 to 200 Ibs. Cannon are classified accord- ing to their nature, uses, and peculiarities, as guns, howitzers, and mortars, or as field, moun- tain, prairie, siege, and seacoast cannon; or again, as rifled and smooth-bored cannon. The principal parts and nomenclature of cannon are shown in fig. 6. The interior of cannon may be divided into three distinct parts : the vent, or channel by which fire is communicated to the charge ; the chamber, or seat of the charge ; and the bore, or that part of the cylinder passed over by the projectile. The size of the vent should be as small as possible in order to di- minish the escape of the gas, and the erosion of the metal which results from it; and ex- periment shows that the interior orifice of the vent should be placed at a distance from the bottom of the chamber equal to a quarter of its diameter, or at the junction of the sides of the chamber with the curve of the bottom. The form of the chamber, or seat of the charge, has an effect upon the force of the gunpowder, as well as upon the strength of the piece to re- sist it ; and experience has shown that its length should in general be equal to its diameter, and its surface should be as small as possible com- pared with its volume. The charges with which solid projectiles are fired being generally greater than one sixth of their weight, the cartridge occupies a space the length of which is greater than the diameter ; the form of the seat of the charge is therefore simply the bore prolonged. This arrangement reduces the length of the charge so that its inflammation is as complete as possible before the projectile begins to move. To give additional strength to the breech, the bottom of the bore is generally rounded into an arc of a circle, but is sometimes hemispheri- cal, tangent to the surface of the bore. All cannon of the newest models have the bottom of the bore finished as a semi-ellipsoid, this form being thought to give greater strength than the hemisphere. The following figures illustrate the various forms of cham- bers in use. In the earli- er days of artillery, when mealed powder was ha- bitually used, it was be- lieved that the longest F.G. 2.-Cyltndrical Cham- P ieC6S aye T the rea *- her. est range. In accord- Fio. 8. Conical Chamber. Fio. 4. Spherical Chamber.