The Wonder Book Of Knowledge Part 51

Where do Pearls Come From?[31]

Below the surface of the ocean, there's a strange, enchanted world.

Living in the midst of its grandeur are most marvelous and delicate creatures that ceaselessly toil to strew the ocean's bed with l.u.s.trous gems--pearls.

Nature provides for the denizens of the deep that make these beautiful gems. The ocean pearl oyster or bivalve (_avicula margaritifera_) and fresh water mussel (_unio margaritifera_) have wonderful homes--their sh.e.l.ls. Coa.r.s.e, rough, rugged, often distorted on the outside, within they are lined with smooth, softly-glowing, iridescent "mother of pearl." The membrane, attaching the bivalve to its sh.e.l.l, extracts lime from the water, building the sh.e.l.l from the inside outward in successive layers, preserving the finest nacreous secretions for the smooth inside lining, thus protecting its delicate body.

In this comfortable home the mollusk is contented, but an enemy sometimes attacks it by boring through its hard sh.e.l.l. Leucodore, clione and other borers, parasitic or domiciliary worms work into the sh.e.l.l, and instinctively the protecting nacreous fluid envelops the intruder.

This is the birth of the pearl. The intruder, now covered entirely with the pearl-nacre, is constantly rolled and lapped about, and successive layers of nacre are applied until in a few years a pearl of great size and value is formed and awaits the hardy, daring pearl fisher.

Pearls were the first gems discovered and used as ornaments in prehistoric ages. Found in their natural state in utmost perfection, needing no cutting nor polis.h.i.+ng, these glowing beads of the sea were the first baubles of savages, tribes and nations. Today the pearl is the favored gem of those who are surfeited with valuable jewels. It is essentially a gem for the wealthy. The connoisseur, accustomed to the possession of jewels, finds in its soft l.u.s.ter a grandeur above that of all the sparkling stones.

Fancy pearls include all those of decided color, having a rare and beautiful tint. "White pearls" include pure white and white slightly tinted with pink, blue, green or yellow. Of these colored white pearls, the delicate, lightly-tinted, pink pearl of fine color and l.u.s.ter known as "rose" is most beautiful. Every white pearl is cla.s.sified according to its respective tint and thus its price is determined, the values ranging in the order named above, from highest for pure white, to lowest for yellowish-white.

What is Cork?

Cork is the outer bark of a species of oak which grows in Spain, Portugal and other southern parts of Europe and in the north of Africa.

The tree is distinguished by the great thickness and sponginess of its bark, and by the leaves being evergreen, oblong, somewhat oval, downy underneath, and waved.

The outer bark falls off of itself if let alone, but for commercial purposes it is stripped off when judged sufficiently matured, this being when the tree has reached the age of from fifteen to thirty years. In the course of eight or nine years, or even less, the same tree will yield another supply of cork of better quality, and the removal of this outer bark is said to be beneficial, the trees thus stripped reaching the age of 150 years or more.

The bark is removed by a kind of ax, parallel cuts being carried around the tree transversely and united by others in a longitudinal direction, so as to produce oblong sheets of bark. Care must be taken not to cut into the inner bark, or the tree would be killed. The pieces of cork are flattened out by heat or by weights, and are slightly charred on the surface to close the pores.

Cork is light, impervious to water, and by pressure can be greatly reduced in bulk, returning again to its original size. These qualities render it peculiarly serviceable for the stopping of vessels of different kinds, for floats, buoys, swimming-belts or jackets, artificial limbs, etc. Corks for bottles are cut either by hand or by means of a machine. The best corks are cut across the grain.

The Story in a Giant Cannon

Origin of the Cannon.

The shotgun and rifle, the familiar weapons of the sportsman and the foot-soldier, are not the ancestors of the cannon, as might be surmised.

On the contrary, the cannon was the predecessor of the musket and its successors. The rifle, however, antedated the rifled cannon, the type of modern artillery. We do not know when cannon first appeared, but it may have been soon after the discovery of gunpowder in Europe. This explosive seems to have been known in China long before knowledge of it reached the west, but we do not know to what extent it was developed and used in that country.

[Ill.u.s.tration: THREE-INCH FIELD GUN UNDER TEST AT FORT RILEY, KANSAS

In the trials conducted by the Board of Ordnance and Fortification of the United States Army. This gun and carriage, complete, weighs 2,020 pounds. Charge, 18.5 ounces of smokeless powder. Weight of projectile, 15 pounds. Muzzle velocity, 1,800-foot seconds.

_Courtesy of the Bethlehem Steel Co._]

The earliest cannon of which we have any knowledge were clumsy contrivances, at first wider at the mouth than at the chamber, and made of wood, and later of iron bars, hooped together with iron rings, a system of the same type as that now in use in the wire-wound cannon.

They at first seem to have fired b.a.l.l.s of stone, iron b.a.l.l.s coming later. A doubtful statement exists to the effect that cannon were used at the siege of Belgrade in 1073, and it is said that Edward III used them against the Scotch in 1327. Other dates of their use are 1338 and 1346, in which latter year Edward III employed them against the French at Crecy. For this we have the authority of Froissart. They were known under the varied names of bombards, serpentines, etc. Twelve cannon cast by Louis VII were named after the twelve peers of France, and Charles V gave twelve others the names of the twelve apostles. Other t.i.tles came later into general use, the royal or carthorne, carrying 48 pounds; the culverin, 18 pounds; the demi-culverin, 9 pounds; the basilisk, 48; the siren, 60, etc. In still later times cannon became known by the weight and the b.a.l.l.s they carried, 6-pounders, 12-pounders, etc. But they are now usually called after the size of their bores, as 6-inch, 8-inch, or 12-inch cannon. The oldest example still in existence is "Mons Meg,"

preserved at Edinburgh Castle. This is one of the iron-bar type, hooped by iron rings. It is supposed to have been used by James II of Scotland, at the siege of Threave Castle in 1455.

[Ill.u.s.tration: THREE INCH NAVAL LANDING GUN, CARRIAGE AND LIMBER

Weight of gun and mechanism, 675 pounds. Length of gun, 74.35 inches (25 calibers). Weight of projectile, 13 pounds. Travel of projectile in bore, 62.9 inches (20.97 calibers). Weight of charge, 18 ounces of smokeless powder. Muzzle velocity, 1,650-foot seconds. Muzzle energy, 246-foot tons. Weight of gun, carriage, limber, drag ropes, tools, etc., and 60 rounds of ammunition, complete, 3,420 pounds. The carriage and limber have each two removable interchangeable ammunition boxes for 12 rounds each, with a box for 12 rounds below the axle of the limber.

_Courtesy of the Bethlehem Steel Co._]

Louis VI used bombards of great length and power against the Flemish in 1477, while as early as 1401 bronze cannon had been cast in several cities of West Prussia. Iron cannon were not cast until near the end of that century. Coming down to the seventeenth century, we are told of the great Bij.a.pur cast-iron gun, the "Lord of the Plain," cast by the Mogul emperor Auremgzebe or by his foes the Mahrattas. This huge gun was 14 feet long, 28 inches bore, and fired a ball of 1,600 pounds weight.

Smooth-bore cannon and mortars of cast-iron and bronze are still retained in some fortresses, though rifled cannon are the only type now made. As late as 1864 smooth-bore 100- and 150-pounder wrought-iron guns were made for the British navy and a few bronze rifled guns were made in 1870 for service in India, but all such guns are now obsolete.

[Ill.u.s.tration: TWENTY-EIGHT TON AUSTRIAN SIEGE HOWITZER WHICH FIRES A THOUSAND-POUND PROJECTILE

The Germans borrowed a large number of these great siege pieces from the Austrians and used them in the reduction of the Belgian defenses. Huge sh.e.l.ls filled with high explosives from these mammoth guns rapidly destroyed the most modern and powerful fortifications known at the beginning of the great war. It is known that against such weapons of offense no fortifications can last and that the employment of such weapons has forced both armies to depend on their trenches as their main defense.]

[Ill.u.s.tration: CONQUERING THE ALPS.

Immense labor and great ingenuity were required to haul the monster Italian guns up the steep mountain sides to their positions.]

[Ill.u.s.tration: THE MOST FORMIDABLE OF THE FRENCH ARMY'S TRENCH ARTILLERY

80-m.m. mountain gun loaded with air-mine weighing 130 pounds. These mines can be thrown for a considerable distance and create havoc in the enemy's trenches if the aim is true.]

[Ill.u.s.tration: THE BENNETT-MERCIER MACHINE GUN

This new automatic machine gun has been adopted by the United States Army, Navy and Marine Corps. It is handled by two men, one to aim and fire it, the other to feed the cartridges which are held in bra.s.s clips of 30 each. The complete gun weighs only about 35 pounds, fires 400 shots per minute, using regular 30-caliber Springfield rifle cartridges, with a maximum range of 3 miles and an effective range of about 2,000 yards. The weapon is air cooled and can be fired steadily for about 10 minutes without undue heating.]

[Ill.u.s.tration: THREE-INCH FIELD GUN, LONG RECOIL CARRIAGE AND LIMBER

Weight of gun, carriage and limber complete, including 36 rounds of ammunition, 4,200 pounds; ground clearance, 22.5 inches. Seats are provided on axle of carriage for two gunners in transportation, one of whom operates the road brake.

_Courtesy of the Bethlehem Steel Co._]

The development of the rifle from the old smooth-bore musket, by cutting grooves or channels in the form of a screw in the interior surface, was found so advantageous in increase of precision of aim and length of range, that the rifling of cannon in time followed and is now universally used. Breech loading has also replaced muzzle loading, another vast advantage in the use of artillery. A form of breech-loading cannon was introduced in the sixteenth century, but the advantageous use of this device is of late invention. An important result of these changes is the use of elongated instead of round b.a.l.l.s, this permitting of the employment of much heavier projectiles for the same width of bore.

Modern Cannon.

Until 1888 the largest cannon in use was the 119-ton Krupp, made in 1884 for Italy; but in 1888-90 the same house produced a 135-ton gun for Cronstadt. The heaviest British gun at that time was of 111-ton weight.

This threw a projectile of 1,800 pounds with a muzzle velocity of 2,216 feet per second. But there later came a reaction in favor of lighter guns and quick firers. The heavy cannon of recent times are not cast, as of old, but are made of forged-steel by what is known as the building-up process. The different parts of these are called the tube, jacket, hoops, locking rings, trunnion rings, wire winding, etc.

Cannons are subject to great stress in firing, this being of two kinds.

One is the longitudinal stress, acting in the direction of the length and tending to pull the muzzle away from the breech. The other is the circ.u.mferential or tangential stress, which tends to split the gun open in lines parallel to the axis of the bore. These stresses are results of the longitudinal and radial pressures of the gas developed by the ignition and explosion of the powder. Such destructive forces have to be guarded against in the building of a cannon and have led to a great development over the old-time casting processes. As long as projectile velocities under 1,500 feet per second were employed cannons cast in one piece sufficed, but when greater velocities were sought, the pressure grew so extreme that no cast or forged metal tube would stand the strain.

[Ill.u.s.tration: THREE-INCH MOUNTAIN GUN AND CARRIAGE

Weight of gun, 206-1/2 pounds. Length of gun, 37.25 inches (12.4 calibers). Weight of projectile, 12 pounds. Travel of projectile in bore, 27.55 inches (9.2 calibers). Weight of charge, 12.5 ounces of smokeless powder. Muzzle velocity, 1,224-foot seconds. Muzzle energy, 123-foot tons. Weight of gun and carriage complete, 726 pounds. This gun and carriage break up into four loads of approximately 200 pounds each.

The equipment carries 16 complete rounds of ammunition with it, which are divided equally among four boxes. The saddles are so made that the load will go on any saddle.

_Courtesy of the Bethlehem Steel Co._]

How Cannon are Now Made.

It was found that the inner surface of the tube stretched more than the outer surface, and that after the inner surface had been stretched to its limit of elasticity the outer part failed to add to its strength, so that further thickness was of no benefit. To do away with this condition cannon were constructed on the principle of varying elasticity, the metal with the greatest elongation within its elastic limit being placed next to the bore, yet in high-powered guns this system failed to yield the result desired and it was replaced by what is known as the initial tension system. This comprised two methods: the plain built-up gun and the wire-wound gun. In the latter certain parts of the gun were wrapped with wire in the form of a ribbon.