MACHINE ENGRAVING. 619 MACHINE GUN. regular distance from the last. In wood-engrav- ing the breadth of the tool, or the deptli to which it is allowed to cut, regulates the distance be- tween the lines and the nature of the tint. For jnetal work the machine may be fitted with a highly tempered steel cutting tool, though in the case of engraving copper plates tlic latter are usually coated with varnish which is scratched by the tool and subsequently etched by acid. In the latter case the intensity of the action of the acid will regulate the thickness of the lines. W hen it is necessary to engiave on stone with a machine, the cutting tool has a diamond point, and the depth of the cut is regulated by means of weights on the tool-holder. The most com- plex engraving is executed wholly by machin- ery, and is employed in the manufacture of bank-notes, bonds, stock certificates, and other papers which it is necessary to protect with a peculiar and individual pattern. By an elaborate system of gearing the cutting tool so moves that it will execute a certain number of symmetrical motions and thus produce elaborate geometrical scrolls and patterns. On such a machine it is possible to make many combinations of figures for a pattern, but it is impossilde to rc]iroduce any given design once it has been traced. See Baxk-Xotes. Maxufactube of. MACHINE GUN (Fr. machine, from Lat. machi)iii, from Gk. /htjxoi'^, Dicchnne. device). A gun in which the operations of loading, extrac- tion, and firing are wholly or partly performed by mechanism. The early history of machine guns is involved in the same mystery that sur- rounds the development of guns and gunpowder. The breech-loader and the revolver are found al- most as far back as we can trace the portable gun ; even farther back there is evidence of at- tempts to produce multiple-firing guns. At the Boston Xa^-y Yard there is a double-barreled bronze gun of Chinese manufacture which was captured in Korea in 1870. According to the Chinese inscription upon it, it was made in 1601. It is about 18 inches long and weighs 14 pounds. It has three reenforcing bands about the breech end of each barrel, and each band has a vent in it. It was therefore arranged to fire in suc- cession three shots from each barrel, the spaces between the vents being am])le for the powder, ball, and wads. Pepys in his diary, date of .luly 3. 1602, says: "After dinner was brought to Sir V. Compton a gun to discharge seven times, the best of all devices that ever I saw, and very serviceable, and not a bauble, for it is nuich approved of and many thereof made." From 1662 to 1861 there are found frequent ref- erences to guns designed for multiple loading, but none seemed to give sufficient satisfaction to gain a permanent place in armaments. The success of the machine gun awaited the development of metal-cased fixed ammunition which appeared (as a military store) during the Civil War and was innnediately followed by magazine and re- peating small arms and numerous kinds of ma- chine guns. Of these early pieces the best was undnvibtedly the Catling, though the Xordenfeldt gun gave good satisfaction as a ship's gini. The French mitrailleuse never was very successful ; it appeared after the Catling was practically per- fected, but was much inferior to it and owes its reputation to fanciful descriptions of some news- paper correspondents who were ignorant of its actual performance. The first machine gun of a Vol. XII.^w. calibre larger than that of small arms was the Hotchkiss revolving cannon. This was invented by Mr. B. B. Hotchkiss, an American residing in France, in 18S7, in response to the call of the French naval officers, who wanted a rapid-firing weapon of larger calibre as a defense against tor- pedo boats. These guns were at first 1 -pounders, as under the rules of war this is the lightest explosive shell ; they were afterwards made to fire 6-pound shells, but were very cumbersome and were replaced five years later by rapid-firing single-shot weapons. The Maxim-Xordenfeldt automatic 1-pounder was first used in the Span- ish-American War, but it was brought out a year or two earlier; it is a development of Sir Hirani JIaxim's smaller automatic gun brought out ten years or more before. Machine guns ma}' be divided into two classes : (a) those operated by hand-power or exterior force; and (b) those ojjerated by the force of the powder gases acting directly upon a piston or through the recoil of the barrel. Representative of the first class are the Catling and Gardner guns, and Hotchkiss revolving cannon, which are not very different in general character, and the Xordenfeldt. which more closely resembles the early forms of mitrailleuse. In the latter the barrels, three or more in munber. have their axes in the same horizontal plane, and are fired by a horizontal lever, one after the other, but so rapidly that the piece is included among the so-called volley-firing guns. A description of the Catling will serve as an illustration of the principle upon which most of the gims of Class A were designed. It was invented by Dr. E. .J. Catling, of Indianapolis, Ind.. in 1861, and in 1862 he had a battery con- structed and in working order, an .accomplish- ment which certainly preceded the appearance of the French mitrailleuse. The gun consists of a series of parallel barrels, usually ten, in common with a grooved carrier and lock cylinder, the whole rigidly secured upon a main shaft. It has as many grooves in the carrier and as many holes in the lock cylinder as there are barrels. Each barrel has one lock, so that a gun with ten bar- rels has ten locks. The operation of the gun is very simple : one man places one end of a feed case filled with cartridges into the hopper, while a second man turns the crank which by the agency of the gearing revolves the main shaft. As the gun is revolved, the separate cartridges drop into the grooves of the carrier from the feed cases and are pressed home ready for discharge. When first invented, the Catling gun differed radically both in principle and action from any form of gun previously in use. and admitted of faster discharges and heavier projectiles, besides which, its method of fire prevented the a<>cumula- tion of recoil. Improvements and alterations in the gim have been largely in the direction of an improved feed case. The objections to the original tin feed case were that it worked irregularly for different angles of elevation, and that the cartridges did not always fall in their proper position in the grooves, with the consequence :hat janmiing fre- quentlv occurred. The 'Bruce Feed' was designed to remedy this last defect. It was constructed on the gravity principle, and consisted of an upright bronze" standard to which was attached a swinging piece containing two grooves, beneath which was an opening, which in turn connected
