The howitzer appears to have had its origin in Germany. piece of ordnance, the mortar, and the carronade, in all of which the diameter of the chamber for the powder, is smaller than the dia meter of the rest of the bore, are first bored all through, nearly to the intended calibre of the cham ber, and then that. part of the bore that requires it is enlarged.
. The cutters, in gun boring, become magnetic, in consequence of being continually rubbed in the same direction, so that the boring dust is seen ad. Bering and hanging from their edges, when they are withdrawn from the gun.
It is required, that the bore shall be a cylin drical cavity, whose axis coincides with the axis of the gun ; for this purpose, care must be taken to place the axis of the boring-bar, and that of the gun, both in one horizontal line, and it is requisite that these two lines continue in this position during the whole operation of boring. The centering of the boring-bar Ibr this purpose, requires to be done by an experienced workman, and an accurately con structed boring-machine is necessary for the conti nuance of the right position.
Whilst on the axis of the mill, the gun has a smooth outer surface given it by turning tools, which are applied in the way usual in turning metals; a wooden gunge, or cut-out profile, of the gun, with its intended mouldings, being applied to know when the has been continued to a proper depth. When this n done, the gun is takeh out of the bor ing-mill,—the square, at the cascabel, is cut off by the chisel,—and the trunions, and other parts which are not susceptible of being turned, are dressed by the chisel. The eyphera and arms which had bean cast on the gun, are finished by the chisel.
A cannon is said to be the ultima ratio repass,— the last argument that governments have recourse to ; and even this severe kind of argument has some times been embellished. Amongst ornamented can non, the brass three-pounder in the Tower, brought from Malta, is a masterpiece: it is covered with carving in a good taste, by a sculptor of Rome.
The touch-hole is drilled by stock and bit, or by drill and how ; the drill being propelled by a lever placed on a carriage, moveable on wheels. A. fi gure of this apparatus is given in the En9clopidie Planches--Fonte. Another apparatus or this pee. pose is figured in Rinrnan, Bergtverks Lexicon, Tab; XIV. fig. 9, 10. See also Monge, Description de P Art de Fabriquer lea Canons, in 4to Pans, 1794.
This work was published by order Of the revolu tionary government, and distributed to the Iron masters and Founders, in different parts of France, for their instruction. It contains, amongst others, figures and descriptions of two kinds of vertical boring machines,—of three kinds of horizontal bor ing machines,—of a machine for turning the trunions, —of two different machines for boring the touch hole,—of a machine for putting copper boshes brass guns,—and of various instruments for examin ing and'proving guns.
Before the gun is sent off, it is examined and pioved in various ways. And first to ascertain whe ther the bore is free from holes, an instrument is em ployed, consisting of several elastic steel prongs dis posed in a circle, and with their sharp points turned outwards ; this being fixed on a hole, is introduced into the bore of the gun, and drawn to and fro; the points of the prongs press against The sides of the bore, and the presence of a hole is,known by one of the prongs getting into the hole, and preventing the instrument from being drawn out directly, unless 'by the use of a ring that is pushed over the prongs to unbend them.
There is another instrument, composed of a board twice as long as the bore of the piece ; along the middle is a groove proceeding in a straight line. IA this groove a button is moveable, and on the button as a centre are fixed two radii or arms; the two ends of these arms within the gun describe a line on the inside of the bore when the button is pushed inwards, whilst the extremities of the arms on the outside describe two lines similar on the part of the board that is situate without the bore : in this way the out line of a longitudinal section of the bore is describ ed, and its sinuosities or deviation from the axis are rendered sensible. This instrument is seldpm used : it requires to be made by a workman skilled in the construction of mathematical instruments, or in watchmaking.
A lighted wax-candle is introduced into the gun for the purpose of seeing any defects there may be. in the box, or the light of the sun is reflected into -the box by a mirror. The strength of the gun is proved by firing it with a large charge of powder ; and by forcing water into the bore by a powerful forcing pump, the touch-hole being stopped, and the mouth of the piece, ao that water ?breed in by the mouth cannot return that way.