THE proof of cannon is made to aƒcertain their being well caƒt, their having no cavities in their metal, and, in a word, their being fit to reƒiƒt the effort of their charge of powder. In artillery the name of chamber, or honeycomb, is given to the flaws or cavities found in the body of the metal of pieces, when they
come from the foundery. The diƒcovery of theƒe defects is of great importance, becauƒe as the metal is weaker in thoƒe parts than in any other, they endanger the burƒting of the piece.* [*]
        The ordinary method of proving cannon is to fire them ƒeveral times with very ƒtrong charges of powder. In making this proof the piece is laid upon the ground, ƒupported, only in the middle, by a piece of wood about 4 or 5 inches thick; and a convenient place is made choice of for this experiment, to prevent accidents.
        When the piece has been fired two or three times, a ƒmall quantity of powder is ƒcattered along the bore, and fired in order to clean it; water is then poured in, and preƒƒed toward the breech by a ƒpunge of nearly the ƒame caliber, and the touch-hole being at the ƒame time ƒtopped with the finger, a ƒtrict ƒearch is made whether the water ouzes out anywhere, and if it does not, it is certain the piece has no clefts or creviƒes.
        Methods are then taken to diƒcover whether there are any chambers in the inƒide of the piece; for this purpoƒe an inƒtrument is uƒed, called a cat. This cat is a piece of iron having one, two, or three claws, or prongs, which are very ƒharp, and diƒpoƒed, when there are three of them, in form of a triangle; this piece of iron is faƒtned to an hampe, or handle.
        To examine a piece, the cat is introduced into the bore, or interior part of it, and if there are any cavities therein, it never fails to diƒcover them. There is yet another kind of cat, different from that juƒt mentioned; this laƒt conƒiƒts of two branches of iron, fixed to the end of a piece of the ƒame metal, each of which has talons or claws of ƒteel. One of theƒe branches has a turning joint, or hinge, governed by a ƒpring, and diƒpoƒed in ƒuch a manner, that when the cat is introduced into the piece, the leaƒt cavity relaxes the ƒpring, and by that means is diƒcovered. M. St Remy tells us, that the founders, to whom theƒe inƒtruments are not at all pleaƒing, call the common cat the Devil, and that with two ƒpring branches the ƒpight of the Devil.
        Wax-lights, and even looking-glaƒƒes, are alƒo made uƒe of to examine the inƒide of cannon. In order to uƒe the looking-glaƒs, or mirrour, it is neceƒƒary the ƒun ƒhould ƒhine out bright; the breech of the cannon being then placed towards the ƒun, and the mirrour overagainƒt the mouth of the piece, it illuminates the hollow cylinder, or bore, ƒufficiently to diƒcover the flaws in it, if any ƒuch there are.
        M. Dulacq, in his treatiƒe on the Mechaniƒm of Artillery, a work full of curious and uƒeful reflections, obƒerves, that the common method of proving cannon, how high ƒoever they may be charged, concludes nothing with reƒpect to the perfection of the piece, becauƒe it does not bring it to the degree of ƒoftneƒs, nor give it the ƒhock and agitation which it receives when it is in danger of burƒting, neither does it give that dryneƒs to the powder which it would have at ƒuch a criƒis.
        The examination by the cat, the wax-candle, and the mirrour, can only prove the concave ƒuperficies of the bore to be ƒmooth, and free from holes or flaws, but none of theƒe experiments can diƒcover the cavities, or hollows, which may happen in the body of the metal. The ƒame may be ƒaid of the experiments made with water and ƒmoke. M. Dulacq is of opinion, that the beƒt method of proof is to fire the piece about 40 times ƒucceƒƒively, as quick as poƒƒible. It is certain that a piece which ƒtands this proof will obtain a kind of certificate that it is well conƒtructed; but the expence of this method, which is very confiderable, deƒerves ƒome attention.
        The method uƒed by M. Valliere, as related by M. Dulacq, is firƒt to fire each piece twice charged with its ordinary bullet, and then to fire it twice more, charging it, inƒtead of a bullet, with a cylinder of fat earth, about two feet in length. This cylinder as it were concenters the action of, or confines the powder in the chamber, or inmoƒt receƒs of the hollow cylinder of the piece, in ƒuch a manner as to make it preƒs on the metal with its utmoƒt force.
This proof is a very good one, and has the advantage of being made with a very (mall expence of powder.
        The ƒame author relates an experiment, which he had ƒeen made at Lyons, upon two pieces of cannon which were caƒt in that city. Each piece was fired above 1500 times ƒucceƒƒively as faƒt as poƒƒible, their charge each time being one third the weight of the bullet; and after this exceƒƒive proof, they were as fit for immediate ƒervice, as if they had not been fired at all. "Their chace was not in the leaƒt widened, their mouth continued even and uniform, and the whole bore or interior cavity appeared perfectly ƒmooth; the founder would have warranted them for as many more diƒcharges at the leaƒt; the touch-hole of one of them was ƒcarce at all enlarged, and the other but very little, both of them being in a good ƒtate for ƒervice."
        This proof; as M. Dulacq, remarks, was very fit to aƒcertain the goodneƒs of pieces caƒt in a new metal; but ƒhould not be made upon any but thoƒe firƒt caƒt, the others made of the ƒame metal need only be proved in the common way.
        Errard de Barleduc, in his Fortification relates an experiment almoƒt of the ƒame kind, made at Paris, by the Sieur Deƒtroz, grand maƒter of the artillery of France, "who was ƒeen, ƒays this author, in the time of Charles the 9th, to fire the ƒame piece of cannon, with the fame powder, two hundred times within the ƒpace of nine hours, without damaging the piece in any refpect." And indeed a great progreƒs had been made in artillery even at that time, by means of the long and bloody wars between Francis the firƒt, and the emperor Charles the fifth.