THERE have been different inventions propoƒed, and put in practice heretofore, for the proof of powder, that is, to aƒcertain its goodneƒs. But his majeƒty, by an ordinance of the 18th of September 1636, which is ƒtill obƒerved, ordered the proof of powder to be made with a ƒmall mortar, which ƒhould carry a bullet of 6o pounds, to the diƒtance of 50 fathom at leaƒt, with only 3 ounces of powder. If the powder threw the bullet to a leƒs diƒtance, it was not received into his majefty's magazines.
        Fig. 5. in Plate 7. repreƒents this mortar, which is called a prover.
        Its dimenƒions, according to the ordinance juƒt mentioned, are as follows:
        a The diameter of the mouth of the mortar, is 7 inches, and 3 4ths of a line.
        b The length of the hollow cylinder, or bore, is 8 inches 10 lines.
        c The diameter of the chamber is 1 inch 10 lines.
        b d The length, or depth, of the chamber, is 2 inches 5 lines.
        e The touch-hole, terminating at the bottom of the chamber.
        f The diameter of the mortar (including the thickneƒs of its metal) at the chace is 8 inches 10 lines.
        g The diameter of the mortar (the thickneƒs of its metal included) at the chamber is 4 inches 8 lines and an half.
        h The diameter of the touch-hole is 1 line and an half.
        a i The thickneƒs of the metal at the ring (not including the moulding or thread) is 10 lines.
        k The length of the braƒs (7) femelle of the mortar, which is 16 inches.

(7) We have called a piece of wood which is placed on the tranƒoms at the top of the carriage, to ƒupport the breech of cannon, a ƒemelle. In the carriage of a mortar for the proving of powder, the part on which the breech of the mortar reƒts is alƒo called a ƒemelle, and is made of the ƒame metal as the mortar, with which it is alƒo caƒt. This ƒemelle ought  to make an angle of 45 degrees with the  mortar, ƒo that if the ƒemelle be placed upon ground of a true level, the line, which is conceived to paƒs longitudinally through the middle of the bore of the  mortar, will make with it an angle of 45 degrees.