VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 140 



it was necessary to employ an enormous weight to confine it; for, though by di- 

 minishing the size of the opening, the weight would be lessened in the same pro- 

 portion, yet it was necessary to make this opening of a certain size, otherwise the 

 experiments would not have been satisfactory; and it was necessary to make the 

 support or base on which the barrel was placed very massy and solid, to prevent the 

 errors which would unavoidably have arisen from its want of solidity, or from its 

 elasticity. In these experiments, first a solid block of very hard stone, 4 feet 4 

 inches square, was placed on a bed of solid masonry, which descended 6 feet below 

 the surface of the earth. On this block of stone, which served as a base to the 

 whole machinery, was placed the barrel of hammered iron, on its support of cast 

 brass, or rather of gun-metal ; which support was again placed on a circular plate of 

 hammered iron, 8 inches in diameter, and ■£• of an inch thick, which last rested 

 on the block of stone. The opening of the bore of the barrel, which was placed 

 in a vertical position, and which was just 4- of an inch in diameter, was closed by a 

 solid hemisphere of hardened steel, whose diameter was 1.1 6 inch; and on this 

 hemisphere rested a weight, employed for confining the elastic fluid generated from 

 the powder in its combustion. This weight, which in some of the most interest- 

 ing experiments was a cannon of metal, a heavy 24-pounder, placed vertically on 

 its cascabel, being fixed to the timbers which formed a kind of carriage for it, was 

 moveable up and down; the ends of these timbers being moveable in grooves cut 

 in the vertical timbers, which being fixed below in holes made to receive them in 

 the block of stone, and above by a cross piece, were supported by braces and iron 

 clamps made fast to the thick walls of the building of the arsenal. This weight was 

 occasionally raised and lowered in the course of the experiments, in placing and re- 

 moving the barrel, by means of a very strong lever. The barrel was 2.78 inches 

 long, and 2.82 inches in diameter, at its lower extremity, where it rested on its 

 supporter, but something less above, being somewhat diminished, and rounded off 

 at its upper extremity. Its bore, of -^ of an inch in diameter, was 2.13 inches 

 long, and it ended in a very narrow opening below, not more than 0.07 of an inch 

 in diameter, and 1.715 inch long, forming the vent, if I may be permitted to 

 apply that name to a passage which is not open at both ends, by which the fire was 

 communicated to the charge. From the centre of the bottom of the barrel was a 

 projection of about 0.45 of an inch in diameter, and 1.3 inch long, forming the 

 vent tube. There was an iron ball, which being heated red-hot, and applied to 

 the vent tube by means of a hole made in it for that purpose, fire was communica- 

 ted through the solid substance of the vent tube to the contained powder, and 

 thence to the charge. 



The powder used in these experiments was of the best quality, being that kind 



called poudre de chasse by the French, and very fine grained. Care was taken to 



dry it very thoroughly, and the air of the room in which it was weighed out for use 



was very dry*. The weights employed for weighing the powder were German 



* Why all this care in dryness, if moisture was expected to increase its force ? 



