The force exerted by the caloric to dissolve a quantity of powder, is regarded as equal to that possessed by the fluid which results from that dissolution, and is named the _force of dissolution_ of powder by fire: and the _surface of least resistance_ is that (as of the ball,) which yields to the action of the fluid. The gunpowder subjected to experiment by this author, was of seven different qualities, varying from 1000, the density of water, down to 946, the density of powder used by sportsmen. It was found by theory, and confirmed by experiment, that the real velocity with which the elastic fluid, considered under the volume of the powder, and penetrated by a degree of heat capable of quadrupling the volume, would expand, when it had only the resistance of the atmosphere to surmount, is 2546.49 feet, that is, about 2734.4 feet English. Comparing the several forces which were calculated for the same quantity of powder, in three different circumstances: 1. When the fluid has only to surmount the atmospheric pressure, it has a force of dissolution which is proper to it, and which in a charge of 8 lbs. of powder (the specific gravity 944.72, for a 24 pounder,) acts upon the surface of the least resistance with an energy equivalent to 9747.8074 lbs. 2. The fluid retarded in its expansion by a surface of least resistance, whose tenacity (occasioned by the compactness and pressure of the wadding, &c.) is t = 31, acquires by its elasticity of force = 52839.1463 lbs. at the instant when that surface yields to its action. 3. If the tenacity t = 298 lbs., the force of the fluid at the moment when the resisting surface yields to it, will be equivalent to 417371.4275 lbs. If each of these forces be divided by the surface of least resistance, the quotient will indicate the equation of each filament, namely, 1st. That of the force of dissolution = 173.63 grains; 2d. when t = 31 lbs. that of elasticity = 923.26 grains; 3d. when t = 298 lbs. force elastic equal to 7433.99 grains. Dividing again these latter values by the length of the charges, we shall have for the mean force of each elementary fluid particle, 1. Force of dissolution, 0.14205 grains. 2. When t = 31 lbs. the force elastic = 0.75540 grains. 3. When t = 298 lbs. the force elastic = 6.08174 grains. It appears, however, that equal charges of powder of the same quality employed in the same piece, produce very different velocities; the more considerable being the resistance to the expansion of the fluid, the less the velocity becomes. Thus, it is found, when t = 31 lbs. the velocity of the ball when expelled at the mouth of the piece, is 1563.6 feet: when t = 298 lbs. v = 1350.9 feet. The following table will exhibit in one view the velocities with which a 24 lb. ball issues from the mouth of a gun, when propelled with the several charges expressed in the first column. 1st. According to the theory developed in the volume, from which we have made these extracts.