The work (W) done by a moving body is commonly expressed by the formula W = MV^2, in which M, or the mass of the body, is equal to w/2g; _i.e._, to the weight divided by twice the intensity of gravity. The work done by our cannon-ball then, would be (1 × (1100)^2)/(2 × 64⅓) = 9,404·14 foot-tons. If, further, we assume the resisting body to be of such a character as to bring the ball to rest in moving ¼ of an inch, then the final pressure would be 9,404·14 × 12 × 4 = 451,398·7 tons. But since, “in the case of a perfectly elastic body, or of a resistance proportional to the advance of the center of gravity of the impinging body from the point at which contact first takes place, the final pressure (provided the body struck is perfectly rigid) is double what would occur were the stoppage to occur at the end of a corresponding advance against a uniform resistance,” this result must be multiplied by two; and we get (451,398·7 × 2) 902,797 tons as the crushing pressure of the ball under these conditions. Note: The author’s thanks are due to his friends Pres. F. A. P. Barnard and Mr. J. J. Skinner for suggestions on the relation of impact to statical pressure. Footnote 13: The unit of impact being that given by a body weighing one pound and moving one foot a second, the impact of such a body falling from a hight of 772 feet—the velocity acquired being 222¼ feet per second (=√(2sg))—would be 1 × (222¼)^2 = 49,408 units, the equivalent in impact of one heat-unit. A cannon-ball weighing 1000 lbs. and moving 1100 feet a second would have an impact of (1100)^2 × 1000 = 1,210,000,000 units. Dividing this by 49,408, the quotient is 24489 heat units, the equivalent of the impact. The specific heat of iron being ·1138, this amount of heat would raise the temperature of one pound of iron 215.191° F. (24,489 × ·1138) or of 1000 pounds of iron 215° F. 24489 pounds of water heated one degree, is equal to 136½ pounds, or 17 gallons U. S., heated 180 degrees; _i.e._, from 32° to 212° F. Footnote 14: Assuming the density of the earth to be 5·5, its weight would be 6,500,000,000,000,000,000,000 tons, and its impact—by the formula given above—would be 1,025,000,000,000,000,000,000,000,000,000 foot-tons. Making the same supposition as in the case of our cannon-ball, the final pressure would be that here stated. Footnote 15: TYNDALL, J., Heat considered as a mode of Motion; Am. ed., p. 57, New York, 1863. Footnote 16: RANKINE (The Steam-engine and other prime Movers, London, 1866,) gives the efficiency of Steam-engines as from 1-15th to 1-20th of the heat of the fuel. ARMSTRONG, Sir WM., places this efficiency at 1-10th as the maximum. In practice, the average result is only 1-30th. Rep. Brit. Assoc., 1863, p. liv.