OF AKTS AND SCIENCES : SEPTEMBER 11, 1866. 137 



have only to calculate the height to which a body will rise under the 

 given conditions, and for which we have a very simple formula, — 



— =h, in which v is the velocity of the shot, g the velocity acquired by 

 a body falling one second, and h the height sought ; 



and we then have our standard unit in pounds raised to a known 

 height. In the case before us we shall find the height to be 40,000 

 feet ; and if we multiply this by the weight of the ball or shot, 32 

 pounds, we have a product of 1,280,000, or 1,280,000 pounds raised 

 one foot high, as the equivalent of the force of a 82-pound shot 

 moving with a velocity of 1,600 feet a second. We can have no diffi- 

 culty in forming a conception of this amount of force, or power, and 

 applying it as a measure of the force of shot of other weights moving 

 with other velocities. We may, in fact, compare it with the force of a 

 steam engine, reducing both to a common measure in the horse power. 

 Thus, the horse power being 33,000 pounds one foot high in one 

 minute, we have i §§§aS~ =z ^ ; or the 32-pound shot, when it 

 leaves the mouth of its cannon, equal to the work of 39 horses during 

 one minute of time. 



Although we may, by this method ascertain, with great exactness, 

 the comparative forces and, consequently, value, of different shot, it 

 requires yet another step of computation to enable us to compare 

 together the value of different guns ; to ascertain their relative strength, 

 whether it be derived from the different materials of which they are 

 made, or the peculiar mode or form of their construction. Thus, sup- 

 pose it to be determined by accurate experiment that a certain ball 

 from a cast-iron Rodman gun has the same force that is possessed by a 

 ball from a wrought-iron coil gun. This fact can give no warrant to 

 the inference that the cast iron is equal in strength to wrought 

 iron, or that a certain method of casting produces a gun of equal value 

 and efficiency to guns made of forged coils. It may be, and must be 

 in this case, that a much greater weight of the inferior metal is 

 required to produce the strength supplied by a smaller amount of the 

 better metal. 



To supply the deficiency of the computation thus pointed out, and 

 extend the proposed standard so as to become a measure of the 

 strength of the gun as well as of the force of the shot, we shall 

 find to require but a moment's attention. Having already seen that 

 our standard 32-pound shot has a force of 1,280,000 pounds one 



VOL. VII. 18 



