﻿14 ON CONSTRUCTING CANNON OF GREAT CALIBER. 



estimating it in the height required by a fluid column to produce it. Suppose the 

 ball impelled by the pressure of a column of the same substance, which would be in 

 this case a column of fluid iron. Then (from the formula v = /^2(fh) we obtain 

 1600= ^ 25^^ _ 40,000 feet, for the height of the column. But this would pro- 

 duce a jet forming a continuous stream. Suppose this stream to be 14 inches in 

 diameter, and divided into a series of short cylinders, each of which, to equal a ball of 

 14 mches' diameter, must be 9i inches long. Now in giving 1,600 feet velocity to 

 this series of cylinders by a superincumbent column, the force will act upon each 

 cylmder only tlirough a space equal to its length. But in a cannon the powder 

 acts, though with a variable force, through the whole bore of the gun. The variation 

 of this force must depend, in every case, upon the quickness of the powder, arising 

 from its composition, fineness of grain, dryness, and the heat received from the gun 

 from previous firings ; and most essentially from the amount of the charge ; and we 

 do not know the exact law of the variation for any one case or condition. Our best 

 judgment, therefore, must be but an approximation to the truth, entirely empirical. 

 But if we cannot determme the truth with exactness, we can at least assign limits 

 ■within which it must be contained, and upon a comparison of the velocities j)roduced 

 by diff"erent lengths of bore, the effect upon the gun itself at different parts of its 

 length, and various other grounds of comparison, I think that we may take the 

 effect of the charge through the whole bore, supposing it to be 112 inches from 

 the ball to the muzzle, and the charge 80 pounds, as equal to the action of the 

 maximum force through a space of not less than one half, nor more than two thirds, 

 of its length. But that I may be sure to assign the maximum so great as to cover 

 all anomalous or accidental conditions, I will take it as sufficient to produce a ve- 

 locity of 1,600 feet a second, if acting constantly through one third the length of 

 the bore. This will give 37i inches, or exactly 4 times the length of the cylinder 

 which foi-ms the equivalent of the shot. Then (from the formula v = >/fs) the 40,000 

 feet above given for the height of the column, becomes ■^°;"" = 10,000 feet;* and 

 if we take the whole force of the powder as equal to its maximum force, acting 

 through two thirds the length of the bore, or 741 inches, our column will become 

 5,000 feet high. In aU cases of pro\idtng strength, we must take the force to be 

 resisted at its maximum. 



* This whole matter may be taken from the formula — =/, which gives the force 12,860 times gravi- 

 tation. But I have preferred to give the more circuitous course, from the pressure of a column, as fixing 

 a better conception of its enormous amount upon the mind. 



