﻿ON CO'STRUCTING CANNON OF GREAT CALIBER. 7 



those charges.* If then we increase, iu the example under consideration, from a 

 charge of 8J- pounds to one of 32 pounds, the stress upon the gun, being as the 

 square roots of these numbers, is raised from 2.88 to 5.65, or from 1 to 1.96. Having 

 already increased the stress upon the gun, by the shot, from 1 to 1.71, if we multiply 

 these together, we have a total increase of from 1 to 3.35. That is to say, if, 

 under the conditions here stated, we load a gun of 2 inches' caliber with 1 shot and 

 i of a pound of powder, and a gun of 10 inches' caliber with 1 shot and 32 pounds 

 of powder, the stress upon each square inch of the bores will be 3.35 times greater 

 with the large than with the small gun ; when at the same time, if the walls of both 

 have a thickness proportional to the diameters of the calibers in each, the large gun 

 will be incapable of sustaining a greater pressui-e per inch than the small one. 

 Even with a charge of 12 pounds of powder, the stress upon the large gun must 

 be more than double that upon the small gun when charged with one third the weight 

 of its ball. 



The preceding examination does not, I think, present the dijfficulties to be over- 

 come in increasing the size of cannon as greater than they really are, and although 

 the results that I have arrived at are from extreme cases, and may be said to be 

 mere deductions, yet they are deductions legitimately drawn from the most reliable 

 experiments that have been made. How then can the necessary strength be ob- 

 tauied I Will it be answered, by an increased thickness "? It is not necessary to 

 examine the obvious objections of the great increase of size and weight that this 

 implies, because no increase that can be given to the thickness wUl increase the 

 strength to a sufficient degree to resist the force requii-ed. To prove this, I must 

 ask attention to a further and somewhat elaborate examination. 



About thirty years ago, Mr. Peter Barlow, of "Woolwich, published a paper in the 

 Transactions of the Society of Ci\-il Engineers, on the hydrostatic press, in which he 

 showed that hollow cylinders of the same materials do not increase in strength in 



* Hutton gives the velocities of the balls as the square roofs of the charges, and the e.'speriments of 

 Captain Mordecai, although giving the velocities of the larger charges somewhat below this ratio, do not 

 wholly contradict it. This assigns to the charges an effect, or power, that is, pressure multiplied by the 

 space, which is directly as the charge. Now this result cannot be produced, with the larger charges, wholly 

 by the continuance of the pressure during the last part of the passage of the ball through the bore, 

 although a large portion of it may be derived from that source ; but there must be a great increase of the 

 tension in the fluid during the first part of the ball's motion, and an equal increase of the strain upon the 

 gun. It appears to me that the hypothesis stated above, and the ratio of force there assigned to different 

 charges, are in perfect accordance with these and other experiments. 



