﻿2 ON CONSTRUCTING CANNON OF GREAT CALIBER. 



I have said that no essential improvement has been made during the present age 

 in the size of cannon. It is true that they have been increased in caliber from 

 seven, up to eight and ten inches, and a few bomb-cannon have been made of twelve 

 inches. But in the use of these the charges are so diminished, to be brought within 

 the limits of safety, that the initial velocities, as inferred from their short ranges, are 

 not so great as those of the old forty-two pounders; while with mortars, those of 

 thirteen inches were used in the time of Vauban, and this remains, stereotyped, as 

 the limit at the present day. 



But to my examination. The properties or qualities of hardness and of tenacity 

 or strength are the qualities indispensable to all cannon, and the superiority of one 

 cannon over another is measured by the excess in Avhich it possesses them. Inertia * 

 is likewise required, in a certain amount, to prevent excessive recoil. Now these 

 properties of strength and hardness are possessed in an eminent degree by bronze 

 and cast-iron, and these bodies alone constitute, in practice, the materials for can- 

 non ; for although various attempts have been made to introduce steel and wrought- 

 iron, it is enough for my present purpose to say, that there are not twenty cannon in 

 use in the world, that are not made of bronze or cast-iron. For strength, bronze is 

 generally taken at 30,000 pounds to the square incli ; that is, that it will require 

 a weight of 30,000 pounds to tear asunder a bar of good gun-metal bronze of one 

 inch area. Following the mean of many experiments, cast-iron has generally been 

 taken at 20,000 pounds. But that I may be sure not to under-estimate the strength 

 of this material, and as it has been considerably improved by gun-makers within a 

 few years, I shall estimate it at 30,000 pounds, or as equal to bronze, although it 

 is not to be relied iipon as so constant in its strength as the latter material. For 

 hardness cast-iron greatly exceeds bronze. This renders it more suitable for very 

 large guns, and it has, in truth, become so exclusively the material for everything 

 above the size of field-pieces, that I shall deal with it alone in the examination pro- 

 posed in this paper. 



Before examining the force of gunpowder it may be well enough to say a word 

 upon the time of its explosion. Is the firing of gunpowder instantaneous 1 This 

 question has been discussed, and experiments made upon it, by Mr. Robins, Dr. 

 Hutton, Count Rumford, and many others, besides a special committee of the Royal 



* This word is used throughout this paper in its strictly technical sense, as the force, or power of re- 

 sisting all change of state, whether it be from rest to motion or from motion to rest ; and I use, without a 

 doubt of its accuracy, the square of the velocity by the mass, as the measure of this force. 



