But there is another cause to which I wish now to direct attention, viz., the jamming of the Lancaster shell, which takes place in the increasing spiral of the oval gun at the very point where the projectile acquires a proportional increase of velocity. The effect of this may be illustrated by running a locomotive at its maximum of speed over an increasing curve in the railroad, with the certainty of landing it in an adjoining ditch. The principle which determines the result is quite immutable: viz., that matter in rapid motion cannot be materially affected by any force inferior to the primary force: the tendency of the body being to go straight forward; whereas a slow train goes round a curve with the greatest ease. Two motions can easily be given to matter in a lower velocity; but not so easily when the velocity is much increased. Hence I fear that the inventor of the Lancaster gun must have had a misconception of the true laws of motion; for by increasing the degree of spiral at the muzzle, instead of at the breech of the gun, he has rendered nearly useless what would otherwise have proved a most formidable engine of war.
From these observations it may, I think, fairly be doubted whether the bursting of cannon is owing entirely to the inferior quality of the cast iron used in their formation; though there can, I think, be no doubt that English cast iron is not only much inferior to what it formerly was, but that it is also inferior to that which is now manufactured in Russia. Why it is so will be subsequently explained.
These defects in cast iron have naturally led to many attempts to substitute for it a more durable metal; and in most cases the metal selected has been wrought iron. Wrought iron has been used, not only in solid cannon, but in the original “hoop and stave:” “staves outside,” and “staves inside,” as in Mr. Mallet’s monster mortar. Forms of gun as numerous as can be conceived have been constructed, only to prove themselves in every case most complete failures. Our friends at the Mersey Works, Liverpool, will, no doubt, demur to this assertion; as “all creations of the mind appear most perfect to the father of the thought.”
Great credit is, however, due to the enterprise and energy displayed by the inventors, forgers, and finishers of this great gun; which has been the wonder of many minds in this age of wonders: and it is a highly important invention, as showing what we, as a people, are capable of producing by our mechanical and engineering skill. But here, in my estimation, the wonder ceases; for so sure as there is any truth in the Scotch proverb, “A silk purse cannot be made out of a sow’s lug,” so surely is it true that no man, however great his genius and working powers, can make a good cannon of wrought iron. When the hardness and ductility of silver can be imparted to and held by lead, then will it be possible to make wrought iron accomplish all the purposes required of a good cannon.
In vain may Mr. Horsfall urge that his gun has never been burst. Why? Simply because it has not yet been subjected to the same amount of pressure on the square inch; neither has it been tested at the same elevation as some other 10-inch guns, which, in proportion to their size have stood a more severe test. It is a fact, which may be clearly demonstrated, that if a 10-inch gun of 95 cwt. be fired at an elevation of 40° with 17 lbs. of gunpowder, then a gun of more than six times that weight would not be overloaded if its due proportion of powder were about 100 lbs. Has this gun been fired with one half of this? Until it has been satisfactorily proved to this extent, we feel sure that the authorities are justified in not considering Mr. Horsfall’s a successful achievement.
Whatever may be Mr. Horsfall’s impression with regard to the advantages of wrought iron for making cannon, I am satisfied, after a long and careful study of the results of all its varieties, from the most ordinary to the most perfect combination that has been manufactured—either for tenacity, tenuity, or resistance of lateral pressures—that it cannot answer in large guns.
This I think any one will admit, after considering the two following facts; which apply equally to all varieties and mixtures of wrought iron.
1. The strength of iron is at its maximum in the smallest mechanical structures.
2. The quality of the metal is improved as it is subjected to greater pressure and condensation.
The extent to which this improvement may be carried has never yet been ascertained; every fresh manipulation improves its quality. The tenacity of wrought iron is best displayed in a wire, drawn out until it is not thicker than a human hair. Large masses of wrought iron are weak and spongy in geometrical progression with the mass, and the crystalline or molecular form increases with the mass. If large forgings are carefully examined, crystals will be found whose facets would produce inches of surface; as was clearly demonstrated by the bursting of a 10-inch gun at Woolwich: made, if we mistake not, by Mr. Nasmyth.