In the first attempt I found the results to vary with the weight of the pendulum of iron plate, and that it was necessary to obtain uniformity of size and surface; as it must be comprehended that the only resisting medium to the pendulous plate was atmospheric resistance, and a dissimilarity of size of surface would invariably give different results. Having a number of plates of the different thicknesses hereafter described, I continued increasing the charge from a definite quantity, until the projectile was driven with sufficient velocity to perforate the plate suspended. The gun selected for this purpose was of heavy material, weighing nearly seventeen pounds, it was three feet long, the metal of the barrel as thick at the muzzle as at the breech, and carried a spherical ball of sixteen to the pound, or one ounce, and which fitted tight with the thinnest patch procurable. The bore was perfectly cylindrical, and plain inside, being polished longitudinally to a high state of fineness. With a charge of twelve drachms of Curtis and Harvey’s diamond grain powder, the ball went through the half-inch plate, but went only a few yards further; denoting that the effort necessary had nearly exhausted its velocity and momentum.
The recoil of the gun was of the most severe description, and the shoulder had to be protected for many explosions previous to this high charge. The larger sized grain was insufficient, ten drachms effecting the greatest extent of power it seemed capable of, and it became quite apparent that the tube would not explode more powder, as indications convinced me: when any more was added, a portion came out unburnt.
The force necessary to effect this, by the above calculation, is 46,795 pounds.
The next plate was 7-16ths thick, and a charge of ten drachms punched the piece out clean; nine and a half drachms were equal to it, when the centre of the pendulum could be hit fairly, because there was then an equal resistance from the atmosphere, which cannot exist in cases where the edge of the disc receives the blow.
I got with ease a perforation in a 6-16ths plate, with a charge of either fine or coarse powder, not exceeding eight drachms; a charge of seven drachms of fine grain was unequal to the task; but seven drachms of the coarse showed evidently greater effects produced, though the perforation was not perfect. Six and a half drachms of No. 2 grain penetrated a plate of 5-16ths thick easily, while it took full six and three-quarters drachms of fine grain; five drachms of the larger perforated a quarter-inch plate, but it took full five and a half drachms of fine grain to effect the same; while a 3-16ths plate took three and three-quarters drachms of fine, or three and a quarter of No. 2 grain; and 1-8th plate was easily punched by a charge of two and a half drachms coarse or three drachms fine. I will place the relative results in a table, with the force effected by each:—
| Oz. | Drachms. | Punched a boiler plate | Equal in force to | |||||
|---|---|---|---|---|---|---|---|---|
| 1 | ball | 12 | of powder | Half-inch | thick | 46,875 | lbs. | |
| 1 | „ | 10 | „ | 7-16ths | „ | 41,015 | „ | |
| 1 | „ | 8 | „ | 6-16ths | „ | 35,155 | „ | |
| 1 | „ | 6 | 1⁄2 | „ | 5-16ths | „ | 29,295 | „ |
| 1 | „ | 5 | „ | 4-16ths | „ | 23,437 | „ | |
| 1 | „ | 3 | 1⁄4 | „ | 3-16ths | „ | 17,578 | „ |
| 1 | „ | 2 | „ | 2-16ths | „ | 11,718 | „ | |
Were I to adopt the established method of calculation, multiplying the weight of ball by the velocity, I should get an answer that would point to the utter impossibility of any such velocity being possible. And yet the result is, according to the rule of figures, correct; but in truth there are exceptions to many rules, for they are only correct when applied to known products.
That the velocity of these balls was much, very much, greater than 7,000 feet per second of time, there cannot be any doubt; it was nearly three times that. Yet I must not conceal the fact, that this punching is the more perfect, the higher the velocity; and it shows how the fibres of iron are separated from a want of vibration to equilibrise the cohesion. Mr. Colthurst found that duration of pressure lessened the ultimate force necessary to punch through metal, and thus it may be that extremely quick pressure may produce the same. Therefore I suspect it is not the most correct theory that calculates force to be accomplished at all times by extreme velocity; there will be found discrepancies in the rule, and one of them arises from no calculation ever having been made with extreme velocities: medium velocities may generally give such conclusions, but the very extreme in this case can never have been taken into consideration at all; as I have very little doubt—in fact, I am certain—that no person ever obtained such high velocity before. It must, and is a vast deal greater, incomprehensibly greater, than any velocity obtained by Hutton; and much more extensive than ever could be obtained, or, in fact, ever will, by any ordnance whatever. I wish much I could have experimented with a gun of greater length and bore, for with one in every way fitted for the purpose, I have no doubt of being able to perforate an inch thickness of plate.
Should any person possessing the opportunity and means, wish to try the experiment, I would advise them to get a barrel of 41⁄2 feet long, 8 bore, to carry a 2 oz. ball, and of a weight to allow of extending the explosion up to 30 drs. of powder; they would then obtain the extent of force I have suggested. There is a certain point to be strictly observed: see that the plate you use is perfectly sound; for if laminated, or composed of various plates not firmly welded and attached, the experiment would be imperfect, as there would be an uneven vibration created, and acting as the hammer does when held against the point of the nail while driving it in, clinches the point, so does the substance in the portions of plate prevent a perforation. An ounce ball, suspended against the back of the pendulum, by the jar or blow it receives and communicates, completely prevents the effect, and the ball is flattened, instead of perforating the object struck: so is it if you place a 1⁄4-inch plate against any support; it thus has the power of perfectly resisting the force of the ball, though fired with considerably more power than is requisite under other circumstances. The effect appears to be chiefly mechanical; the outer fibres are driven in upon those behind them with such quickness that they lose cohesion, or are condensed quicker than the waves of vibration travel, thus giving them no means of communicating the vibration. But when punched, the rapidity of their motion produces in the metal a sound of the most intense vivacity, which plays upon the ear for a considerable period, with rather a pleasant effect. Lead alone is capable of being used in this experiment; except, of course, the precious metals, which it would not be convenient to use. Even an adulteration of the slightest quantity of solder is sufficient to prevent the result which lead, pure, will invariably give. Lead projected against lead, if sufficiently thick, cannot perforate, but the lesser portion becomes flattened; a cast-iron ball fired against lead, with a certain velocity, is broken into pieces, affecting the lead comparatively little: showing beautifully the peculiarity of dense incompressible bodies to resist most effectually the greater the velocity with which they are struck. Water will, if struck very sharply with the flat of a sword, act against the blow in a way to splinter the blade into pieces. The greater the velocity with which a ball is fired into water, the less the depth of penetration; thus showing clearly the many excellent properties of dense incompressible bodies as projectiles, and proving the objection that lead is too soft for artillery to be without a foundation, and only entertained from a want of knowledge of its nature.
A point of great importance was exemplified during these experiments; and as the question has lately given rise to considerable discussion, it will be well that the facts should be stated.