myself of this opportunity to direct attention to the circumstance, that although I have made the attempt to improve the quality of our irons by experimental research, I find that these experiments, although perfect and correct as far as they go, are nevertheless incomplete, and there is still wanting a continuation of the series on different irons, commencing with No. 1 and ending with No. 3 or No. 4 qualities. There is also wanting a much more extended series of investigations upon mixtures, rate of cooling, and all those combinations which in practice are known to improve the quality of the metal produced. This information would be of great value to the practical Founder and Engineer; and I trust that the Government will either establish a series of experiments on this subject, or afford the means of conducting them on a scale calculated to ensure correct and satisfactory results.

In conclusion, I have to remark that the gun marked E is an improvement upon the other four. It stood the same number of rounds as A, but with this difference, that it indicated a closer and stronger-grained metal, attributable, as I conceive, to the remelting of the iron in the first place, and subsequently by raising the head to increase the density of the mass by pressure.

To this latter circumstance, however, I attach less importance, as I have invariably found a closer and more compact combination of the materials of crystallisation by the remelting process.

I have the honour to be,

Sir,

Your faithful and obedient Servant,

To the President of the Select Committee on Ordnance.

WM. FAIRBAIRN.

299

APPENDIX II.

SIR WILLIAM ARMSTRONG, in a letter to the Times,' June 26, 1865, seems to have abandoned all hopes of making guns of sufficient calibre and power to contend with targets similar to that representing the 'Hercules,' in which the Admiralty achieved so decided a success over the 300-pounder gun. Sir William states, in his letter to the editor, that the account given in the 'Times' of this experiment is isolated, namely, 'That although the victory remained conspicuously with the target, yet it is beyond a doubt that the very reverse of this result would have happened had the 600-pounder been tried against it instead of the 300-pounder.' 'I am very sorry,' says Sir William, very candidly, 'I cannot concur in this opinion. Powerful as the 600-pounder has proved itself to be, I confess I have great doubts of its obtaining the mastery over the "Hercules" target, unless the enormous charges already used with that gun be still further increased. Notwithstanding its past performances, it may not improperly be beaten by a target which, although only twice as heavy, is four times as strong as the "Warrior" target. I say four times as strong, because with the same quantity of material the resistance of a plate to the impact of a shot increases as the square of the thickness, so that the 9-inch armour of the "Hercules" target is, if the iron be equally good, four times as strong as the 4-inch armour of the "Warrior." The backing also, from its vastly greater thickness, and the enormous quantity of iron framing combined with it, may be roughly estimated as stronger in the same proportion. Against this massive target three 12-ton shunt guns were fired, at a distance of only 200 yards, with charges varying from 45 lb. to 60 lb. of powder. In the instance of the 60-lb. charge, a steel shot of 300-lb. weight and 10-inch diameter, struck the centre of the 9-inch armour-plate with a velocity of 1,450 feet per second. This is equivalent to an initial velocity of rather more than 1,500 feet per second, which is the full velocity due to the charge of 60 lb., and yet the blow was barely sufficient to break through the armour, and did not materially injure the backing. At short range the penetrating power of a steel shot is almost exclusively determined by the magnitude of the charge. The mode of rifling makes no difference, and the size of

the bore has but little influence, seeing that the greater velocity obtained with a large bore compensates for the diminished resistance opposed to the shot from a small bore. To increase the effect we have nothing to look to but increase of charge. Now, the service charge of the 600-pounder fired with a rifled shot is 70 lb., and I cannot anticipate that the penetration effected by this charge will be more than proportionate to that obtained with the 60-lb. charge fired from the 300-pounder gun. Judging from the effect produced, I incline to think that about double the power of 60 lb. of powder will be necessary to force a clear passage through the entire target at a distance of 1,000 yards, and if so, a gun that will bear a charge of 120 lb. of powder will be required to produce that effect. A smaller charge may suffice for the lodgment of a shell, but in any case I believe that more powder will be needed than has yet been used with our largest gun. It is much to be regretted that the delusive practice of designating the power of a gun by the weight of its shot, without reference to the charge of powder, should be continued. The force exerted obviously depends upon the quantity of powder effectively consumed, and it is well known that penetration is not materially assisted by the mere increase of the weight of the projectile. In rifled guns the shot may be lengthened or shortened, so as to be of any weight, and, consequently, according to the usual mode of designation, the gun may be called whatever the maker pleases. I have fired projectiles of 1,000 lb. from the 7-inch service breech-loader; but I should convey an absurdly-exaggerated idea of the power of that gun if I were to call it a 1,000-pounder. In your article upon the experiments against the "Hercules" target it is stated that 600-pounders are being made in scores upon the continent, and that from thirty to forty such guns have already been manufactured in this country for the Russian Government. This intelligence, I may observe, is strangely at variance with the statements of wellinformed Russian officers who have recently visited this country officially on questions affecting artillery. But at any rate it would be highly desirable to have definite particulars of these so-called 600-pounders. The proof-charge applicable to guns of the class of the only 600pounder which has been tried in England, would, according to the present Government regulations, be 874 lb.; but no rifled guns, either for Russia or elsewhere, has been proved at Woolwich with more than 60 lb. of powder. These, therefore, are not such guns as our military authorities would rank as 600-pounders. Moreover, the number of rifled guns which have been proved at Woolwich, even with so high a charge as 60 lb., is not more than six, if indeed it be so many. Scores of 600-pounders ought to make some noise in the world, and I pause

to be satisfied of their existence before proceeding to ask after their performances.'

These remarks on the power of guns from such an authority as Sir William Armstrong show that, notwithstanding his great experience and the skill he has brought to bear on construction for the last five years, he is still in doubt as to the possibility of constructing a gun of sufficient strength to penetrate the 'Hercules' target. We have already noticed what we consider to be necessary in the construction of large guns; but the difficulty which presents itself is how to burn the requisite quantity of powder, and how to construct a gun strong enough to resist the charge. It has been demonstrated that if we increase the size of the gun we must also increase the charge of powder. The force, it will be observed, is not directly as the diameters, but as the squares, in order to give the desired and proportionate powers of penetration. It therefore follows that Sir William Armstrong is correct in his admission of the doubts and difficulties which surround this important question of obtaining any great increase in the power and strength of artillery.

On this question Mr. W. Cawthorne Unwin, B. Sc., has favoured us with a letter, which appeared in 'The Engineer,' vol. xx. p. 22, in which he remarks, with reference to Sir William Armstrong's conclusions, that

'To the statement that the diameter of the shot in the case of steel projectiles has little influence on the penetration because "the greater velocity obtained with a large bore compensates for the diminished resistance in the plates opposed to the shot from a small bore," I am unable to assent. This implies that the work communicated to the shot per pound of powder increases in the same ratio as the bore, the resistance of the plates increasing in that ratio. On the contrary, I find that such data as are accessible prove the velocity communicated to be nearly constant for charges proportional to the weight of the shot in similar guns. Thus, to take a single instance from data given in Sir William's letter, comparing the old 68-pounder and the 300-pounder, I find that the work communicated to the shot is only 9 per cent. greater in the latter case than in the former; whereas the diameter of the shot, and consequently the resistance of the plates, is 33 per cent. greater. Hence since in practice the calibre of guns necessary to perforate armour-plates increases as the thickness of the plates augments, the charges required will increase in a higher ratio than that of the squares of the thickness of the plates; and, therefore, the point at which the targets will be found to be superior to the guns-the defence to beat the attack-will, by so much, be the sooner reached.

'For the sake of brevity, I shall simply refer here to the principles enunciated in two previous letters in vol. xiv. of the "Engineer,” pp. 247, 248, taking the formulæ there given as proved.

'Let w be the weight, v the velocity, and r the semi-diameter of a shot striking an armour-plate of the thickness d; then we have foundw v2 T r d2.

. (1)

where T is a constant. But, with similar guns, having similar projectiles and charges having a constant ratio to the weight of the shot, the velocity is nearly constant. Hence

That is, for similar guns as above, the maximum thickness of armour-plate perforated will vary as the cube roots of the weights of the shot; or, in other words (on the present system), the denomination of the gun. And the weight of shot (the charge being in a constant proportion) required to penetrate different thicknesses of plate will be (not as the square, but as) the cubes of those thicknesses.

'To whatever extent it is ultimately found that the vis viva per Ib. of powder increases with the bore, these formula will need to be corrected.

'If, instead of deducing the formula theoretically, we merely assume

w = Ddx

and deduce the value of x from a series of experimental results, we have

x=

log w-log wi
log d-log d

And applying this to the Shoeburyness results on cast-iron shot, and averaging the values obtained, we get x 2.47. So that

'I have calculated the value of the constants C and D for two

cases.