Volltext Seite (XML)
24 THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. [January 1,1S6S. authorities; and at the end of 1860 the Government determined to submit the whole matter to the investigation of a mixed Special Com mittee which was appointed in January, 1861. This Committee consisted of six members—Sir John Hay (Chairman) representing the Navy, Major Jervois the Royal Engineers, and Colonel Henderson the Royal Artillery; and to these were added three members whose qualifications were of a more technical character, viz., the eminent metallurgist Dr. Percy, F.R.S., and two of our own pro fession—Dr. Fairbairn, M. Inst. C.E., and Dr. Pole, M. Inst. C.E., whose names are too well known in this room to render necessary any remark on their qualifications for the investigation in question. The first step taken by the Committee was to collect, by oral evi dence, the opinions of a great number of engineers and others practically acquainted with the manufacture and use of ironwork; and the great diversity of the views thus gathered showed the obscurity in which this novel application of material was involved. The Committee then commenced their experiments, beginning with trials of simple iron plates of various sizes and thickness, and manu factured in different ways, and they arrived early at certain general deductions on points which had previously been uncertain ; for example, they reported that out of many varieties of material tried the best for resisting shot was wrought iron;—that this should be of the softest and toughest possible quality, any hardness or steely character being very prejudicial;—that, catena paribus, the resisting power, up to a certain limit, varied nearly as the square of the thickness;—that cor rugations, bosses, or irregularities of surface were disadvantageous, plain surfaces being best ;—and the plates should be as large, and with as few joins as possible. The Committee further proceeded to examine, and test by actual trial, various constructions of iron defences, both for ships and for land fortifications, the former however receiving their principal attention. This work occupied them for more than three years, during which time a great number of experimental targets were made on a great variety of principles, and were thoroughly tested with artillery at Shoeburyness. These trials, on so thoroughly a practical a scale, led to experience of great value, not only as to the strength and capability of the material generally to resist shot from certain guns, but also as to the modes of fastening, the effect of various kinds of backing, and the general prin ciples which should guide iron defensive construction. But perhaps the most valuable result of the Committee’s labours, or at any rate, the result most interesting in an engineering point of view, was the great improvement effected through their means in the manufacture of iron in large masses. The Committee from the first adopted the principle of making all their trials and results open to the inspection of all parties legitimately interested in the subject. The makers of iron plates were especially invited to witness the experiments, and to study the results produced, being afforded at the same time the benefit of all information in the Committee’s possession which could throw light on the subject. Independently of the public satisfaction given by this open system, which, I believe, has been subsequently followed in other ordnance experiments, these opportunities were of the greatest use to the iron-makers, for by no other means could they have obtained such complete insight into the nature of the problems to be solved, and the conditions necessary for their solution. The iron-makers availed themselves willingly of these opportu nities, and the result was strikingly marked in the improvement effected. When the Committee began their labours, the manufacture of armour plates had only been attempted by one or two makers, and even in their hands was little more than tentative; the quality was very uncertain, and no great reliance could be placed on the resisting power of any plate above three inches thick. But during three years’ experience, many excellent makers had come into the field; the gene ral average of quality became greatly improved and much more certain, and plates 5 in. and 54 in. thick, could be produced with their full resisting power. In the middle of 1864, the Iron Plato Committee was dissolved, and their functions re-transferred to the military and naval authorities. I cannot but think this step to have been injudicious; for although doubtless the Government of the day thought that the question had arrived at such a stage of development as no longer to require special technical treatment, yet they omitted, 1 think, the important conside ration that the comparative question between guns and iron defences was, then at least, in a high degree progressive, and that, if improve ment was to go on, the technical treatment of the subject must still be necessary; and experience has shown this to be true. The Committee have left behind them full records of everything they did, containing, in four large volumes of Reports and Proceedings a mass of information of great interest and value, and forming a com pendium of almost all that was then known on the subject. It is to be regretted that these volumes are not published. I find it on record in our correspondence, that one of the members of the Committee, Dr. Pole, obtained the special permission of the Government to give to this Institution a summary of the contents of these volumes, and I take the opportunity of reminding that gentleman that his under taking to that effect has not yet been fulfilled. The attention of the Iron Plate Company was principally directed to plates to be applied to ships; recent circumstances have led to the temporary re-appointment of a Government committee on iron plates, similarly constituted to the last, and comprising the same Civil mem bers ; and it is to be hoped that their labours may not be prematurely checked, but that they may be allowed to pursue their investigations on the application of iron plates to land forts, so far as to afford safe data to our Royal Engineers, and to prevent the serious evils which might result from the large application of iron to our Fortifications on any system which had not been fully investigated, and thoroughly tested. I also venture to submit that the hands of the Committee would be strengthened by the addition of a naval architect, expe rienced in the building of armour-clad ships. During the last few years the size and thickness of iron plates have greatly increased. The plates of the “ Warrior,” constructed in 1861, were 4 J inches thick; those of the “ Bellerophon ” are 6 inches thick; while the “ Hercules” has plates of 8 inches, and 9 inches thick at the water-line. In France, the plates used for the navy have been in creased to the thickness of 15 centimetres, or 6 inches, and the “ Ma rengo” and the “Ocean” will have at the water-line plates of a thick ness of 20 centimetres, or nearly 8 inches. A wrought-iron plate, 14 feet long and 6 feet 6 inches wide, and 15 inches thick, has been pre pared for trial at Shoeburyness. Some of the principal manufacturers (Messrs. J. Brown and Co., C. Cammell and Co., and the Millwall Iron Company) now offer to roll plates about 20 feet long, 6 feet wide, and 15 inches thick; but it may be doubted whether plates of such thickness and size can at present be so perfectly manufactured as to give their full proportionate resistance: the production of thoroughly sound and t.i ill rm plates of large size, 10 inchesthick, may, however, I believe, be regarded as an accomplished fact. Concurrently with the production of iron plates for purposes of pro tection there has been a great increase in the size and destructive power of ordnance. Some of the earliest guns known were compound, or built guns. In the Royal Military Repository at Woolwich is one of Henry VI. (1422 to 1461), composed of two circles of longitudinal iron bars, imperfectly welded, and close hooped with iron rings, with a bronze powder-chamber inserted in the breech :—indeed for guns of any size a built gun was a necessity’ at a period when the manipulation of large masses was a rare and difficult operation. The great bombards at Edinburgh and Ghent, closely similar to one another in design, and those of English manufacture at Mont St. Michel, arc notable instances of large built guns, which, however, could probably not have stood one full charge of powder of modern strength. The development of art in the fifteenth century, which revived large bronze castings for ornamental purposes, led, perhaps, to the use of bronze for guns. In the year 1543, in the reign of Henry VIII., Ralph Hogge is stated to have cast, at Buckstead, in Sussex, the first cast-iron guns used in England, but it was not until a much later period that cast-iron guns were largely used in England, or at all on the Continent. For many years before the Crimean war, brass and iron guns had been made with very little change of form; but when public opinion was drawn to the application of mechanical im provements to the production of guns of great size and strength, clever designs were brought forward by so many that I will not attempt here to give even a list, much less to assign to each its due proportion of merit; but the large wrought-iron “Horsfall gun” of the Mersey Company and the monster mortar of Mr. Mallet may bo cited as two remarkable examples. The “Horsfall” was a smooth-bore gun, in one piece, weighing 21 j tons, and having a calibre of 13 inches; and it is now mounted at Tilbury Fort. Mr. Mallet’s mortars were compound, weighing 41 tons, with a calibre of 36 inches, from one of which, with a charge of 70 lbs. of powder, a shell weighing 2,395 lbs. was thrown 2,759 yards, burying itself 8 yards in the ground on its fall. The limited practice with this mortar was interrupted by the fracture of a tie-bolt; but it is greatly’ to be regretted that no further experiments have been made with it, or with the second piece, which has never been fired. The remembrance of tire discussions held in this room will recall the names of Sir W. Armstrong, M. Inst. C.E., Mr. Whitworth, M. Inst C.E., Mr. R. Mallet, M. Inst. C.E., Mr. Longridge, M. Inst. C.E., Captain Blakely, R.A., and others, as having either investigated the scientific principles which should direct the construction of great guns, or applied those principles to various forms of construction. You will all remember that in 1860 breech-loading rifled guns were the order of the day, and that neither brass nor cast-iron, as materials, were con sidered to fulfil the necessary conditions. The designs which had earned the greatest consideration, both from the Government and the public, had been produced by those two distinguished members of our body, Sir William Armstrong and Mr. Whitworth ; and as far as the construction of the guns was then concerned, the leading points of dif ference were, that while the Armstrong gun was built up of several rings or tubes of coiled wrought iron shrunk over one another, and over a steel lining, with small grooves to take a soft coated projectile, the Whitworth gun was built up of tubes of mild steel, forced with a taper over one another, and over a steel lining, the bore being poly gonal, with a hard mechanically-fitting projectile.