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In the production of this work I have found it convenient to divide it into parts; and as each part may be taken as a separate treatise, a brief analysis of each particular subject, as it follows in consecutive order, may be of service to the reader.

I. The Introductory Notice contains a brief history of the rise and progress of Naval Construction since the time when Iron was first employed for that purpose.

This embraces almost entirely my own personal experience; and, as one of the pioneers and first experimentalists who proved the value of Iron applied to Shipbuilding, I am probably competent to write on the subject with some authority.

II. The whole of this division--comprised in Chapters II., III., IV., and V.-treats of the Law of Strains, and the properties of the material—how it should be disposed in the construction of vessels in order to meet the force of wind and sea; and how the material in the different parts should be proportioned and distributed so as to equalize their powers of resistance to the alternation of strains which the different parts undergo when the ship is afloat. As a guide to Iron Ship Building, I have considered it necessary to give an analysis of he experiments on the strength and other properties of plates, angle-iron, &c. The results of this analysis are chiefly taken from my own experiments,* and from those of the late Professor

* See · Philosophical Transactions,' Part II. (1850), page 677.

Hodgkinson, to whom science is indebted for many new and important discoveries.

These experiments embrace almost every known mechanical property of Iron;

and the knowledge thus obtained has furnished data for the construction of ships, and other structures employed in the useful and industrial arts. The ultimate powers of resistance of Iron to tension, compression, torsion, &c. are taken from the same source; and to these reference may be made for guidance in the selection and distribution of the material when applied to the purposes of Shipbuilding

Another important question to which I have alluded is the Jointing of Iron Plates, and the Form of Joints required in Shipbuilding. Here I have endeavoured to show what kind of riveted joint is requisite in order to attain the maximum powers of resistance in the longitudinal and transverse joints ; and, moreover, to impress on the minds of Naval Architects the necessity of careful attention to experimental facts, which are of much greater value in the art of Shipbuilding than most persons imagine. A single defective joint may endanger the safety of a ship; how much greater, therefore, must be the danger if the principle throughout be unsound, and the whole of the joints of an imperfect character ! A sound system of riveting is a most important desideratum in shipbuilding, and on no account should it be left to the judgment of ignorant and irresponsible persons.

To the frames and ribs of ships I have directed the same careful attention; and although it may be difficult to estimate the strains to which they are subject, it is nevertheless necessary, in order to give rigidity and strength to the hull, that strong ribs should be provided to retain the vessel in shape, and to receive the outer sheathing or plating. On these points I have,

* Mr. Kirkaldy published, a few years since, a detailed series of experiments on Iron and Steel, in which will be found much useful information on the strengths and other properties of these materials.

however, to refer the reader to the eighth division, where he will find the question more fully investigated.

In this division I have introduced a series of experimental researches on Cellular Constructions, first exhibited in the construction of the Britannia and Conway Tubular Bridges, and more recently in H.M.S. Bellerophon. These researches will, I trust, be found of great value in Shipbuilding. For many years I have earnestly called public attention to this new system, believing it to be the strongest and most economical form of construction for seagoing vessels. It is the only true form for resisting the force of compression : and the form of the hull and upper deck gives double security, not only from the superior strength of the parts, but from the additional security of a double bottom, rendering a vessel so constructed what is technically called an unsinkable ship.

III. This division-Chapter VI.-treats of the comparative merits of wood and iron-built ships; and I have given examples, deduced from experiment, showing the superior advantages of the latter construction. From the facts recorded, it is evident that the superior strength of iron, as compared with the very best description of oak or teak, is sufficient to establish its claims as the best kind of material for shipbuilding. But this is not all; for when we consider the way in which the parts are united, and the form in which the junction of the plates is effected by rivets, the whole of the sheathing becomes almost homogeneous, and the strength nearly equal to that of the solid plate. On this principle a carefully-riveted iron ship may be looked upon as jointless, and hence its value as a strong and durable structure. In short, an iron ship, with its iron sheathing riveted to the frames, may be considered as uniform in its powers of resistance, and superior to anything yet accomplished by any other material with which we are acquainted.

Wood sheathing, when attached to iron ribs, is, to say the

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