the pioneers of progress by whose aid mechanical science and art have attained their present high state of perfection.

In conclusion, I can only allude in passing to one of the greatest wonders of our age, the electric telegraph; and although not, strictly speaking, within the province of mechanical art, it may safely be included among the achievements of the last half century of which we have been speaking. The phenomenon of the electric current, when practically employed in the transmission of intelligence, cannot be viewed in any other light than the crowning triumph of the age; and it must ever be a subject of congratulation to us that in our lifetime the spark of heaven-if I may use the expression—was commissioned to be our swift obedient minister in conveying thought and intelligence from man to man (irrespective of distance or of time) to the remotest parts of the earth.

244

LECTURE V.

THE STRENGTH OF IRON SHIPS.

[Read before the Polytechnic Institute in Liverpool, and at the opening Session of the Institute of Naval Architects in London.]

IT is nearly thirty years since the construction of iron ships for sea-going purposes was first entered upon; and I believe I was the first to show, in conjunction with Messrs. John and McGregor Laird of Birkenhead, the superior strength and security of iron vessels. After a long series of experiments in the construction of different forms and dimensions, it was found that the resisting powers of an iron vessel, when properly constructed, could be depended upon for navigating the open sea, and was much better calculated, as respects lightness, capacity for cargo, &c., than one composed of the best English oak. These considerations induced Messrs. John and McGregor Laird and myself to commence iron-ship building on a large scale, and thus to realise an expensive and laborious series of experiments on the value of these constructions. Hence I founded the works now occupied by Messrs. John Scott Russell and Co. at Milwall, London, in which establishment (carried on under my own direction from 1835 to 1848) upwards of one hundred vessels were built; and the applicability of iron to the purposes of naval architecture was then and has since been fully demonstrated in the construction of several splendid steamers, such as the Great

Britain, the Persia, and the Great Eastern, and also of sailing vessels of very large tonnage.

But although considerable improvements have been introduced in the design and construction of iron vessels during the last quarter of a century, the subject does not seem to have been theoretically or practically investigated to the extent to which the importance of the subject so justly entitles it. My own experiments related chiefly to the strength of the material itself, its distribution, and the value of different kinds of riveted joints as compared with the solid plate.

Nothing has, however, been done, so far as I know, in determining the strength of an iron ship en masse; and the object in view in the present paper is to inquire into the strength of iron vessels as they have been and are now constructed, and to ascertain if there exist any hidden weakness which may be remedied by a more judicious distribution of the material.

Of late years it has been found convenient to increase the length of steamers and sailing vessels to as much as eight or nine times their breadth of beam; and this for two reasons: first, to obtain an increase of speed by giving fine sharp lines to the bow and stern; and, second, to secure an increase of capacity for the same midship-section, by which the carrying powers of the ship are greatly augmented. Now, there is no serious objection to this increase of length, which may or may not have reached the maximum. But unfortunately it has hitherto been accomplished at a great sacrifice of the strength of the ship. Vessels floating on water and subjected to the swell of a rolling sea-to say nothing of their being stranded or beaten upon the rocks of a lee shore are governed by the same laws of transverse strain as simple hollow beams like the tubes of the Conway and Britannia T

Bridges. Assuming this to be true, and, indeed it scarcely requires demonstration, it follows that we cannot lengthen a ship with impunity without adding to her depth, or to the sectional area of the plates in the middle.

If we take a vessel of the ordinary construction, or what some years since was considered the best construction, 300 feet long, 41 feet 6 inches beam, and 26 feet 6 inches deep, we shall be able to show how inadequately she is

Fig. 44.

Fig. 45.

designed to resist the strains to which she would be subjected. Such a vessel would be sheathed with plates of an inch thick (working transversely from the keel to the deck on each side) for 13 feet on each side of her keel, inch plates for a distance of 10 feet 6 inches round each side of the bilge, and inch plates for the remainder to the upper deck; her keel would be 12 × 4 inches, with

plates on each side 2 feet wide by 1 inch thick, and in addition to this there would be a hollow stringer, similar to fig. 44, 18 × 12 inches, riveted to the angle-irons of the frames 2 feet 3 inches above the keel. At the top of the upper deck are two plates and angle-irons, forming an open box B, fig. 45, on each side 18 x 12 inches, which, together with two small stringers along the deck and two at the sides, as shown at a a and b b, fig. 46, would con

stitute the only power for resisting a tensile or compressive strain arising from transverse flexure.

On referring to the midship-section of a vessel of these dimensions, fig. 46, it will be seen that the upper deck is not constructed so as to give stability to the ship, and is totally out of proportion with the quantity of material in the other parts of the hull. If we take a vessel such