the sooner we shall be prepared to repel aggression from whatever quarter we may be assailed. It is well known that every change in our habits and conditions of life is sure to be resisted "tooth and nail" by all those who wish to maintain the dignified position of " as you were." This standing at ease is out of fashion now-a-days, and we must either move on, or be left a stranded wreck in the tide of progress. I am most desirous to impress these facts upon you, and upon the authorities of the Admiralty, where so much must be done in initiating a new system of naval tactics before we can be prepared for the exigencies of a maritime war, possibly not far distant, and which, whenever it arrives, will have to be maintained by the agency of steam. Steam rams may or may not come into use, but it is certain that increased steam power and increased speed in the Navy may give to the nation that ascendency in maritime affairs which more than anything else is its greatest security considered in its relations with other countries. I am, therefore, most anxious to see our own Navy foremost in power and perfect in discipline, so that England may long continue in pride and glory the mistress of the seas.

IRON SHIPBUILDING.-This is a subject with which I have been intimately connected for many years, and to the advance of which I have had the honour of contributing. I was the first to commence iron shipbuilding in London, and, I believe, was the second to send an iron vessel to sea, From 1829-30 to 1848 I built upwards of 120 iron vessels, some of them upwards of 2000 tons burden, and nine of which were built in sections at Manchester, and the remainder on the banks of the Thames at Millwall. If time permitted I could give you the whole history of this important branch of industry, and show from what small beginnings one of our largest branches of industry has sprung. Suffice it to observe that in 1829-30 Mr. Hous

ton, of Johnstone, near Paisley, launched a light gig-boat on the Ardrossan Canal for the purpose of ascertaining the speed at which it could be towed by horses with three or four persons on board. To the surprise of Mr. Houston and the other gentlemen present it was found that the force of traction, or labour the horses had to perform in towing a light boat of this description, was much greater at a velocity of six or seven miles an hour than at nine miles an hour. This anomaly in the trials was puzzling in the extreme, and it was in this stage of the experiments that I was requested by the Council of the Forth and Clyde Canal to visit Scotland and institute a series of experiments with light boats in order to determine the law of traction, and to clear up the anomalies of Mr. Houston's experiments.

The Forth and Clyde experiments commenced in the spring of 1830, first with wooden, and ultimately with light iron boats; and these experiments led to the construction of iron vessels upon a large scale and on an entirely new principle of construction, with angle iron ribs and wrought iron sheathing plates. With the exception of these iron canal boats the first iron vessel was made in 1822, and was navigated from this country to Havre de Grace by Admiral, then Captain, Napier, with the intention of employing it upon the Seine. The next iron vessel was built by myself, at Manchester, and another (the Alburka) by Laird, both of which were completed, and went to sea in 1831. From that time to the present iron vessels have been built of all sizes, from the smallest wherry up to the Leviathan of the Great Eastern Navigation Company.

The experiments on the Forth and Clyde Canal occupied a series of years, and no less than five experimental vessels were made at a cost of several thousand pounds; the results not only elucidated the phenomena of diminished

traction at high velocities, but led to a new construction of iron vessels, and other structures, of which wrought-iron formed the whole or the principal material. These experiments, however, did not accomplish the ardent wishes of the proprietors of canals, who at that time were alarmed at the progress of railways, in consequence of the competition at Rainhill, in the same year, for the best locomotive engine. It was then railways versus canals; and although in the experiments we obtained a velocity as high as fourteen miles an hour with a light boat drawn by horses, we never could obtain more than seven and a half to eight miles by steam.

IRON HOUSES.-Iron as a building material is not confined to ship-building alone; it is employed in almost . every other department of useful art, and is now largely applied to the construction of houses. When cast and wrought-iron are united in these constructions, they form some of the most convenient and beautiful combinations possible. All the forms of highly decorative architecture, cornices, mouldings, &c., can be produced in castings from pattern models; and these united together with plates either corrugated or plain, and securely riveted to a framework of angle or T iron, give to a house of this kind erected upon a basement of stone or brick the characteristics of a cheap and handsome edifice. Warehouses, shops and private residences are now built in this way, and I might instance the large edifices recently erected in New York, Glasgow, and other places, where the whole of the street façade is constructed of iron, and that in a style of architecture perfectly symmetrical and in harmony with the finest stone buildings in either city.

As a material for street architecture, it is admirably adapted, from its powers of repetition and security from fire; and I am one of those who have great faith in iron walls and iron beams, and although I have both spoken

and written on the subject, I cannot too forcibly recommend it to public attention. It is now twenty years since I constructed an iron house with the machinery of a corn mill for Halil Pasha, then Seraskier (commander-in-chief) of the Turkish army at Constantinople. I believe it was the first iron house built in this country, and was constructed at the works at Millwall, London, in 1839.

IRON BRIDGES form another class of constructions in which, of late years, iron has been most extensively employed, both in its cast and malleable conditions. Iron is employed for bridges on three principles, the suspension chain, the horizontal beam or girder, and the arch. The earlier bridges were of cast-iron, and were erected in the form of large semicircular arches, sustained by heavy abutments, formed of masonry. The introduction of castiron in this form dates from a period not more remote than 1779, when Mr. Pritchard, with the aid of Messrs. Darley and Reynolds, constructed a bridge over the Severn at Colebrookdale, and even in this first attempt it indicated its superiority over stone for large spans. From that time to the present a very large number of cast-iron arched bridges have been erected, both for railway purposes and for ordinary road traffic, but none of them have exceeded 250 feet span.

The introduction of railways created a demand for a great number of bridges of small span for crossing roadways and canals, in cases where it was requisite that the depth. of the bridge should be as small as possible. For spans of forty to fifty feet, this demand has been admirably met by the introduction of cast-iron beams, with a perfectly horizontal soffit, but for larger spans they are objectionable and dangerous. The best form for larger spans, where castiron is required to be used, is the flat arch with a versed sine of about 1-20th the length of the chord. This description of girder partakes of the properties of the beam as

well as the arch; it does not depend entirely upon voussoirs, as an arch of equilibrium, being partly retained in form by the unyielding nature of the abutments resisting the thrust of the arch; and from its connection at the joints by bolts, it becomes a beam with a large camber, supporting the load by its resistance to compression and extension, along the top and bottom flanches.

The true development of girder bridges was not, however, attained, until the experiments in connection with the erection of the Conway and Britannia tubular bridges, determined the true forms and proportions in which wrought-iron should be distributed to resist the enormous strains to which bridges of wide span are subjected. Wrought-iron as a material for bridges is free from the objections which attach to cast-iron; it is uniform in strength and texture, of well-ascertained properties, entirely free from those irregular strains to which cast-iron is subject from unequal contraction in cooling; and, moreover, its tensile and compressive strengths when arranged in suitable forms do not bear so great a disproportion to each other as is the case with cast-iron. Hence the introduction of wrought-iron for railway and other structures in which certainty of construction and security from danger are required, has proved to be one of the most important eras in the history of bridges.

It will not be necessary to trace the origin and course of the experiments which were instituted to determine the proper form and dimensions of the tubular bridges which cross the Conway and the Menai Straits. Suffice it to observe, that in the construction of the Chester and Holyhead railway, it was found necessary, in order to comply with the demands of the Admiralty (who watched over the interests of the navigation of the Straits), to erect a bridge of colossal dimensions, having four spans, and leaving a clear opening on each side of the centre pier of 460