unnecessary material where it is absolutely doing serious injury by adding weight where it is not wanted, and where it has to be permanently supported; charging the structure, whatever it may be, with a load not its own-an incubus, in fact, which remonstrates and never relaxes in its reproaches till the structure is ultimately destroyed. We are no advocates for ships, bridges, boilers, and similar constructions being contracted for by weight, as the tendency on the part of the contractor is to offer low rates, and to make up for the deficiency in price by increase of weight. This system of sacrificing quality for weight is in boilers and bridges a general practice; and how frequently do we hear of ship plates as being synonymous with iron that is not to be trusted, and totally unfit for such a service! Assuming, however, that no seagoing vessel should have plates and angle iron which are not capable of sustaining a tensile strain of less than 20 to 22 tons per square inch, and assuming also that they are sound and ductile, we should then have, according to the construction referred to, the following proportions, viz.

Square Inches

For the bottom section, from the centre keelson to c on each side, }

forming the cells and double bottom

For the upper deck and 8 feet down the sides, including}

stringers, &c.

And taking the intermediate spaces between the double bottom and 8 feet below the upper deck at

We have for the whole section at midships

460

340

Now, supposing the material in the transverse section to be distributed as represented in the annexed

By formulæ (7) and (8), Art. 69, Chap. XIV., we have a1=160, a2=100, a,=460, α=80+250=330, D=35, a2 =8, K=1050.

=h

Distance neutral axis from the upper edge
={(330+460) 35+100 x 8}=21 ... (7)

12

I=330 {1 × 352 + (21 − 1 × 35)2 } + 160 × 212 + 100 (21 −8) 2 +460 (21-35)2=215348 (8)

S

...

Io oro; and taking s1 = 20 tons, s=18 tons.

10

h

When the top is yielding by this load, viz., 3076 tons, with 18 tons per square inch, the bottom section would undergo only about 12 tons.

This deficiency is to some extent made up in practice by the wooden deck, which acts to some extent in its resistance to tension, and considerably more in its resistance to compression, and the breaking strain may therefore be taken at 4000 or 8000 tons equally distributed.

Fig. 81.

b

The other portions of the structure and the union of the plating to the stern-post and cutwater at the bow and stern

respectively, are entitled to consideration. In the construction of an iron ship it is necessary to have an iron stern-post, to which the sheathing plates and rudder are attached. In most cases they are of the form shown in fig. 81, and consist of a large forging recessed to receive the ends of the plates-doubleriveted-and the thimbles or sockets in which the rudder revolves, as shown at a and b b. At the bottom the post terminates in a strong forging prepared to receive the foot of the rudder, and to unite at the same time with the bottom plates, which are thickened under the centre keelson; and as there is no keel, this forging and the plate must be firmly secured by rivets forming the junction of the stern-post and the bottom sheathing of the ship. The same method of construction may be observed in the union of the hull with the cutwater, which being similar to that of the stern-post, renders further description unnecessary.

The foregoing remarks are directed almost exclusively to sailing-vessels, or what are called clippers, carrying passengers and goods. Those intended for steamers with screw-propellers would be nearly of the same build, but differently prepared at the stern for the reception of the screw, where a double and more elaborate forging would be required, and other local conditions, well known to the engineer and builder, and which, therefore, we need not attempt to describe. The same observations will apply to paddle-wheel steamers, and the same principle of construction also applies, in so far as it relates, to the hull, and the distribution of the material.

3. Having thus investigated what may be considered the best principle of construction for iron vessels of a mercantile character, we now come to the more important question of Ships of War, which, owing to other causes besides those of seagoing properties and strength, require careful consideration.

When we consider the purposes to which vessels of war may be applied, and the resistances they have to encounter, to say nothing of the many conveniences that are required for lodging some hundreds of men in a small space, and that room must be provided for steam-engines, boilers, and coals; that the vessel must carry heavy guns and some hundreds of tons of armour-plates bolted to her sides; that she must have a beak

of enormous strength, calculated to run down and sink an enemy's ship; moreover, that she must be swift for the chase, and equally alert in making her escape when overpowered by a superior force-we have some idea of a modern ship of war. Now, to construct a ship with all these qualifications and conveniences is the duty of the builder, and although the means are at hand, with the knowledge and skill of the Controller and the Lords Commissioners of the Admiralty, yet it is nevertheless an arduous and responsible duty which both parties are called upon to perform.

On this important subject it may be assumed, that a landsman is not the proper person to direct constructions of this kind, nor would it be prudent for us to enter upon the task, if it were not well known that a musician is not the person to make the instrument on which he plays, nor is the mariner who navigates the vessel, the only one calculated to design and build the ship. On the contrary, these duties devolve upon those who are neither musicians nor seamen, but who are notwithstanding better prepared for the task from their education, knowledge, and long experience in the use of wood and iron in its application to these constructions. It is sufficient for the sailor to navigate and fight the ship, without burdening him with the laws of construction, and to leave to other hands the duty of providing suitable vessels on which the safety and the honour of his country depends. What is therefore wanted is proper and suitable vessels, and we may rest assured there will be no want of skill in their management nor lack of courage in the fight when duty calls upon the officers and crews of Her Majesty's Navy to assert and maintain the honour of the British flag.

It has been noticed that ships of war, having the same seas to navigate and greater risks to encounter than merchant vessels, should be made proportionately stronger than those intended for a different service, and the construction of iron ships calculated for the purposes of war present other considerations besides those which are required in building vessels exclusively commercial. They may be thus considered:

1st. Their tonnage or magnitude.

2ndly. General principles of construction.

3rdly. Ironclads such as the 'Bellerophon' and 'Warrior.' Lastly. The American system of construction.

These are the subjects which we propose to discuss, and taking into account the numerous points which have to be considered, we must leave to other and more experienced hands an immense amount of detail with which we are unacquainted, and which necessarily must be omitted. In the leading features of the construction we may, however, be enabled to offer some useful suggestions; and taking them in the order given above, we have to treat of

1st. The Magnitude or Tonnage of Ships of War.—This is a question of deep importance to the country, and doubtless it has received careful attention on the part of Her Majesty's Government. Since the first introduction of plated armourvessels, many changes and many improvements have been effected both as regards the manufacture of the plates and the guns to which they offer resistance. For a long time these antagonistic forces were nearly balanced; but as the plates were thickened and improved, the guns were strengthened and enlarged, until it was found that guns could be made to perforate plates much thicker than a ship of ordinary size could carry. As much as 6, 8, and even 10 inches thickness of plate have been perforated and smashed by guns of large calibre, throwing bolts and shot varying from 300 to 600 lbs. in weight, and which, with increased charges of powder, would pierce much greater thicknesses of plates than our largest ships are calculated to support. This was the state of the enquiry when the Iron Plate Committee left off their labours, and it has now to be considered what description of iron, what weight and thickness of plates should be introduced, and how distributed, to resist these formidable weapons of attack.

It has been suggested and strongly recommended that our ships of war should be greatly enlarged, in order to carry armourplates of any required thickness; but we have had some experience in the unmanageable nature of large ships in the case of the Great Eastern,' and it appears from all previous experience that the smaller description of vessels, from 2,000 to 2,500 tons burden, are infinitely more active and sufficiently large to carry armour-plates as a protection from the shot of powerful guns,