In our country little is used but oak and pine; but in England experiments have been made in almost every wood under the sun, and the general conclusion has been reached that East India teak is the best. The great difficulty to be overcome is the decay of the timbers with dry-rot, or fungi that grow and extract all the juices of the wood until it crumbles away under the least pressure or strain. Merchant vessels are more subject to this than men-of-war, ventilation being the only means to arrest its progress. By the Marine surveying laws, a ship is only allowed to remain on the first-class list twelve years, it being calculated that in such time decay has well advanced. Cases have been known where a well-built oak ship would in a few months be useless from dry-rot.

The comparative qualities of wood, according to the English valuation, for ship-building are: First, Teak, mahogany, pencil-cedar, Spanish and French oak. Second, Red cedar, white oak, and Spanish chestnut. Third, American oak, chestnut, larch, tamarac, pitch-pine, and ash. Fourth, Red pine, elm, birch, spruce, and beech. Fifth, Hemlock. American builders place our oak higher.

Experiments on the power of timber to resist crushing, breaking, and pulling apart, show that yellow pine withstands a pressure of 5375 pounds

pounds; while the cohesive strength of ash is 17,000 pounds to the square inch, and oak 10,000 pounds. A stick of oak, 8 inches by 12, and 15 feet in length, required a weight of 19,153 tons before it would break. Many experiments have also been made with timber to prevent its decay, sometimes by immersion in liquids, sometimes by drying it in ovens and kilns, and sometimes by injecting chemical substances into its pores. The process of salting timber has been in use for over half a century, and is perhaps the only real practical preserving that has yet been done. Corrosive sublimate, chloride of zinc, sulphate of copper, and kreosote, have all been used with certain success in saturating the fibres of the wood; and timber has been subjected to currents of heated air of 114° Fahrenheit, which reduced its weight 20 per cent. in sixteen days; but with all the success of these experiments none of them have been brought practically to bear in the building of the ship.

Now for the launch. We have a mass of timber, copper, iron, etc., weighing somewhere about 3000 tons, which we are anxious to get into the water with safety to ourselves and it.

As a representation of our ship's bottom I will give you an angle, in looking at which you will be kind enough to imagine that you are standing at the bow of the vessel and looking down her length. I have before mentioned that the keel of the ship is laid on a declivity of ths of an inch to a foot; and now, in our efforts at a successful launch, it will be necessary that we

THE SHIP

с

should give the sliding ways, or plane upon which she is to glide into the waters, a still greater slope. We will even go so far as to give them ths of an inch declivity to each foot of distance. The smaller the vessel the greater is the declivity, much depending on the weight of the mass moved in making its own momentum. These sliding ways, which I shall mark a, are smooth plank laid upon heavy timbers, forming a continuous line from the ship to the water, and are laid when the tide is low that they may reach far out. Upon these sliding ways rest the bilgeways, marked b, much as the runner of a sled rests on the snow. These bilge-ways, which are about ths of the length of the ship, and connected with her by certain upright timbers-c, called poppets, and others called stopping up, the latter of which are used amidships, the poppets before and abaft. The poppets are confined to the side of the ship by a plank, marked d, which is bolted to the ship's side, and farther strengthened by cleats, e, which are also screwed

to the bottom. The lower ends of the poppets rest upon a plank, f, called a sole-piece, which is placed on the upper side of the bilge-ways, the sole-piece having a groove taken out of it to receive a tenon cut in the lower end of the poppet. We have now to provide for these bilgeways keeping the track when once they begin to move our ship along the sliding ways and toward the water. This is done by placing a timber, called a shore, marked g, from the keel of the ship to the inside of the bilge-ways: this prevents the bilge-ways slipping inward, while a strip, entitled a ribbon, will prevent them going outward, nailed along the sliding ways, and secured from any chance of being forced away by a shore reaching from its outside to the ground marked h and i.

This is the outline of the machinery of the launch. The additions must be made at the time of launching in the shape of wedges, grease, and soft soap. The wedges used are two upon each poppet and are called slices, marked k. They are inserted between the sole-pieces and the bilge-ways, and, just previous to the hour of launching, men are stationed at them with mallets, who, driving these wedges, raise the huge mass just sufficient to allow the blocks upon which she was built to be removed. This removal is made with all the blocks but those in the foremost part of the ship, which are split away piecemeal, and the great structure rests upon the cradle confined only by a single piece

of timber called a dog-shore. This dog-shore holds her back from slipping away into the waters by being placed on one end against a secure point on the ship, the other against a cleat on the bilge-ways. To it there is affixed a trigger and a string that, on the word being given, the dog-shore may be pulled away and the ship be free. Only one thing is necessary, which is to see that the sliding ways and the under side of the bilge-ways are well covered with grease, oil, or soft soap, that the least possible friction may ensue, and the stately ship go smoothly into her future home.

All is now ready! The gorgeous banners and gay streamers are floating and fluttering from every available point. The decks are crowded with happy people. The crowds stand in hushed and breathless expectation. The work is done,

and not even the click of a hammer is heard, nothing but the ripple of the full flood-water that breaks up to the shore, struggling as it were to kiss the great ship that is so soon to nestle upon its bosom.

A fair creature, "God's last, best gift to man," comes forth from the group upon the deck, with a flushed cheek and a sparkling eye, and casts the christening wine against her bows, calling the ship aloud by the name she shall henceforth bear. In an instant the stout voice of the builder is heard ringing over the rail, "Down, dog-shore!" and to the music of a thousand shouts the grand ship glides away with a laughing plunge into the element in which she is to make all her future conquests, whether they be of war or of commerce. Hurrah!

Once more let me, even though we have our

wooden castle finished and out upon her mission, recall your attention to ships. This time I desire to say only a few words about iron ships; and I shall not detain you long, for the very simple reason that the general theory is the same as in wood, making only the difference that, while in large vessels it is wrought in pieces, and the floors and futtocks laid upon and from it, in the smaller the keel is merely a groove made upon the bottom plate by subjecting it to pressure in a mould

while hot. Still, with the aid of my chalk, I will

boiler. The iron sheets only differ in quality, the boiler iron being much the best. These sheets vary in size, according to the calibre of the vessel, but the usual size is three feet by nine. In thickness they vary greatly, ranging from half an inch to seven-eighths, and of course heavy in proportion.

Upon the construction drawings being made for an iron ship they are dispatched to the foundry, and each plate is got out the exact required size. The best of this plate is made in the Pennsylvania foundries, and upon reaching the spot whereon the ship is to be built, requires only the preparation of bending, and punching for the rivets before being added to the frame. To achieve the bending the plate becomes, for a sufficient space to give it a fine red heat, the tenant of the furnace. From its fiery bed it is dragged forth upon a heavy iron floor, where, under the hammers of the moulders, it is brought

PUNCHING MACHINE.

DRILLING MACHINE.

to whatever curve may be required. The next move is to send it through the punching machine, the powerful machinery of which, worked by two men with the aid of steam, cuts a line of holes about its edge, three-quarters of an inch in diameter, with about the same ease that a healthy Miss of twelve would send her teeth through a slice of bread and butter. After this preparation the sheet is ready to become part of the vessel, and is riveted to the sheet that has gone before by overlapping, the rivet being driven from the inside, a second workman on the outside clenching it. In small vessels rivets are used to confine these sheets to the frame, but in large, bolts, the holes for which are drilled by a machine also worked by steam-power, and eating through the iron with a certainty calculated to give you a pain in the bones with the mere idea of your being a piece of iron.

This outside sheeting is graduated in thickness from the keel up, the thickest and best iron being nearest the keel. In small vessels the outside sheeting generally constitutes the ship, perhaps with the addition of inside wood planking; but in large vessels the outer sheeting is precisely the same as in wooden ships, but half the covering of the frame, the inside being covered in a similar manner, making, as it were, one vessel inside the other.

Another matter worthy for consideration is the method followed in iron ships of dividing