to about 23 feet as the water was absorbed. With cotton the difference increases gradually, the rate being slower the harder it is pressed; this applies also to fine goods hard pressed and well bound.

8.

Vessels have been built with one, two, and three bulkheads; some with one forward and one amidships, others with one at each end and one amidships; but they invariably show signs of hardship at the places where the bulkheads are attached to the side, loosening the rivets, and, in some cases, cracking the plates through the holes where extra means have not been taken to secure them.

9. It would seem, then, that bulkheads in an iron ship, except they be numerous enough for safety, are useless, and even injurious, by creating rigid places; but where there are enough, they become important as ties, thus preventing vibration and alteration of shape, and diffusing local strains over the whole fabric, besides providing security against collision, grounding, &c. At least five bulkheads are required for vessels loaded to seven-tenths their extreme capacity, and they require to be arranged in the manner pointed out in section 6. 10. The introduction of fore and aft partitions in the Great Eastern might be advantageously copied into merchant vessels, and would take the place of keelsons, stanchions, &c.

JOHN JORDAN, Surveyor of iron ships.

586. Exterior. All cases of deterioration of iron, whether in the hulls of ships when lying long in port, bobstay bolts and chains, and chain cables at the water-line in a copper-bottomed ship, paddlebeam spurs, &c., are generally traceable to the action of copper in the presence of sea-water. It is stated that the contact of the iron plating of La Gloire, French ship-of-war, with her copper sheeting, produced a strong galvanic action injurious to the ship, and that a quantity of wine in the hold was entirely spoiled by it. A number of exceedingly sensitive shell-fish of a species unknown in 1862, were found attached to her bottom. The plates of an iron ship's bottom have frequently been found seriously honey-combed near and around the metal valve seatings. In 1844, when H.M. Steam-Sloop Cormorant went (under canvas only) from Tahiti to Valparaiso, the floats were removed and the paddle-wheels lashed; on arrival it was found that the lower inner arms of the wheels (those nearest the ship) were eaten away by galvanic action induced by her copper sheathing, but the other arms remained intact. The after keel and stern post of an iron ship of war has been much corroded by her having a gun-metal screw propeller. There are instances of the corrosion of iron ship's bottoms by their being laid up in dock alongside vessels with copper or yellow metal on their bottoms. When pustules of oxide are found on iron ship's bottoms which have always used red lead, they have arisen most probably from galvanic action induced by copper in some form or other being near, or by the partial use of preparations containing copper in some shape or other. Several steam companies determined in 1862 to discontinue the use of red lead for coating iron

ships inside or out; they found that where a blister occurred, water had gathered underneath, and that by some combination of the paint and iron with the water, the latter became acidulous, and invariably destroyed the surface of the iron and corroded it. These companies now use zinc paint, and fill all interstices with a cement made in part with iron filings, forming a kind of asphalte. The contact of lead, such as pipes, &c., with iron, is now in all cases avoided. Iron is injured almost as much by contact with lead as with copper. When the surfaces of wrought iron and cast iron are brought near each other in sea-water, they furnish the elements of an active electrical battery and consequent loss of material. Through this a cast iron tank, 160 feet long by 40 wide and 5 deep, fell to pieces in Portsmouth dockyard, in June, 1863; the tie rods, which were of wrought iron, had lost a material portion of their original substance.

587. Iron Ships Compasses. The Underwriters at Liverpool, published, 14th May, 1862, a valuable report on this subject, which is given at length below. This report is followed by the specifications of the iron screw steam ship Himalaya, built by Messrs. MARE & Co., for the PENINSULAR AND ORIENTAL Co., and sold by them to the Admiralty.

Newly-launched iron ships, while fitting out, should be kept, if possible, with the head in the opposite direction to that in which they were built, or as near to it as circumstances will permit. Compass deviations observed in port should be tested at sea as soon as opportunity occurs, especially in new iron ships. The vibration of the machinery in iron steamers may affect the magnetism of the ship, and cause a small alteration in the deviation of the compass. Compass deviations usually change in amount very gradually as the ship changes her geographical position. The deviations of a compass placed near vertical iron, like a steering compass, generally change more, on change of geographical position than those of an elevated or standard compass. This change may not show itself while the ship is upon certain courses, but must be guarded against when the course is altered. When an iron ship has been long on one course, and then is put on a new course, she is likely to err in the direction of the old course: thus a ship, after being for some time on a westerly course, and changing to north or south, will go to the west of her new course. Besides the ordinary deviation of the compass, there is a deviation caused by the heeling of iron ships, which may increase or decrease the deviation observed when the ship is upright. There appears to be no deviation from heeling when the ship's head by compass is east or west, but it increases as the ship's head is moved from these points, and is greatest when ship's head by compass is near north or south. Cases have been observed in which the deviation resulting from heeling has amounted to as much as two degrees for each degree of heel of the ship; that is, without altering the real direction of the ship's head, the apparent alteration in direction has amounted to forty degrees, by heeling the ship from ten degrees to starboard to ten degrees to port! In north latitude, in ships built head to the northward,

with their compasses in the usual position, the deviation from heeling is much larger than in ships built with their head to the southward. In north latitude, the north end of the compass needle is drawn to the high or weather side of the ship, as she heels over; the effect being, when this deviation is not allowed for, that an iron ship, with a list on northerly courses, goes to windward of her apparent course, and on southerly courses goes to leeward of her apparent course. The deviation which arises from heeling will vary with the dip of the magnetic needle. In high south latitudes, where the dip is south, the north end of the needle has been observed to deviate towards the low side of the ship. A small deviation towards the low side has also been observed, in north latitude, in some ships which were built in a southerly direction. It is desirable, therefore, that all iron ships which are liable to heel over should be swung, at least once, with a list to port and with a list to starboard, as well as upright, so as to enable the navigator to estimate what allowance he must make when the ship heels. The compasses of those iron ships which change their latitude very much cannot be properly compensated by fixed magnets only, but should be partly corrected by vertical iron. The record of careful observations made in high southern latitudes, for ascertaining the deviation when ship's head by compass is east or west, will greatly assist the compass adjuster in perfecting the magnetic compensation of the compasses whose deviations are so observed. The caps and pivots of the compass cards should be frequently examined at sea, and the blunt pivots and cracked or otherwise injured caps should be replaced by new. Compass errors arising from mechanical causes of this kind are not unfrequent, and are often wrongly attributed to changes in the ship's magnetism.

46

W. W. RUNDELL.

Swinging iron vessels for adjustment. There appears sufficient reason for swinging a new iron ship or steamer immediately before each of the first two or three voyages: that all iron vessels should be swung immediately before the first voyage following any considerable repair; whenever the position of the standard compass is changed; or when the master is changed, unless he had charge as chief officer the preceding voyage."

IRON SCREW STEAM SHIP HIMALAYA-SPECIFICATIONS.

Dimensions. Length of keel 340 feet, beam 44,, deep 31; 3,437 tons. Keel, bar-iron, 10×5 inches, to be rabbeted half the thickness of garboard strake into the keel; other half rounded over.

Stem, 16 inches broad at bottom by 5 inches thick, and checked same as keel to where the cutwater comes on the stem, and to be 8 x 4 inches at the top.

Stern Post, 10 inches broad and 5 inches thick, tapering to 10 × 4 inches at the spar deck, and a heel left on the after side to bear the rudder, with eyes for the pintles, turned so as to form a knee forward on the keel. The plate aft to run over the post to form a place for the rudder.

Frames, of angle-iron 7×5× inches for 120 feet in midships, 20 inches from centre to centre, extreme fore and aft that, to taper to 21 inches 6 × 1 × } inches; 22 inches 5× 3 × inch; and 24 inches 4×3×7 inches. The butt plates to fill up the space between the frames, so as to form a series of trussings

throughout the vessel's body. In engine and boiler space, and for ten frames before and abaft it, the frames to be doubled in the bottom, and a reverse angleiron on every second frame from floor to gunwale 4×3× inches the whole length of vessel, for fastening the ceilings to.

Plates. Garboard strake for 150 feet in midships, 1-inch plates as broad as can be procured or worked; remainder fore and aft to taper by inch to the extreme end to 18 inch; bottom plates to inch to the 6 feet water-line for 160 feet in midships, before and abaft this inch from the 6 feet water-line to gunwale inch, except the upper plate 2 feet 6 inches broad by inches thick, to form the waterways; all double rivetted from keel to gunwale, and all butts to be flush; upper strake to go to top of waterway. Spar deck plates 4 inch thick; all spaces formed by projection of the plates to be fitted with liners, so as to avoid using small pieces of rings. The butts to be perfectly close, as well as the seams; no pieces will be allowed to be put and caulked over. The countersinking to be carefully done, and all the rivets to be full and smooth outside of plates and to be chipped down while hot. In punching to take great care to prevent unfair holes.

Floors, 22 inches deep in engine and boiler space, of § inch plates, with angleiron 4 × 3 × inch on top of every floor, to run from 3 to 5 feet up the turn of bilge, the floors in fore and aft hold to be 22 inches deep, inch thick, with angle-iron on top 4×3× inches. The floor plates to run 4 feet on the turn of bilge over each side of frame in one piece.

The main keelson in midships to run the whole length of the vessel on top of the reverse angle-irons, and floors to be 16×18 inches and § inch thick, the side keelsons to run as far fore and aft as the vessel's mould will admit. Keelsons in engine room as required by engineer.

Breast-hooks, 5, 11 feet long, 1 inch thick, secured to frames by reverse angle-irons well rivetted; one crutch on fore and after peaks, running square to point of contact.

Pillars in holds, between keelsons and beam, 4 inches diameter.

Bulkheads water-tight, one in fore peak, one before the engines, one aft the boiler, one in after hold; all to be -inch plate, tapering to inch at top plate, stiffened with 4×3 inches angle-iron 3 feet 6 inches apart.

Beams. For upper deck, plate, 9×1⁄2 inch, with two angle-irons on top, 3×2 inches, finished on lower side with angle-irons 2×24 inches, as described for main and lower decks. Main deck, of plate, 12 × § inches with 2 inches angleirons on top, 4×3× inches. Beams and knees to be all welded in one piece, except in engine and boiler space, where they will be in lengths, to allow the machinery to go down to the vessel, and to have angle-iron 4×3×1 inches on each side of top edge, finished on lower edge with inch round iron, or angleiron, 3×3× inches, to run over end of beam plate at least 3 feet, or as may be decided on. Lower deck of 11x inches, with 4×3× inches angle-iron on top; lower edge finish as main deck.

Stringers. Angle-iron all round the gunwale, 6×4 × inches, with a covering-plate, 26 inches, rivetted to gunwale and to upper side of deck beams; same in main and lower decks, 26× inches. To have aft, five diagonal iron straps, 8x inches, rivetted to reverse angle-iron.

Vessel to be rivetted, butt straps or plates to overrun strakes, tight and strong work,

588. When rounding the Cape of Good Hope, on her passage from Singapore, September, 1863, the Dewa Gungadhur, Capt. MACKENZIE, sprung a leak below. Part of the cargo was got on deck and covered with tarpauling. A rivet was out of a butt in the third plate from the keel just abaft the foremast. The hole was plugged with wood. The first calm weather after, the master placed in it a permanent screw bolt prepared with gutta percha washers, outside and inside. It was thus accomplished:-A spike nail was tied to the end of a skein of twine and forced through from inside; other spikes were attached at intervals of two feet, until a sufficient quantity was payed out. The ship's bottom was then swept with a fishing line which caught the spikes, which were hauled on board. The prepared rivet was then lashed to the twine, the spikes were cut off and the end of the rivet secured; the washers were then put on, the bolt screwed down, and all made secure. In another case, a cork was tied to the end of a long piece of twine and passed through the hole; it came to the surface and gave place to a screw bolt, which was then pulled into the hole and secured.

589. ISINGLASS, a glue made of the sounds and air bladders of fish the sturgeon especially, which is plentiful in the river Volga and the Caspian Sea; specific gravity 1-111. Baltic, in bales, receives. same freight as clean hemp per ton of 44 poods gross; in casks onefourth more. A fat of isinglass 3 to 4 cwt.

590. IVORY, the tusks and teeth of elephants; the best comes from Ceylon; an inferior sort is obtained from the hippopotamus, wild boar, &c. It is also exported from Bombay, the Cape of Good Hope, and Alexandria; specific gravity 1.825. In the East India trade it is usually stowed on the top of the cargo, between the beams. On the West Coast of Africa it is placed in the lazarette; the negroes here commit great depredations while loading. Great care ought to be exercised when shipping large tusks in Bombay or Zanzibar, where they are freely used as beam fillings over cotton bales in one port and orchilla weed in the other. The tusks being hollow and brittle at the larger end, are very liable to be chipped and broken through the rough and careless handling of the black stevedores, when stowing; and from the negligent manner in which they are placed, it frequently occurs that they are heard in heavy weather rattling and striking against each other. It is equally necessary when discharging, to look sharply after the dock labourers, as whole tiers of bales are broken out regardless of the beam fillings, and pockets, small bags, and large tusks, come down with a crash, to the manifest deterioration of the cargo. Sometimes it has occurred that