in Heaving Down the different Classes of H.M. Ships at Malta.

were caulked in and payed. The starboard chain pump dills were plugged and covered, and the pigeon holes between the bulkheads closed up.

Five bilge pumps were rigged, two at the fore, two at the main, and one at the after hatchway; in the squares of which stages were erected for the working parties. The lower deck was scuttled abreast these hatchways to permit the passage of water from the orlop.

The masts were stripped of everything excepting the lower rigging, and fished on the fore and after sides, with single spars reaching from the lower deck to the tressle-trees. These were

lashed in nine places and wedged taut. They were supported on the starboard side by shores, the heels of which rested on elm planks in the water ways; the deck being shored up underneath. Of these there were three; the first reaching to within 6 inches of the tressle-trees; the second, one third lower; and the last, another third below the second; their upper ends being chamfered were lashed to the masts. The bellies of the masts were further supported by horizontal shores of 3-inch oak boards which projected from thence to the main shores, three of them butting on the first, and one on each of the others. The heels were also shored in the holds on the port side.

On the port side the masts were secured by out-riggers composed of balks of timber, which butting against the coamings and bitts, &c., projected through the ports. Of these the main had five on the lower deck 40 feet long and 2 feet in the square, and four on the main deck 35 feet long and 18 inches square. The fore had four on the lower and three on the main deck of similar proportions, and the outer ends were shouldered and cleated about 18 inches from thence for the rigging to butt against.

consisted of eight The latter were

The out-rigger martingales were 8-inch rope, fitted with thimbles in their ends; their middle taken with a round turn over the ends of the spars and seized, and set up with lanyards; those of the main deck to chocks in the lower deck ports, and those of the lower deck to shackle bolts which were driven through the ship's side and forelocked. The preventer rigging for the main mast shrouds and one pendant of 13-inch rope. fitted with a long and short leg, and an eye splice in the end of each. In placing them on the mast-head the long leg, which set up to the foremost lower deck out-rigger, was pu foremost, the short one to the foremost main deck out-rigger Two pair of shrouds were placed over the mast-head to form a bolster, then the purchase blocks, then the remainder of the shrouds; lastly, the pendant with a lashing eye. This rigging was pulled up by double 20-inch blocks, double stropt, th eye of the shroud being taken through the strop and toggled The lower block strops went over the end of the outriggers, th falls were 7-inch. The fore-mast was secured just as th main, excepting that it had but one fish, and that was on th after side.

The runners were carried forward on each mast t

support the stays. The mizen-mast was additionally supported by the long tackles.

The wedges being removed, the masts were steadied over against the port partners, after which the starboard rigging was tautened.

up by the runner pendant The tripping cables were

The purchase lashings were set from one mast-head to the other. brought from the opposite side of the harbour, under the bottom, and secured through the starboard upper deck ports to the port side, one being forward and the other aft. The Fore Chains were broken downwards (although previously shored) by the pressure of the foremost of these cables when heaving down.

The heaving down occupied twenty minutes, and the ship was eased up once to set up rigging; on which occasion, it was found that the long shore of the main-mast had butted against and injured the tressle-tree.

When first down, the fullness of the buttocks caused the stern to rise so high as to be inconvenient for the workmen, therefore eighty butts were secured under and below the fore-chains before heaving down the second time. This had the desired effect of keeping the keel parallel, and enabling the repairs to be carried on at the gripe and stern at the same time.*

A very instructive lesson on this subject will be found in an account of the heaving down of the "Melville," published by Captain Harris. That officer remarks that the ship leaked when down as much as 268 tons in ninety-six minutes, although nine hand-pumps and five engines were at work all that time, a quantity which it took 210 minutes to pump out when righted; but that she leaked less when the main-deck ports, which we observe were open in the Melville and Formidable in the first instance, were closed. He also calls attention to the importance of preserving the original distance between the fore and main-mast heads, when setting up the rigging afresh; otherwise in heaving down, the masts spread apart, and the purchase falls do not look straight into their sheaves. In the case of the Melville's pumps, the lower ones discharged into tubs on the lower deck, into which the lower ends of the upper pumps were placed.

In cases where the vessel has been dismasted, or where it would

It is well to nail battens fore and aft on the deck before heaving down, otherwise it is most difficult to pass along.

be impossible to procure sufficient length of purchase falls, &c., the bottom is turned out of the water by means of Spur derricks. H.M. ship "Success," for instance, was thus repaired. The upper ends of the derricks were cleated on the ship's side, the lower, to which the purchase blocks were lashed, were secured

Fig. 226.

from rising by turns of the chain cable, that were passed under the bottom from the opposite side, being steadied by guys led from forward and aft. (Fig. 226.)

CHAP. XXV.

STEAM ENGINE.

In this, as in other scientific subjects, our object is to excite a taste for inquiry and lead on to better books. It is, therefore, only pretended to give an outline of the general nature of the Marine Steam Engine, referring readers to those comprehensive explanations that have been published by more qualified writers.*

"The simplest view of the marine steam engine is to consider it as a propelling machine, moved by vaporised water.

To turn

* Marine Steam Engine, by Professor Maine. Ditto, by Robert Murray, Esq Ditto, by Captain Robinson, R.N. Ditto, by Lieutenant Gordon, R.N.

water into vapour or steam there are boilers and furnaces. From the boilers steam passes to the cylinder, in which a piston moves, the piston (generally) carries a rod which works a crank, the crank turns a shaft, and the shaft a wheel or screw." *

d

Fig. 227.

The two leading properties of steam are its expansive force and its facility of condensation, both which are shown by the use of a glass tube as in the figure.

Let a represent a glass tube with a bulb at its lower end. It is held in a brass ring to which a wooden handle is attached, and contains a piston c, which (as well as its rod) is perforated, and may be opened or closed by the screw at top, d; it is kept central by passing through a slice of cork

at e.

When used, a little water is poured into the bulb and carefully heated over a spirit lamp; the aperture in the piston rod being open, the air is thus expelled, and when steam freely follows it, the screw may be closed, when, on applying cold to the bulb (as for instance, putting it on the surface of a little mercury in a glass), the included steam is condensed, and a vacuum formed, which causes the descent of the piston, in consequence of the air pressing upon it from above.

On holding again the bulb over the lamp, steam is reproduced and the piston again forced up and these alternate motions may be repeatedly performed by the alternate applications of heat and cold.†

The true nature of heat is not known; it operates on solids by conduction, and on fluids by connection. In the former process it passes through the body without derangement of its particles ; in the latter those which are nearest the heat are displaced. "If heat be applied to a vessel of water, the particles near the bottom are heated first, and expanding become specifically lighter, and ascend; colder particles occupy their space, and ascend in their turn, and thus a current is established." +

* Pamphlet by Admiral Fitzroy.

+ Brandt's Manual of Chemistry. Tomlinson, Nat. Phil.