heavy squalls) from the North-westward, Northward, or Northeastward; after which violence a rising glass foretells improving weather, if the thermometer falls. But if the warmth continue, probably the wind will back (shift against the sun's course), and more Southerly, or South-westerly wind will follow. "The most dangerous shifts of wind, and the heaviest Northerly gales, happen after the mercury first rises from a very low point. "First rise, after very low, Indicates a stronger blow.' "The greatest depressions of the barometer are with gales from the South-east, Southward, or South-west; the greatest elevations with winds from North-west, Northward, or North-east. 66 'Although the barometer generally falls with a Southerly, and rises with a Northerly wind, the contrary sometimes occurs; in which cases the Southerly wind is dry, and the weather fine; or the Northerly wind is wet and violent. When the barometer sinks considerably, high wind, rain, or snow will follow; the wind will be from the Northward if the thermometer is low (for the season), from the Southward if the thermometer is high. "Sudden falls of the barometer, with a Westerly wind, are sometimes followed by violent storms from North-West or North. "If a gale sets in from the Eastward or South-east, and the wind veers by the South, the barometer will continue falling until the wind becomes South-west, when a comparative lull may occur; after which the gale will be renewed, and the shifting of the wind towards the North-west will be indicated by a fall of the thermometer as well as a rise of the barometer. "Wind usually veers with the sun, (right-handed in Northern places, left-handed in Southern parts of the world). When it backs more wind or bad weather may be expected. "Instances of fine weather with a low glass occur exceptionally, but they are always preludes to a duration of rain or wind, if not both. "After being warm and calm weather, rain or a storm is likely to occur; or at any time when the atmosphere has been heated much above the usual temperature of the season. "There may be heavy rains or violent winds beyond the horizon, and the view of an observer, by which his instruments may be affected considerably, though no particular change of weather occurs in his immediate locality. "Whether clear or cloudy, a rosy sky at sunset presages fine weather; a red sky in the morning bad weather; a grey sky in the morning fine weather. "When the sun sets in a clear, An easterly wind you need not fear.' "Soft looking or delicate clouds foretell fine weather, with moderate or light breezes; hard-edged oily-looking clouds, wind. “A dark, gloomy blue sky is windy; but a light bright blue sky indicates fine weather. 66 Generally, the softer clouds look, the less wind (but perhaps more rain) may be expected; and the harder, more greasy,' rolled, tufted, or ragged, the stronger the coming wind will prove. Also a bright yellow sky at sunset presages wind; a pale yellow, wet: and thus, by the prevalence of red, yellow, or grey tints, the coming weather may be foretold very nearly. "After fine clear weather the first signs in the sky of change are usually small, curled, streaked, or spotted clouds, followed by an overcasting of vapour, that grows into cloudiness. This murky appearance, more or less oily or watery, as wind or rain will prevail, is a sure sign. The higher and more distant the clouds seem to be, the more gradual, but extensive, the coming change of weather will prove. 66 Misty clouds forming or hanging on heights, show wind and rain coming. When sea birds fly far to seaward fine weather may be expected; when they hang about the land, expect stormy weather. "When distant objects are unusually visible, wet if not wind may be expected. Unusual twinkling of the stars, halos, winddogs, and the rainbow, are more or less significant of increasing wind if not approaching rain. "Squalls are generally preceded, or accompanied, or followed by clouds; but the very dangerous 'white squall' of the West Indies and other regions, is indicated only by a rushing sound and by white wave crests. 666 Descending squalls' come slanting downwards off high land, or from upper regions of the atmosphere. "A squall-cloud that can be seen through, is not likely to bring so much wind as a dark continued cloud extending beyond the horizon." In keeping the Journal, for the sake of brevity, the force of the wind and state of the weather are expressed thus: 0. Calm. WINDS. 1. Light air just perceptible. 2. Light breeze: ship going from one to two knots. 3 Gentle breeze: from two to four. 4. Moderate four to six. 5. Fresh when royals can be carried. 6. Strong breeze: first reef and top-gallant sails. 7. Moderate gale: double reefs, topsails. 8. Fresh gales: treble reefed topsails and courses. 10. Whole gale: close reefed main-topsail. 11. Storm: storm staysails. 12. Hurricane: no canvas. "Cirrus expresses a cloud, like a lock of hair, consisting of streaks, wisps, and fibres, vulgarly called "mares' tails." "Cumulus," a cloud in dense convex heaps in rounded forms definitely terminated above, indicating saturation in the region of air, and a rising supply of vapour from below. "Stratus" is a continuous extended level sheet, but must not be confounded with the flat base of the Cumulus. "Cumulo-stratus," or anvil. shaped cloud, is said to forerun heavy gales. 'Nimbus," a 66 dense cloud spreading out into a crown of "Cirrus" above, and passing beneath into a shower. The Siphon, which is so useful in discharging the contents of one cask into another, in such places as the hold or between decks, where it would be difficult to raise one uppermost, is constructed on the principle of atmospheric pressure. Fig. 7. The tube A F B, is filled with fluid, and the open ends being stopped, it is then inverted, as in the figure, and the ends are opened. In some cases, the tube is placed in the vessel, and the air withdrawn by suction through a small mouth-piece on the bent part; upon which the tube becomes filled with fluid. The pressure of the fluid in F A, tending to cause it to flow out of the tube, is equal to the weight of a column AP, reaching from A, to the level of the highest portion of the tube; also the pressure of the external fluid at A, tending to cause it to flow into the tube, is equal to the weight of a column of the height a C, together with that of a superincumbent column of air; hence the fluid is pressed at A inwards, by the weight of a column of air, diminished by the weight of a column of fluid c P. At B, the fluid is pressed into the tube, by the weight of a column of air, diminished by the weight of a column of fluid D Q. So long then as the column D Q is greater than the column c P, the fluid is pressed into A with greater force than into B, and therefore moves in the direction AF B, until the surface c comes to the level of D. The column will, however, be broken when C P is more than 30 inches in height if the fluid be mercury, and when more than 34 feet in height when the fluid is water. Thus a siphon cannot be made to raise water more than 34 feet, or mercury more than 30 inches; or to raise it at all in a vacuum." * Moseley's Mechanics. CHAP. IV. CONSTRUCTION. SHIPS are built or repaired, according to circumstances, on a Slip, in a floating, or dry, or wet Dock. Where there is a regular and considerable rise and fall of tide, excavations are made in the land near the water, faced with solid masonry, and mostly having entrances fitted with gates or Caissons, which serve either to retain or exclude the tidal waters as desirable. Those on a larger scale, and which are always kept full of water, are called wet docks or basins. These are, in fact, artificial harbours, in which vessels are always kept afloat whilst undergoing internal repairs, loading or unloading, fitting for, or being kept ready for going to sea. Commercial wet docks usually have "locks" (as in a canal) attached to them, so as to admit of the entrance and egress of vessels at any time of tide without losing more water than necessary. In Naval wet docks, the ships generally requiring as much water outside as in, one barrier in the form of a caisson is used, but which is seldom worked excepting at high water. It is deeper The Dry Dock is both deeper and narrower. because it is necessary to have more water in the dock at the time of docking a ship than at its entrance. This is for the purpose of gaining depth enough for the Angle Blocks on which the keel of the ship is to rest, and is effected by having the floor of the dock somewhat below the low water mark. Then after closing the entrance, the dock is drained either by pumping, or letting the water run off with the falling tide through channels, called Culverts. It is narrower, because when not water borne, the ship requires to be supported by Shores; which, abutting on the sides of the dock, bear against those of the ship on being set taut by wedging. (Fig. 8.) Formerly, the ship when in dock rested on a row of square blocks of wood, which were kept in their place with ballast. In order to get at her keel for repairing or coppering, &c., it was necessary to lift her bodily off the blocks by numerous shores simultaneously driven up with wedges. This operation not only involved the services of hundreds of mechanics, but strained |