the stern to prevent the pin from coming out. The knots are measured from marks on the line, at the distance of twelve or fifteen fathoms from the log. The glass is therefore turned at the instant that the log passes over the stern; and, as soon as the sand in the glass has run out, the line is stopped; the water then being on the log, dislodges the pin, so that the board, now presenting only its edge to the water, is easily draw aboard,—the number of knots and fathoms, which has run off at the expiration of the glass, determine the ship's velocity. The half-minute glass and divisions on the line should be frequently measured, to determine any variation in either of them, and to make allowances accordingly. If the glass runs thirty seconds, the distance between the knots should be fifty feet. When it runs more or less, it should be corrected by the following analogy :-As thirty is to fifty, so is the number of seconds of the glass to the distance between the knots on the line. As the heat or moisture of the weather has often a considerable effect on the glass, so as to make it run slower or faster, it should be frequently tried by the vibrations of the pendulum.

As many accidents attend a ship during a day's sailing,—such as variableness of winds, the different quantity of sail carried, &c.,-it will be necessary to heave the log at every alteration; and, even if no alteration be perceptible, yet it ought to be occasionally heaved.

NOTE F.-P. 5.

BALLAST AND LADING.

The ballasting and dunnaging of ships have been already treated of (ante, p. 249); and here it is only necessary to remark further, that the ballast must be placed in such a position, as that, when the ship is fully loaded, no alteration in it may be required. The object in ballasting ought to be, to place the centre of gravity neither too high nor too low, nor too far forward nor too far aft, so as to correspond with the shape and trim of the vessel, with reference to the cargo she is to load and the quantity of ballast she requires; and the centre of gravity of this part of the displacement by the ballast, may be found, when the difference is known between the light draught of water and that to which it is proposed to bring her, when she is loaded. Ships having cargoes of light goods on board, require a greater quantity of ballast, which falls to be increased according to the greater lightness of the cargo; and, when iron ballast is used, it is first stowed fore and aft, from bulk-head to bulk-head, and then the shingle ballast is spread and levelled over the whole. If sand

ballast is used, care must be taken to prevent the bottom of the pumps from drawing in the sand, by protecting these with tarred canvas or matting. But there has been patented an ingenious .mode of ballasting ships, by means of water introduced into the hold, which is divided into a number of water-tight compartments. Partitions are placed between the ribs or timbers, which are made up by boarding, and the joints carefully caulked; over the planking are placed sheets of felt, such as are usually used for the sheathing of ships' bottoms; over these may be placed sheets or plates of iron, which, being made perfectly tight, form a series of tanks capable of holding water, by which the ship is ballasted.-British Cyclop.

NOTE G.-Chap. II.

WIRE-ROPE STANDING RIGGING.

Wire-ropes are now used for the standing rigging of ships, instead of hemp or chain rigging. The improved wire-rope is patented, and the patentees are Messrs Newall & Co., Gateshead-on-Tyne, and North Dock, Sunderland; and, in the preface by them, to their tables of the sizes and weights of the wire-rope standing rigging, its advantage and superiority are stated to be:

There is a reduction in the size and weight of the standing rigging, when made of the patent improved wire-rope, compared with the size and weight, when made of the best hempen rope. The reduction in size is such, that the bulk of the wire-rope rigging is only one-sixth that of hemp, while the weight is reduced to nearly one half. It is cheaper than hemp-rope;—it is more durable; and, though a little less elastic than well-seasoned hemp-rigging of the best quality, it does not stretch permanently under great strains, as hemp rigging does. The advantage of lightness in the standing rigging, must be known to every practical seaman; as the removal of a weight of several tons from the great height, which the average of the standing rigging occupies above the centre of buoyancy, must increase the stability, and particularly the steadiness of the ship. The less bulk is of advantage in a circumstance, which has been frequently appreciated by the captains of vessels having auxiliary steam-power, when making way against the wind. The superior durability of wire-rope has now been tested by upwards of thirteen years' experience of ropes, "running" and "standing," in all varieties of circumstances. The patentees have made direct experiments on the amount of stretch and the springiness or degree of elasticity of well-seasoned hemp and wire-rope shrouds, of equivalent strength, under strains equal to

one-third of that which would break them, or greater than that to which they are commonly exposed in ordinary practice; and these experiments have shewn that, while the stretch or permanent lengthening of the wire-rope is nothing compared with that of hemp, -the difference of springiness is not more than one inch in favour of hemp, in the longest shrouds :-practically, therefore, the less elasticity of wire-rope is of no importance. And another valuable quality of wire-rope rigging is,-its not being liable, by changes in the atmosphere, to those sudden alterations of length to which hemp is subject, and which every seaman knows give rise to inconvenience and great labour in setting up the rigging, and to serious accidents, when, as often happens, the change takes place in a single night, in circumstances which render it impossible to set up the rigging, before the mischief has ensued.

NOTE H.-P. 34.
BLOCKS.

Blocks are single, double, treble, or fourfold, according as the number of sheaves is one, two, three, or four. The sheaves, or wheels on which the rope runs, are grooved to receive the rope, and have in their centre, a brass or iron bush, with a through hole to receive the pin, on which the sheaves turn;-the outside of iron or wood is called the shell, and the sides of it are called the cheeks; and that part of a block by which it is made fast to any particular object, is the strap, usually made of rope or iron. A running block is attached to the object to be moved; a standing block is fixed to some permanent support. Usually, blocks are named, either from their shape, their purpose,—or their mode of application.

NOTE I.-Chap. IX., p. 40.

REEFING TOPSAILS FROM THE DECK.

This ingenious contrivance has been found to answer admirably. The sail reefs itself; and from the time the yard is lowered, it is close-reefed in two seconds; so that, in nautical affairs, this may be ranked as one of the wonders of the age. The invention is not expensive, because the sails and topsail yards now in use, can be easily altered, at an expense not exceeding £15 per yard and sail. This was invented by Mr H. D. P. Cunningham, R.N., private secretary to Admiral Moresly; and the invention has been patented.

NOTE J.-P. 157.

NUMBER AND DIMENSIONS OF BOATS WITH WHICH SEAGOING SHIPS ARE TO BE PROVIDED.

NOTE K.-Pp. 158, 219.

ADMIRALTY NOTICE RESPECTING LIGHTS TO BE CARRIED BY SEA-GOING VESSELS TO PREVENT COLLISION.

By the Commissioners for Executing the Office of Lord High Admiral of the United Kingdom of Great Britain and Ireland, &c., &c.

By virtue of the power and authority vested in us by the Act 14 and 15 Victoria, cap. 79, dated 7th Aug. 1851, we hereby require and direct that the following regulations be strictly observed :

Steam Vessels.

All British sea-going steam vessels (whether propelled by paddles or screws) shall, within all seas, gulfs, channels, straits, bays, creeks, roads, roadsteads, harbours, havens, ports, and rivers, and under all circumstances, between sunset and sunrise, exhibit lights of such description, and in such manner, as is hereinafter mentioned, viz. :—

When under steam.

A bright white light at the foremast head. A green light on the starboard side. (A red light on the port side.

1. The mast-head light is to be visible at a distance of at least five miles in a dark night with a clear atmosphere, and the lantern is to be so constructed as to shew a uniform and unbroken light over an arc of the horizon of twenty points of the compass, being ten points on each side of the ship, viz., from right ahead to two points abaft the beam on either side.

2. The green light on the starboard side is to be visible at a distance of at least two miles in a dark night, with a clear atmosphere; and the lantern is to be so constructed as to shew a uniform and unbroken light over an arc of the horizon of ten points of the compass, viz., from right ahead to two points abaft the beam on the starboard side.

3. The red light on the port side is likewise to be fitted so as to throw its light the same distance on that side.

4. The side lights are, moreover, to be fitted with screens, on the inboard side, of at least three feet long, to prevent the lights from being seen across the bow.