In the majority of iron ships, while the ship is in the northern hemisphere and the compass above the upper deck, the north point of the compass is drawn to windward as the ship heels. If the ship is kept steady on one compass course, she will be found to windward of her supposed position when on northerly, and to leeward when on southerly courses. If the ship is kept steady on a fixed point in the horizon, she will appear by compass to fall off as she heels on northerly, and to come up on southerly courses.

In steering by compass, in order to make good a given compass course, keep away on either tack as the ship heels when on northerly courses, and keep closer to the wind on either tack when on southerly courses.

Ships which have the north point of the compass drawn to windward in the northern hemisphere, will, especially in high southern latitudes, have it drawn sensibly to leeward.

In the northern hemisphere iron ships should be built head south magnetic, or nearly so, as the part of the ship on line of upper deck which is north in building is much less strongly magnetized than the part which is south.

To neutralize the large deviations found in iron ships, provide two powerful magnets, and draw two lines on the deck directly under the centre of the compass intersecting one another at right angles, the one line running fore and aft, the other athwartship.

Place the ship's head correct magnetic north or south and place one of the magnets on or below the deck, with its centre on the fore and aft line, and parallel to the athwartship line: if the north point of the compass is attracted towards the starboard side, place the blue end of the magnet to port, and vice versâ, then move the magnet to or from the compass until the needles point correct magnetic north or south. Then place the ship's head

correct magnetic east or west, and place the other magnet on or below the deck, with its centre on the athwartship line, and parallel to the fore and aft line; if the north point of the compass is attracted towards the stern, place the red end of the magnet aft, and vice versa, then move the magnet to or from the compass until the needles point correct magnetic east or west. Then bring the ship's head to one of the intercardinal points N.E., S.E., S.W., or N.W., correct magnetic, and put as much soft iron chain in the boxes as will overcome the quadrantal deviations. These adjustments must be made with the ship perfectly upright.

To compensate for the heeling error, put the ship's head magnetic north or south, and heel her over as far as practicable; if the north point of the compass is drawn to windward, keep the red end of a vertical magnet placed in the centre of the pillar of the binnacle uppermost, but if to leeward, the blue end, and move the magnet up or down immediately under the centre of the compass until the needles point correctly.

As it is difficult, and often impracticable, to heel the ship, the error may be corrected as follows:—Having found the time in which a dipping needle placed on shore, and deflected say 20 degrees in an east and west plane, will take to make ten vibrations; place the same instrument in the binnacle on board, with its centre in the position of the point of suspension of the compass needles; place the ship's head magnetic east or west, and having deflected the needle as before, move the vertical magnet up or down as the case may be until the time due to ten vibrations corresponds with that previously found on shore, then fix the magnet.

Although compasses may be adjusted by magnets before a ship sails, and the adjustment hold good for that locality, yet as the ship changes her position, and alters not only the variation but the dip of the needle, the

relative forces of magnetism alter also, and the corrections cease to be reliable.

Many fine vessels have been lost, while others have found themselves far out of their reckoning, in consequence of too little time having been given for observations to verify the Steering Tables, and too little attention paid to the following simple Rules :

After steering for some time on easterly courses, expect easterly deviation if you turn to the north, or westerly deviation if you turn to the south.

After steering for some time on westerly courses, expect westerly deviation if you turn to the north, or easterly deviation if you turn to the south.

The reason for this is, that true northern polarity (blue), or true southern polarity (red), induced in the starboard and port ends of deck beams, and starboard and port sides of ships, while steering east or west, remains for some time after she has altered course to north or south.

This warning is particularly important for ships of war, after firing guns when on easterly or westerly courses, if the course is then changed to north or south; and more particularly if the change of course is effected under canvas, without the shaking of the ship's magnetism produced by the action of the engines and propeller.

The warning is also important for ships steaming through the Mediterranean eastwards or westwards, and then turning south, through the Suez Canal, or north, round Cape St. Vincent; and for ships steaming eastward from America, and then turning northwards or southwards into St. George's Channel.

C

DEVIATION BY THE BEARING OF A DISTANT

OBJECT.

The method of determining the deviations of the standard compass, by finding the correct magnetic bearing of a distant object, and hence the deviations, is as follows: Place the ship's head by the standard compass on the eight cardinal points, and observe the bearing of a distant object, say ten miles off, as she steadies on each point successively, then tabulate the results as in the subjoined forms, and find the correct magnetic bearing of the object (if not already found by taking the compass ashore) by the following rule: When the bearings are all of one name, add them together, and divide by 8, the result is the correct magnetic bearing of the same name as the standard compass bearings.

If some bearings are north and some south, subtract the less number from 180 degrees, so that all the bearings will be of one name, then divide by 8, the result is the correct magnetic bearing.

If the bearings are all north or all south, while some are east and some west, add all the easts together, then the wests, substract the less from the greater sum, and divide by 8, the result is the correct magnetic bearing of the distant object, to be named after the greater sum.

The difference between the correct magnetic bearing thus found, and the observed bearings of the object by the standard compass on board, will give the deviations of the compass, which are named East when the correct magnetic bearing is to the right, and West when to the left of the bearing from on board.