length lies in the North and South line, while its North-seeking end is at the spot marked North on the card. The card, with its attached magnet, has only horizontal motion, and is mounted so as to rest on a steel pivot that rises from the centre of the bottom of a brass or copper bowl. The bowl has a glass cover, so that the indications of the card may the more readily be seen and read off; and to facilitate this a vertical

line is painted inside the bowl, to show in what direction the ship's head may be at any time.

The instrument described is the Mariner's Compass, which, by the aid of gimbals, is fitted into a wooden or brass binnacle, or perhaps into a skylight, wherever it can be best seen by the man at the wheel, or for taking bearings.

To box the compass, or, in other words, to name

the various points of it, must be acquired most accurately. Many persons imagine this to be so puzzling, that they give it up at once and for ever; but the whole business should be accomplished in about a quarter of an hour. To begin with, when once a quarter of the compass or circle is mastered, the rest is easily accomplished, for the same rule or arrangement applies to the other three quarters. I will now give two simple rules by which to learn the whole.

1. When the letters indicating two points are united, the point meant is half-way between the two; thus, N.E. is half-way between N. and E.; S.S.W. half-way between S. and S.W.

2. When the letters are joined by the word by, or the letter b, the point meant is the one which comes next after the first, going towards the second; thus, S. by W. is next to south, going west; N.E. b N. is next to N.E., going north.

Each of the points is also subdivided into half and quarter points; thus, N.W. W. is north-west and a quarter of a point more towards the west.

It is a common thing in connection with the calculations in Navigation to express the points of the compass numerically; thus, N. 3 pts. E. stands for N.E. b N., S. 4 pts. W. for S.W. W., and so forth. Similarly, it is often convenient to read the compass in degrees; thus, N. 53° E. means North 53 degrees towards East.

Now give special heed to what follows. The compass is taken to be the representation of the visible horizon, in the centre of which you stand on the deck of the vessel; consequently you must always look to your compass as if you were in its centre; otherwise you will misapply the terms right and left as applied to a course bearing:

Thus, one point to the right of N.E. is N.E. b E. ; and one point to the left of N.E. is N.E. b N.

But, one point to the right of S.E. is S.E. b S.; and one point to the left of S.E. is S.E. b E., looking from the centre of the compass towards S.E.

The direction in which the ship is steered is the compass course, which requires to be corrected for leeway (if any is made), for variation, and for deviation, if an iron ship.

I append the Names of the Points of the Compass, with their numerical and angular values.

THE VARIATION OF THE COMPASS.

The magnetic needle, when unaffected by any surrounding iron, points to the magnetic poles of the earth, and the direction in which it trends at any place is called the magnetic meridian. As the magnetic poles are not coincident with the earth's true poles, which are the extremities of the axis of revolution, and between which the true meridians trend, it follows that the magnetic meridian forms an angle with the true meridian, and this is the Variation of the compass. In different parts of the world the variation differs, not only in amount, but also in direction; thus, over the North Atlantic, the greater part of the South Atlantic, and the Indian oceans, the variation is called Westerly, inasmuch as the North-marked end of the needle lies to westward of the true North, while over the Pacific Ocean it is called Easterly, because the North-marked end lies to eastward of the true North. In British waters the variation ranges between 19° W. in the Straits of Dover and 27° W. off the West Coast of Ireland and off the Hebrides.

You can understand that the two areas of easterly and westerly variation are separated by lines where there is no variation—i.e. where the magnetic needle shows true North and South; one such line trends through Eastern Europe, Asia, and Australia; another runs through North America, the east end of South America, and the S.W. corner of the South Atlantic. Everywhere the variation is constantly undergoing a gradual change in its direction; the annual change in our waters amounts to 8'.

In London and off the Isle of Wight, where the variation is 1910 W., the true North is indicated by the

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compass direction which we call N. by E. E., or N. 1910 E. (in 1879).

All charts are engraved true North and South, East and West; but in various places the compass is engraved with its variation, which will easily be understood on inspection.

You must learn to convert compass courses and bearings into true, and the converse, and to do it with facility.

To correct compass courses and bearings for variation. RULE:—When the variation is westerly, apply it to the left of the compass indication; when easterly, apply it to the right.

Ex. Course by compass N.E., with variation 1 points westerly, gives true course N.N.E. E., which is 12 points to left of N.E. Ex. Course by compass N., with variation 2 points westerly, gives true course N.N.W. W.

Ex. Course by compass S. 6 W., with variation 2 points westerly, gives true course S. E. E.

Ex. Course by compass S.E. E., with variation 2 points westerly, gives true course E. by S.

Ex. Bearing by compass W.

N., with variation 1 points westerly,

S.

W., with variation point easterly, W., which is point to right of

gives true bearing W. b S. Ex. Course by compass N. 6 W. gives true course N. N. 6 W. W. Ex. Bearing by compass S. W. gives true bearing S.W. W.

S., with variation 1 points easterly,

To reduce true courses and bearings to compass courses and bearings. RULE:—Apply westerly variation to the right of the true indication; easterly variation to the left.

Ex. True course W., with variation 24 points westerly, gives compass course N.W. W. W., which is 24 points to right of W. Ex. True course N. E., with variation 1 points westerly, gives compass course N.N.E.

Ex. True course S.E. b S., with variation 2 points westerly, gives course to be steered S. b E.