ference of this card is divided into 32 points, and these again into half and quarter points, and also sometimes into 360 degrees. The four principal points, or, as they are called, the cardinal points, are the North (represented by N.), South (S.), East (E.), and West (W.); the East being to the right, and the West to the left, when facing the North.

All the points of the compass are called by names composed of these four terms.

Thus, the points half-way between the cardinal points are named by the two adjacent cardinal points; hence, the point midway between the north and east is called north-east (and represented by NE.); so, midway between the south and east is called south-east (written SE.); in like manner, we get south-west (written SW.), and north-west (written NW.).

A point half-way between one of these last and a cardinal point is called, in like manner, by a name composed of the nearest cardinal point and the adjacent point NE., SE., SW., and NW.; thus the point midway between the N. and NE. is called north-north-east (written NNE.), while that midway between the E. and NE. is called east-north-east (written ENE.). In like manner we get the six following: ESE., SSE., SSW., WSW., WNW., and NNW.

The points next the eight principal points—namely, N., NE., E., SE., S., SW., W., NW.-are named by placing by between the letter representing the point to which it is adjacent and the next cardinal point in the same direction. Thus the point next to the north on the east side of it is called north by east, and written N. by E., whilst that adjacent to the north but towards the west is written N. by W.; in this manner we get other sixteen points. We have thus got names to all the thirty-two points of the compass.

A half-point is the middle division between two points, and can be named by either of the points between which it lies and the first cardinal point reached after passing it, placed after the; thus, the half-point between NE. and NE. by N. can be named either NE. N. or NE. by N. E., so also the half-point

NW., SE., and SW., are and the cardinal point

between W. by N. and WNW. may either be written WNW. W. or W. by N. N. The half-points adjacent to the cardinal points, and also those adjacent to NE., always named by these letters with the next after on the same side as the half; thus N. E., N. W., SE. S., SW. W., &c. The same holds for a quarter-point, and for three-quarters of a point; thus the point of the compass which is of a point nearer to the N. than NE. by N. is also

of a point nearer to the E. than NNE., it may therefore be either called NE. by N. N., or NNE. E.; the latter is, for several reasons, the best.

167. Repeating the points of the compass in their proper order and in any direction is called boxing the compass, and is one of the first things that a seaman learns; but their utility is not confined exclusively to navigation, for in walking across a new country or through a strange city, no impressions will be

The Azimuth Compass.

of the compass.

168. The AZIMUTH COMPASS is a compass of superior construction, particularly adapted to observe bearings. It is mounted on a tripod stand, and is fitted with vertical sight vanes, for the purpose of observing objects elevated above the horizon; one of these vanes has a long and narrow slit, and in the other there is an opening of the same kind, but wider, with a wire up and down the middle of it, exactly opposite the slit.

VARIATION OF THE MAGNETIC NEEDLE.

169. The needle points to the magnetic north, which in most places does not agree with the true north: the difference between the bearing of the magnetic and true north is called the variation of the compass.

The variation is named easterly when the magnetic north is to the east of the true north, and westerly when it is to the west of the true north. The variation is different at different places, and is constantly changing, though slowly, and in a long course of years it changes, at the same place, from easterly to westerly, and conversely.

170. To find how to correct the compass course or bearing, suppose one compass card to be placed over another, the under one being the true one; then, if the compass have two points of easterly variation, the north of the upper compass will be on the NNE. point of the true, and in order to bring it correct it will have to be turned through two points to the left, supposing we look from the centre of the compass to the circumference. Again, if the variation of the compass were 2 points westerly, the north of the upper card would be over the NNW. W. point of the true, and therefore to make it coincide with the true compass, it would be necessary to turn the upper card through 2 points to the right.

F

Problem V.

171. When the compass course and the variation of the compass are given, to find the true course.

RULE.

When the variation is easterly, apply it to the right of the compass course or bearing; when westerly, apply it to the left of the compass course or bearing, to get the true course or bearing.

Example I.

Given the compass course NW. W., and the variation of the compass 2 easterly, to find the true course.

Here the compass course is N. 4 W., and the variation being easterly must be applied to the right, thereby bringing it 22 nearer to the north, that is, within two points of the north; the true course is therefore NNW.

Example II.

Given the compass course WSW. S. and the variation 1 points westerly, to find the true course.

Here the compass course is S. 5 W., and the variation is westerly, and hence must be applied to the left, thereby bringing it 1 points nearer to the south, that is, within 4 points of the south; the true course is therefore SW.

Exercises 14.

In the following exercises the true courses are required:

(160.) Compass course SW. by W.,

variation 2 pts. E.

172. Given the true course and the variation of the compass, to find the compass course.

RULE.

If the variation be westerly, apply it to the right; but if easterly, apply it to the left of the true course, and the point thus determined will be the compass course.

Example I.

Given the true course E. by S. S. and the variation 1 points W., to find the compass course.

Here the true course is S. 6 E., and the variation being westerly, is applied to the right, which gives S. (6-12) E. = S. 4 E. or SE. E., which is the compass course required.

Example II.

Given the true course WSW. W., and the variation 2 easterly, to find the compass course.

Here the true course is WSW. W. S. 6 W., and the variation being easterly is applied to the left, and therefore subtractive, wherefore the compass course is S. (61-2}) W. = S. 41 W. SW. W. = the compass course required.

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