N.N.E., etc.; but his surveying data which find no place in his memory, but are simply consigned to his note-book, are necessarily registered in degrees.  To give every facility for carrying out this principle, a round of paper should be pasted in the middle of the traveller’s pocket-compass card, just large enough to hide the ordinary rhumbs, but leaving uncovered the degrees round its rim.  On this disk of paper the points of the compass (true bearings) should be marked so as to be as exact as possible for the country about to be visited.

Errors in Magnetic Bearings.—­The compass-needle is often found to be disturbed, and sometimes apparently bewitched, when laid upon hill-tops; even when they consist of bare masses of granite.  The disturbance is easily accounted for by the hornblende in the granite, or by other iron-bearing rocks.  Explorers naturally select hills as their points of triangulation; but compass observations on hill-tops, if unchecked by a sextant observation of the sun’s bearings, are never so reliable as those taken on a plain.

[Sketch of card as described on following pages].

Bearings by Sun and Stars.—­It requires very great practice to steer well by stars, for, on an average, they change their bearings even faster than they change their altitudes.  In tropical countries, the zodiacal stars — as Orion and Antares—­give excellent east and west points.  The Great Bear is useful when the North Pole cannot be seen, for you may calculate by the eye whereabout it would be in the heavens when the “pointers” were vertical, or due north; and the Southern Cross is available in precisely the same way.  The true North Pole is about 1 1/2 degree or 3 diameters of the full moon, apart from the Pole star; and its place is on a line between the Pole Star and the Great Bear.  An almanac, calculated to show the bearing, and the times of moonrise and moonset, for the country to be travelled over, as well as those of sunrise and sunset, would be a very great convenience; it would be worth while for a traveller accustomed to such calculations to make one for himself.

Diagram.—­The diagram (preceding page) is intended to be traced in lines of different colours, when it will be found to be far less confused than at present.

Its object is to enable a traveller to use the sun, both as a rude watch and as a compass.  The diagram is calculated for the latitude of London, but will do with more or less accuracy for the whole of England.  A traveller going to other countries may easily draw up one for himself, and on a larger scale if he prefers it, by using the Azimuth tables and the Horary tables of Lynn.

The diagram represents, 1st, circles of equal altitudes; 2ndly, the path of sun, stars, etc., for each 10th degree of declination; 3rdly, the hour angles, all projected down upon—­4thly—­the level compass card.

Thus, six circles are drawn round the centre of the compass card at equal distances apart, each ring between them representing a space of 15 degrees in altitude.