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Bearings by Compass, Sun, &c.   283


Pocket Compass.-A pocket compass should not be too small ; if one of the little toy compasses be carried in the pocket, it should be as a reserve, and not for regular use. A toy compass will of course tell N. from N.N.E., and the like; and that may be very useful information, but the traveller will find that he constantly needs more precise directions. He doubts the identity of some hill or the destination of some path, and finds on referring to his map, that the difference of bearing upon which he must base his conclusion, is small he therefore requires a good sized compass, to determine the bearing with certainty. One from 12 to 2 inches in diameter is practically the best. It should have plenty of depth, so that the card may traverse freely, even when the instrument is inclined : it should be light in weight, that it may not be easily jarred by a blow : the catch that relieves the card, when the instrument is closed, should be self-acting and should act well : lastly the movements of the needle should be quick ; one that makes slow oscillations should be peremptorily refused, whatever its other merits may be : the graduation of the degrees on the card should be from 0° to 360°, North being 0° and East 90°. I wish some optician would make aluminium cards. The material can be procured as foil, like tinfoil. It can then be stamped and embossed, in which case it retains its shape perfectly, but I cannot satisfy myself as to a good pattern, nor do I see how to make the North and South halves of the disc sufficiently different in appearance.

Compass for use at night.-The great majority of compasses are well-nigh useless in the dark, that is, when it is most important to be able to consult them. They are rarely so constructed, that the difference between the north and south sides is visible by moonlight or by the light of a cigar or piece of tinder. The more modern contrivances are very effective ; in these the southern half of the compass card is painted black, the northern being left white. With a very faint light, this difference can be appreciated. In compasses consisting simply of a needle, the north end of the needle should have a conspicuous arrow-head. It is extraordinary