Very well explained indeed, my self-sufficient friend; but you have not answered the question. You have told us what a compass is like, and one of the uses to which it is applied; but you have not yet told what it _is_. A man who had never heard of a compass might exclaim, "What! a needle! Is it a darning needle, or a knitting needle, or a drawing-through needle? And which end points to the north--the eye or the point? And if you lay it on the table the wrong end to the north, will it turn round of its own accord?" You laugh, perhaps, and explain; but it would have been better to have explained correctly at first. Thus:-- The mariner's compass is a small, flat bar of magnetised steel, which, when balanced on a pivot, turns one of its ends persistently towards the north pole--the other, of course, towards the south pole; and it does this in consequence of its being magnetised. A card is fixed above, sometimes below, this bar of steel (which is called the needle), whereon are marked the cardinal points--north, south, east, and west--with their subdivisions or intermediate points, by means of which the true direction of any point can be ascertained. "Aha!" you exclaim, "Mr Author, but you yourself have omitted part of the explanation. _Why_ is it that the magnetising of the needle causes it to turn to the north?" I answer humbly, "I cannot tell;" but, further, I assert confidently, "Neither can anybody else." The fact is known, and we see its result; but the reason why magnetised steel or iron should have this tendency, this polarity, is one of the mysteries which man has not yet been able to penetrate, and probably never will. Having explained the nature of the compass, as far as explanation is possible, we present our reader with a picture of one. It will be seen that there are four large points--N, S, E, and W--the cardinal points above referred to, and that these are subdivided by twelve smaller points, with one little black triangular point between each, and a multitude of smaller points round the outer circle. To give these points their correct names is called "boxing the compass,"--a lesson which all seamen can trip off their tongues like A, B, C, and which most boys could learn in a few hours.