A man, to make a success of prospecting, must have what is known as "a good eye for a country." Given that faculty he will readily pick up the little knowledge of surveying that is sometimes almost indispensable. A tape measure, and a prismatic or surveying compass, are all that he is likely to require in laying off to his own satisfaction the extent of his claim, or any similar simple operation. The surveying compass has two fixed sights, and a Jacob staff mounting, into which a wooden support is inserted. The north end of the compass is always pointed ahead, while the needle, which of course indicates the magnetic north, gives the bearing of the line run toward that north. Now, magnetic north is not by any means the same thing as true north, in fact in very few localities on the earth's surface are they the same, and then never for long. In the extreme east of the United States the needle points some twenty degrees to the west of true north, and in Alaska it points thirty-five degrees to the eastward of it. There is therefore one meridian somewhere in the central valley where the true north corresponds with the magnetic north, but as the magnetic pole is always shifting this never remains true of the same meridian for long. [Illustration: SURVEYING COMPASS.] When there is no local magnetism from iron ores, or rocks containing magnetite, the needle is fairly reliable, though never perfectly accurate, but when such attraction exists the compass is unsatisfactory. Such areas of attraction, however, are usually limited, and by squinting back, taking what is known as a "back sight," a local attraction may be detected, and in that case ranging by rods must be resorted to until the compass needle once more seeks its true position. To range by rods the course of the line having been determined by retracing the route followed to the last reliable mark, a stake is driven in at that point, and the surveyor standing some little distance behind it on the correct line directs an assistant to place another rod in such a position that the first hides it from view. It will then be on a prolongation of the line, and this operation being continued the surveyor will, in due time, find himself beyond the reach of the local attraction that deflected his needle and can resume compass work.