You may have a pocket compass of surveyor's pattern, such as the common military compass in a square wooden box, used in our army. Observe that on a surveyor's compass the E and W marks are transposed, and don't let this fool you in the field.
In using a compass look out for local attraction. Put your gun or axe aside; a knife, or belt buckle, or other piece of metal may deflect the needle. If there is anything in your equipment that might do this, test the instrument first on the ground a pace away, and then in your hand. The compass should not be kept near iron, even when not in use, as the needle is likely to be demagnetized.
A compass needle may be demagnetized when traveling in an electric car if carried in a valise or knapsack and set down on the floor over a powerful motor, if the needle is clamped, as it should be when not in use. To strengthen the magnetism of a compass needle, unclamp it and lay the instrument near a motor or generator or strong magnet; then, when it has stopped quivering, clamp it again and leave it under the influence of the magnetic current for a short time.
A compass may become bewitched by a body of ore that you may be passing over, but such experiences are rare. If you suspect something of the sort, carry the instrument away, it need not be far, and test again. You are far more likely to be bewitched yourself.
No compass can tell you which way camp lies when you are lost. So the first and best place to use it is in camp, before you go anywhere. If there are landmarks visible from camp, take their bearings, and locate them on a sheet of paper or in your notebook. Then, if you are in a flat country, run a base-line as described in Chapter III. If in a hilly region, climb the nearest height, and from it make a sketch map of the surrounding country, with streams and prominent landmarks noted and their bearings shown. Carry that map always with you, and add to it as you learn the country. No matter how rude it may be, it is likely to come in mighty handy.
An experienced woodsman may photograph the landscape op his brain, but not one city man in a hundred car do so with certainty that it will not have blurred or faded away when he gets bewildered. So don't let any false modesty keep you from using your pencil: the man who laughs at an amateur (or anybody else) for doing so is most likely a Reub who never has been a hundred miles from his own front door.
When traveling in a region where there are plenty of outlooks, the weather being clear, the sun and visible landmarks are sufficient guides. When you do use a compass on the march, and the country is not too difficult, it will be enough to hold the instrument in one hand, and, without waiting for the needle to stop swinging, note the point midway of the limits of its motion and take that for north, unless the magnetic declination is considerable (see below).
In level, heavily timbered country, one must take greater pains if he wants to reach a definite point. Lay the compass on the ground, or on any higher object that will hold it level. Or, if both hands are| free, hold it in both of them at half-arm's length, with elbows resting on your sides, so as to bring the instrument straight in front of the center of your body. Then face some tall tree or other conspicuous feature of the landscape in direct line with youi objective and as far off as you can see. Check the vibration of the needle by quickly tipping the compass until the end of the needle touches the glass, and repeat until needle stops quivering. Now level the box and take the bearing of your landmark. Walk to it, and take a sight on something else in the same line.
Where you cannot see out to take bearings in this way, consult the compass every two or three minutes; for it is the easiest thing in the world to get off a true course at such times, and a few degrees' swerve, if not soon detected, will carry you far astray.
When some obstacle obliges you to make a detour, sight some landmark ahead, if you can, before you go around. If there be none visible, then estimate your winding with great care, and get back in line again as soon as you can. It is rarely the case that one can travel any distance in the wilderness without swerving very often from a true course; so the art of averaging windings should be practiced until one becomes adept.
When following a stream, note how many tributaries you cross. When following a divide, note how many abutting ridges you pass on each side. You will need that knowledge when you return, and it must be exact.
The north end of a compass needle does not point to the true north, except in certain places as noted below. It points to the mannetic pole, which lies far south of the north pole and about seven degrees west of the meridian of qo°W.
The places where a compass does point to the geographic north are those situated along what is called the "agonic line," or "zero curve," or "line of no variation." This is not a straight line from north to south like a meridian on the map, but has many waves and loops, and runs in the main easterly of south. At present the agonic line runs from Mackinac Island, in Lake Michigan, loops west and then diagonally through eastern Michigan to central Ohio, makes a big loop north toward Lake Erie and back, south to the Ohio River, makes two big loops east and west in eastern Kentucky, runs south through western Virginia, loops wrest in eastern Tennessee and then far back east, goes down through western North Carolina, loops east again, and then runs diagonally down through Georgia and out into the Atlantic. This line is not stationary, but has a slow movement westward called the "annual change." Nobody knows the cause of these vagaries: magnetic variation is a mystery as yet unsolved.
Now note this: at all places east of the agonic line the north end of a compass needle points to the west of true north (more and more as the distance increases), and everywhere west of this line it points easterly.