The Brunton line of sportsman’s compasses incorporates many features first developed on our professional-grade instruments; they are the finest popular-usage compasses available today.
Your Brunton sportsman’s compass has numerous features which make it easy to work with and increase its usefulness. Take a few moments to study your compass, referring to the appropriate diagram (below) and you will be able to understand the following instructions with little or no difficulty.
The magnetic compass has been used as a direction-finding device for thousands of years, ever since it was discovered that a magnetized needle will point in a constant direction when left free to rotate.
This is so because the earth is surrounded by a magnetic field, and a magnetized object will orient itself to that field, given the opportunity.
Specifically, it will align itself so that it points toward the earth’s North magnetic pole, The North magnetic pole is located near (but not precisely at) the geographic North pole.
Primitive compasses consisted of an iron needle which had been stroked with a magnetic rock and then suspended from a thread, or struck though a piece of cork or wax and placed in a bowl of water.
Although these compasses were not very precise, they nonetheless helped early explorers and navigators find their way from one point on the earth’s surface to another, by providing a constant direction indicator.
Today’s compasses work on the same principle, nut are far more sophisticated. In addition to a freely turning magnetic needle, a modern, high-quality compass will have a movable, calibrated dial and a sighting system for use in obtaining accurate bearings. More advanced compasses can also be adjusted to compensate for the fact that the earth’s magnetic poles are not located precisely at the geographical poles. (The error caused by this difference is called declination , and it varies depending upon your location.)
A bearing is the degree reading or direction from your position to another object. Thus, if you were in the field and a mountain peak was directly East of your position, the bearing of the mountain would be 90 ° . If the peak were directly South, its bearing would be 270 ° .
(The term azimuth is sometimes used instead of bearing.)
To take a bearing hold the compass level in front of you. The sighting line should be pointing toward the object on which you are taking a bearing. (Fig. 2). With the sighting line pointing straight to the object, carefully turn the dial until the orienting arrow and the magnetic needle are lined up (Fig. 2A).
Be sure the arrow and needle are lined up correctly and not backwards. The bearing to your object is now the degree reading indicated at the sighting line.
located in the Hudson’s Bay region and moves slightly from year to year.
Because the magnetic pole is not at the true geographic North pole, compass readings will not correspond accurately to map directions unless the compass is adjusted to compensate for the difference ion location.
The angel between magnetic North and true North is called magnetic declination , and it varies depending upon where you are in relation to the magnetic and geographic poles.
When you are in a position such that true North and Magnetic North are “lined up” with each other, the declination is zero. The zero declination line passes through Lake Michigan and extends through
Florida, as shown in Fig. 3.
If you know the bearing in degrees to an object from your present location, it is a simple matter to find your line of travel to that object.
First, rotate the compass dial until the known object is next to the sighting line.
Then, hold the compass in a horizontal position, so that the magnetic needle is free to rotate, and pivot yourself until the orienting arrow is aligned with the magnetic needle. The sighting line on the compass now indicates the appropriate direction of travel to reach your objective.
Before using your Brunton compass, it is advisable to make sure it is properly adjusted to compensate for the local angle of declination.
is Declination?
The magnetic needle in your Brunton compass points towards the earth’s North magnetic pole, which is
If you are East of the zero declination line, your compass will point
West of true North, This is called westerly declination. If you are
West of the zero declination line, your compass will point East of true
North (easterly declination). For example, in Texas, at the 8 ° declination line, your compass magnetic needle would point 8 ° East of true North. Conversely, Maine, at the 20 ° declination line, the needle would point 20 ° to the West of true North.
Since maps and directions are usually based on true North, declination error must be considered whenever you use your compass. Fortunately your compass is easily adjusted to compensate for declination error.
The following steps are used to adjust your compass. Figure 1 shows compass parts important to declination adjustment. Figure 4 illustrates the adjustment procedures. Figure 5 shows examples of declination settings after adjustment.
1.
Determine the declination in your area through use of the isogonic chart.
2.
Squeeze the center vial with thumb and index finger of the left hand.
3.
With right hand, rotate outer dial until the arrow is lined up with the desired declination angle on the declination scale.
4.
With declination set for your area, your compass will indicate true North.
A topographic map shows hills and valleys by contour lines.
Each contour line represents a constant elevation in feet or meters above sea level. The interval of height between lines is stated on the map. This interval or vertical distance is represented by the space between contour lines. Thus, lines close together indicate that elevation is changing rapidly, while lines far apart indicate a gradual elevation change.
With practice you can recognize at a glace, hills, valleys, ridges or cliffs. Interpretation of the contour lines enables the sportsman to select the best possible route from one point to another. It also enables him to identify landmarks by determining his position or bearing relative to those landmarks.
A topographic map index for your state can be obtained from:
Map Information Office
U.S. Geological Survey
General Services Building
8 th and F Streets, N.W.
Washington, D.C. 20405
Figure 6 illustrates how terrain is shown on a topographic map.
Your Map.
Topographic maps have a diagram showing the magnetic declination angle. One method of constructing magnetic lines is simply extend the magnetic arrow on the map with a straight edge, Then we use the extended line as a reference to draw parallel lines at about one-inch intervals.
a Map.
If you wish to travel from your present location to some destination on the topographic map, simply place your compass on the map so that the long edge of the base is in a lone from your location to the desired destination.
(See Figure 7.)
Next, hold the compass in a steady position and rotate the dial so that the arrow and lines on the transparent bottom of the compass are parallel with the magnetic North lines you drew on the map. Be sure that the North side of the dial is toward North on the map. (See
Fig. 8.) The bearing to your destination now appears at the sighting line nearest the destination. Your line of travel can now be found using the method explained under section, How to Find Your Line of
Travel When the Bearing is Known .
