Few professions have been as closely associated with an instrument and a physical phenomenonn

   Strangely enough, over recent decades as the use of the magnetic compasses has declined, the scientific knowledge of the earth's magnetic field has been expanding. An accepted physical model of the earth's magnetic field, which was listed by Albert Einstein as one of the ten major challenges to physicists, is still not available but geophysicists are united in acceptance of an essentially complete physical understanding of the phenomenon. From this standpoint it is a little like the weather. Everyone knows what causes the weather such as the jet stream, those tropical lows, collisions between hot wet and dry cold air, etc. but no one has a mathematical equation into which you can plug parameters and calculate the weather for the next month.
  
   The important difference between the weather and the earth's magnetic field is that the weather changes on a daily, if not hourly, basis while the earth's primary magnetic field, discounting sun induced magnetic storms, has a cyclic change period which is measured in ten's to 100's of centuries. Thus, a realistic analogy of the magnetic field to the weather would be that it started raining about 200,000 years ago and we are now in the waning 1000 to 2000 years of the shower. All we have to do in our era is describe the rain drop rate around the world. For the earth's magnetic field this translates to a description of the magnetic field strength and direction (declination and dip) around the globe.

    It takes three numbers to fully describe the earth's magnetic field. These numbers are usually the total field strength plus two angles defining the direction; declination and dip. Declination, the angle between the direction to the North magnetic pole and true North, is the number with which surveyors are most concerned. Declination, in a historical context, is a function of three variables, latitude, longitude and time. This leads to the major difficulty in dealing with declination. From a table of declination values a three dimensional interpolation must be performed to calculate the declination for a specific location and a specific time.

    This is a very messy calculation to make by hand and has many opportunities for mistakes. It is of course an ideal application for computers which, once programmed and provided with the needed data base, will make the calculations quickly and without error.

  Two computer programs are available to surveyors for this purpose, one from NOAA in Boulder, CO and one from CBU Software in Orlando, FL. The NOAA program, USHD, was written many years ago and has a minimal number of "operator friendly" attributes. The program will produce a disk file of declination for any latitude and longitude entered by the user. Declination is provided at ten year intervals prior to 1900 and at five year intervals after 1900. According to NOAA representatives the program will, for some inputs, "bomb"; or fail to operate due to program code errors.

    The CBU Software program, MAGDEC is a Windows program and uses the same data base as USHD. MAGDEC was written for ease and convenience of use by surveyors. In addition to declination for any year or a plot of the annual value of declination, the program will transform bearings from one year to another, a convenience in analysis of plats and deeds.

  For any location and time the declination is determined by the sum of three effects. The dominate effect is the primary magnetic field of the earth. It is generally accepted that the primary field is generated by electrical currents flowing in the molten metallic inner layer of the earth. Another factor influencing the observed magnetic field is the magnetism of natural features in the earth’s crust, rocks, metallic ores, etc. The residual magnetic
fields from cultural objects, railroads, metal buildings, fences, etc. can be included in this group.

    The third factor is the magnetic field generated by currents flowing in the ionized layers of the earth's atmosphere induced by streams of particles (protons) originating from the sun. The influence of the sun on the earth's magnetic field is well proven. The diurnal declination variations of typically many minutes of arc are caused as the earth faces the particle stream from the sun and then, as night approaches, is shielded by the mass of the earth itself. This effect makes early morning or late afternoon the "best" time for compass readings.

    Magnetic storms are well correlated with the appearance of a large number of sun spots on the solar disk. Because of the lower speed of the particles from the sun spots or flares associated with the sun spots the onset of magnetic storms, both timing and intensity, can be predicted with a high degree of certainty. NOAA's Solar Environment Laboratory provides this service free of charge. The forecast is available in a recorded message at 303-497-3235.

    Most industrialized nations have governmental entities which monitor the earth's magnetic field. In the U.S. this service is performed by NOAA (National Oceanic and Atmospheric Agency) in Boulder, CO and the U.S. Geological Survey in Golden, CO, a part of the Department of Interior.

    Generally, NOAA's work tends to be more scientific and exploratory while the USGS mission brings the needed services on magnetic field data to users in the form of isogonic charts, printed reference material and direct assistance. Susan McLean of NOAA's National Geophysical Data Center directs programs dealing with the earth's magnetic field. She has compiled a listing of over 700 scientific reports published between 1836 and the early 1990's which deal with the earth's magnetic field. These reports are narrowly focused on the earth's magnetic field, excluding the subjects of crust variations and solar magnetic storms, the other two factors influencing which way the compass needle points.

    Surveyors have not been the only users of magnetic field technical data. Minor Davis at NOAA relates how ships at sea once used knowledge of the change of declination with latitude and longitude to locate themselves at sea. Local declination was observed by comparing the direction to the North star and magnetic North and attempted to locate themselves at sea with the results.

    According to Jill Caldwell at USGS one currently active use of declination data is for automatic directors of satellite antennas on mobile homes and campers. With accurate location from GPS and current declination data, the satellite TV antennas can be automatically aimed to intercept a satellite signal.

    The currently accepted theory of how the earth's magnetic field got started is that electrical currents were first induced by the sun into the molten metal inside the earth. The electrical currents were then amplified by a dynamo effect from the earth's rotation. Very slowly with time this current field and the magnetic field it produces decays. All indications are that we are currently in the waning years of a cycle which has been repeated many times during the earth's life. Data on the strength of the earth's magnetic field shows that it has been decaying for many years, a trend which will cause it to eventually be reduced below the crust level.

    At one time it was thought that periodically the earth's magnetic field reversed itself, the north pole becoming the south and vice versa. Books were written on this subject of reversals which occurred every 100 to 300 thousand years. The "reversals" were tracked in time by measuring the orientation, age and magnetism of rocks on the earth's surface. Currently it is believed that the field simply decays with time and eventually the natural
residual magnetism of the earth's crust and the magnetic field induced by the sun in the ionosphere become predominate. Under this condition there could be many localized &;north poles&; scattered across the earth's surface, all very weak. This field, dominated by local magnetic features, would be modulated by the diurnal magnetic field produced by the interaction of emissions from sun spots, or the flares associated with sun spots, and the earth's ionosphere.

    In addition to decaying in strength with time, the orientation of the earth's primary magnetic field, or location of the magnetic poles, changes with time. This change in orientation is called the secular change in the field. The dip and declination angles change around the globe, changing more rapidly in the North due to the proximity to the magnetic pole. These changes are measured continuously at magnetic observatories around the world and the results are published for the use of the public.

    Accurate declination data can be very valuable in many surveying problems. The following problem has been posed to surveyors to illustrate the utility of applying declination to magnetic bearing records. In attempting to locate a boundary assume the following data is available:

• in a deed call, boundary bearing from a monument is N32E terminating on a waterway about 5000 feet from a monument. 

• A 1904 plat, same line, N33.5E

• From a 1994 survey with a compass:  

• a timber cut line (1962) at N36.75E

• Minor occupation remnants at N38E  

    The question is which line should be platted as the boundary and why. The 1.25 degree difference between the occupation remnants and the timber cut line is 110 feet at the waterway at the end of the 5000 feet length of the boundary.    Using accurate declination data for the location, Lat:39 25 30, Long:83 40 50, the answer quickly becomes apparent.

    The declinations for the years in question were:

• 1878 1 Deg 18 Min East 1904 0 Deg 15 Min West

• 1962 1 Deg 29 Min West 1994 4 Deg 46 Min West
  

Using these values it is found that the deed call, the 1904 plat and the 1994 survey of found old occupation remnants are the same line. The timber cut line of 1962 was based on the 1904 plat without correcting for the declination change between 1904 and 1962. The boundary is the line from the old occupation remnants which is the same line as the deed call and the 1904 plat.