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geodetic surveying 1940-1990

1807 - 1940


Joseph F. Dracup
Coast and Geodetic Survey (Retired)
12934 Desert Glen Drive
Sun City West, AZ 85375-4825


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ABSTRACT

The United States began geodetic surveys later than most of the world's major countries, yet its achievements in this scientific area are immense and unequaled elsewhere. Most of the work was done by a single agency that began as the Survey of the Coast in 1807, identified as the Coast Survey in 1836,renamed the Coast and Geodetic Survey in 1878 and since about 1970 the National Geodetic Survey, presently an office in the National Ocean Service, NOAA. An introduction containing a brief history of geodetic surveying to 1800 is followed by accounts of the American experience to 1940. Broadly speaking the 1807-1940 period is divided into three sections: The Early Years 1807-1843, Laying the Foundations of the Networks 1843-1900 and Building the Networks 1900-1940. The scientific accomplishments, technology developments, major and other interesting events, anecdotes and the contributions made by the people of each period are summarized.

PROLOGUE

Early Geodetic Surveys and
The British-French Controversy

The first geodetic survey of note was observed in France during the latter part of the 17th and early 18th centuries and immediately created a major controversy. Jean Picard began an arc of triangulation near Paris in 1669-70 and continued the work southward until his death about 1683. His work was resumed by the Cassini family in 1700 and completed to the Pyrenees on the Spanish border prior to 1718 when the northern extension to Dunkirk on the English Channel was undertaken.

The survey created a major controversy. For the results indicated that the earth was a prolate ellipsoid, which contradicted Issac Newton's 1687 postulate that it was an oblate figure. To resolve the hue and cry that followed, the French Academy of Sciences in Paris proposed in 1733 that the length of the meridian be measured near the equator and compared with that obtained in France. Later it was decided to do the same in the Arctic region. The Torne River valley north of Tornio in Lapland on the Swedish-Finnish border was chosen as the northern site and observations were begun in 1736 and completed two years later.

The results showed conclusively that one degree of the meridian was longer in Lapland than at Paris and proved Newton's postulate to be correct. The expedition to Peru, the present day Ecuador departed in 1735 and returned nine years later with results that confirmed the Lapland finding, i.e. one degree of the meridian is shorter at the equator than in France.

Early Instrumentation

These truly remarkable efforts by the French and their associates were carried out with very primitive instruments in comparison with equipment available 50 years later, yet the very best available then. Furthermore, the observations were secured under extreme conditions especially in the high Andes of South America. In Peru, the angle observations were made with quadrants having 2-3 ft. radii and two telescopes, one fixed, the other moveable and equipped with micrometers for finer readings, the latter used perhaps for the first time. The horizon was closed on each set of observations and usually involved 6 or 7 angles. The average closing error was on the order of 2 minutes indicating the accuracy of each angle at 20" to 30".

Base lines in Peru were measured using wooden rods, each 20 feet long and were standardized daily or more often with an iron toise (about 6.4 English feet) that was carried along and kept in the shade. The base line in Lapland was measured over the frozen Torne River using similar, although longer (33 ft.) apparatus.

Great Britain

Great Britain began geodetic surveys in 1784 under the direction of Major General William Roy. A site for the first base line, about 5 miles in length, was selected on Hounslow Heath in what is present day west London and the initial measurement was made using rods of Riga pine. Large errors were noted between measurements made when the rods were wet and dry and the line was remeasured with glass tubes constructed by Jesse Ramsden. After 1791 base lines were measured with 100 foot steel chains. Jesse Ramsden's theodolite with a 3 ft. circle reading to 1" built in 1787 was used for the angle observations and despite its weight of about 300 lbs. good progress was obtained in the triangulation including a connection between Dover and France in 1787. Roy died in 1790 and after a delay of about one year, the triangulation was resumed and completed in 1822. Between 1936-1950 a new, denser network with ties to several points of the earlier triangulation was observed.

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Last Updated: June 8, 2006 9:24 AM

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