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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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Ramsden's Direction Theodolite

Ramsden's direction theodolite is certainly among the 4 or 5 greatest technological advances ever in geodetic surveying. As a case in point, prototypes continue in use by almost all countries. In the field of general surveying however, the invention by the French of the repeating theodolite about 1790 is of equal importance for it is the basis for the instrument most surveyors have employed. Regardless of their almost universal use in the private sector, repeaters have been shown to be less accurate than direction instruments. In theory, the opposite is the case, in practice however, repeaters' more moveable parts and mechanical motions required to operate them contribute to larger error sources.

As for the French, as you might expect they still preferred repeating theodolites for higher order surveys as late as 1963 when a new connection between England and France was made. Instruments employed that year were repeating types, presumably reading to 1" with eye pieces having moveable cross hairs so that as many as 10 readings could be obtained from each pointing. One point of interest. This new connection between Portsmouth and Cherbourg was only possible because Bilby towers were available.

First Level Datum

As might be anticipated The Netherlands established the first level datum in 1682 and carried out surveys along rivers and some shoreline between 1797 and 1812. However, the first geodetic leveling was not begun until 1875. By contrast, Great Britain started their geodetic leveling in 1841 and completed it about 20 years later. In almost all instances geodetic levelings were undertaken after the triangulation was well on its way or completed.

By 1800, most of the countries of Europe had drawn up plans or were on their way in establishing triangulations that in 1842 spanned the continent from the Mediterranean Sea on the south to the Arctic regions on the north and from Ireland, England and the Atlantic Ocean on the west to the interior of Russia on the east.

Ferdinand R. Hassler -- The Founder

The United States entered this world of geodesy in 1807 and while 25 years passed before the primary work could be initiated, its achievements were soon recognized by much of the world. At the beginning and along the way for 25 years however, there were many trials and tribulations to be overcome. The country was very fortunate indeed that a man of the caliber of Ferdinand R. Hassler was selected to lead the effort for one of lesser resolve would have given up early, the problems were many and difficult. Hassler was 37 years old when he was named the first superintendent of the Survey of the Coast and 62 when he began the first major triangulation in 1832. There were many depressing and disillusioning periods for him in the intervening years.

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. Some of the material such as that related to instruments and computations is given intoto in one section or another even though the period covered spans two or more sections. Also, the brief histories for Geodetic Astronomy, Gravity and Reconnaissance Surveys cover the years 1807-1990.


1807: Survey of the Coast Created

Geodetic surveying began in the United States on February 10, 1807 with the creation of the Survey of the Coast by Congress in the presidency of Thomas Jefferson. Ferdinand R. Hassler, a Swiss born geodesist, who conceived the plan was placed in charge and served in that capacity on and off until his death in 1843. Nothing was accomplished for several years because appropriated funds were not released due to political opposition and unsettled conditions in Europe, the source of needed equipment. Finally in 1811, $25,000 was disbursed and Hassler immediately went to England to have instruments made to his design and specifications and to purchase other equipment and scientific books. He remained there during the War of 1812, returning in 1815.

First Field Surveys

First field surveys were carried out in 1816-17 near New York City where a small scheme of triangulation consisting of 11 points, scaled by two measured base lines was accomplished to an accuracy that would approach present day second-order, class I. Hassler performed the reconnaissance to select the station sites, directed the base line measurements and observed all the angles with the recently acquired 24 in. theodolite, built by Edward Troughton of London to his specifications.

The first point occupied for geodetic observations in the U.S. was identified as WEASEL located on a low mountain about 2 miles south of Patterson, NJ on July 16, 1817. It was marked by a 6" deep drill hole filled with sulphur. In 1934, it was reported that the top of the mountain had been blasted off destroying the station. Blasting is among the very few ways to obliterate a mark of this type.

None of the original stations are thought to exist today, although WEASEL and SPRINGFIELD were included in the primary triangulation southward from NYC observed in 1838. Station CHERRY HILL, one end of the base line at the northern end of scheme, near Englewood, NJ was destroyed by sub-division construction in the late 1970's only a few days before personnel were scheduled to move the point to a protected area. In 1987, the American Society of Civil Engineers placed a plaque at the approximate location of original station CRANETOWN, north of Montclair, NJ, noting the site as a National Historic Civil Engineering Landmark.

Hassler Dismissed

Almost immediately on its completion, politics reared its ugly head once again and Hassler was dismissed. For about 15 years he tried his hand at several occupations before being reappointed to his position in 1832. First he worked as an assistant on the U.S.-Canada northeast boundary surveys, then made an unsuccessful attempt at farming in a remote site on the St. Lawrence River where his wife left him. After that he took a position as a gager at the NY Custom House, followed by a period of unemployment during which he wrote several books on advanced mathematics and developed the polyconic map projection still used today. Finally in 1830, he received an appointment as superintendent of the new Office of Weights and Measures. This office remained in the Coast and Geodetic Survey until 1901 when it was spun off to become the National Bureau of Standards. This was a dark period for both Hassler and American geodesy.

Hassler Reappointed

Once back on the job he immediately began geodetic surveys on Long Island, NY that have continued, more or less unabatedly until today. The instruments and equipment that Hassler had made or purchased were more than adequate for the task at hand. This was attested to by a French astronomer who said in 1832 --- at the time of construction, the instruments were twenty years in advance of the science of Europe. Having the best of tools is no guarantee, of course for the best of results. In surveying best means the most accurate and to reach that goal requires, in addition to the instrumentation, trained and conscientious personnel and proper observing procedures. The sum total of all the requirements can be broadly categorized as standards of accuracy. In that regard, Hassler set standards of highest accuracy for these early surveys that remain the hallmark of American geodetic work.

He personally made all the observations at the primary stations, yet at the same time trained his assistants James Ferguson and Edmund Blunt on the secondary surveys so that they could step in when necessary to do his job --- and they did. In the year after Hassler's death in 1843, Ferguson measured the KENT ISLAND base line in Maryland, Blunt the MASSACHUSETTS base, and they shared his role in observing the primary triangulation.

The first station occupied was BUTTERMILK on June 11, 1833. It still exists and is located on what is now the Rockefeller estate in Westchester County, NY.

The Great Theodolite

Prior to October 18, 1836, the observations were made using the 24 in. theodolite mentioned previously. On that day and until his death in 1843, he employed a 30 in. instrument that he proudly called the Great Theodolite. Designed by himself, built by Troughton, the finest instrument of its day was used first at station WEST HILLS on the northern shore of Long Island, a point that remains in place even now. Its weight of 300 lbs. was of little concern to Hassler, having used a 36 in. Ramsden theodolite, an instrument of similar weight in the trigonometrical survey of Switzerland. He simply strengthened the oversize carriage used for transporting the 24 in. instrument, a fairly heavy piece in itself weighing perhaps 200 lbs.

Two characteristics of the Great Theodolite are seldom mentioned, one, it was designed as a repeating instrument and two, it had a 24 in. vertical circle. Hassler employed it in the direction mode as did others later, until destroyed in 1873 and it must be assumed that the final construction was as a direction theodolite.

Hassler's Base Lines

The two base lines measured for the 1816-17 survey at Gravesend Bay near present day Coney Island (4.7 mi) and at Englewood, NJ (5.8 mi) were not considered accurate enough nor probably long enough to scale the primary triangulation then underway. Both bases were measured with iron chains, each link one meter in length. Accordingly, Hassler measured his only primary base line at Fire Island on the south shore of Long Island in 1834 using four 2 meter iron bars laid end to end. It was not a direct measurement. In order to take advantage of the level beach, the principal measurement followed a route from WEST BASE somewhat southerly of the direct line to a point about 255 meters west of EAST BASE. The point was connected to EAST BASE by angle and distance with the distance between the terminals obtained by computation.

His methods were acclaimed by several scientific societies, but as always the real proofs of the pudding are the agreements with the nearest base lines as computed through the triangulation. The checks were excellent, about 1:100,000 with the MASSACHUSETTS base, EPPING base, ME and KENT ISLAND base, MD, measured in 1844, 1857 and 1844 respectively and about the same accuracy with nearby EDMI lines observed in the 1970's.

Hassler's base apparatus was used for the MASSACHUSETTS and KENT ISLAND bases. The EPPING base was measured with the Bache-Wurdemann compensating equipment. The FIRE ISLAND base is 8¾ miles in length and marked at the terminals by red sandstone monuments 4 ft. high and about 1 ft. square with a rounded top and at intervals of 2,000 meters by stoneware cones. Records state the marks are lost, however it is unlikely that much of an effort was made to find them, especially the intermediate ones. With today's equipment it wouldn't take a huge effort to settle the question once and for all time.

The FIRE ISLAND base was computed through the triangulation to the line WEST HILLS - RULAND on the north side of Long Island, a line Hassler called his mountain base from which the triangulation east and north and to the south was extended. This triangulation eventually ran from Calais, ME southward to Dauphin Island near Mobile, AL then westward to New Orleans, LA a distance of 1,623 miles with the field work done between 1833 and 1898.

Massachusetts Commonwealth Survey

The Coast Survey was not the only agency establishing triangulation at the time. In 1830 the Massachusetts legislature decided to prepare maps of the commonwealth based on a trigonometric survey. Colonel James Stevens was placed in charge and began operations including the measurement of a 7.4 mile base line along the Connecticut River, near Northampton.

The measurement was carried out with compensating apparatus 50 ft. in length designed by Dr. Joseph Rice. No other information is available about Joseph Rice and little is known about his apparatus although the methodology was reported in one or two scientific journals. Nevertheless, the principle he employed was about 15 years ahead of its use in the Coast Survey, albeit his work was known there. The first application of the compensation principle was by the Ordnance Survey of Ireland on the Lough Foyle base in 1827.

A theodolite on loan from the Coast Survey was used for angle observations until its recall in 1834. After that time an instrument of their own design was employed. Stevens resigned in 1834 and Simeon Borden, formerly an assistant took over with the bulk of the work still to be done and completed the survey in 1838.

The results were not published until 1846 and the positions were given as tangent plane coordinates based on the location of the points in one of 5 zones. This was the first use of plane coordinates on a large scale in America. In 1935 it was reported that little use was made of the coordinate system, a situation not too different from that found today.

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