The Great Theodolite

This sketch shows Ferdinand Hassler's "Great Theodolite," a massive, 300-pound instrument that was used for surveying for almost 40 years.

Sketch of Ferdinand Hassler's Great Theodolite

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Having a 30-inch diameter circle and weighing in at 300 pounds, the "Great Theodolite" shown in this image required the reinforcement of Survey of the Coast Superintendent Ferdinand Hassler's specially built equipment carriage. This theodolite had a platform built around it to enable Hassler to move around the instrument and read angles without disturbing the instrument itself as it was sighted on a station. The highly accurate instrument was capable of making what now would be considered first-order horizontal observations. Represented as 1:100,000 ("one part in one hundred thousand"), "first-order" work means that there is only one unit of error for every 100,000 units of survey work.

The instrument was so well built that it remained in continuous use from its time of purchase in 1836 until November 1873, when it was struck by a tornado while in use in Georgia. Hurled from its stand, it was irreparably damaged.

Historic Reference

Built to his own design by Troughton and Simms of England in 1836, the Great Theodolite was Hassler's pride and joy. It was considered the finest instrument of its day. According to Hassler's correspondence with the Secretary of the Navy, the craftsmanship of its construction and its accuracy were so admired in London that the men of science there wanted it to remain with them longer for their further examination.

When the theodolite arrived in the U.S., Hassler was delighted with it. However, it is somewhat amusing that he could not resist improving on an instrument he termed "splendid." Shortly after the theodolite arrived, Hassler set his instrument makers to constructing some replacement parts for it of his own design.

  • Instrument Shown: The Great Theodolite, manufactured to order by Troughten and Simms of England
  • Location: Unknown
  • Manufacture Date: Approx. 1836
  • Dates of Use: 1836 to 1873
  • Photo date: Unknown

Works Consulted

Dracup, J.F. (1994). Geodetic Surveys in the United States 1807-1940. Retrieved May, 2006, from:

Hassler, F.R. (1820). Principle Documents Relating to the Survey of the Coast of the United States and the Construction of Uniform Standards of Weights and Measures for the Custom Houses and States. Vol. III (pp. 19 and 63).

Schott, C.A. (1902). The Eastern Oblique Arc of the United States and Osculating Spheroid (p. 47).

Theberge, Capt. A.E. The Coast Survey 1807-1867. Retrieved June, 2006, from:

Related Web Sites:

The Coast Survey 1807-1867

National Geodetic Survey