Wild T-3

The "T-3" theodolite was introduced in 1925. With its 10.5-inch telescope, this theodolite had a range of up to 60 miles. It saw heavy use between 1952 and 1984.

Wild T-3

The Precision theodolite, later known at the T-3, was introduced by Heinrich Wild in 1925, and in 1952, it replaced the Parkhurst in the Coast and Geodetic Survey. The glass horizontal and vertical circles, 5.5 and 3.73 inches in diameter respectively, were read to 0.2 seconds. The 10.5-inch long telescope had a range of 20-60 miles.

The image below shows triangulation observations being made with a Wild T-3 theodolite from atop a steel Bilby tower. Bilby towers were constructed with both an inner and outer tower. The inner tower (on which the theodolite was mounted) was entirely separate from the outer one, on which the observer stood. This construction prevented the observer's movements from affecting the instruments.

In this 1977 photo, a T-3 theodolite is mounted on top of the inner tower of a Bilby, with the skyline of Chicago on the horizon. Ron Ramsey, who later served as the National Geodetic Survey's Geodetic State Advisor for Michigan, demonstrated proper observing technique by keeping open the eye not using the telescope.

Historic Reference

According to a history authored by Coast and Geodetic Survey retiree Joe Dracup:

"Early fears that these small optical reading theodolites were unstable proved unfounded. Some observers found the T-3's stubby gun-sight pointers inadequate for night work and to resolve the problem taped beer can/bottle openers to the top and bottom of the telescopes. Fortunately, this piece of equipment was never in short supply on parties. Later illuminated finders, similar to those found on Parkhursts, were added. ... economic benefits were accrued by replacing Parkhursts with T-3's. For the most efficient operation, the Parkhurst required a 3-person observing unit, an observer, recorder and lightkeeper, who also read the second (B) micrometer. For T-3's, the observer makes all the readings and on many occasions the light-keeper was no longer needed, leaving the slots open for forming more observing units or showing additional lights."

  • Instrument Shown: Wild T-3 theodolite
  • Location: Chicago, Illinois
  • Manufacture Date: 1927 to 1985
  • Dates of Use: Large scale usage from 1952 to 1984; still used for special projects after 1984
  • Photo date: 1977

Works Consulted

Dracup, J.F. Geodetic Surveys in the United States 1807-1940. Retrieved July 28, 2006, from: http://www.ngs.noaa.gov/PUBS_LIB/geodetic_survey_1807.html.

Smithsonian Virtual Surveying Instrument Collection. Theodolite. Retrieved on July 28, 2006, from: http://americanhistory2.si.edu/collections/surveying/object.cfm?recordnumber=747913.

Related Web Sites:

National Geodetic Survey