Buff & Buff termed this an "air-craft theodolite" as made for the U. S. Weather Bureau, noting that it could be used for aeronautic or military purposes. The Signal Corps of the U. S. Army acquired this example around the time of World War I, and transferred it to the Smithsonian in 1923. The horizontal and vertical circles are read by verniers to 6 minutes of arc. The finish is anodized. Since the telescope is "broken," the eyepiece remains at the same height regardless of the elevation of the objective. A. De Quervain introduced this design in 1905, and it remains popular to this day.
Ref: Buff & Buff, Surveying Instruments (Boston, 1918), p. 104.
U.S. Department of Agriculture. Weather Bureau, Instructions for Making Pilot Balloon Observations (Washington, D.C., 1928).
U.S. Army, Meteorological Observer. Training Manual No. 31 (Washington, D.C., 1925), pp. 183-189.
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