Smithsonian - National Museum of American History, Behring Center

Physical Sciences Collection - Surveying and Geodesy

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Telescopic Alidade - click to enlarge

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Telescopic Alidade

Catalogue number:

"E. R. WATTS & SON 1914 No 34"

length 15 inches; telescope 12 inches long


The vertical arc of this alidade is graduated to 30 minutes and read by vernier and magnifier to 5 minutes. The two long edges of the base are beveled; one is equipped with a parallel rule. Since the pedestal and telescope can fold down flat against the base, the instrument is easily portable. Casella offered a similar instrument, describing it as "Reeve's Pattern Folding Alidade." E. R. Watts & Son was established in London in 1857.

Ref: C. F. Casella & Co., Ltd., Surveying and Drawing Instruments and Appliances (London, about 1940), p. 30.

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