Watts & Son Telescopic Alidade

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, and 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." The "E. R. WATTS & SON 1914 No 34" signature refers E. R. Watts & Son, a firm that was established in London in 1857.
Ref: C. F. Casella & Co., Ltd., Surveying and Drawing Instruments and Appliances (London, about 1940), p. 30.
Currently not on view
Object Name
alidade (telescopic)
E.R. Watts and Son
base: 15 in; 38.1 cm
telescope: 12 in; 30.48 cm
place made
United Kingdom: England, London
ID Number
catalog number
accession number
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center


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