Description

Wooden Circumferentor by H.S. Pearson (Portland) ca. 1810-30

 A rare wooden American circumferentor (surveying compass).

Signed: “ H. S. PEARSON PORTLAND”

Material: wood, paper, brass, glass

Dimension: 34.5cm (13 ½”) long; compass diam. 17cm (6 ¾”); sights 17cm (6 ¾”) high

Condition: good, please note a crack in the back of compass affecting part of the paper card and needle old but not original.

The principle of the circumferentor is quite different from the theodolite, where a compass may be used for orientation, but thereafter the scale  remains stationary while an index moves to the sights.

While the theodolite was well suited to surveying a settled landscape with its artificial landmarks of boundaries and buildings, the circumferentor was more appropriate in a survey of undevoloped land, based on the natural magnetic meridian.

Thus the circumferentor became a standard instrument in America.

The use of wood is another characteristic feature of early American instruments.

Ref.: J.A. Bennett 1992- A decade of accessions. Selected instr. acquired by Whipple Museum between 1980 and 1990.for an identical instrument (n.33)

Unknown to S.A Bedini 1964 – Early American Scientific Instruments and their Maker.