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Physical Sciences Collection - Surveying and Geodesy

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Transit - click to enlarge

Transit - click to enlarge

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Transit

Catalogue number:
1985.0599.01

Inscriptions:
"J. C. SALA MAKER SAN FRANCISCO 825"

Dimensions:
height 10.5 inches; horizontal circle 6 inches diameter; vertical arc 2.5 inches radius; needle 4.25 inches; telescope 10.5 inches long; hanging level 5 inches

Discussion:

J.C. Sala described this instrument as an Engineer's Complete Transit, and priced it at $235. The horizontal circle is silvered, graduated into 64 units (each unit is equal to one hundred mils), and read by opposite verniers to 30 parts. One mil (or military degree) equals 3.375 arc minutes. A variation arc, outside the compass at E, extends 30 degrees either way; the vernier reads to single minutes. The vertical arc, also silvered, is graduated into 30 minutes of arc, and read by vernier to single minutes. There is a clamp and tangent attachment to the telescope axis, as well as a gradienter attachment for determining gradients, distances, and differences of level.

Joseph Charles Sala (1841-1916) was born in Italy, moved to San Francisco around 1861, and worked as an instrument maker for John Roach. Following Roach's death in 1891, Sala went into business for himself, advertising as "Successor to John Roach" and boasting of his many awards from the Mechanics' Institute of San Francisco.

Ref: J.C. Sala, Illustrated Catalogue and Manual of Civil Engineers' and Surveyors' Instruments (San Francisco, 1896).

Further Information:

Roach
Transit

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