surveyor's compass
Date1822-1843
Inventory Number1996-1-0059a
ClassificationSurveyor's Compass
Subject
Maker
Samuel Thaxter & Son
fl. 1822 - 1843
Maker
W. & L. E. Gurley
1845 - 1968
Owner
George L. Vose
1831 - 1910
Cultural Region
Place of Origin
Place of Use
Dimensionscompass: 17.7 × 15.3 × 35.5 cm (6 15/16 × 6 × 14 in.)
case: 9 × 37 × 18.9 cm (3 9/16 × 14 9/16 × 7 7/16 in.)
case: 9 × 37 × 18.9 cm (3 9/16 × 14 9/16 × 7 7/16 in.)
Material
Accessoriesmahogany box with brass hinges and hooks; two mounting attachments; detachable slit sights; tripod, see 1996-1-0059b
DescriptionSilvered brass bi-level magnetic compass with raised divided circle and 8-point wind rose. The east and west points are reversed.
The compass is incorporated into fiddle-shaped brass level bar. Fixed to the top of level bar are two small brass spirit levels with oval glass windows, one on either side of the compass. The spirit level on the north side is perpindicular to the bar; the level on the south side is parallel to the bar.
At each end of the level bar is an L-shaped slit sight, fixed by a removable screw whose knob, projecting below the level bar, has two knurled rings around its edge. A socket for attaching the the compass to a tripod sits directly below the compass; it has a knob with two knurled rings around its edge.
The compass is stored in a mahogany box with brass hinges and hooks. A W. & L. E. Gurley trade card is pasted to the inside of the box lid. Also in the box are two mount adaptors, one having a knob with two knurled rings around its edge.
The compass is incorporated into fiddle-shaped brass level bar. Fixed to the top of level bar are two small brass spirit levels with oval glass windows, one on either side of the compass. The spirit level on the north side is perpindicular to the bar; the level on the south side is parallel to the bar.
At each end of the level bar is an L-shaped slit sight, fixed by a removable screw whose knob, projecting below the level bar, has two knurled rings around its edge. A socket for attaching the the compass to a tripod sits directly below the compass; it has a knob with two knurled rings around its edge.
The compass is stored in a mahogany box with brass hinges and hooks. A W. & L. E. Gurley trade card is pasted to the inside of the box lid. Also in the box are two mount adaptors, one having a knob with two knurled rings around its edge.
Signedengraved on compass face: S. Thaxter Boston
written on paper glued inside box lid: From / Geo L. Vose. / Brunswick Me / Recd. July 17 1872 / Ex 1^20
printed on paper glued inside box lid: FROM W. & L. E. GURLEY, / MANUFACTURERS OF / Civil Engineers' and Surveyors' Instruments, / TROY, N. Y.
Curatorial RemarksImages B501050, B501051, B501052 may be removed. They are duplicated (in better exposure) by B501465, B501466, B501467.
FunctionFor use in calculating horizontal angles, in surveying.
To determine the horizontal angle between two targets, the user first mounts the compass on a tripod at his starting position. Then he levels the instrument using the two spirit levels attached to the level bar.
Next, the user rotates the compass until he can sight the first target. He takes down the value on the compass scale to which the north needle points. He then rotates the compass until he can sight the second target, and takes down the value on the compass scale to which the north needle points. The difference between the two values (taking direction of rotation into account) gives the horizontal angle between the two targets, with respect to his starting point.
To determine the horizontal angle between two targets, the user first mounts the compass on a tripod at his starting position. Then he levels the instrument using the two spirit levels attached to the level bar.
Next, the user rotates the compass until he can sight the first target. He takes down the value on the compass scale to which the north needle points. He then rotates the compass until he can sight the second target, and takes down the value on the compass scale to which the north needle points. The difference between the two values (taking direction of rotation into account) gives the horizontal angle between the two targets, with respect to his starting point.
Historical AttributesDonated to Bowdoin College by G.L. Vose on July 17,1872.
Troughton & Simms
Date: circa 1840
Accessories: mahogany box with brass handle; sun shade for telescope
Object number: 5234
Troughton & Simms
Date: circa 1840
Accessories: mahogany box with brass hinges and hooks
Object number: 5232
Peter & John Dollond
Date: 1780-1800
Accessories: mahogany box with brass hooks, hinges, and handle; tripod (see 5240b)
Object number: 5240a
John Frederick Newman
Date: circa 1835
Accessories: mahogany case with brass hinges and hooks
Object number: 5239
Spencer, Browning & Rust
Date: circa 1800
Accessories: mahogany case with brass hooks and hinges; lens cap
Object number: 5137
R. Iseli
Date: circa 1880
Accessories: walnut case with two adjustment tools, objective lens cap, and lens shade; Iseli trade card (inside box lid)
Object number: 5229
Troughton & Simms
Date: circa 1830
Accessories: mahogany case with brass hooks and hinges, and felt protectors; additional eyepiece; magnifier; adjustable mirror; tripod mount; foot plate (5208b); tripod (5208b)
Object number: 5208a
Buff & Berger
Date: circa 1880
Accessories: mahogany case; sunshade; screws; dust cover
Object number: 5143a
James E. Moody
Date: circa 1880
Accessories: mahogany case; sunshade; dust cap; tripod (5141b)
Object number: 5141a
Edward Nairne
Date: circa 1790
Accessories: mahogany box with clasp closure
Object number: 5228
See also/See also
