azimuth circle for a mariner's compass
Date1919
Inventory Number5330b
ClassificationMagnetic Compass
Subject
Maker
E. S. Ritchie & Sons
founded 1867
Cultural Region
Place of Origin
Dimensions5.7 x 15.8 x 15.8 cm (2 1/4 x 6 1/4 x 6 1/4 in.)
case: 9.5 x 27.9 x 27.9 cm (3 3/4 x 11 x 11 in.)
case: 9.5 x 27.9 x 27.9 cm (3 3/4 x 11 x 11 in.)
Material
Accessoriescase
DescriptionAzimuth sighting ring for Ritchie compass, 5330a:
Blackened brass ring with scale marked off by degrees and numbered by tens from 0-360°. Three brass knobs project from rim. There are two sets of sights.
At the 90° position there is a cylindrical convex mirror attached to a hinge. (The back of the mirror is marked "Ritchie Boston." Directly opposite it on the ring at the 270° point, there is a right-angle prism in a housing with a cylindrical lens below. Light from the sun is reflected by the mirror to the prism and through the lens, appearing as a bar of light on the compass card. A small bubble level is behind the prism housing on the rim of the circle.
The other pair of sights is for taking bearings of terrestrial objects as well as the sun. At the 180° point there is a hinged vane with a slit sight. Opposite it at 0° is another hinged vane with vertical wire and a black mirror hinged separately behind it. These are mounted over a right-angle prism. Beneath the prism is a window with a central wire. The window looks down at the rotating compass card. The user reads the card by looking across the ring into a second window on the side of the prism housing.
The azimuth ring has its own case, matching the case of the marine compass.
Blackened brass ring with scale marked off by degrees and numbered by tens from 0-360°. Three brass knobs project from rim. There are two sets of sights.
At the 90° position there is a cylindrical convex mirror attached to a hinge. (The back of the mirror is marked "Ritchie Boston." Directly opposite it on the ring at the 270° point, there is a right-angle prism in a housing with a cylindrical lens below. Light from the sun is reflected by the mirror to the prism and through the lens, appearing as a bar of light on the compass card. A small bubble level is behind the prism housing on the rim of the circle.
The other pair of sights is for taking bearings of terrestrial objects as well as the sun. At the 180° point there is a hinged vane with a slit sight. Opposite it at 0° is another hinged vane with vertical wire and a black mirror hinged separately behind it. These are mounted over a right-angle prism. Beneath the prism is a window with a central wire. The window looks down at the rotating compass card. The user reads the card by looking across the ring into a second window on the side of the prism housing.
The azimuth ring has its own case, matching the case of the marine compass.
Signedon top of ring: E. S. RITCHIE & SONS. / BROOKLINE, MASS.
on rear of mirror housing at 90°: RITCHIE / BOSTON
Inscribedstenciled on case lid: H. R. / No. 81
Curatorial RemarksE. S. Ritchie received his first patent (#49,157) for an azimuth circle in 1865, and another (#481,625) in 1892.
FunctionAzimuth circle mounted on the compass is used to take bearings, especially of the sun and other heavenly bodies. A primary reason is to find the direction of true north as opposed to magnetic north.
Part of marine compass #5330a.
Part of marine compass #5330a.
ProvenanceInstitute of Geographical Exploration, Harvard University; transferred to CHSI October 1955.
Samuel Thaxter & Son
Date: 1825-1843
Object number: DW0519
Buff & Buff Manufacturing Company
Date: circa 1905
Accessories: wood case; leather case; right-angle prism; plumb bob; oil flask; tripod (5174b)
Object number: 5174a
Reynolds & Son
Date: circa 1910
Accessories: mahogany case with instructions pasted inside lid
Object number: 1998-1-1426
C. F. Casella & Co. Ltd.
Date: circa 1920
Accessories: leather carrying case; long leather strap with brass loop at end
Object number: 5100
Ernst Leitz (company)
Date: circa 1930
Accessories: case
Object number: 1997-1-2018
W. & L. E. Gurley
Date: ca. 1884
Accessories: solar attachment; case; level; green filter; sun shade; tripod (5163b)
Object number: 5163a
Ernst Leitz (company)
Date: circa 1930
Accessories: case
Object number: 1999-1-0020e
Carl Zeiss Jena
Date: circa 1926
Accessories: wooden box with two hook-and-eye latches to fasten front opening; in instrument file: instruction book (photocopy); Geissler tube labeled "H2"; carboard tube containing German thermometer C in stainless steel holder that screws into instrument; glass bottle with cork stopper labeled "Monobromnaphthalin, Germany nD=1 658"; small round cardboard box labeled "For Pulfrich Refractometer" containing one tubulure
Object number: 1996-1-0229
Parent/Child
