reflecting circle
Date1826-1840
Inventory Number5321a
ClassificationReflecting Circle
Subject
Manufacturer
Troughton & Simms
1826 - 1923
Cultural Region
Place of Origin
Dimensions14.2 x 31.5 x 28.7 cm (5 9/16 x 12 3/8 x 11 5/16 in.)
circle diam: 27.2 cm (10 11/16 in.)
box: 15.5 x 29.5 x 29 cm (6 1/8 x 11 5/8 x 11 7/16 in.)
circle diam: 27.2 cm (10 11/16 in.)
box: 15.5 x 29.5 x 29 cm (6 1/8 x 11 5/8 x 11 7/16 in.)
Material
Accessoriesmahogany box, telescope and sight tube (5), magnifying lens (vernier)
DescriptionIntroduced by John Troughton in 1796, this instrument is the English model of the reflecting circle. The full circle has three index arms, each one equipped with a vernier (one of which has a tangent screw for precision measurements). The smallest division on the verniers is 20". A magnifying lens (in the box) can be used to get a clearer view of the vernier scales. Around the circle is a finely engraved silver scale divided into 720°, but only marked on the right half: 140°-0-140°.
A variety of telescopic sights can be installed on the instrument. As for the octant or sextant, three filters can be moved into position in front of the mirror to block the sunlight while making altitude measurements. Finally, two fixed brass and wood handles are used to support the instrument, depending on whether one is making an altitude sighting or a measurement reading.
A variety of telescopic sights can be installed on the instrument. As for the octant or sextant, three filters can be moved into position in front of the mirror to block the sunlight while making altitude measurements. Finally, two fixed brass and wood handles are used to support the instrument, depending on whether one is making an altitude sighting or a measurement reading.
In Collection(s)
Signedon indices: Troughton & Simms, LONDON.
Inscribedon indices: 251
FunctionThe reflecting circle is used like a sextant, but observations can be repeated around the circle and averaged for greater accuracy.
Troughton & Simms
Date: 1826-1840
Accessories: mahogany box, telescope and sight tube (5), magnifying lens (vernier)
Object number: 5321b
William Cary
Date: 1789-1825
Accessories: small eyepiece (box)
Object number: 5230a
Edward Troughton
Date: circa 1810
Accessories: Square walnut box, U-shapedhandle assembly, additional handle, eye shade tube, telescope, eyepieces (2), screw driver, eyepiece shades (2), vernier magnifier
Object number: 5316
Keuffel & Esser Company
Date: 1940-1960
Accessories: carrying case
Object number: 2003-1-0139
Legey
Date: circa 1838
Accessories: shades with double tabs (4); shades with single tab (4); screwdriver and square key.
Object number: 5268