Sextant by Jesse Ramsden with case

Made:
1770-1775 in London and Piccadilly
maker:
Jesse Ramsden
and
Nevil Maskelyne
Sextant, 15-inch with two removable viewing telescopes Sextant, 15-inch with two removable viewing telescopes Sextant, 15-inch with two removable viewing telescopes Sextant, 15-inch with two removable viewing telescopes Engraving detail on Sextant Engraving detail on Sextant Jesse Ramsden sextant. Cropped view for gallery use Jesse Ramsden sextant Jesse Ramsden sextant. Detail view of measurment scale Jesse Ramsden sextant

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Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

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License this image for commercial use at Science and Society Picture Library

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Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

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License this image for commercial use at Science and Society Picture Library

License

Buy this image as a print 

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License this image for commercial use at Science and Society Picture Library

License

Buy this image as a print 

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License this image for commercial use at Science and Society Picture Library

License

Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

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License this image for commercial use at Science and Society Picture Library

License

Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

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License this image for commercial use at Science and Society Picture Library

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Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

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License this image for commercial use at Science and Society Picture Library

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Sextant, 15-inch with two removable viewing telescopes
Science Museum Group
© The Board of Trustees of the Science Museum, London

Sextant, 15-inch with two removable viewing telescopes
Science Museum Group
© The Board of Trustees of the Science Museum, London

Sextant, 15-inch with two removable viewing telescopes
Science Museum Group
© The Board of Trustees of the Science Museum, London

Sextant, 15-inch with two removable viewing telescopes
Science Museum Group
© The Board of Trustees of the Science Museum, London

Engraving detail on Sextant
Science Museum Group Collection
© The Board of Trustees of the Science Museum, London

Engraving detail on Sextant
Science Museum Group Collection
© The Board of Trustees of the Science Museum, London

Jesse Ramsden sextant. Cropped view for gallery use
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Jesse Ramsden sextant
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Jesse Ramsden sextant. Detail view of measurment scale
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Jesse Ramsden sextant
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Brass sextant by Jesse Ramsden, in fitted mahogany keystone case, made 1770-75, Piccadilly, London. Sextant has polished brass 120° scale (-2° to 136°) with 20’ divisions and brass vernier (30”), three index-filter shades (red & green), one horizon filter (red) and ‘Maskelyne flap’ for greater accuracy when taking a sight of the Sun or Moon. Fitted with threaded telescope bracket for sighting telescope (130mm –inverted image).

Sextants were navigational instruments used to measure angular altitudes of celestial bodies whilst at sea, enabling mariners to determine latitude and local time. They were also used to calculate longitude at sea using the so-called ‘lunar distance’ method, carried out by comparing an accurate measurement of the angular distance between the Moon and a fixed star to a set of precalculated tables.

Sextants underwent a number of design improvements throughout the 18th century. Astronomer Royal Nevil Maskelyne made recommendations for ensuring accuracy despite unavoidable imperfections in the grinding of glass when taking sights of the Sun or Moon, which included the introduction of a hinged brass ‘Maskelyne flap’ as seen on this instrument. This sextant design by Jesse Ramsden was a similar type supplied to Captain Cook for his voyages in 1772 and 1776.

Details

Category:
Astronomy
Object Number:
1928-924
Materials:
brass (copper, zinc alloy), wood (unidentified), mahogany (wood) and glass
Measurements:
overall: 435 mm x 438 mm x 97 mm,
type:
sextant and instrument case
credit:
Mr Thomas H. Court

Parts

Case for Hadley type brass framed sextant

Case for Hadley type brass framed sextant

Case for a 15-inch sextant, by Ramsden, London

Materials:
wood
Object Number:
1928-924 Pt1
type:
instrument case
Sextant by Jesse Ramsden

Sextant by Jesse Ramsden

Brass sextant by Jesse Ramsden, Piccadilly, London, 1770-75. Sextant has polished brass 120° scale (-2° to 136°) with 20’ divisions and brass vernier (30”), three index-filter shades (red & green), one horizon filter (red) and ‘Maskelyne flap’ for greater accuracy when taking a sight of the Sun or Moon. Fitted with threaded telescope bracket for sighting telescope (130mm –inverted image). The ins...

Materials:
brass (copper, zinc alloy) , glass , mahogany (wood) and metal
Object Number:
1928-924 Pt2
type:
sextant