Accession No
2897
Brief Description
refracting telescope, by Wray, 3rd quarter 19th century
Origin
London; England
Maker
Wray
Class
astronomy; optical
Earliest Date
1850
Latest Date
1875
Inscription Date
Material
metal (brass, oxidised brass, steel); glass; wood (two types); cloth (felt)
Dimensions
telescope length 1220mm; diameter 118mm; aperture 90mm box length 853mm; breadth 232mm; height 187mm tripod height 1920mm; breadth 300mm; depth 250mm rod length 1082mm; eyepieces bag length 175mm; breadth 90mm; height 50mm
Special Collection
Provenance
Purchased from Christie’s, South Kensington, London, England; lot 110, 21/10/1982.
Inscription
‘WRAY
LONDON’ (eye-end)
‘Wray, London.’ (object glass cell)
Description Notes
Brass refacting telescope. Doublet object glass, components held loosely by threaded ring in screw-fit cell. Push-fit brass object glass cover. Focus by rack and pinion moved by knurled knob at eye-end. Three push-pull draw tubes. Push-fit mount for screw-fit two-lens eyepiece with screw-fit eyestop and filter. Finder mounted on body, with object glass in threaded brass cell on draw tube moved by side handle, push-fit cover, 2 lens eyepiece in push-fit tube. Oxidised split ring on body with two brass trunnions.
Fork altazimuth oxidised brass mount on wooden tripod stand.
Brass stay linking stand with eye-end of body, with rack and pinion altitude adjustment (the stand attachment is broken).
Two spare eyepieces and one cover for eyepiece (latter possibly not for this instrument).
Wooden box with painted steel fasteners and hinges.
Condition good (eye-end support is broken, box poor); complete.
References
Events
Description
The refracting telescope uses a lens to focus the observed image. Its exact origin is disputed, but it first appeared among Dutch spectacle makers at the beginning of the seventeenth century.
Great discoveries were made using the refracting telescope. Galileo’s work Siderius Nuncius (The Starry Messenger, 1610) describes his discoveries of the mountains on the moon, new stars and the moons of Jupiter.
Galileo’s telescopes consisted of a concave and a convex lens which gave an upright image of low magnification. The Keplerian telescope, which was the main type used in astronomy before the invention of the reflecting telescope, has two convex lenses, which gave an upside-down image with a wider field of view. It can be modified for use on land by adding an extra eyepiece lens, which gives an upright image.
The main problem with refracting telescopes is that they suffer from chromatic aberration. When light travels through an ordinary lens each colour is bent through a different angle. A spectrum of colours would appear around the image being viewed.
An improvement to the quality of telescopic images came in 1758, when John Dollond started manufacturing a special lens made of two different sorts of glass. This reduced chromatic aberration by bringing two particular wavelengths of light into a common focus. Achromatic lenses and improvements in glass-making made both small and large refracting telescopes popular in the nineteenth century. Refracting telescopes are still in use today but are usually small telescopes designed for amateur users.
Created by: Jenny Downes
FM:44189
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