Accession No
0867
Brief Description
reflecting telescope, Gregorian, English [attributed], 1730 (c)
Origin
England [attributed]
Maker
Class
astronomy; optical
Earliest Date
1730
Latest Date
1730
Inscription Date
Material
metal; brass; wood; cloth; shagreen; hide; snake skin
Dimensions
l (barrel) 166 mm;d (barrel) 45 mm; d (objective) 37 mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stuart Whipple from M. Landau, Paris, France, on 05/04/1938.
Inscription
Description Notes
Brass gregorian telescope, red shagreen covered barrel. Brass band with screw holds barrel to pillar stand with double wingbrass piece for screwing stand into black snake skin covered, red velvet lined, fitted box with brass lock. Cover. Secondary mirror (speculum metal) moved by milled ring around barrel. Brass ring with attached spring screws into barrel and holds speculum metal objective. Eyepiece tube screws into ring and has screw in eyepiece shade.
good condition
with box
References
Events
Description
Named after James Gregory who proposed the basic design of the catadiopric telescope in Optica promota (1663), the instrument employs two aspherical mirrors instead of lenses. A parabolic primary mirror focuses light onto a flat or elliptical secondary mirror, which reflects light back through an aperture in the center of the eyepiece. Due to the difficulty of producing aspherical mirrors with sufficient accuracy, this telescope design did not become marketable until the 1720s. This example is covered in ray skin, or shagreen, a popular decorative material for optical instruments during the eighteenth century.
08/07/2014
Created by: Allison Ksiazkiewicz on 08/07/2014
FM:39725
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