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Inventory no. 20020 - Former Display Label

English GREGORIAN REFLECTING TELESCOPE
c.1710

Brass, etc.; with weighted wooden stand. The tube of the telescope was originally covered with fish-skin, but this has decayed. Unsigned and undated.

This is probably the oldest surviving example of the reflecting telescope invented, in 1661, by James Gregory (1638-75), described in his Optica Promota, 1663. (James Gregory, F.R.S. 1668, Professor of Mathematics, St. Andrews, 1668, Professor of Mathematics, Edinburgh, 1674.)
In the Gregorian telescope the eye-piece is directly behind a concave mirror, which has a hole in the centre. Through this hole the image is reflected by a small adjustable concave mirror at the further end of the tube.

This instrument has an aperture of 2'. It is focussed by turning the threaded rod at the side of the tube. As originally sold these instruments were accompanied by a small hand-augur for boring a hole in the side of a post or tree, into which the mounting could be screwed, when the telescope was "used abroad".

Wright describes this instrument in his catalogue of the Orrery Collection, 1731, as "A Small Reflecting Tellescope on a Stand New Fashion".

[Orrery Collection, no. 12]
Lent by Christ Church.

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