Gregorian Reflecting Telescope with Stand, English, c. 1710

English Gregorian reflecting telescope of brass with a

weighted wooden stand. The tube of the telescope was originally covered with fish-skin, but this has decayed. Unsigned and undated, but c.1710 likely.

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. 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".