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Gregorian Reflecting Telescope

Signature Nairne, London

Date circa 1770
Dimensions English Metric
Main Tube Length 13.7in 348mm
Main Tube Diameter 2.9in 73mm
Total Length 29.3in 432mm
Height of Base 11.0in 280mm
Primary Mirror Diameter 2.7in 68mm


This telescope has a small brass cylindrical barrel.  The primary speculum mirror is a concave paraboloid, with a central hole, and is kept in place at the rear of the barrel with a screw-in backing plate.  The small secondary mirror is a concave ellipsoid.  It is attached by a slender arm to a screw-driven carrier which slides for several inches along the front interior part of the barrel.  This configuration of primary and secondary mirrors is called Gregorian.  The focusing thumbscrew, at the eyepiece end of the barrel, is the long shank design, attaching to the secondary mirror carrier through a slot near the front end of the barrel. The eyepiece tube screws into a hole in the center of the backing plate, which holds the primary mirror in place.  The two-lens eyepiece is the Huygens type.  The Telescope is signed "Nairne  London" in large script on the top of the barrel, at the back end, with the eyepiece to the left.  The scope mounts on a brass column, with horizontal and vertical swivel joints, to a folding tripod with cabriole legs. It comes with a fitted mahogany case.




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