Telescopes, Astronomical and navigational instruments, Optical equipment

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Portable reflector telescope


Object connections:

Collection Telescopes, Astronomical and navigational instruments, Optical equipment
ExhibitionsShips, Clocks & Stars: The Quest for Longitude
User collections William Wales by NMMCollections
Gallery locationNot on display
PeopleHistorical Association: Cook, James
EventsTransit of Venus, 1769
Publication(s)Captain James Cook Navigator
View this book in the library

Object details:

Object ID AST0941
Description This is a portable Gregorian (reflector) telescope. It is signed JAMES SHORT LONDON 208/1205 = 18 meaning it has a focal length of 18 inches (457.2mm), and that James Short had made 208 of that size out of a total 1205 telescopes by the time he made this one. This telescope is similar to one used by James Cook on his 1769 expedition. Telescope: The barrel is made from brass. It has adjustable inclination and rotary movement (or altitude and azimuth movement). Attached to the top of the barrel is a refracting telescopic sight. There is an eyepiece cap and two brass eyepieces. The longer of the two is 97 mm the shorter and more powerful eyepiece is 77 mm. Within the barrel are primary and secondary (objective) specula (mirrors). There is a screw thread for the focusing of the secondary mirror which is done through use of the rod attatched to the barrel. There is a spare secondary mirror in a tin box which gives a higher power to each eyepiece. The length with the larger eyepiece is 707 mm. The height to the top of the sight is 550 mm, the diameter of the barrel is 105 mm and has 457.2mm (18 inch) focal length. Stand: The telescope is mounted on a pillar stand with three folding claw legs. The pillar stand divides in two at the middle of the pillar. At the division point it rotates to give the azimuth movement. There is a knob to lock the position in azimuth. In altitude there is free movement which can be locked and also a fine adjustment mechanism. This works by a large semi-circle attached to the telescope with groves on the outside against this there is a rod with a screw thread. A large objective end cap is missing.
Date made 1738-68

Artist/Maker Short, James
Place made London, England
Credit National Maritime Museum, Greenwich, London. Caird Fund.
Materials Key ivory (CITES); mahogany; specula; brass
Measurements Overall: 560 mm x 700 mm x 340 mm
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