Portable heliometer

This is an heliometer for sun observation made by J. Dollond & Son. It is a reflecting Cassegrain telescope on a portable stand, and is fitted with one of Dollond's earliest object glass micrometers.

Telescope: The barrel is made of brass. Adjustable inclination and rotary movement. The barrel itself is rotated by means of a handle attached to an axis. There is a numbered dial around the eye-end of the barrel. On each end of the top of the barrel are attachments for sighting. It has a screw-on eyepiece and primary and secondary specula. (mirrors) Screw thread focusing of secondary mirror by means of a rod attatched to the barrel. The key attached to the mounting is for adjusting the telescope in horizontal plane. The length of the barrel with the eyepiece in 325 mm.

Stand: The telescope is mounted on a brass pillar with three collapsable claw legs. The stand is not original to the telescope but was made by Dollond in 1752-1761.

Object Details

ID: AST0957
Collection: Astronomical and navigational instruments
Type: Telescope
Display location: Display - ROG
Creator: Dollond & Aitchison
Date made: circa 1755
Credit: National Maritime Museum, Greenwich, London
Measurements: Barrel: 470 x 250 mm; Barrel: 65 mm

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