Portable altazimuth telescope. Five altazimuth instruments all made by Troughton and Simms were used in the Transit of Venus expeditions of 1874 and 1882. Four (including AST0962) were commissioned in 1870 from Troughton and Simms specially for the British Transit of Venus expeditions of 1874. A 5th (this one) 'D' had been acquired in 1866.

Each of the 5 altazimuth telescopes were labelled according to their destination on the 1874 expeditions. 'A' was sent to Egypt; 'B' to Hawaii; 'C' to Rodriguez Island; 'D' to New Zealand and 'E' to Kerguelen Island. After these two expeditions A was sold to Imperial College in 1929, B to the Observatory in Cape Town, South Africa, C was lost at sea, while D and E came to the NMM in 1973.

Telescope: This instrument is engraved "Troughton and Simms, London 1866" on the telescope tube. It has a lens aperture of 1.5inch diameter, a focal length of 26 inches, an overall length along the main axis of 18inches and the diameter of the setting circle is also 18inches. The scale is made of silver.

Stand: An altazimuth instrument is a telescope with scales and mounting that allow both local coordinates, the altitude and the azimuth of a star to be measured without the need of any additional apparatus.

Box and accessories: The instrument has its own fitted leather covered box, 1 spirit level, 1 lamp, keys, 3 eyepieces, 3 shades and a paper label, in what maybe Airy's hand, which reads "List of contents. Telescope & vertical circles, striding level, 4 eyepieces (29, 45, 66, 100)".