2-979-636 - The Print Collector/Heritage Images

Transit Instruments at the Cape Observatory, [South Africa], 1857. 'The Transit Instrument...was constructed from the designs of the Astronomer Royal, Professor Airy...The optical parts...were made by Troughton and Simms; and the engineering work by Ransomes and Sims...By a very ingenious arrangement of microscopes in the stones which carry the bearings of the instrument, eight readings are taken of each observation, and may all be taken from one point, without the observer having to actually visit the different points of the circle. The instrument weighs nearly a ton, but is so accurately balanced that it is under perfect control, and may be easily moved by one finger. A very beautiful system of parallel motion carries a trough full of mercury for taking observations by reflection. This trough being filled from the bottom of a bottle, the surface of the mercury is always clear'. From "Illustrated London News", 1857.