Soon after his arrival in 1910 as Astronomer Royal, Dyson arranged to borrow Cookson’s Floating Zenith Telescope and its hut from the Cambridge Observatory so that he could carry out investigations into the variation of latitude. The hut, which was wooden with a tiled roof, was erected in the Observatory Courtyard in August 1911, roughly where the French Observer’s Hut used for the 1902 longitude determinations had previously stood. In order to minimise refraction anomalies, the hut had been designed with double walls, with special arrangements to promote the circulation of air in the space between them. There were doors at the north and south ends, but no windows. The opening in the roof for observing was designed to minimise air-currents. There were three outer shutters on each side of the central ridge, and an internal set of three shutters. When the telescope was moved to a new building in the Christie Enclosure in 1936, the old hut was put to use as a store. In 1948/9, it was fitted up to accommodate a petrol-driven generator which had been obtained in order to have a standby power-source for the quartz clock installation. The hut was demolished along with the other buildings in the courtyard in 1959/60 when the Observatory site was converted into a museum
The new building for housing the Cookson was erected in the year 1935/6 in the extreme north-east corner of the Christie Enclosure adjacent to the south collimator house of the Cooke Reversible Transit Circle. The central section of the roof was mounted on wheels, running on rails and could be opened or closed by turning a handle inside the building.
The telescope was removed from the shed in the courtyard on 8 June 1936, dismantled and overhauled prior to being re-erected in the new building. It was brought back into use on 25 July. In 1936/37, a portion of the new building was screened off and converted into a small dark room for loading plate carriers. It was found that on warm sunny days the roof and the south and west walls became heated, causing temperature gradients in the hut from north to south and from east to west, which would have produced apparent displacements of the zenith, so the following year, white painted louvred frames, were fitted on the roof and the south and west sides of the building to eliminate the temperature gradients.
During the Blitz, the telescope received minor damage when the exposing shutter above the instrument was detached by blast and dropped on the telescope. Observations ceased in September 1940 when the telescope was partly dismantled. The telescope was completely dismantled in 1951 and the building demolished in 1959 in preparation for the Christie enclosure to be returned to the Park.
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