One of two thermostats for the magnetic recorder room at the Royal Observatory's magnetic department in Abinger, Surrey, each with two loops of differently expanding metal. Inscription: PAT Nos 5311, 1912 110938, 1916, 24633, 1919, JOHN GRUNDY LTD TYLDESLEY, LANCS & LONDON.

These patent numbers refer to the thermostat patents created by Herbert Hamilton Grundy (1880-1932).

For an illustration of these thermostats in use, see 'True as the Needle to the Pole', The Sphere, 16 April 1927, p.97.

Due to increasing electrical interference and vibrations from nearby railway lines, the Magnetic Department of the Royal Observatory moved to a new location at Abinger, Surrey, in 1924. Observations continued here until 1957 when the Department was moved again to Hartland, north Devon, where it continues today under the management of the British Geological Survey. Some additional observations were made at the Royal Observatory's new location at Herstmonceux.