This is a beautifully simple scientific instrument. Its only moving part allows it to be set at the correct angle for the latitude of the recording site. Once that is set, the instrument records the duration of bright sunshine across each day; this requires that a new card be inserted behind the glass sphere, in one of three positions depending on season (and hence on the height of the sun in the sky). Whenever the sun is shining, the sphere focuses its rays onto the card, causing it to char in that spot; the number of hours of sunshine can be determined by measuring the resultant trace.
Although other more sophisticated instruments are now used to record sunshine, this highly reliable type of solar recorder is still used alongside them at weather stations in many countries, including Australia. As they have been available since the 1880s, their continued use can provide long runs of comparative data.
The sunshine recorder was designed by John Campbell and improved by George Stokes, both in the UK. It was made by the firm run by Rudolf Fuess sometime after he moved to his new premises in Steiglitz, Berlin, in 1892. Originally installed at Sydney Observatory, it was passed on to the New South Wales Bureau of Meteorology sometime in the early twentieth century. It was not used for many years and was donated to the Powerhouse Museum by J. M. Moss of the New South Wales Bureau of Meteorology in 1963. When Sydney Observatory became a part of the Powerhouse Museum in 1981, the instrument was reunited with others in the Observatory's collection.