This brass orrery movement consists of pulley wheels are held between plates and mounted on a wooden dodecagonal base. Anthony Turner writes in his catalogue 'Science and Music in 18th-Century Bath' (1977), that the instrument resembles James Ferguson's 'calculator' (1749), an adaptation of his four-wheeled orrery (1746). It is not known whether this example was made by Ferguson or the Herschels.

This object was found amongst William Herschel's equipment at Observatory House in Slough and kept by his heirs until sold at auction in early 1958.