A Newtonian primary mirror of speculum metal with a focal length of 1ft 6ins. The mirror is very thick for its diameter, especially in an annulus about the centre of the back. It is badly chipped at the edge, but the chip is mostly at the back and encroaches only a little onto the front surface. An attempt was made to test it by Foucault's method on 17 June 1924, but the focal length proved inconveniently short for the apparatus and no zonal test was carried out. The figure appeared even, without zones and the characteristic 'parabolic' shadows were very prominent. It is probably a very good mirror. It lies loosely in a somewhat rusted tin case with hinged lid.

William Herschel, with help from his brother Alexander and his sister Caroline made a number of these mirrors to go in the telescopes they made to use and to sell. A mirror of this size and focal length would have been used in one of their 10-ft telescopes.