Correspondence with instrument manufacturers, other observatories, astronomers, inventors, etc., regarding instruments not held at the Royal Observatory, including letters asking for advice and requests to borrow or buy equipment. The papers include the following material:

Miscellaneous correspondence, 1905-1937, including letters regarding plates needed for the trigonometrical surveys of India, 1909-1910; a new Evershed solar spectroscope, 1905-1906; and the renewal of an observatory dome in the Aldershot Command, 1937.

Miscellaneous correspondence, photographs, blueprints, etc., 1908-1918, including material relating to a Duplex astrographic micrometer for the Cordoba Observatory; a blueprint of Troughton's first zenith telescope; an astrographic micrometer for the Sydney Observatory; and astronomical models by William Wilson for colleges and schools.

Miscellaneous correspondence, 1918-1920, including papers regarding an equatorial telescope by Negretti and Zambra; a printing chronograph for South Australia; the Baker Sextant No. 12; a new microscope for the astrograph at Sydney; and transit instruments A62 and A64, returned from Malta.

Miscellaneous correspondence, 1921-1928, including letters concerning the purchase of a Zeiss planetarium by London County Council.

Miscellaneous correspondence, 1929-1934, including letters regarding the 4-inch transit for the Mount Faber Observatory, Singapore, and the Osborne Telescope.