A guardbook of letters received by Flamsteed, with some drafts of replies and some copies of both, 163 folios. The correspondents are mainly in the English provinces, although some write from abroad, and there are also original letters from Flamsteed to Sir Jonas Moore. The letters date primarily from 1671 to 1719, but a few are either undated or possibly earlier. Apart from those to Moore, most of the letters are of the eighteenth century. Many of the sheets have rough arithmetical notes on the dorse in Flamsteed's hand. The contents include a copy of an extract from J. Remoquietanus' observations of a transit of Mercury, 1631 (2r); a letter from Johann Hevelius to the University of Cambridge, 1679 (4r); a copy of a certificate from the Académie Royale des Sciences, Paris, 1699 (8r); a letter from Marin Mersenne to Theodore Haak [1640s] (16r); 'Instructions for the Master of the Mathematicall Schole' [at Christ's Hospital] (40r-41r); an account of the early history of astronomy (66r-67r); 'Mr Gregorys notes of errors in my copy of observations 1st volume' (75rv); a printed prospectus for the 'Atlas Coelestis', 25 October 1725 (100r); and Samuel Clowes' commission as surveyor of New York, 1700-1701 (118rv).

The correspondents include Seth Ward; Cassini; J. Chardellou; G.G. Leibnitz, Volfsbourg; Solomon Penny; J[osiah] Burchett, Admiralty; Sir David Michell, the Ordnance Office (mostly on longitude matters); James Gregory; Sir Jonas Moore; Edmond Halley; Andrew Glen; Captain Jevell (or Jewell); James Pound, cousin of John Flamsteed; Captain [Henry] Stanyan; Henry Thomas (a naval lieutenant); George Young; Abraham Sharp; Dr Th. Hill, Peterborough; Stephen Thornton, Kent; Matthew Wright, Crewe; Samuel Molyneux; Jack Bookey, Burstow; William Bossley; Luke Leigh; Thomas Brattle, New England; William Burtsal, Bungay; John Caswell; H[enry] Cressener; Derrick Dobler; William Derham; William Ella; and N. Fatio [de Duillier].