A summary of correspondence related to the discovery of Neptune in 1846 is here presented. Around 440 letters from about a dozen different archives – in London, Cambridge, Cornwall, Paris and Washington – are assembled. You can search by: who sent the letter, who received it, the archive, the year and month, nationality of sender, or even by a keyword, inserted into the ‘letter summary’ section. There are some two dozen correspondents altogether, of which ten are included in the pull-down menus, and likewise there are ten searchable archives in the pull-down menu. One can combine these criteria, for example inserting ‘Airy’ and ‘1846’ will call up all the relevant letters by him in that year.

Click here to visit the Neptune Correspondence

You can search by a year or a month, eg ‘1846 November,’ and it will list all those letters in chronological order. For each letter, the location of the original is specified wherever possible, and then in separate section(s) the archive location and that of any copies is also given (N.B., ‘ALS’ means ‘autographed letter, signed,’ i.e. the original copy). The original letters as sent to Airy are kept in the RGO’s ‘Neptune File’ now at Cambridge, while those sent to Adams are in the John’s College Library; those sent to Challis are in the Institute of Astronomy archives (where Challis worked); those sent to Sheepshanks (RAS secretary) are in the RAS archives; and those sent to Herschel are in the Royal Society archives

The first line of each letter is given, plus a summary of its contents. These are the letters which I have selected as essentially relevant to the discovery of Neptune. Because this is the first-ever integrated collection of relevant Neptune-discovery correspondence, it makes possible a proper telling of the story. An RAS grant has enabled this archiving work, following the recovery of the RGO’s Neptune-file from Chile in 1999. In addition, there may be a sizeable collection of German correspondence which my colleague Dr Craig Waff is collecting. Comments and criticisms, such as letters that should be added, are welcome, sent to: nk[at]

Five nationalities are here searchable, for senders of letters. The one exception here is France: ‘French’ will select both senders and recipients. It may be especially valuable to follow the sequence of letters to and from Paris, and for this reason I have taken the liberty of putting both of these together.

You can search for archives with the pull-down menu and choose one of these:



The Royal Greenwich Observatory’s ‘Neptune File,’ assembled by Airy, kept in the Cambridge University Library, (RGON).

The Cambridge Institute of Astronomy collection, i.e. James’ Challis file, now in the University Library, Cambridge (IoA)

St John’s College Library, Cambridge: correspondence of J.C. Adams (JCL)

Donald MacAlister’s collection, of transcripts of Neptune-related correspondence, to or from J.C.Adams, kept at St John’s College, Cambridge (McA).

The library of Trinity College, Cambridge, holding Sir William Whewell’s correspondence (TC)

Some letters kept in the UL at Cambridge, not in the Neptune-File (RGO 6).


The Royal Society library’s John Herschel correspondence. This includes both authentic letters and a large collection of transcribed letters (‘RS:HS’).

The Royal Astronomical Society’s library has letters of RAS Secretary Richard Sheepshanks, plus those of Augustus de Morgan (RAS).


Cornwall Record Office collection, at Truro, of Adams family manuscripts (CRO).


Archives of the Observatoire de Paris (Obs de Paris)

The library of the Institut de Paris has Le Verrier’s correspondence (Inst de P.)

Institut de France: a book published in Paris in 1911, ‘Centenaire de la Naissance de U. J. J. Le Verrier.’ (Inst de F.)


For US letters, eg ‘Nat’ in the Archive box will pull up those published in the US National Intelligencer (4 letters) while ‘Nav’ will produce one in the Naval Observatory records. Likewise two may be found in the German Astronomische Nachrichten and ‘Astr’ will find these. There are our sole records for these letters, which means that my US colleague Dr Craig Waff and I have not been able to find any originals for them.


Letters to and from the brothers of John Couch Adams, viz. Thomas, George and William, can be obtained by writing in these names; whereas selecting ‘Adams’ in the drop-down menu will only select for the astronomer. Likewise, the letters sent by Airy’s wife can be found by writing in ‘Richarda Airy’.

Comments upon the location of letters may be found in the ‘notes’ appended, eg the mysterious fate of the four letters by Richarda Airy (G.B. Airy’s wife), probably lost somewhere in the CUL, of which I have only ever seen copies. Many of the original letters of the Astronomer Royal G.B.Airy are unobtainable, and only the ‘press copy’ remains – the blotting paper record of his letter, often illegible - kept in the ‘Neptune File’. Almost all ‘Airy’ letters in the RGO’s Neptune file are of this form, not originals.

Two of the archives here used are web-checkable: those of John’s College library, and of the Adams manuscripts at Truro, Cornwall. For the former, the route is:, ‘participating institutions,’ ‘St Johns College Library’, ‘J.C.Adams’, then select the box. For the latter, the route is:, ‘search,’ with ‘Cornwall Record Office’ as location and ‘Adams’ as keyword, then ‘Search,’ select ‘Adams Family of Litcott,’ then ‘Catalogue in full.’

Originally the Neptune-file was smartly bound and had gold lettering with ‘RGO file’ etc on the front, as Eggen presumably ripped off when he stole it., however it still has its spine intact. A full set of photocopies of the RGO’s Neptune-file was acquired by Dennis Rawlins, made in Chile in 1999 upon Eggen’s demise (without permission of the proper owners of the file, who would not have given it). No index has ever been made of its contents. Airy named his file: ‘papers relating to the discovery, Observations and Elements of Astrea, Neptune, Hebe, Iris, Flora, colours of Astrea, Neptune’ (its opening and closing sections are about the discovery of asteroids).

Letters kept at St John’s College, Cambridge are classified either as John’s College Library (JCL), which has original letters, or as the collection made by Sir Donald MacAlister (McA), around the turn of the 19th century, which are copies of letters, related to Adams and Neptune. The latter collection has been so valuable, because many of the originals are now illegible. Likewise the Royal Society’s collection of John Herschel letters includes its own collection of original letters, plus many others copied out by a descendent of Herschel, which are far more legible. There are three different Neptune-related collections at Cambridge’s University Library: the ‘Neptune file’ of the now-deceased Royal Greenwich Observatory, which has been returned from Chile; the Institute of Astronomy’s collection, recently donated to the CUL, i.e. the collection of letters that were held by James Challis; and other RGO archives, which a few that are relevant.

The MacAlister collection at St John’s extends over J.C. Adams’s whole life, for a projected biography that was never accomplished; it is kept in eight of their boxes, subdivided into folders with several letters per folder. (eg McA 33:7 is the 7th folder in box 33). To pull up the MacAlister collection letters here included, I suggest using both the ‘Archive’ and ‘Copy archive’ boxes: any original copy of a letter will occupy the ‘Archive’ box, and in that case the MacAlister copy will appear in the ‘Copy archive’ box.

The Institute of Astronomy collection was archived by David Dewhurst, as given in Patrick Moore’s ‘The Planet Neptune.’ I have here followed Dewhurst in giving the first line of each letter. This collection duplicates that of the RGO for letters sent by Airy to Challis, because it has the originals.

Shortly after John Herschel’s death (1871), his son col. John Herschel had the letters arranged and copies prepared (in the family house at Slough), after which he returned the originals to whomever they belonged, for a biography which he never completed. These hand-copied letters give no indication as to where the originals are kept. These were thoroughly indexed and collated into 25 volumes, then a grandson, the rev Sir John Herschel, donated most of this in 1944 to the Royal Society.

The Calendar of John Herschel’s Correspondence (Mike Crowe Ed.), omits letters Herschel sent to Airy about Neptune, because the Neptune file was absent while it was prepared; and also omits some Herschel letters in the MacAlister collection, because the computer indexing of the Adams papers in St John’s College Library, which made evident what was contained in them, was only completed in the 1999. I have followed the example of this Calendar in giving a short summary of each letter.

Despite being the 7th Astronomer-Royal, Airy’s MS somehow got filed as ‘RGO.6’ by the Royal Greenwich Observatory. There are now some eight hundred ‘boxes’ of Airy material, comprising over a hundred yards of shelf-space (!) in the Cambridge University Library. Their filing, quite an exhaustive business, excluded the Neptune file as it had gone missing when this was all done, in the 1980s. It has now been archived as MS.RGO.6/96A; while the Institute of astronomy papers (Challis’ collection) are filed under ‘Obsy D.3.’

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