Unfinished Business: William Herschel's Sweeps for Nebulae

Caroline Herschel's autobiographies, ed. by Hoskin Michael (Cambridge, 2003), 43.

Halley Edmond , “An account of several nebulae or lucid spots like clouds”, Philosophical transactions, xxxix (1714–16), 390–2; Philippe Loys de Chéseaux, letter to “Monsieur mon très cher grandpère” read before the Académie Royale des Sciences on 6 August 1746 but unpublished until 1884; de Lacaille N.-L. , “Sur les étoiles nébuleuses et des amas d'étoiles …”, Mémoires de l'Académie Royale des Sciences, 1755, 286–96. For full information on these and other lists, see Jones Kenneth Glyn , The search for the nebulae (Chalfont St Giles, 1975, and now available from the publishers of History of science).

Messier Charles , in the Connoissance des temps for 1784 (but published in 1781).

Caroline Herschel's autobiographies, ed. by Hoskin (ref. 1), 71.

See Hoskin Michael , “William Herschel's 40ft reflector: Funding and functions”, Journal for the history of astronomy, xxxiv (2003), 1–32.

Hoskin Michael , “Caroline Herschel as observer”, Journal for the history of astronomy, xxxvi (2005), in press.

Caroline Herschel's autobiographies, ed. by Hoskin (ref. 1), 71–72.

Original typescript of The Herschel chronicle by Constance A. Lubbock (Cambridge, 1933) in possession of the William Herschel Society, chap. 7, 32. On William as a natural historian, see Schaffer Simon , “Herschel in Bedlam: Natural history and stellar astronomy”, The British journal for the history of science, xiii (1980), 211–39.

RAS MS Herschel W.4/1.4, f. 338.

On William's theoretical investigations of nebulae, see Hoskin Michael , “William Herschel's early investigations of nebulae: A reassessment”, Journal for the history of astronomy, x (1979), 165–76.

Herschel J. F. W. , “Catalogue of nebulae and clusters of stars”, Philosophical transactions, 1864, 1–137; Dreyer J. L. E. , “A new general catalogue of nebulae and clusters of stars, being the catalogue of the late Sir John Herschel, revised, corrected and enlarged”, Memoirs of the Royal Astronomical Society, xlix (1888).

In 17 CD-Roms (£125) or three DVDs (£100), available from the Membership Secretary of the Royal Astronomical Society, ronw@ras.org.uk.

The analysis that follows is based principally on Caroline's zone catalogue of stars observed in sweeps (RAS MS Herschel C.3/2) and on her fair copy of records of sweeps (W.2/3, originals in the Royal Society Library).

Writing in April 1784 in a paper read to the Royal Society the following month (“Account of some observations tending to investigate the construction of the heavens”, Philosophical transactions, lxxiv (1784) 437–51, p. 437), he says that “at present” the instrument is confined to “a meridional situation”.

Rosse's Like Lord “Leviathan of Parsonstown” two generations later. On the Leviathan see Hoskin Michael , “Rosse, Robinson, and the resolution of the nebulae”, Journal for the history of astronomy, xxi (1990), 331–44.

On the 29th William viewed the Andromeda Nebula with the telescope turned to the east. He then attempted several sweeps in that direction, but could not establish due east with sufficient precision for his purpose. See the comment before sweep 286 in RAS MS Herschel W.2/3.3.

Herschel William , “Catalogue of one thousand new nebulae and clusters of stars”, Philosophical transactions, lxxvi (1786), 457–99, p. 459.

Ibid., 458.

Those numbered II.1–4, III.1, V.1, VI.1 and VIII.1 in the catalogue, ibid.

The width of each sweep is recorded by Caroline in RAS MS Herschel C.3/2.1.

An eyewitness account of Caroline at work is in Ashworth William B. Jr , “Faujas-de-Saint-Fond visits the Herschels at Datchet”, Journal for the history of astronomy, xxxiv (2003), 321–4.

In the libraries of both the Royal Society and the Royal Astronomical Society.

Smeaton John to Michell John , 4 November 1785, copy (3 pp. folio), RAS MS Radcliffe Hornsby 78; I am grateful to Dr J. A. Bennett for supplying me with a copy of this document. Letter of M. Pictet published in four parts in Journal de Geneve , no. 11 (13 October 1787), quotation from p. 54; I am grateful to Andreas Maurer for supplying me with a copy this document.

Herschel , op. cit. (ref. 17).

See Dreyer J. L. E. (ed.), The scientific papers of Sir William Herschel (London, 1912), i, p. xlii. In a Newtonian reflector the light passes down to the base of the tube where a parabolic mirror reflects it back to a small, flat secondary mirror set at an angle of 45°. This secondary mirror reflects the image sideways to the eyepiece, but the reflection inevitably results in a loss of light. William's major reflectors were large enough to allow him to dispense with the secondary mirror and peer instead directly down the tube: Although his head would then obstruct some of the light that would otherwise have entered the tube, because the tube was so wide this was an acceptable price to pay for avoiding the loss of light at the secondary mirror.

See Hoskin , op. cit. (ref. 10).

Hoskin , op. cit. (ref. 5).

Herschel William , “Catalogue of a second thousand of new nebulae and clusters of stars”, Philosophical transactions, lxxix (1789), 212–55.

Bennett J. A. , “‘On the power of penetrating into space’: The telescopes of William Herschel”, Journal for the history of astronomy, vii (1976), 75–108, p. 88.

Sweep 523, on 15 February. An attempt five days earlier had proved abortive.

RAS MS Herschel C.3/2.

4 March 1796: “About 13° preceding and 5 or 6' north of the Georgian Planet [Uranus] is a nebula…”, RAS MS Herschel W.2/1.13. The nebula became I.272 in the catalogues of nebulae and clusters.

Hoskin Michael , The Herschel partnership (Cambridge, 2003), 115.

Herschel , op. cit. (ref. 17), 457.

Herschel William , “Catalogue of 500 new nebulae, nebulous stars, planetary nebulae, and clusters of stars”, Philosophical transactions, xcii (1802), 477–528.

Royal Society L&P XII, 34.

Herschel John Mrs , Memoir and correspondence of Caroline Herschel, 2nd edn (London, 1879), 108.

They appear as III.979, 980 and 981 (26 September) and II.908 and 909 and III.982 and 983 (30 September).

III.984 (observed on 17 November 1784) and II.910 and III.985 (24 March 1791).

The papers were, as always, published in Philosophical transactions, and are reprinted in Dreyer's edition (ref. 25). Their substance, with discussion and identification of the nebulae cited, is to be found in Hoskin Michael A. , William Herschel and the construction of the heavens (London, 1963).

Herschel William , “Astronomical observations relating to the construction of the heavens …”, Philosophical transactions, ci (1811), 269–336, p. 271.