William Lassell and the Ring of Neptune: A Case Study in Instrumental Failure

Herschel J. , “Address delivered by the President (Sir J. F. W. Herschel. Bart.) on presenting the Honorary Medal of the Society to William Lassell, Esq., of Liverpool”, Monthly notices of the Royal Astronomical Society , ix (1849), 87–92. p. 87.

Huggins W. , “Obituary of William Lassell” in “Report of the Council to the sixty-first Annual General Meeting”, Monthly notices of the Royal Astronomical Society , xli (1881), 188–91, p. 188.

Von Humboldt A. , Cosmos: A sketch of a physical description of the universe (English transl., London. 1852), iv, 476, footnote 16.

Baum R. , The planets: Some myths and realities (Newton Abbot. 1973), chap. 6.

See Hetherington N. S. , “Neptune's supposed ring”, Journal of the British Astronomical Association , xc (1979), 20–29, Hoyt W. G. , “Reflections concerning Neptune's ‘ring’”, Sky and telescope , lv (1978), 284–5, and Elliot J. L. , “No evidence of rings around Neptune”, Nature , ccxciv (1981), 526–9.

Hind J. R. , “Discovery of Le Verrier's planet”, letter to the editor, The Times , 1 October 1846, 8. Neptune was often referred to as “Le Verrier” for some time after its discovery.

The cutting is located between the entries for 2 and 3 October 1846 in one of Lassell's notebooks: Lassell papers 9.7, Royal Astronomical Society Archives (hereafter cited as RASA). The references to Lassell's notebooks follow those given in Bennett's J. A. “Catalogue of the archives and manuscripts of the Royal Astronomical Society”, Memoirs of the Royal Astronomical Society , lxxxv (1978).

Lassell J. Herschel to W. , 1 October 1846, Royal Society Herschel papers (H.S.22.285).

Entry for 3 October 1846 in Lassell papers 9.7, RASA.

Entry for 10 October 1846 in Lassell papers 9.7, RASA. The satellite was Triton, Neptune's largest moon.

Entry for 26 October 1846 in Lassell papers 9.7, RASA.

Entry for 29 October 1846 in Lassell papers 9.7, RASA.

Entry for 10 November 1846 in Lassell papers 9.7, RASA.

Entry for 11 November 1846 in Lassell papers 9.7, RASA.

Lassell W. , letter to the editor, The Times , 14 October 1846, 7. The letter is dated 12 October.

Lassell W. in the collection of various “Observations of Le Verrier's Planet”, Monthly notices of the Royal Astronomical Society , vii (1846), 154–7, p. 157.

Reported in “Observations of Le Verrier's Planet”, ibid. , 165–8, p. 167.

Hind's search for Neptune is discussed in Smith's Robert W. “The discovery of Neptune”, in preparation.

Hind J. R. , “Schreiben des Herrn J. R. Hind an den Herausgeber”, Astronomische Nachrichten , xxv (1847), 205–8, p. 207. The letter is dated 8 December 1846. See also a note on Hind's claims in “Observations of Le Verrier's Planet”, Monthly notices of the Royal Astronomical Society , vii (1846), 165–68, p. 168.

Challis J. , “Second report of proceedings in the Cambridge Observatory relating to the new planet (Neptune)”, Astronomische Nachrichten , xxv (1847), cols 309–14, col. 310.

Ibid. .

Challis W. Lassell J., 19 January 1847, Cambridge Observatory Archives. See also Sheepshanks W. Lassell R., 9 February 1847, Sheepshanks papers, RASA.

Challis J. , “Schreiben des Herrn Professor Challis, Direktor der Cambridge Sternwarte, an den Herausgeber; ‘Observations of Le Verrier's planet taken at Cambridge Observatory’”, Astronomische Nachrichten , xxv (1847), 229–32. Lassell reported this to Sheepshanks: See Lassell W. Sheepshanks R. , 9 February 1847, Sheepshanks papers, RASA.

Sheepshanks W. Lassell to R. , 9 February 1847, Sheepshanks papers, RASA.

See Baum , The planets , 134–9.

Reported in “Report of the Council to the twenty-seventh Annual General Meeting”, Monthly notices of the Royal Astronomical Society , vii (1847), 193–231, p. 217.

Challis W. Dawes to J. , 7 April 1847, Cambridge Observatory Archives.

Herschel W. Dawes to J. , 21 April 1847, Royal Society Herschel papers (H.S.6.81).

Ibid. This letter solves the problem raised by Hetherington ( op. cit. (ref. 5)) of the apparent disagreement between the inclination measurements of Lassell and Challis.

Draft of letter by Challis J. , 3 May 1847, Cambridge Observatory Archives.

Ibid. .

Entry for 7 July 1847 in Lassell papers 9.8, RASA.

Herschel W. Lassell to J. , 14 August 1847, Royal Society Herschel papers (H.S. 11.134). A few days earlier Lassell had written to the Astronomische Nachrichten and commented that he had noticed on two or three occasions the same appearance of the ring as in 1846, “But nothing more strongly confirmatory, and I wait to see the planet more nearly on the meridian, and for a state of atmosphere that will bear the application of higher powers than are necessary to see the satellite” ( Lassell W. , ”Schreiben des Herrn Lassell an den Herausgeber”, Astronomische Nachrichten , xxvi (1848), 165–8, p. 168).

Nichol W. Lassell to J. P. , 17 August (?) 1847. Copy in Lassell papers 8.2, RASA.

Sheepshanks W. Lassell to R. , 8 September 1847, Sheepshanks papers, RASA.

Entry for 8 September 1847 in Lassell papers 9.8, RASA.

Entry for 8 September 1847 in Dawes papers 3 (Observing journal 1847–1858), RASA.

Lassell W. , “The planet Neptune and his satellite”, letter to the editor, The Times , 24 September 1847, 7.

Challis J. , Astronomical observations made at the observatory of Cambridge , xv (1848), Appendix 1, 20.

Entry for 21 August 1849 in Lassell papers 9.11, RASA.

Entry for 27 November 1849 in Lassell papers 16.1, RASA.

Lassell W. , “Observations of Neptune and his satellite”, Monthly notices of the Royal Astronomical Society , xii (1851), 155.

J. Nasmyth to Royal Astronomical Society, 5 December 1852, RAS letters, RASA.

Lassell W. , “Extract of a letter from Mr. Lassell”, Monthly notices of the Royal Astronomical Society , xiii (1853), 36–39, p. 38.

Entry for 11 November 1852 in Lassell papers 16.3, RASA.

Entry for 15 December 1852 in Lassell papers 16.4, RASA.

These observations are discussed by Baum , op. cit. (ref. 4), chap. 5.

See Hetherington , op. cit. (ref. 5), 27.

Herschel W. Lassell to J. , 12 October 1846, Royal Society Herschel papers (H.S.11.130).

Sheepshanks W. Lassell to R. , 8 September 1847, Sheepshanks papers, RASA.

Entry for 11 November 1846 in Lassell papers 9.7, RASA.

Lassell W. , “Description of a machine for polishing specula etc., with a description for its use …”, Memoirs of the Royal Astronomical Society , xviii (1850), 1–20, p. 17.

Entry for 14 May 1851 in Lassell papers 16.2, RASA.

Entry for 29 October 1852 in Lassell papers 16.3, RASA.

Airy G. B. , “Substance of the lecture delivered by the Astronomer Royal on the large reflecting telescopes of the Earl of Rosse and Mr. Lassell, at the last November meeting”, Monthly notices of the Royal Astronomical Society , ix (1848), 110–21, p. 118. Airy's observations were of course made at an early time in the career of Rosse's giant telescope, and Rosse was later to devise various other systems to combat flexure, some of which Airy describes in the same paper. The question of flexure problems in large speculum metal reflectors is taken up by Smith Robert W. in “The telescopes of William Lassell”, in preparation.

However, it is likely that such measures were not attempted until Lassell began his observations of Neptune in 1847, and then he employed his “excellent” parallel wire micrometer by Dollond for position and distance determinations of Neptune's satellite as well as for measures of the projections of the supposed anse of the ring: See Lassell W. , “The planet Neptune and his satellite”, letter to the editor, The Times , 24 September 1847, 7. Lassell's behaviour is here worth comparing with that of the professional Challis. In particular, Lassell apparently made no attempts to measure the ring's position until Challis had done so. Challis indeed took his first measures but three days after his initial sighting of the ring. We are thus given a view of Lassell's determined but, in 1846, essentially amateurish approach to the problem of the ring's existence.

On 30 September 1846, Hind told Challis that he had observed Neptune's “Distinctly perceptible” disk and that it is “bright”. No mention was made of any irregularity of form: Hind J. Challis J. , 30 September 1846, Cambridge Observatory Archives.

It is not clear if Lassell knew of William Herschel's spurious detection of rings around Uranus. Preconception played a central rôle in Herschel's observations of the newly discovered planet for at first he thought he had found a comet and, moreover, measured it to be increasing in size just as he had anticipated a comet would do, this despite the fact that Uranus was then decreasing its size as seen from the Earth: See Austin R. H. , “Uranus observed”, British journal for the history of science , iii (1967), 275–84, and Schaffer S. , “Uranus and the establishment of Herschel's astronomy”, Journal for the history of astronomy , xii (1981), 11–26.

Berman M. , “‘Hegemony’ and the amateur tradition in British science”, Journal of social history , viii (1975), 30–50, p. 40. On amateurs in late nineteenth-century astronomy see Lankford J. , “Amateurs and astrophysics: A neglected aspect in the development of a scientific speciality”, Social studies of science , xi (1981), 275–303.

This is taken up in more detail in Smith's Robert W. “The telescopes of William Lassell”, in preparation.

Smyth W. H. , The cycle of celestial objects continued at the Hartwell Observatory to 1859. With a notice of recent discoveries, including details from Aedes Hartwellianae (London, 1860), 417. However, the idea that Neptune has a ring took many years to disappear completely. For example, a set of ten English mechanical astronomical slides dated c. 1865 includes one of Neptune with a ring: Tesseract: Early scientific instruments Catalogue C, Winter 1983 (Hastings-on-Hudson, N.Y., 1983), lot number 2.