The Relationship between the Ramsden Circles at Palermo and Dunsink

On the dates of Piazzi's travel, see Chinnici Ileana Foderà Giorgia Brenni Paolo , “The Ramsden Circle at the Palermo Astronomical Observatory”, Bulletin of the Scientific Instrument Society, lxxi (2001), 2–10, pp. 2–3.

“Ho parlato ancora a Ramsden pel quadrante e pel cerchio. Egli crede che non vi sia a bilanciare un momento tra il primo, ed il secondo, e che ove si abbia quest'ultimo, il primo sia interamente inutile” (“I have spoken again with Ramsden about the quadrant and the circle. He believes that there is no comparison between them, and once you possess this last one, the first one is entirely useless”), Piazzi to Cassini, 21 August 1788, Observatoire de Paris-Archives MSS autographes, B4/11bis. The reasons for Ramsden's conviction are reported by Piazzi in a letter to Lalande: Piazzi Giuseppe , “Lettre sur les ouvrages de M. Ramsden, Londres, 1er Sept. 1788”, Journal des sçavans pour l'année 1788, 744–52, p. 751–2. In 1790 Jean-Dominique Cassini, known as Cassini IV, demonstrated the scientific grounding of Ramsden's strong opinion (see Cassini Jean-Dominique , «Application du cercle à l'observation des hauteurs méridiennes des Astres», Mémoires de l'Académie des Sciences, Année MDCCLXXXX, 617–24).

Ussher Henry , “Account of the observatory belonging to Trinity College, Dublin”, Transactions of the Royal Irish Academy, i (1787), 3–21, pp. 6–7 (footnote).

“Il [Ramsden] espère ensuite achever celui de Dublin qui a douze pieds et que vous avez vu fort avancé…” (“He [Ramsden] hopes afterwards [i.e. after having completed the Palermo Circle] to finish that one for Dublin which is twelve foot [in diameter] and that you have seen well advanced…”), Piazzi, op. cit. (ref. 2), 752.

“M. Ramsden, le plus célèbre ingénieur qu'il y ait actuellement pour les grands instruments, ne veut plus faire que des cercles entiers; il en a fait un de 5 pieds, en 1788, pour M. Piazzi, astronome de Palerme; il en fait actuellement un de 8 pieds pour Paris, et un de 11 pieds pour Dublin” (“Mr Ramsden, the most famous current maker of large instruments, does not want to build other than entire circles; he has made a five-foot circle in 1788 for Mr Piazzi, astronomer in Palermo; he is making an eight-foot one for Paris and an eleven-foot one for Dublin”), Jérôme de Lalande, L'astronomie, ii (Paris, 1792), 591. Anita McConnell suggests that this discrepancy could be due to the difference between the English and French feet (private communication, 13 October 2008). The two measurements are very close, as twelve English feet are equal to 3.65 metres and eleven French feet are equal to 3.57 metres.

See Robinson Thomas R. , “Dublin Observatory”, Nature, iii (1871), 445–6.

See Pearson William , An introduction to practical astronomy (London, 1829), 423.

Another equatorial, with 5-ft circles, had been ordered by Ussher for the Dunsink Observatory (see Usher , op. cit. (ref. 2), 7 (footnote)), but it was never made (see McConnell Anita , Jesse Ramsden (1735–1800) (London, 2007), 115).

See Chinnici , op. cit. (ref. 1), 2. The Shuckburgh equatorial was delivered in 1791, as related in Shuckburgh George , “An account of the equatoreal instrument”, Philosophical transactions , lxxxiii (1793), 67–128, p. 76 (footnote). Shuckburgh's account contains a very detailed description of the instrument, which shows a strong resemblance to the Palermo Circle, delivered just two years earlier (see below).

See McConnell , op. cit. (ref. 8), 131.

” [Ramsden] ne ha uno di otto piedi, ed io stesso più volte l'ho veduto, già avanzato, e fu intrapreso pel Duca di Sermoneta, che in seguito tolse la commissione …” (“He [Ramsden] has an eight-foot circle well advanced and I myself have seen it several times, it was commissioned by the Duke of Sermoneta who later withdrew the commission …”), Piazzi to Cassini, London, 21 August 1788, Observatoire de Paris-Archives MSS autographes, B4/11bis.

“Questo egli è pronto a cederlo a lei, e porvi mano per finirlo sì tosto, che avrà terminato il mio, che deve servirgli per modello. Ma su ciò vi è tempo ancora …” (“This one [the circle initially commissioned by the Duke of Sermoneta] he [Ramsden] is ready to give to you after the completion of mine, which will serve him as a model. But it takes time …”), Piazzi to Cassini, ibid. In his letter to Lalande, Piazzi writes that, after the Palermo Circle, Ramsden will deliver the Paris (ex-Duke of Sermoneta's) Circle and then the Dunsink Circle (see Piazzi , op. cit. (ref. 2), 752). From this working plan, it is possible to argue that in 1788 the construction of the Duke of Sermoneta's Circle was more advanced than that of the Dunsink Circle.

On the instruments Cassini ordered from Ramsden, see McConnell , op. cit. (ref. 8), 141–6.

Besides the circle, Piazzi ordered several other instruments from Ramsden: Namely, a transit instrument, a comet-seeker, a sextant, a barometer and a portable achromatic telescope (see Serio Giorgia Foderà Chinnici Ileana , L'Osservatorio Astronomico di Palermo (Palermo, 1997), 60–64, 85, 101–2). The last three instruments are now in the Palermo Observatory Museum (Museo della Specola).

See Piazzi to the Prince of Torremuzza, London, 8 October 1787 in Chinnici ., op. cit. (ref. 1), 3. Piazzi was aware that Ramsden was unreliable in delivering instruments and he intended to withdraw the order if Ramsden had not started construction within the following three months. Therefore, it can be argued that the construction of the Palermo Circle began not later than December 1787.

See Chinnici , op. cit. (ref. 1), 4.

Piazzi , op. cit. (ref. 2).

“Il est occupé actuelment à veiller tous les jours sur le celebre Ramsden pour lui faire terminer un superbe instrument, qui rendra l'observatoire de Palerme un des plus interessans de l'Europe. Je lui ai bien conseillé de ne pas quitter Londres, qu'il n'ait fait embarquer cet instrument …” (“He [Piazzi] is presently occupied every day in keeping an eye on Ramsden to make him deliver an excellent instrument which will make the Palermo Observatory one of the most interesting ones in Europe. I have advised him not to leave London before this instrument is put on board ship …”), Lalande to the Viceroy, Paris, 10 October 1788, in Lettre du R. P. D. Joseph Piazzi C. R. Théatin à Monsieur de La Lande sur les ouvrages de Mr Ramsden (Palermo, 1788), [3]. Piazzi's letter about Ramsden's works was separately published in Palermo and Lalande's letter to the Viceroy appears as a foreword; probably the local publication of the letter was suggested by Lalande in order to justify Piazzi's long absence from Palermo.

In May 1789 the vertical circle had been divided and, in August, Piazzi proudly announced the completion of the Palermo Circle and his departure from London; see Chinnici ., op. cit. (ref. 1), 4.

On the construction of the Palermo Circle, see McConnell , op. cit. (ref. 8), 131–5, and Chinnici , op. cit. (ref. 1), 4–5.

“Le plus grand équatorial qui ait jamais été fait est celui qu'il [Ramsden] destine actuellement à M. le Chevalier Shuckburgh, & auquel il travaille depuis neuf ans. Le cercle de déclinaisons a quatre pieds de diamètre, de manière qu'on puisse les observer à une seconde près, & la lunette est placée entre six colonnes qui forment l'axe de la machine, & dont l'assemblage tourne autour de deux pivots établis sur deux massifs de maçonnerie” (“The greatest equatorial ever made is the one he [Ramsden] now assigns to Sir Shuckburgh, & on which he has been working for nine years. The declination circle is four feet in diameter, so that it will be possible to observe the second of arc, & the telescope is placed within six columns which constitute the axis of the instrument & whose assembly turns around two pivots fixed on two masonry blocks”), Piazzi , op. cit. (ref. 2), 749–50.

See Wayman Patrick A. , Dunsink Observatory 1785–1985 (Dublin, 1987), 33.

“Il devient encore un cercle mobile azimutal en ajoutant un cercle horizontal au-dessous de l'axe …” (“It may be used also as an azimuthal circle, by adding an horizontal circular scale under its axis …”), Piazzi , op. cit. (ref. 2), 751.

“Le cercle vertical de M. Piazzi est divisé, on travaille à diviser le cercle azimutal …” (“The vertical circle for Mr. Piazzi is divided, they are working on the division of the azimuthal circle …”), Lalande to Oriani, Paris, 2 May 1789, Brera Observatory Archives.

See Chinnici , op. cit. (ref. 1), 4, and McConnell , op. cit. (ref. 8), 133.

See refs 11–12.

For other technical arrangements, in fact, the most appropriate ‘model’ could have been the Shuckburgh equatorial, which was in a more advanced state of construction than the Palermo Circle, at that time (see ref. 21).

Piazzi Giuseppe , Della Specola Astronomica de' Regj Studj di Palermo, libri quattro (Palermo, 1792), 15–46.

“M. Piazzi, à Palerme, plaça son cercle de cinq pieds, fait par Ramsden, et qui est un des plus beaux instruments d'astronomie qu'on ait faits” (“Mr Piazzi in Palermo has installed his five-foot circle, made by Ramsden, and it is one of the most beautiful astronomical instruments ever made”), Jérôme de Lalande, Bibliographie astronomique; avec l'histoire de l'astronomie depuis 1781 jusqu'à 1802 (Paris, 1803), 706. Relating to the performance expected from the Palermo Circle, it is worth mentioning that in 1790 Maskelyne suggested a similar instrument for the Armagh Observatory. It was however decided to purchase a Troughton equatorial; see Bennett J. A. , Church, state and astronomy in Ireland (Belfast, 1990), 22–26.

Piazzi Giuseppe , Praecipuarum stellarum inerrantium positiones mediae ineunte saeculo XIX (Palermo, 1803), pp. xxxv–xxxviii. A second edition was published eleven years later: Piazzi Giuseppe , Praecipuarum stellarum inerrantium positiones mediae ineunte saeculo XIX ex observationibus habitis in Specula Panormitana ab anno 1792 ad annum 1813 (Palermo, 1814).

“… animadvertam, circulum orizontalem parum utilitati esse, nec suis carere incommodes. Etenim praterquam quod stellarum azimuta difficile est accurate observare, & eorum calculus satis prolixus est; instrumentum ipsum semel in meridiano positum, ex quacumque vel levissima causa ab eodem dimovetur. Cum igitur major observationum numerus fiat in meridiano, consultius foret azimutalem circulum e medio tollere, & verticalem ad tubi meridiani normam in ipso meridiano constituere” (”… I give notice that the horizontal circle is of little use and not short of disadvantages. Actually, in addition to its being difficult to observe accurately the stellar azimuths and time-consuming to calculate them, the instrument once set into the meridian, draws away from it for any cause, ever the slightest. Therefore, since the majority of the observations are carried out on the meridian, it should be convenient to put aside the azimuthal circle and to fix the vertical one on the meridian like a transit instrument …”), Ibid., p. xxxviii.

“Firmiter itaque positis hinc & inde ferreis palis, inter quos circulus collocandus, eisdem aptentur apparatus omnes micrometrici, microscopici, aliique quibus opus erit; ex simplici ligno extructa inde machinula, qua facile circulus inverti possit, omnia commoda constructio haec exhibebit, atque illud praecipue, quod oppositis circuli positionibus observationes fieri queunt: In quo sane maxima super caetera, hujus instrumenti praestantia constituta est” (“Therefore, once secured firmly to iron poles on opposite sides, the circle being in the middle, all micrometers, microscopes and other necessary accessories will then be applied. Once built this simple wooden machine, the circle can be easily inverted by means of it; this construction shows all the advantages and especially that observations can be carried out in opposite positions of the circle: This facility gives this instrument its superiority over all others”), ibid.

“Novae hujus constructionis descriptionem & formam ipse jam dedi pro Specula domestica, quam sibi parandam proponit Princeps Pulchrimontis, Joseph Ventimiglia, scientiarum & Astronomiae preasertim amantissimus” (“I have already given the description and the drawing of this new construction to the Prince of Belmonte, Giuseppe Ventimiglia, who is a great lover of the sciences and especially astronomy, for the private observatory he intends to build”), Ibid.

McConnell's hypothesis is that part of its framework may have been incorporated into Piazzi's apparatus. See McConnell , op. cit. (ref. 8), 131.

See Pearson , op. cit. (ref. 7), 423.

See ref. 32.

Taylor W. B. S. , History of the University of Dublin (London, 1845). For a comparison, see the description of the machine by Piazzi, cf. ref. 33.

See Wayman , op. cit. (ref. 22), 35.

See Pearson , op. cit. (ref. 7), 424.

In 1792 a royal decree established the title of Astronomer Royal for Ireland for Andrews Professors. See Wayman , op. cit. (ref. 22), 22–24.

See Maskelyne N. , “Extract of a letter from J. Brinkley, on the parallax of Alpha Lyrae”, Philosophical transactions of the Royal Society , c (1810), 204–10. See also Brinkley John , “An account of observations made with the eight feet astronomical circle, at the Observatory of Trinity College, Dublin, since the beginning of the year 1818, for investigating the effects of parallax and aberration on the places of certain fixed stars; also the comparison of these with former observations for determining the effects of lunar nutation”, ibid., cxi (1821), 1821–60.

See Wayman , op. cit. (ref. 22), 44–46.

See Serio G. Foderà , “G. Piazzi and the proper motion of 61 Cygni”, Journal for the history of astronomy, xxi (1990), 275–82.

“Non ha guari che mi son venute da Londra le transazioni filosofiche del 1813. In esse ho vedute le prime osservazioni di Pond col suo Cerchio murale. Dal poco che misteriosamente ne dice mi sono formato qualche idea di questo nuovo miracoloso stromento. Se non sono altrimenti nell'errore, con buona pace dell'Astronomo di Greenwich, con buona pace di Troughton, Artefice … dico che gl'inconvenienti a cui vanno soggetti i microscopi fissi non sono punto inferiori a quelli del filo a piombo. Oltre di che il maggiore vantaggio che presenti il Cerchio si è il rovesciamento, e questo è impraticabile secondo la costruzione del Troughton. Prima che sorga un nuovo Ramsden deve trascorrere tempo assai, ed io certamente non sarei per cambiare il mio Cerchio con altro qualunque di Troughton” (“I have recently received from London the Philosophical Transactions for 1813. There I have seen the first observations by Pond with his mural Circle. From the few notices he mysteriously gives, I have got a general idea of this new prodigious instrument. If I am not mistaken, in spite of the Greenwich Astronomer's advice, in spite of the maker's [Troughton's] advice…. I say that the drawbacks of using fixed microscopes are not at all less than those of a plumbline. Moreover, the major advantage of the circle is its inversion and this cannot be done in Troughton's design. Before a new Ramsden is born, much time has to pass and I certainly wouldn't change my Circle with any other by Troughton”), Piazzi to Delambre, Palermo, 15 November 1814, Paris Observatory Archives. In 1813 Pond had strongly criticized the efficiency of the Palermo Circle; see McConnell , op. cit. (ref. 8), 134.

On the restoration of the Palermo Circle, see Brenni P. Chinnici I. Serio G. Foderà , “The restoration of three large telescopes of the Palermo Astronomical Observatory”, Bulletin of the Scientific Instrument Society, lxxi (2001), 11–16, pp. 11–12.

See McConnell , op. cit. (ref. 8), 117.

See Wayman , op. cit. (ref. 22), 265–6.