Tracing Ramsden's ‘Plumbline Level’

See, for instance, Howse Derek , “The Greenwich list of observatories: A world list of astronomical observatories, instruments and clocks, 1670–1850”, Journal for the history of astronomy, xvii (1986), part 4.

See Bennett James A. , “The English quadrant in Europe: Instruments and the growth of consensus in practical astronomy”, Journal for the history of astronomy, xxiii (1992), 1–14.

On the degree of accuracy attained by the English makers in the eighteenth century, see Chapman Allan , “Accuracy of angular measuring instruments used in astronomy between 1500 and 1850”, Journal for the history of astronomy, xiv (1983), 133–7.

On the role played by these instruments in creating an astronomical community sharing a common scientific practice, see Bennett , op. cit. (ref. 2), 13.

In October 1783 a formal proposal for establishing a geodetic link between the Greenwich and Paris Observatories was sent to the English authorities; this important Anglo-French project was successfully operated in the years 1787–90. See, for example, Forbes Eric G. , “The geodetic link between the Greenwich and Paris Observatories in 1787”, Vistas in astronomy, xxviii (1985), 173–81; Martin Jean-Pierre McConnell Anita , “Joining the observatories of Paris and Greenwich”, Notes and records of the Royal Society, lxii (2008), 355–72.

Maskelyne Nevil , “Concerning the latitude and longitude of the Royal Observatory at Greenwich; with remarks on a memorial of the late M. Cassini de Thury”, Philosophical transactions of the Royal Society, lxxvii (1787), 151–87, p. 151.

On the reputation of the English makers in France, see Bennett , op. cit. (ref. 2), 5–11.

McConnell Anita , Jesse Ramsden (1735–1800): London's leading scientific instrument maker (London, 2007), 141–2. On the superiority of the Greenwich quadrant in respect to the Paris instruments, see the statements from the astronomers of that time, quoted in Bennett , op. cit. (ref. 2), 4.

Bennett , op. cit. (ref. 2), 10. It was only in autumn 1787 that an order was placed by Jean-Dominique Cassini (1748–1845), known as Cassini IV, the son of Cassini III and his successor as director of the Paris Observatory, during his visit to London for planning the cross-channel geodetic operations of the above mentioned triangulation (see ref. 5). On that occasion, Cassini IV commissioned from Ramsden a mural quadrant, an equatorial telescope and a transit circle: McConnell , op. cit. (ref. 8), 141–2.

Cassini III died on 4 September 1784 and the memoir was transmitted on 28 April 1785; see Maskelyne , op. cit. (ref. 6), 153.

Maskelyne , op. cit. (ref. 6). On the delay in replying to Cassini III's memoir, see Forbes's explanation: Forbes , op. cit. (ref. 5), 174.

Maskelyne , op. cit. (ref. 6), 157.

Ibid., 159.

Maskelyne proved that the latitude of Paris measured by the French astronomers, particularly by Nicholas Lacaille (1713–62), was too large: ibid., 170–80. On the longitude, he compares the observations of eclipses of Jupiter's satellites observed in Paris and at Greenwich and he considers the resulting differences of meridians “as being within a few seconds of the truth” (ibid., 186), thus confirming the correctness of the English measurements of the Greenwich longitude.

McConnell , op. cit. (ref. 8), 87.

Ibid., 91–2.

Ibid., 80.

Ibid., 95–6.

Piazzi Giuseppe , “Lettre sur les ouvrages de M. Ramsden, Londres, 1^er Sept. 1788”, Journal des sçavans pour l'année 1788, 744–52, p. 751.

Ibid., 751. The quadrant, ordered in 1786, was finished at the end of 1790 and installed at Brera Observatory in 1791: McConnell , op. cit. (ref. 8), 138–9.

See Chinnici Ileana Serio Giorgia Foderà Brenni Paolo , “The Ramsden's Circle at the Palermo Astronomical Observatory”, Bulletin of the Scientific Instrument Society, lxxi (2001), 2–10, p. 3. On the superiority of circular instruments, see also Chapman Allan , Dividing the circle (London, 1990), 108–22.

Maskelyne , op. cit. (ref. 6), 159.

[ Ramsden Jesse ], “A method of examining the total arc of a quadrant”, [1788], [1]. Archivio Storico INAF — Osservatorio Astronomico di Palermo, Fondo Piazzi, 74.14.

Ibid., [2]–[3].

Ibid., [3].

On Peter Layland and other Ramsden workmen, see McConnell , op. cit. (ref. 8), 64.

[Ramsden], op. cit. (ref. 23), [10].

Ibid., [11].

Piazzi , op. cit. (ref. 19), 751. Piazzi often visited Ramsden's workshop during his stay in London from autumn 1787 to summer 1789, in order to supervise the instruments being made for Palermo Observatory — A transit instrument and a famous 5-ft circular scales altazimuth; see Chinnici Foderà Brenni , op. cit. (ref. 21).

“C'est pour ce bel instrument que M. Ramsden a imaginé un moyen pour rectifier l'arc de quatre vingt-dix degrés sur lequel un habile Astronome avoit élevé quelques difficultés; mais avec un fil horizontal & un fil à plomb formant une espèce de croix qui ne touche point au quart de cercle, il lui montra qu'il n'y avoit pas une seule seconde d'erreur sur 90 degrés, & que la différence venoit d'un mural de Bird où l'arc de 90 degrés contient plusieurs secondes de trop, & qui n'avoit jamais été vérifié par une méthode aussi exacte que celle de M. Ramsden”, Piazzi , op. cit. (ref. 19), 751. English translation from McConnell, op. cit. (ref. 8), 89–90.

[Ramsden], op. cit. (ref. 23), [11]. In 1787 Hornsby realized that something was wrong in his quadrant; see Knox-Shaw Harold Jackson John Robinson William H. , The observations of the Reverend Thomas Hornsby at the Radcliffe Observatory (London, 1932), 80. It is possible that just the discrepancies with the observations at Blenheim led him to have suspicions about his instrument.

On the manuscript, see Chinnici Ileana Randazzo Donatella , “A manuscript by Ramsden in Palermo Observatory Library”, in preparation. Piazzi drafted a treatise on astronomical instruments during his visits at Ramsden's workshop, as stated in a letter to Del Ricco (see ref. 58).

Ramsden , op. cit. (ref. 23).

Since the figures referred to in the manuscript are missing, a tentative reconstruction of them, based on the text, was made in the 1990s by Giorgia Foderà at the University of Palermo. The reconstruction was made with the help of the technician Filippo Mirabello (University of Palermo). See Ileana Chinnici and Giorgia Foderà Serio , “A little known instrument by Jesse Ramsden” (poster), XVI Scientific Instrument Symposium, Prague, National Technical Museum, 22–25 September 1995.

The method of observing the intersection of plumbline and wires with the dots by means of lenses was initially used for checking the transit instruments. It is described by Piazzi: “… dans la méthode de M. Ramsden … le fil à plomb ne passe quelquefois que par les images des pojnts, qui sont formées au foyer d'une lentille … l'exactitude n'est pas diminuée & il n'y a aucune parallaxe; ce n'est pas le point qui me servira, disoit-il une foi en plaisantant, c'est seulement le ghost (comme on dit les esprits ou le revenants).” Piazzi , op. cit. (ref. 19), 750.

Vince Samuel , A treatise on practical astronomy (Cambridge, 1790), 119–21. It is possible that the manuscript was originally intended for Vince's treatise; see Chinnici Randazzo , op. cit. (ref. 32).

The letter was acquired by the Brera Observatory from an auction house in 2006. About its acquisition, see http://www.brera.inaf.it/docM/OAB/eventi/biblioteca/letteraBarnaba.html; for its full transcription, see: http://www.brera.inaf.it/docM/OAB/eventi/biblioteca/trascrizione.html.

Oriani himself had gone to London to negotiate the commission in 1786; he had visited Ramsden's workshop several times, finally ordering a quadrant matching that of the Duke of Marlborough, except that it did not turn on its supporting axis, but was to be fixed. McConnell , op. cit. (ref. 8), 138.

See the sketch (Figure 4(b)).

The Austrian consul who acted as negotiator.

“Tout ce qui regarde immédiatement le grand Quart de Cercle de Ramsden, est déjà arrangé car je connaissais d'avance presque toutes les pièces. Mais j'ignore encore l'usage des pièces en bois de cette figure [Figure 4(b)] qui ont rapport peut-être à la vérification de l'instrument, j'ose donc prier Votre Excellence de demander à Ramsden un petit mot là-dessus. Il a été impossible jusqu'à cette heure d'en obtenir le moindre éclaircissement par l'entremise de M. Songa, et par conséquent elles restent ici sans utilité.” Oriani to von Brühl, Milan, 23 April 1791 (Archivio Storico INAF — Osservatorio Astronomico di Brera, Corrispondenza Scientifica).

McConnell , op. cit. (ref. 8), 139–40.

De Cesaris Angelo , “De quadrante murali quem Speculae Mediolanensi construxit Iesse Ramsden Londini”, Ephemerides astronomicae anni 1792 (Milan, 1791), 73–104.

Ibid., 100–4.

“Non dissimili artificio radius nonagesimi gradus potest in sua sede explorari, simulque utilissime inquiri utrum primus & extremus radius complectantur quadrantem geometrice absolutum. Hanc investigationem nova prorsus & elegante ratione sic Ramsden est persecutus. Tubo telescopii apposuit duo puncta, insculpta ut supra, suis item ut supra perspicienda microscopiis, alterum in regione centri, alterum imminens laminae Nonnii: Curavit autem potissimum, ut eorundem punctorum directio parallela foret lineae actae per centrum quadrantis, perque zero Nonnii. Tubum ad positionem verticis deduxit, convenientibus in zero lineolis Nonni & arcus. Tum ex seiuncto apparatu perpendiculum demisit, eiusque filum deduxit ad punctum in superioribus tubi locatum. Cum res ita se habent, quemadmodum se habere debent, idem filum congruit etiam puncto inferius sito. Sin aliter, quadrans manubrio urgetur, dum hoc etiam punctum apte obveniat filo. Tunc, quantumvis deturbato quadrante, indicium fiet certissimum, ea duo puncta, in ea tubi positione, prorsus constitui in ipsa verticis directione, quam demonstrat lex naturae & perpendicoli. Tubus iam convertatur ad gradum usque nonagesimum, Nonniusque ibi conveniat: Ea ipsa puncta, quippe tubo haerentia, aequalem conversionem confecisse debent, & si quadrans absolute perfectus fuerit, eadem dirigentur in linea horizontis.

“Hanc lineam periclitatus est auctor inversione ingentis normae: Qua quidem ratione inversionis nihil est opportunius ad explorandas astronomicas machinas. Duplam igitur normam ligneam, ad extrema tubi pertingentem, instruxit hinc & hinc metallicis laminis cum tenuium filorum segmentis positis in directione horizontis: Quae fila suo cochlearum artificio admovit ad bina ea puncta tubi. Interim perpendiculum ab alto normae descendens ad pedes amplius octo, explorari conferrique debuit cum decussato reticulo, quod haerens lateri normae, suo item ingenio, adduci poterat ad filum huius perpendicoli. En igitur in filo perpendiculi certissima linea verticis; & siquidem norma geometrice accurata habeatur, linea aeque certissima horizontis in segmentis filorum hinc & hinc haerentibus eidem normae. At quae accuratio geometrica in eiusmodi rerum natura frustra praesumitur; eadem artificio inversionis felicissime obtinetur. Norma igitur invertitur: Idem filum perpendiculi ad idem reticulum, providentissime transpiciendum, constanter servatur: Eadem puncta tubi ad fila normae, mutatis vicibus, referuntur & explorantur: Quo facto aut nullus error quadrantis, aut duplus se prodere debet.

“Haec fere summa Ramsdeniani apparatus, quo quidem nihil accuratius excogitari posse videtur. Eundem, silentio praeteritis subsidiariis partibus ad appendendam, admovendamque normam, strictim hic exposui, cum propositum habeam conferre in iustum commentarium ea, quae pertinent ad comprobandam machinam, si per otium licebit.” De Cesaris , op. cit. (ref. 43), 102–4.

“Non è da ommettere che il Ramsden, il quale conosceva tanto bene le parti più delicate ed essenziali degli stromenti, sentì le conseguenze della mancanza d'inversione ne' Murali appoggiati a pilastro immobile, e vi supplì coll'ingegnoso suo livello a filapiombo, che non conosciuto in addietro, applicò per la prima volta, come io credo, al nostro Murale. Con tale livello si determina la precisa misura dell'arco totale di novanta gradi, e la posizione delle linee orizzontale e verticale.” De Cesaris Angelo , “Osservazioni del Sole al quadrante murale dall'anno 1791 all'anno 1802”, Appendice alle effemeridi dell'anno 1804 (Milan, 1803), 46–72, p. 49.

In Vince's description, it is simply designated as “apparatus” or “instrument”, without any specific name (see ref. 36).

De Cesaris Angelo , “Di una nuova specie di livello a filapiombo per la verificazione de' quadranti astronomici”, Appendice alle effemeridi astronomiche di Milano per l'anno 1806 (Milan, 1805), 49–56.

“Lo stromento fu detto da lui [Ramsden] livello a filapiombo, perché diretto primariamente a conoscere per mezzo del filapiombo la posizione di una data linea, rispetto al livello orizzontale.” De Cesaris, op. cit. (ref. 48), 49.

“… a soddisfare alle dimande, che mi sono venute sul proposito, ed a secondare similmente certa lusinga di essere utile facendo conoscere più compitamente questa macchina, di cui il solo Vince fa parola, ne do una spiegazione alquanto più estesa.” De Cesaris , op. cit. (ref. 48), 49–50.

De Cesaris does not mention Ramsden's test at Blenheim, probably to avoid contradicting himself since, a few years before, he supposed that the plumbline level had been applied by Ramsden for the first time to the quadrant in Brera (see ref. 46).

See Battioni Gianluca Locatelli Paola , 1800–1809 Catalogo della corrispondenza degli Astronomi di Brera (Milan, 1991), ii, 520–2.

See Ibid., 523.

See Barsanti Danilo Rombai Leonardo , Leonardo Ximenes, uno scienziato nella Toscana lorenese del Settecento (Florence, 1987), 228.

See Borchi Emilio MacIi Renzo , Osservatori astronomici nell'età di Leonardo Ximenes (Florence, 2008), 95–6.

See Ibid., 89–94.

See Barsanti Danilo , Stanislao Canovai e Gaetano Del Ricco: Il sodalizio umano e scientifico di due scolopi fiorentini fra XVIII e XIX secolo (Florence, 1988), 44. Del Ricco, together with Stanislao Canovai, was very active as a translator of scientific books into Italian; the Leçons élémentaires de mathématiques (1770) by Joseph-François Marie, one of the most successful treatises of mathematics of that time, was translated and published by Canovai and Del Ricco in 1781 and in 1793.

Piazzi to Del Ricco, Palermo, 12 July 1804 (Archivio Osservatorio Ximeniano 98, 16). This interesting letter is accompanied by a sketch of the various pieces to be used for adjusting the quadrant. It is also worth mentioning that, in this letter, Piazzi describes as “obscure” the description of the apparatus given by De Cesaris in 1803, thus reinforcing the need for a more detailed commentary.

Del Ricco certainly had commissioned an altazimuth from Ramsden in 1797 (see Ramsden to Del Ricco, London, 19 September 1797; Archivio Osservatorio Ximeniano 98, 8) but the instrument was never delivered (see Lockie to Del Ricco, London, 15 April 1800, Archivio Osservatorio Ximeniano, 98, 10).

Chinnici Foderà Brenni , op. cit. (ref. 21), 3. See also McConnell, op. cit. (ref. 8), 113.

McConnell , op. cit. (ref. 8), 144–6.