Nicolas Fatio de Duillier

1664 (Basel) – 1753 (Madresfield, England)

The astronomer-mathematician Fatio, originator of a mechanistic theory of gravity, is now known primarily as an associate of others. At 18 he introduced himself to Cassini with an account of Saturn’s rings, subsequently studying under him in Paris. Going to the Netherlands to warn William of Orange of a plot against him, he worked with Huygens, then settling in London became Newton’s very close friend (exciting some latter-day speculation as to its nature, Newton seemingly suffering a breakdown when the relationship ended). He was friendly with Locke and corresponded widely, including with Leibniz, whom he charged with ‘stealing’ Newton’s invention of calculus.

Nicolas Fatio de Duillier knew…

John Flamsteed

1646 (Denby, England) – 1719 (Burstow)

One of the founders of modern astronomy, Flamsteed’s observations led to the most complete and detailed star catalogue to date. His trustful friendship with Newton became acrimonious when Flamsteed objected to the unauthorised publication and amendment of his data by Halley (whom he had always detested); Arbuthnot met Flamsteed in a coffee shop to placate him, but passed on a lie. He corresponded with both Cassinis (describing Jean-Dominique as a most valued friend), with Hevelius, Rømer, Kirch and Boulliau. He never got on with Hooke, described Sloane as a bulky gentleman, and eventually succeeded in burning three quarters of Halley’s edition.

John Flamsteed knew…

Johann Gottfried Galle

1812 (Pabsthaus, Germany) – 1910 (Potsdam)

Le Verrier wrote praising the rigour and lucidity of Galle’s astronomical work, and proposing from his own calculations that a new planet might be found in a specific direction. Encke had previously failed to publish his assistant Galle’s work on Saturn’s rings, and only grudgingly allowed him to use the observatory on the night that he quickly confirmed Neptune’s existence where Le Verrier had suggested. Galle knew Bessel, corresponded with Airy, and helped Humboldt with many calculations needed for his magnum opus, ‘Kosmos.’

Edmond Halley

Edmund Halley

1656 (Haggerston, England) – 1742 (Greenwich)

Notable for much more than his comet, the prodigy Halley started observing with Flamsteed even before the Royal Observatory was built. His catalogue of Southern stars made his name aged 22, though Flamsteed – never hurried, and later his professional enemy – criticised his hasty methods. Cassini, met in Paris, advised him on observing the transit of Mercury. Halley discussed the shape of an orbit with Wren and Hooke, but beaten by the maths, asked Newton for the answer. He knew Pepys and Arbuthnot well, met Leibniz en route to Vienna, and travelled to Danzig to resolve Hevelius and Hooke’s acrimonious dispute.

Edmond Halley knew…

Anders Celsius

1701 (Uppsala, Sweden) – 1744 (Uppsala)

Although Celsius is best known for the temperature scale bearing his name, he was primarily an astronomer. Having visited the main centres of astronomy in Europe, meeting Cassini among others, he was instrumental in the expedition led by Maupertuis going to Swedish (now Finnish) Lapland rather than to Norway; Clairaut was a companion on this difficult journey to establish the Earth’s true shape, which led to Cassini’s obstinate defiance of their findings. Celsius gave short shrift to Swedenborg’s ideas about magnetic declination. Linnaeus, a correspondent, recommended the flipping of the temperature scale shortly after Celsius’ death.

Anders Celsius knew…

Roger Joseph Boscovich

Ruggero Giuseppe Boscovich;Ruđer Josip Bošković

1711 (Ragusa, now Dubrovnik, Croatia) – 1787 (Milan)

Boscovich, not as well known as he might be, held strikingly advanced ideas about space/time relativity and the nature of atoms, among much else. His wide-ranging correspondents included Euler, Jacobi, Bernoulli, Lagrange, Priestley, Spallanzani, Méchain, Metastasio and Voltaire. Old friends in France included Nollet, Lacaille, Lalande (struck by his extreme spirituality and profundity) and especially Clairaut, who admired his vast culture and personal dynamism. He met Buffon and Franklin, impressed Burney, discussed Newton with Johnson (in French and Latin), was initiated into the mysteries of Guy Fawkes’ Night by Maskelyne, and was resented by d’Alembert.

Tobias Mayer

1723 (Marbach, Germany) – 1762 (Göttingen)

Mayer is known for lunar observation, particularly in relation to navigation; he also drew superb lunar maps. Mayer wrote to Euler (who had already heard of the young man) about astronomical refraction and lunar theory; they corresponded for four years, and Euler helped him to a professorship. Lacaille and Mayer wrote to each other particularly about the 1761 Passage of Venus, each arguing that the other’s instrument was less accurate than his own (Mayer was right, though Lacaille wasn’t to know it). Lambert, interested like Mayer in colour perception, visited him in Göttingen, and extended his work.

Jérôme Lalande

Joseph-Jérôme Lefrançais de Lalande

1732 (Bourg-en-Bresse, France) – 1807 (Paris)

Lalande produced the best planetary tables of his time, tried to get Galileo’s and Copernicus’s works unbanned, promoted the work of female astronomers, and once ate spiders to demonstrate their harmlessness. He met Maupertuis, Euler, Voltaire and La Mettrie in Berlin aged 19, taking lunar sightings to triangulate with his colleague Lacaille’s from Capetown. He met Maskelyne in London, Boscovich in Rome, and got migraines from doing calculations to help Clairaut. Piazzi, Delambre and Méchain were his students, Messier and Herschel friends, von Zach a correspondent, and Helvétius, Franklin, and Lacépède masonic colleagues. Voltaire disparaged him; d’Alembert compared him to vermin.

Jérôme Lalande knew…

Anders Johan Lexell

Andrei Ivanovich Leksel;Anders Johan Leksel

1740 (Åbo, Sweden, now Turku, Finland) – 1784 (St Petersburg)

Lexell, who spent most of his career in Russia, is known for his work on cometary orbits and on spherical geometry. He arrived in St Petersburg when its eminence grise, Euler, was over 60 and practically blind. He helped Euler in his work as one of his disciples, became his friend and chosen successor, and was present when he died (Lexell himself however dying young, barely a year later). Linnaeus was one of his correspondents. Although Lexell wrote at least once to William Herschel, the discoverer of Uranus, confirming its status as a planet and calculating its orbit, the extent of any further contact is not clear.

Anders Johan Lexell knew…

Charles Piazzi Smyth

1819 (Naples, Italy) – 1900 (Ripon, England)

Smyth’s reputation as an innovative astronomer and meteorologist has tended to be obscured by his eccentric obsession with the Pyramids and with the British as the lost tribe of Israel. Piazzi (whose name he took) was his godfather and a significant early influence. As a young man he worked alongside Herschel in South Africa; Herschel’s opposition to metric measurement contributed to Smyth’s farfetched belief in the inch’s Egyptian ancestry. The famous engineer Stephenson lent him his yacht, accompanying him on an important trip to Tenerife. Draper and Abbe were both correspondents.

Charles Piazzi Smyth knew…