QUIZ – Solution
It is the magnetic clock

A Timeline

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This timeline traces the origins of Athanasius Kircher's magnetic clock from theoretical and practical studies of magnetism in the early

seventeenth century.

View an interactive map of the transmission of information about the magnetic clock








1600 William Gilbert publishes De Magnete (On the Magnet), in which he puts forward the hypothesis that the Earth is a great magnet. Experiments carried out with a "terrella", or small spherical magnet, convince him that the earth rotates around its poles because of terrestrial magnetism. 

1609 Johannes Kepler publishes his Astronomia Nova (New Astronomy), in which he puts forward the hypothesis that the planets were moved by a magnetic force. 

1618-21 Kepler publishes his Epitome astronomiae Copernicanae (Epitome of Copernican Astronomy), which further develops his hypothesis that the planets are carried around the sun by a magnetic force emanating from a rotating sun. 

1632 Galileo publishes his Dialogo sopra i due Massimi Sistemi del Mondo (Dialogue on the Two Chief World Systems). He includes an argument against Gilbert's assertion that a spherical magnet will rotate every twenty four hours. 

1633, 15 June: Godefrid Wendelin writes a letter from Brussels to the Minim scholar Marin Mersenne in Paris to inform him of a magnetic clock invented by a Jesuit professor in Liège, Fr. Francis Line. The clock contains a wax globe that appears to rotate in imitation of the sun's motion.

1633 22 June. Galileo is sentenced by the Inquisition of being "vehemently suspected of heresy" for teaching the Copernican doctrine in his Dialogo and is forced to make a public abjuration in the Dominican Church of Santa Maria sopra Minerva in Rome. 

1633-4 Line's magnetic clock comes to the attention of the Papal Nuncio of Cologne, Monsignor Pierluigi Caraffa. Caraffa has the clock brought to his home, where he observes it for several days and finds it to keep good time. His Jesuit confessor, Father Sylvester Pietrasancta, publishes a  description and illustration of Line's clock in a book of emblems published in Antwerp, Silvestro Pietrasancta's De Symbolis Heroicis

1634 December: Monsignor Caraffa and his confessor travel to Aix-en-Provence, where they visit Nicholas Claude Fabri de Peiresc at his home, the Château de Beaugencier. Peiresc is shown the description of Line's magnetic clock given in Pietrasancta's work. 

1634, December 18: Peter Paul Rubens, responsible for designing the frontispiece to Pietrasancta's book, writes to Peiresc to say that he has "talked with men of ingenuity who have seen and operated it with ease, and have the greatest admiration for it". Rubens even offers to ride from his home in Antwerp to Liege to visit Line and obtain more details of the clock. 

1635, 1 April: Peiresc writes from Aix to Galileo (under house-arrest in Arcetri, near Florence), describing the "hydraulic clock" in enthusiastic terms. He believes that the instrument could provide a demonstration of the Copernican theory, writing that "it seems to be a proof and testimony that has fallen from heaven into the hands of a Jesuit father, rather than those of somebody of another calling, to leave no room for suspicion against the testimony of the Father who invented it or the other who published it, to demonstrate the error of those who find such repugnance in the Copernican doctrine and in that which Your Lordship proposed about it as a problematic joke (i.e. Galileo's Dialogo)". According to Peiresc, Caraffa had examined the clock in his own home for several days and found it to be very accurate. 

1635, 17 April: Peiresc writes again to Galileo informing him that he is attempting to use the magnetic clock in his efforts to convince Cardinal Francesco Barberini, the papal nephew, to have the charges against Galileo reduced, and to free him from imprisonment. 

1635, 12 May: Galileo writes a letter to Peiresc, explaining that he had made a similar invention many years before, and suggesting that the base of Linus's device contained a hidden magnetic clock, whichthat moved another magnet hidden in the hollow copper sphere. The sphere, in Galileo's version, was suspended at the boundary between salt water and fresh water due to its intermediate specific gravity. 

1635, 18 June: Peiresc writes to Gassendi to say that he has heard more information about the machine from an eyewitness, Dormalius, who claims that the inner sphere was originally made of wax, but that Linus then chose a hollow copper globe. The fact that the globe moved back to its position when displaced horizontally led Peiresc to be very suspicious that a hidden mechanism, like that described by Galileo, was responsible for the rotation of the globe. 

1640: 8 March: Responding to hisKircher's request for magnetic observations, the Jesuit Lorenz Mattenkloth writes to Athanasius Kircher from Münster to ask him if he has heard about Line's magnetic clock, and if he has an explanation for its mechanism. On the same day Grégoire de Saint-Vincent also writes to Kircher telling him about the invention of the machine by "some English Father" 

1641: Athanasius Kircher publishes his Magnes, sive de arte magnetica in Rome. The work includes the first published description and illustration of the secret mechanism of the magnetic clock, and a lengthy attack on the magnetic arguments in favour of Copernicanism put forward by Gilbert and Kepler. 

Website created by Michael John Gorman, April 2001.

Comments, questions or suggestions to mgorman@stanford.edu