Ismaël Bullialdus

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Ismaël Bullialdus

Ismaël Bullialdus (September 28, 1605 - November 25, 1694) was a French astronomer.

Bullialdus was born Ismaël Boulliau in Loudun, Vienne, France, the first surviving son to Calvinists Susanna Motet and Ismaël Boulliau, a notary by profession and amateur astronomer. At age 21 he converted to Catholicism, and by 26 was ordained as a priest. In 1632 he moved to Paris, where he worked as a librarian for the Bibliothèque du Roi with brothers Pierre and Jacques Dupuy, traveling widely within Italy, Holland and Germany to purchase books. In 1657 he became secretary to the French ambassador to Holland, then once again a librarian, and in 1666 moved to the Collège de Laon. During the final five years of his life, he returned to the priesthood at the Abbey St Victor in Paris, where he died.

Bullialdus was a friend of Pierre Gassendi, Christiaan Huygens, Marin Mersenne, and Blaise Pascal, and an active supporter of Galileo Galilei and Nicolaus Copernicus. It is for his astronomical and mathematical works that he is best known. Chief among them in his Astronomia philolaica, published 1645, in which he proposed that the force of gravity follows an inverse-square law:

As for the power by which the Sun seizes or holds the planets, and which, being corporeal, functions in the manner of hands, it is emitted in straight lines throughout the whole extent of the world, and like the species of the Sun, it turns with the body of the Sun; now, seeing that it is corporeal, it becomes weaker and attenuated at a greater distance or interval, and the ratio of its decrease in strength is the same as in the case of light, namely, the duplicate proportion, but inversely, of the distances that is, 1/d².

Isaac Newton later made this idea precise in his 1687 work, the Principia, which praised Bullialdus's work for its inverse square hypothesis and accurate tables.

Bullialdus was one of the earliest members of the Royal Society, London, having been elected on April 4, 1667, seven years after its founding. The Moon's Bullialdus crater is named in his honor.

[edit] Principal works

De natura lucis (1638)
Philolaus (1639)
Expositio rerum mathematicarum ad legendum Platonem utilium, translation of Theon of Smyrna (1644)
Astronomia philolaica (1645)
De lineis spiralibus (1657)
Opus novum ad arithmeticam infinitorum (1682)
Ad astronomos monita duo (1667)

[edit] Further reading

Nellen, H. J. M., Ismaël Boulliau (1605-1694), Astronome, Épistolier, Nouvelliste Et Intermédiaire Scientifique, Studies of the Pierre Bayle Institute Nijmegen (SIB), 24, APA-Holland University Press, 1994. ISBN 9030210346.