[473] Ars nova et magna gravitatis et levitatis; sive dialogorum philosophicorum libri sex de aeris vera ac reali gravitate, Rotterdam, 1669, 4to.
[474] Volume I, Nos. 1 and 2, appeared in 1803.
[475] His daughter, Mrs. De Morgan, says in her Memoir of her husband: "My father had been second wrangler in a year in which the two highest were close together, and was, as his son-in-law afterwards described him, an exceedingly clear thinker. It is possible, as Mr. De Morgan said, that this mental clearness and directness may have caused his mathematical heresy, the rejection of the use of negative quantities in algebraical operations; and it is probable that he thus deprived himself of an instrument of work, the use of which might have led him to greater eminence in the higher branches." Memoir of Augustus De Morgan, London, 1882, p. 19.
[476] "If it is not true it is a good invention." A well-known Italian proverb.
[477] See page [86], note [132].
[478] He was born at Paris in 1713, and died there in 1765.
[479] Recherches sur les courbes à double courbure, Paris, 1731. Clairaut was then only eighteen, and was in the same year made a member of the Académie des sciences. His Elémens de géométrie appeared in 1741. Meantime he had taken part in the measurement of a degree in Lapland (1736-1737). His Traité de la figure de la terre was published in 1741. The Academy of St. Petersburg awarded him a prize for his Théorie de la lune (1750). His various works on comets are well known, particularly his Théorie du mouvement des comètes (1760) in which he applied the "problem of three bodies" to Halley's comet as retarded by Jupiter and Saturn.
[480] Joseph Privat, Abbé de Molières (1677-1742), was a priest of the Congregation of the Oratorium. In 1723 he became a professor in the Collège de France. He was well known as an astronomer and a mathematician, and wrote in defense of Descartes's theory of vortices (1728, 1729). He also contributed to the methods of finding prime numbers (1705).
[481] "Deserves not only to be printed, but to be admired as a marvel of imagination, of understanding, and of ability."
[482] Blaise Pascal (1623-1662), the well-known French philosopher and mathematician. He lived for some time with the Port Royalists, and defended them against the Jesuits in his Provincial Letters. Among his works are the following: Essai pour les coniques (1640); Recit de la grande expérience de l'équilibre des liqueurs (1648), describing his experiment in finding altitudes by barometric readings; Histoire de la roulette (1658); Traité du triangle arithmétique (1665); Aleae geometria (1654).