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ICERON (JOHN FRANCIS,) in biography, a French monk and ingenious mathematician in the seventeenth century, was born at Paris, in the year 1613. He early displayed a love of learning, and by the progress which he made in his elementary studies, afforded fair promise of future excellence. At the age of nineteen he entered into the order of Minims, and before he had gone through his course of philosophy, discovered that his predominant inclination was to the study of mathematical sciences, to which, after he had completed his theological course, he devoted all the time that was not necessarily occupied by the duties of his profession. The science of optics was what principally engaged his attention; and he left behind him, in different houses belonging to his order, particularly that at Paris, some excellent performances, which afforded satisfactory evidence of his profound skill in this branch of the mathematics. He was twice sent on business to Rome, and was appointed regent of the philosophical classes. Afterwards he was nominated to accompany father Francis de la Noue, vicar-general of the order, in his visitation of all the convents of Minims in France. The similarity of their taste proved the means of introducing him to the acquaintance of Des Cartes, who entertained a great regard for him, and made him a present of his "Principles of Philosophy." Their intimacy, however, which commenced in 1644, proved but of short duration, since our

young monk fell sick at Aix, in Provence, and died there in the autumn of 1646, when he was only thirty-three years of age. This event was lamented as a considerable loss to the republic of letters. He was the author of the following works, which are held in high estimation. "The Interpretation of Cyphers, or, a Rule for the perfect Understanding and certain explanation of all Kinds of simple Cyphers, taken from the Italian of the Sieur Anthony Maria Cospi, secretary to the Grand Duke of Tuscany; enlarged, and particularly accommodated to the French and Spanish Languages," 1641, octavo; "Curious Perspective, or artificial Magic, produced by the wonderful Effects of Optics, Catoptrics, and Dioptrics," &c. 1638, folio; which was only introductory to his "Thaumaturgus Opticus, sive, admirandæ Optices, Catoptrices, et Dioptrices, Pars prima, de iis quæ spectant ad visionem directam," 1646, folio. On this work he was employed six years, and was prevented by his death from proceeding to the completion of the intended second and third parts, relating to the effects of reflection from plane, cylindrical, and conical mirrors, and the refraction of crystals. This task his friend father Mersenne undertook, not only by correcting what Niceron's papers in Latin and French would furnish towards it, but by supplying what might be necessary to perfect it. But the other occupations of this learned mathematician, during the two remaining years of his own life, prevented him from