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156 away with time." One of his pupils was Gregory of Saint-Vincent († 1667), whom Leibnitz places on an equality with Descartes as a geometrician. "Although a circle-squarer, he is worthy of mention for the numerous theorems of interest which he discovered in his search after the impossible, and Montucla ingeniously remarks that no one ever squared the circle with so much ability, or (except for his principal object) with so much success."

Another disciple of Clavius was Matthew Ricci († 1610), the illustrious mathematician and apostle of China, who published also a vast number of valuable observations on the geography and history of China. Father Schall of Cologne († 1669), a prominent mathematician and astronomer, was appointed director of the "Mathematical Tribunal" in Pekin, and revised the Chinese calendar.

Within the last few years the attention of mathematicians has been drawn to the Jesuit Father Saccheri, Professor of mathematics at Pavia. Non-Euclidean mathematics is now recognized as an important branch of mathematics. The beginnings of this system have sometimes been ascribed to Gauss, the "Nestor of German mathematicians". But recent research has proved that as early as 1733 Father Saccheri had published a book which gives a complete system of Non-Euclidean geometry. Beltrami, in 1889, and Staeckel and Engel in 1895, pointed out the great importance of the work of Saccheri.