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338 nearly everywhere enriched by original observations. In his treatise De Animalibus (Vol. VI. of his works) he begins by a study of the spinal column, calls the sponges the lowest forms of animal life, improves on the zoological classification of his forerunners, and includes good descriptions of the fauna of the Arctic, and at the same time admits the legendary monsters of the Bestiaires of the tenth century, the barnacle-goose, anser arboreus, for example.

His botany is said to be full of errors. He quotes Pliny's facts relating to the fecundation of the date-palm, and correctly explains them, it is believed for the first time. The term affinity is first used in his chemical writings. There was no branch of knowledge that he did not treat, from mineralogy to magnetism, and it is noteworthy that he describes the magnet as in use by navigators in his time.

It is not necesarynecessary [sic] in this place to speak of the achievement of St. Thomas Aquinas, the pupil of Albertus. His work does not lie in the field of physics, but in the universe of man. His Summa treats more than five hundred questions, but only one section refers to the phenomena of the material world. One remark may be made on the activity of the thirteenth century. Every one of the distinctly 'modern' problems was propounded in that age. Few were solved; but substantially all of them were stated. When a problem is clearly stated it is at least half solved.

The most noted figure in the generation preceding Copernicus was Regiomontanus, who is always thought of in company with his colleagues Purbach and Walther. They formed part of a group of German and Italian astronomers, calculators and teachers, no one of whom made any signal advance, but all of whom were well instructed in the fashion of the time. There are many names of men forgotten to-day among this group; but, on the other hand, the faint beginnings of a critical spirit are here and there to be noted. The Almagest was not always taken as infallible; observation began to be accepted as a test of theory. Dominicus of Bologna, the teacher of Copernicus, is a marked example of the new spirit.

George Purbach (or Beurbach, from his native village), professor of astronomy in the University of Vienna, was born in 1433 (died 1461), and studied at Vienna and in Italy. He was a votary of the old astronomy, and his chief work, Theoricæ Novæ Planetarum (1460), is a development of the doctrine of crystalline spheres. At the same time he was an ardent student of Ptolemy. The epicycles of Ptolemy were a geometrical conception; the crystalline spheres of Eudoxus and Purbach a crude cosmological idea; they could not be reconciled with nature. In so far Purbach was on the wrong road. He saw, however, the necessity for further observations of the planets and for