There appears to be only the slightest evidence that Campano was acquainted with the work of Alfonso. His presentation of the subject, in all probability, was altogether independent of a knowledge of the Alfonsian tables. It is interesting to observe that in the day when astrology was in great favor in the universities of Europe, Campano continued to be interested in genuine astronomical science. Albertus Magnus, in his ‘Liber de coelo et mondo,’[90] devotes an entire chapter to a theoretical consideration of gravitation, asserting that the earth is spherical (Spherica sive orbicularis necessario), and proceeds to a demonstration of the theory, in which he practically follows the arguments of Aristotle, that every particle of the earth away from the center is continually in movement seeking that center, the result being the formation of a spherical body. He advances further, as argument in proof of a spherical earth, that the shadow it casts in an eclipse of the moon is circular. Sacrobosco (John of Holywood or Halifax) (fl. 1230),[91] who was active in the first half of the thirteenth century, much of the time as professor of mathematics in the University of Paris, prepared a work bearing the title, ‘Tractatus de sphaera,’ being in part a summary of the ‘Almagest’ of Ptolemy. In this work the theory of a spherical earth is supported in much the same manner as was done by Campano. The ‘Tractatus’ proved to be one of the most important quasi scientific geographical and astronomical textbooks of the later middle ages, being frequently copied, and frequently printed after the invention of that art.[92] Further reference might be made to a belief in a spherical earth, as held by Roger Bacon (1214-1294),[93] by Thomas Aquinas (1225-1274),[94] by Vincent of Beauvais (1190-1264),[95] by Dante (1265-1321),[96] and still others of the thirteenth, fourteenth, and fifteenth centuries. It should, however, be stated that nowhere in the works of these authors does there appear a reference to the construction of terrestrial globes, and only incidentally the implication that they knew of or approved the construction of celestial globes. The increasing interest in geography and in astronomy in the closing years of the middle ages led most naturally, in time, to much activity in globe construction, and to this fact attention is directed in the following chapter. NOTES