But there was another book that had more influence upon Columbus than all the others; and this was the “Imago Mundi” of Cardinal d’Ailly. It was a kind of encyclopædia of geographical knowledge, in which the author had endeavoured to bring together all the prevailing views in regard to the form of the earth. In the copy of this remarkable book, still preserved in the Columbian Library at Seville, there are still to be seen numerous marginal annotations by Columbus himself. These notes make us absolutely certain that the navigator studied very carefully and early became familiar with the beliefs of all the geographical writers of antiquity and of the Middle Ages. It is natural to ask the question why, if the earth was known to be spherical, and if the compass was already in existence, voyages of discovery were so long delayed? If one looks at the geographical works of the time, one sees everywhere taught the notion that the unknown regions were peopled with monsters ready to devour any who approached. One of the pictures in the Nuremberg Chronicle, for illustration, represents the Atlantic as filled with monsters so huge as to be able and ready to lift any ship easily upon its back and dash it to destruction. The Arabs believed and taught that in the torrid zone the moisture was so much sucked up by the heat of the sun that the residue was impervious to the passage of ships. Popular credulity everywhere seemed to gain the mastery over science. The early Anglo-Saxon scholars believed that the earth was a globe; but in spite of all their teaching, we find in an early Anglo-Saxon tract, intended to convey abstruse information in the form of a dialogue, the following question and answer:-- “_Question_: Tell me, my son, why the sun is so red in the evening? “_Answer_: Because it looketh down upon hell.” It must be conceded that this doctrine was sufficiently discouraging to western navigation.