246 cosmos. 



the Almagest. As he, like the Arabs, always calls Hippar- 

 chus Abraxis, we may conclude that he also made use of only 

 a Latin translation from the Arabic. Next to Bacon's chem- 

 ical experiments on combustible explosive mixtures, his theo- 

 retical optical works on perspective, and the position of the 

 focus in concave mirrors, are the most important. His pro- 

 found Opus Majus contains proposals and schemes of practi- 

 cable execution, but no clear traces of successful optical discov- 

 eries. Profoundness of mathematical knowledge can not be 

 ascribed to him. That which characterizes him is rather a 

 certain liveliness of fancy, which, owing to the impression ex- 

 cited by so many unexplained great natural phenomena, and 

 the long and anxious search for the solution of mysterious 

 problems, was often excited to a degree of morbid excess in 

 those monks of the Middle Ages who devoted themselves to 

 the study of natural philosophy. 



Before the invention of printing, the expense of copyists 

 rendered it difficult, in the Middle Ages, to collect any large 

 number of separate manuscripts, and thus tended to produce 

 a great predilection for encyclopedic works after the exten- 

 sion of ideas in the thirteenth century. These merit special 

 consideration, because they led to a generalization of ideas. 

 There appeared the twenty books DeJRerum Natura of Thom- 

 as Cantipratensis, Professor at Louvain (1230) ; The Mir- 

 ror of Nature {Speculum, Naturale), written by Vincenzius of 

 Beauvais (Bellovacensis) for St. Louis and his consort Mar- 

 garet of Provence (1250) ; The Book of Nature, by Conrad 

 von Meygenberg, a priest at Ratisbon (1349) ; and the Pic- 

 ture of the World (Imago Mundi) of Cardinal Petrus de Al- 

 liaco, bishop of Cambray (1410), each work being in a great 

 measure based upon the preceding ones. These encyclopedic 

 compilations were the forerunners of the great work of Father 

 Reisch, the Margarita Philosophica, the first edition of which 

 appeared in 1486, and which for half a century operated in a 

 remarkable manner on the diffusion of knowledge. I must 

 here pause for a moment to consider the " Picture of the 

 World" of Cardinal Alliacus (Pierre d'Ailly). I have else- 

 where shown that the work entitled " Imago Mundi" exer- 

 cised a greater influence on the discovery of America than 

 did the correspondence with the learned Florentine Toscanel- 

 li.* All that Columbus knew of Greek and Roman writers, 



* See my Examen Crit., t. i., p. 61, 64-70, 96-108; t. ii., p. 349. 

 " There are five memoirs De Concordantia Astronomia cum Theologia, 

 by Pierre d'Ailly, whom Don Fernando Colon always calls Pedro de 



