PKEFACE 



COGITATIONES DE NATURA RERUM. 



THIS piece was printed by Gruter among the Impe 

 tus Philosophici ; from which we may probably con 

 clude that it had not been transcribed into the volume 

 of Scripta in Naturali et Universali Philosophid : l but 

 that is all. There is nothing to determine the date of 

 composition, unless it be the absence of any allusion to 

 the new star in Ophiuchus in the place where the new 

 star in Cassiopeia is mentioned. See note, x. The 

 value of the argument will be more easily understood 

 by comparing the passage in question with a passage 

 of the same import in a work, obviously later, where 

 both these stars are mentioned together. In both cases 

 the question under discussion is the immutability of the 

 heavens. In the Cogitationes de Natard Rerum, of 

 which the date is unknown, we find, &quot;... mutationes 

 in regionibus coelestibus fieri, ex cometis quibusdam 

 satis liquet ; iis dico qui certam et constantem config- 

 urationem cum stellis fixis servarunt ; qualis fuit ille 

 qui in Cassiopea nostra astate apparuit.&quot; This star 

 in Cassiopeia appeared in 1572. But another of the 

 same kind, and no less remarkable, appeared in Sep- 

 1 See above, p. 194. 



