512 ADDITIONS. 



I have, in the part of the Philosophy referred to, discussed the 

 merits and defects of Francis Bacon's Method, and I shall have occa- 

 sion, in the next Book, to speak of his mode of dealing with the posi- 

 tive science of his time. There is room for much more reflection on 

 these subjects, but the references now made may suffice at present. 



CHAPTER V. 



Progress in the Middle Ages. 



Thomas Aquinas. 



AQUINAS wrote (besides the Summa mentioned in the text) a Com- 

 mentary on the Physics of Aristotle : Commentaria in Aristotelis 

 Libros Physicorum, Venice, 1492. This work is of course of no scien- 

 tific value ; and the commentary consists of empty permutations of ab- 

 stract terms, similar to those which constitute the main substance of 

 the text in Aristotle's physical speculations. There is, however, an at- 

 tempt to give a more technical form to the propositions and their 

 demonstrations. As specimens of these, I may mention that in Book 

 vi. c. 2, we have a demonstration that when bodies move, the time and 

 the magnitude (that is, the space described), are divided similarly ; 

 with many like propositions. And in Book viii. we have such propo- 

 sitions as this (c. 10) : " Demonstration that a finite mover (movens) 

 cannot move any thing in an infinite time." This is illustrated by a 

 diagram in which two hands are represented as engaged in moving a 

 whole sphere, and one hand in moving a hemisphere. 



This mode of representing force, in diagrams illustrative of mechan- 

 ical reasonings, by human hands pushing, pulling, and the like, is still 

 employed in elementary books. Probably this is the first example of 

 such a mode of representation. 



Roger Bacon. 



This writer, a contemporary of Thomas Aquinas, exhibits to us a 

 kind of knowledge, speculation, and opinion, so different from that of 

 any known person near his time, that he deserves especial notice here ; 



