OF NATURAL PHILOSOPHY. 19 



in which consists the logic of the schools ; secondly, 

 notation, which, applied to number, is arithmetic, 

 and, to the more general relations of abstract quan- 

 tity or order, is algebra; and, thirdly, that higher 

 kind of logic, which teaches us to use our reason in 

 the most advantageous manner for the discovery of 

 truth ; which points out the criterions by which we 

 may be sure we have attained it; and which, by 

 detecting the sources of error, and exposing the 

 haunts where fallacies are apt to lurk, at once warns 

 us of their danger, and shows us how to avoid them. 

 This greater logic may be termed rational* ; while, 

 to that inferior department which is conversant with 

 words alone, the epithet verbal f may, for distinc- 

 tion, be applied. 



(15.) A certain moderate degree of acquaintance 

 with abstract science is highly desirable to every 

 one who would make any considerable progress in 

 physics. As the universe exists in time and place ; 

 and as motion, velocity, quantity, number, and 

 order, are main elements of our knowledge of ex- 

 ternal things and their changes, an acquaintance 

 with these, abstractedly considered, (that is to say, 

 independent of any consideration of the particular 

 things moved, measured, counted, or arranged,) 

 must evidently be a useful preparation for the more 

 complex study of nature. But there is yet another 

 recommendation of such sciences as a preparation 

 for the study of natural philosophy. Their objects 

 are so definite, and our notions of them so distinct, 

 that we can reason about them with an assurance, 



* Ao7os, ratio, reason. t Aojos, verbum, a word. 



c 2 



