286 PHYSICAL SCIENCE IN THE MIDDLE AGES. 



or new generalizations. He undertakes only to give 

 what is virtually contained in his author ; to deve- 

 lope, but not to create. He is a cultivator of the 

 thoughts of others: his labour is not spent on a 

 field of his own; he ploughs but to enrich the 

 granary of another man. Thus he does not work 

 as a freeman, but as one in a servile condition ; 

 or rather, his is a menial, and not a productive 

 service : his office is to adorn the appearance of 

 his master, not to increase his wealth. 



Yet though the commentator's employment is 

 thus subordinate and dependent, he is easily led 

 to attribute to it the greatest importance and dig- 

 nity. To elucidate good books is, indeed, a useful 

 task ; and when those who undertake this work 

 execute it well, it would be most unreasonable to 

 find fault with them for not doing more. But the 

 critic, long and earnestly employed on one author, 

 may easily underrate the relative value of other 

 kinds of mental exertion. He may ascribe too 

 large dimensions to that which occupies the whole 

 of his own field of vision. Thus he may come to 

 consider such study as the highest aim, and best 

 evidence of human genius. To understand Aris- 

 totle, or Plato, may appear to him to comprise all 

 that is possible of profundity and acuteness. And 

 when he has travelled over a portion of their 

 domain, and satisfied himself that of this he too 

 is master, he may look with complacency at the 

 circuit he has made, and speak of it as a labour 



