A Librarian's Work. 345 



treatises should be classed under the rubric of 

 Philosophy, another under Natural Religion, and 

 a third under Dogmatic Theology. 1 But while it 

 would thus be impracticable to place our final re- 

 liance on any other arrangement than an alpha- 

 betical one, it by no means follows that a subsidi- 

 ary subject-catalogue is not extremely useful. He 

 who knows that he wants Lloyd's book on the 

 undulatory theory is somewhat more learned in 

 the literature of optics than the majority of those 

 who consult libraries. For one who knows as 

 much as this, there are twenty who know only 

 that they want to get some book about the un- 

 dulatory theory. Now a subject-catalogue is pre- 

 eminently useful in instructing such people in the 

 literature of the subject they are studying. They 

 have only to open a drawer that is labelled " OP- 

 TICS," and run along the cards until they come to 

 a division marked " OPTICS Wave-Theory" and 

 there they will find perhaps a dozen or fifty titles 

 of books, pamphlets, review articles, and memoirs 

 of learned societies, all bearing on their subject, 

 and en'abling them to look it up with a minimum 

 of bibliographical trouble. Such a classified cata- 

 logue immeasurably increases the usefulness of a 



1 See the excellent remarks of Professor Jevons in his Principles of 

 Science, ii. 401. 



