INTRODUCTION 



first or its principal subject, we may link on to this number, 

 by means of a colon, the number denoting the second or the 

 subsidiary subject. Thus : 



5 : 8 Science and Literature. 



843 : 17 Ethics of French fiction. 



These different methods of division may be freely used in 

 combination. Thus : 



51(42 : 44)04 Essay on Mathematics in Britain and France. 



So long as only the ordinary digits are used in the class 

 numbers, the arrangement of books on the shelves presents 

 no difficulty. They follow each other in the ascending order 

 of the decimal fractions employed. Thus : 



'5 



504 



'53 



5726 

 61 



But when brackets and colons are used as well as digits, 

 it is convenient to adopt the convention that these come in 

 the alphabetical order of their names (bracket, colon, digit), 

 the cipher taking precedence of all three on the familiar 

 indexing principle, " Nothing precedes something". Thus : 



5504 



55(85) 

 '55 : 59 

 '55 = 7 

 '553 



A book can stand in only one place on the shelves and 

 can have but one class number. Its title, however, may be 

 repeated in a catalogue in as many classes as it has subjects. 

 When entered in the class of its main or first named subject, 

 the number is printed in ordinary roman type ; when entered 

 also in any other class (where the book does not stand) the 

 number is printed in italics. Thus : 



55 GEOLOGY. 



55 : 56(41) Geology and Palaeontology of Scotland. 



