2 4 o THE POPULAR SCIENCE MONTHLY 



schematic diagrams in which the essential elements of a generalized con- 

 clusion are summarized. Analytical and systematic essays should 

 include diagrams of ideal forms, as well as pictures of corresponding 

 actual forms. Grouped block diagrams showing successive stages 

 of development are serviceable, because they so compactly present the 

 normal succession of a series of complicated forms, and thereby so 

 greatly aid the understanding of the text. It may, indeed, be fairly 

 claimed for such diagrams that, by permitting the abbreviation of 

 explanations, they save at least as much space as they occupy. It should 

 be added, however, that there is good reason for thinking that the full 

 value of graphic illustrations has not yet been reached ; and that active 

 invention as well as better training will surely lead to notable advances. 

 Eegional essays should be illustrated by maps and pictures, and espe- 

 cially by simplified and generalized diagrams, in which the distribution 

 of the larger features may be so clearly shown. Outline map-diagrams 

 and profiles are so much less serviceable than block diagrams, that the 

 latter are to be preferred whenever it is possible to prepare them. 



The guiding principle here, as in the preceding suggestions, is that 

 everything possible should be done to make the author's meaning easily 

 and clearly intelligible to the reader. 



