282 REPORTS ON THE STATE OF SCIENCE.—IQI3. 
affords a measure of the breadth of the types. 
Strictly speaking, this cannot be measured by the 
reader of a book. A sufficiently good estimate 
can be made when it is recollected that there are 
twenty-six letters in the alphabet, and accordingly 
a word of thirteen letters should not fall short, to 
a material extent, of half the lengths stated in the 
third column. A rough rule may be given thus: 
The number of letters per running inch or 25 mm. 
should not on the average exceed— 
6or 7 letters for readers under 7 years. 
8or g 3 * Troma) 7 tO. ges 
TiOlea2 8 He ast SOLO Oa 
13 ” ” ” fe) to 12 ” 
13 or 14 3 ‘3 over 12 533 
By ‘interlinear space’ is meant the vertical 
distance between the bottom of a short letter and 
the top of a short letter in the next line below. 
This space between the lines should vary in 
proportion to the size of the type. Too little 
space is a source of fatigue in reading, for it 
involves difficulty in passing from the end of a line 
to the beginning of the line below. Very wide space, 
on the other hand, has no advantage as regards 
legibility, and involves waste of paper and unde- 
sirable increase in the size of the book. Columns 
4 and 5 of the table indicate a suitable proportion. 
g. The length of the line is important in a school- 
book intended for continuous reading. Other 
things being equal, the longer the line the greater 
the excursions of the eyes and the greater the 
difficulty in passing from one line to the next. 
Very short lines, on the other hand, demand too 
frequent a change of direction in the movement of 
the’ eyes. The use of lines longer than “the 
maxima given in the last column of the table is 
sure to cause fatigue to a considerable proportion 
of readers. | 
