ON THE INFLUENCE OF SCHOOL-BOOKS UPON EYESIGHT. 279 
The practice of printing from stereos produces 
quite satisfactory results, provided that the stereo 
is carefully made from new or little-worn type. A 
slight thickening of all the lines results from stereo- 
typing, but this in no way detracts from legibility. 
Stereos should not be used when they begin to show 
signs of wear. The ordinary text of school-books 
which are intended for continuous reading should 
not be printed in double columns. 
7. Character of type.—The type should be 
clean-cut and well-defined. Condensed or com- 
pressed type should not be used, as breadth is even 
more important than height. The contrast between 
the finer and the heavier strokes should not be great, 
for hair-strokes are difficult to see. On the other 
hand, a very heavy-faced type suffers in legibility 
through diminution of the white inter-spaces, as, for 
example, when the space in the upper half of the e 
is reduced to a white dot. In an ideal type the 
whites and blacks are well balanced in each letter, 
and it is easy to discriminate between e, c, and 0, 
between fand J, and between Aand k; and to recog- 
nise m, nn, nu, nv, w, in. The general form of the 
letters should be broad and square rather than 
elongated vertically; thus the letter o should 
approach the circular shape. Legibility is not in- 
creased by adding to the height of a letter without 
adding to its width. There should be a lateral 
shoulder on every type so that each letter is distinct. 
Long serifs should be avoided, and any extension 
sideways which forms or suggests a continuous line 
along the top or bottom is detrimental. 
The upper half of a word or letter is usually 
more important for perception than is the lower 
half, because the upper half of most letters has a 
more distinctive shape than the lower. In some 
1 For explanation of technical terms, see Appendix. 
