544 POPULAR SCIENCE MONTHLY 



These minimal forms as stated by Burgerstein and Netolitzky 

 should be made requirements, except that possibly the distance between 

 letters is not so important as they urge. The minimum of six or seven 

 letters per running centimeter is a convenient approximate gauge which 

 can be quickly applied and is not too stringent. 



Griffing and Franz found that legibility increased somewhat, though 

 not greatly, with increase in the distance between the lines, with the 

 leading, as it is called. Cohn thinks it important that there should be 

 a minimum interlignage of 2.5 millimeters, and Sack requires the same. 

 Javal does not find that interlignage increases legibility appreciably, 

 and thinks that the space used for interlignage had far better be 

 given to an increased size of letter without interlignage. The leading 

 is doubtless a mistake when the size of type is below the requirements 

 made above. The size of type should by all means be increased instead, 

 as this is by far the most important of the factors conditioning fatigue. 

 However, a certain amount of leading should be required in school 

 books, at least, but hardly more than Cohn's minimum of 2.5 milli- 

 meters. 



As to length of lines there is a general consensus in favor of the 

 shorter as against the longer lines, with a tendency to favor 90 milli- 

 meters as a maximum, some placing the maximum at 100 millimeters. 

 The latter is doubtless too high. Javal, who has studied the matter 

 very carefully, insists that the maximum should be considerably below 

 even 90 millimeters. He names as one of the principal causes of 

 fatigue in reading, and as a cause tending to produce and aggravate 

 myopia, the considerable amount of asymmetrical accommodation re- 

 quired as the eye moves along a long line, the amount increasing always 

 with the length of the line. Even with the page squarely before the 

 reader, unless he makes constant and fatiguing movements of the 

 head while reading, the reading matter is always farther from one 

 eye than from the other, except at a middle point, and the reader 

 strains to accommodate for both distances, especially for objects held 

 so near as is the page in reading. 



Against the long lines is also to be urged the difficulty and dis- 

 traction incident to finding the place at each turn to the next line, 

 increasing always as the lines are longer. Besides, the longer lines 

 require a greater extent of eye-movement for a given amount of read- 

 ing. This comes from the fact, verified by various experimenters, that 

 the eye does not traverse the whole line in reading, but begins within 

 the line and usually makes its last pause still farther within, reading 

 the first and last parts of the line in indirect vision. The amount of 

 this indentation tends to be a constant amount irrespective of the 

 line's length, and is consequently a larger proportion of the line's 

 length in the shorter lines. There is thus an important lessening of 



