HYGIENIC REQUIREMENTS IN PRINTING 543 



these should be enforced rigorously, in the printing of school-books and 

 government publications, at least. If enforced here, they will tend to 

 extend to all printing. 



In studying the psychology and pedagogy of reading during some 

 years past, the writer has been thrown in contact with the experimental 

 work bearing, upon the establishment of norms for printing. The 

 present article is an attempt to sum up the results of investigations 

 made thus far, and to state the requirements which they warrant us 

 in making of the printer. 



The size of the type is perhaps the most important single factor. 

 The experiments of Griffing and Franz showed that fatigue increases 

 rapidly as the size of the type decreases, even for sizes above eleven 

 point, or above a height of 1.5 millimeters for the short letters like v, s, 

 etc. The various investigators are generally agreed that this should 

 be made a minimum for the height of the short letters. Matter printed 

 in this size of type is read faster, and individual words are recognized 

 more quickly, than where the type is smaller. Besides, Griffing and 

 Franz found that the effect of insufficient illumination is less marked 

 with the larger type. Preferably the height of the small letter should 

 be somewhat above the minimum stated, though when the height is 

 much above two millimeters Weber's experiments indicated that the 

 speed of reading is decreased. 



The thickness of the vertical strokes of the letters should not be 

 less than .25 millimeter, according to Cohn, preferably .3 millimeters, 

 according to Sack. This thickness of the letters has been found by 

 Javal and others to be a very important factor in increasing legibility 

 and thus in decreasing fatigue. Griffing and Franz found, however, 

 that hair lines might form parts of the letter without decreasing the 

 legibility provided the other parts were thick. They find it possible, 

 however, that such hair lines may increase fatigue. The minimum of 

 thickness stated above should be insisted on for the main lines. 



The space within the letters, between the vertical strokes, should 

 not be less than .3 millimeter, according to most investigators. Sack 

 finds .5 millimeter to be preferable. There is probably little to be 

 gained by increasing the distance between the letters beyond that which 

 is usual in the better printed books of the present time. Burger- 

 stein and Netolitsky would require that this distance should be greater 

 than the distance between two c neighboring ground strokes ' of a 

 letter, and Sack would make the minimum distance .5 to .75 millimeter. 

 Burgerstein and Netolitzky would not allow more than six or seven 

 letters per running centimeter, and would require as much as two 

 millimeters between words. With these requirements Sack is in 

 agreement. It should be remembered that any very unusual 

 separation of the letters of a word is distracting and should 

 be avoided. 



