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. Burgerstein and Netolitsky would require that this distance should be greater than the distance between two '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.
