There is a technical as well as an optical reason for determining the length of line by measurement of the types themselves. It will be seen by Example [509] that the copy adjusts itself to the various lengths of lines, or, in the vernacular of the printer, “works out line for line.” If fourteen-point type, instead of twelve-point type, were set in lines measuring fifteen picas in length, the compositor would have more difficulty in adjusting the spaces between words, as these spacing points would number two less. This difficulty is usually solved by regrettable wide spacing between words or more regrettable spacing between letters.
Testing types used on newspapers, selecting for the purpose the most used newspaper linotype face (see lower part of Example [510]), we find that the length of line for six-point should be thirteen picas and for seven-point fourteen picas. As actually used in newspapers, the length of line is usually twelve and a half or thirteen picas.
Approved Type Sizes and Space Between Lines.—The type in the upper part of Example [509] also illustrates the sizes of type and the amount of space between type lines that investigators have determined are minimum for use on schoolbooks.
Dr. Cohn, whose findings in these matters have been practically indorsed by educational boards and writers on school hygiene, stipulates that for first-year school children the vertical measurement of the lower-case o should be at least 2.6 millimeters, with space between lines (measuring vertically between a lower-case o in one line and a lower-case o in the line above or below) of 4.5 millimeters. Twenty-two-point Caslon Oldstyle, with long descenders (not shown here), conforms to these measurements.
For the second and third years, the measurement of the o should be at least 2 millimeters, with space between lines of 4 millimeters. Eighteen-point Caslon Oldstyle, with long descenders (as shown in Example [509]), conforms to these measurements.
The fourteen-point size meets the requirements for the fourth school year—at least 1.8 millimeters, with space between lines of 3.6 millimeters.
After the fourth school year the type should measure not less than 1.6 millimeters, with space between lines of 3 millimeters, to which twelve-point Caslon Oldstyle, with long descenders, conforms.
The descending strokes are sufficiently long in the eighteen-point size to maintain between the lines of type the amount of spacing stipulated by Dr. Cohn, but in the fourteen-point size it was necessary to add a two-point lead and in the twelve-point size a one-point lead.
In comparing one font of type with another, it is not accurate to compare, say, eleven-point with eleven-point. Not infrequently one type-face has been pronounced more readable than another, when the preferred type-face was really a twelve-point face on an eleven-point body, with the descending strokes mutilated to allow for such an arrangement. The faces should be compared by the Cohn method given above.