An em quadrate [■] is a short blank type, in thickness equal to the
square of the letter of the fount to which it belongs; an en quadrate [▮]
is half that size.
The first line of a paragraph is usually indented an em quadrate; but
when the matter is leaded or the measure is wide, an em and en, or two or
even three ems may be used. An em quadrate is the proper space after a
full-point when it terminates a sentence in a paragraph.
En quadrates are generally used after the semicolon, colon, &c., and
sometimes after an overhanging letter. They are useful in spacing.
Em and en quadrates, and figures as well, should be entirely exact and
uniform in body, as even a trifling variation will be apparent when they
are arranged in table or figure-work; and no ingenuity on the part of a
compositor can rectify the zigzag appearance caused by irregular types.
The inconvenience arising from founts of the same body not agreeing in
depth is great, where the quadrates, through necessity, are sometimes
mixed. The founts cast by MacKellar, Smiths & Jordan are not liable to
this charge, as their moulds for all regular type of a specific size
harmonize perfectly, and the quadrates and spaces work together.