Spaces are short blank types, and are used to separate one word from
another. To enable the compositor to space even and to justify with
nicety, they are cast to various thicknesses,—viz. five to an em,
[[symb]] or five thin spaces; four to an em, [[symb]] or four middle
spaces; three to an em, [[symb]] or three thick spaces; and two to an
em, [[symb]] or two en quadrates, which may with propriety be reckoned
among the number of spaces. Besides these, there is what is called
the hair-space, which is cast extremely thin, and is found useful in
justifying lines and assisting uniformity in spacing.