nes are all of
the same length, although they do not contain the same number of
letters. The compositor brings this about by arranging his words and
spaces skillfully. The spaces must be as nearly as possible of the
same length, and yet the line must be properly filled. If a line is
too full, he can sometimes place the last syllable on the following
line; if it is not full enough, he can borrow a syllable, and he can
at least divide his space so evenly that the line will not look as if
it were broken in two.

Not many years ago all type was set in this manner; but several
machines have now been invented which will do this work. In one of the
best of them the operator sits before a keyboard much like that of a
typewriter. When he presses key _a_, for instance, a mould or matrix
of the letter _a_ is set free from a tube of _a_'s, and slides down to
its place in the stick. At the end of the line, the matrices forming
it are carried in front of a slot where melted type metal from a
reservoir meets them. Thus a cast is made of the matrices, and from
this cast the printing is done. This machine is called a linotype
because it casts a whole line of type at a time.

Most book work is done on the monotype machine. When a manuscript
goes to the press to be set up in this way, the copy is given to the
keyboard operator who sets it up on a machine which looks much like
a typewriter. Instead of writing letters, however, the machine punches
tiny holes in a strip of paper which is wound on a roll. When the
roll is full it goes to the casting room where it is put on another
machine containing hot type metal and bronze matrices from which the
letters of the words are to be cast. The holes in the paper guide the
machine to make the type much as a perforated music roll guides a
piano to play a tune. The reason why the machine is called a monotype
is that the letters are made one at a time, and _monos_ is the Greek
word for _one_.

By the linotype and monotype machines type can be set in a "galley,"
a narrow tray about two feet long, with ledges on three sides. When a
convenient number of these galleys have been filled, long slips are
printed from them called "galley proofs." These have wide margins, but
the print is of the width that the page of the book will be. They are
read by the proof-readers, and all such mistakes as the slipping in
of a wrong letter, or a broken type, the repetition of a word, or the
omission of space between w