The "Linotype" series of manuals--textbooks, really-- by the Mergenthaler Linotype company were to instruct in the proper operation and maintenance of the Linotype machine, long used by periodicals and newspapers before supplanted by new technology. The Linotype was a tall machine that a skilled linotyper (modern = keyboardist) selected buttons to line up brass letter molds (matrices) which were filled with hot printers metal (there was actually an integral crucible to one side to provide the hot metal to the machine) to produce sticks of finished type (linecasting).