Yesterday's post prompted me to learn about newspapers and magazines printing photographs, and today it's typesetting.
Wikipedia's Typesetting article says:
The time and effort required to manually compose the text led to several efforts in the 19th century to produce mechanical typesetting. While some, such as the Paige compositor, met with limited success, by the end of the 19th century, several methods had been devised whereby an operator working a keyboard or other devices could produce the desired text. Most of the successful systems involved the in-house casting of the type to be used, hence are termed "hot metal" typesetting. The Linotype machine, invented in 1884, used a keyboard to assemble the casting matrices, and cast an entire line of type at a time (hence its name).
There is a separate article on the Linotype machine.