German-American clock-maker and inventor Ottmar Mergenthaler of Baltimore invented the first mechanical typesetting machine or composing machine that could set complete lines of type, or slugs. By speeding up typesetting this machine revolutionized print production, first in newspapers where speed in producing frequent daily editions was required. The machine eventually became known as the Linotype.
Mergenthaler developed the first simple prototype in 1883, and in 1884 he
"conceived the idea of assembling a line of dies or female matrices and casting into them molten metal to form a complete slug or line of type. . . . The matrices in these machines were stamped on the edges of upright bars, each bar containing the letters of the entire alphabet, the operation of the keyboard acting to set up stops which allowed these bars to descend to the proper distance, when a cast was taken from the aligned matrices. The wedge justifier, or the invention of which litigation afterward developed, was incorporated in the second machine built, in 1885.
"The impossiblity of correcting errors as soon as discovered led to the conception of the independent matrix machine, which was next built in 1885, and this marked the advent of the Linotype as a new factor in the printing world."
The first "direct band type casting machine" was in test operation by July 1884. The first machine with "independent or free matrices" was in operation on July 15, 1885.
Because the Linotype in operation was very loud, it was common for deaf people to be hired to operate them because they were not bothered by the high noise level:
Schlesinger ed., The Biography of Ottmar Mergenthaler, Inventor of the Linotype (1989) 18-23. Thompson, History of Composing Machines (1904) 100.