When setting type by hand you can add a word space between each word as you compose the type into your stick. The comp has four different width spaces available in the typecase: a 3-em space, a 4-em space a 5-em space and a thin space. The nomenclature is potentially confusing: a 3-em space is not as you might assume 3-ems wide, it means that three of these spaces will make up one em; thus a 4-em space is narrower than a 3-em space and so on. When you reach the end of the line you can see whether you need to add more space , or maybe take out some. This means you’d go back over the line substituting smaller word spaces or maybe adding thin spaces to fill out the line. Every line however has to be exactly the same length, so it can be locked up in the forme, without any loose type dropping out. For the human brain justification and word spacing is a relatively simple operation: we are good at judging even spacing. For a machine it’s a nightmare.
For a machine the difficulty of word spacing is that it doesn’t know how much space will be left over in the line until it’s finished setting it. With early typesetting machines this means someone had to go back over the line afterwards and drop in word spaces to fill out the line exactly. If they ended up with too much type in the line then they would have to break the last word, turning part of it over (following the strict rules) to the next line. After that the word spacing would have to be adjusted all over again to fill the measure. Clearly, no matter how slick your keyboarding was, having to do this every time the end of a line in reached would slow you down the process — back down actually to about the same speed as a hand type setting.
Here’s a Monotype keyboard. As the keys are depressed they perforate the paper tape seen cropped off at the very top of the picture. Knowing the width of each character the machine counts down from the full measure, The revolving drum with the ruled grid just below the paper tape shows the current calculated result. The little arrow on the descending bar shows the operator the point at which the line should be ended and spaces added and trips a warning bell. So at the end of each line, the paper tape carries an indication of how wide every word space in that line should be. When the tape goes to the caster it is read backwards, and thus for each line, the first thing the caster knows is how wide each word space should be in that line. Pretty neat.
Early Linotypes, introduced first in 1884, had no solution to the problem, and a second operator had to insert spaces before the line of type was cast. The solution to this slow-down in operation was spacebands. A tapering space band in two sliding pieces, wider at the bottom, narrower at the top would be placed between the matrices making up every word. When the line was full the space bands would be hammered upwards, expanding equally to exactly fill the measure. The Mergenthaler Company was sued for their use of this patent, and adapted their system to a similar step-driven system which wasn’t as smooth in operation. After much litigation J. D. Schuckers was awarded the patent rights to the double wedge justification system. He sold the patent to John Raphael Rogers for a relative song, and the Mergenthaler Company had to acquire the rights when they bought out the Rogers Typograph Company in 1895 for $416,000. At this point they abandoned the step system.
The problem of word spacing which was so hard for machines to solve has now reverted to the simple problem it is for the human eye and brain, now that just that sort of knowledge is available in the computer.
For evidence of a word space being printed in error see Word space.