Sentence:  If it be only a "Single Letter" or two that drops, he thruſts the end of his "Bodkin" between every "Letter" of that Word, till he comes to a <WSD>"Space</WSD>": and then perhaps by forcing thoſe "Letters" closer, he may have room to put in another <WSD>"Space</WSD>" or a "Thin <WSD>Space</WSD>"; which if he cannot do, and he finds the <WSD>"Space</WSD>" ſtand "Looſe" in the "Form"; he with the "Point" of his "Bodkin" picks the <WSD>"Space</WSD>" up and bows it a little; which bowing makes the "Letters" on each ſide of the <WSD>"Space</WSD>" keep their parallel diſtance; for by its Spring it thruſts the "Letters" that were cloſed with the end of the "Bodkin" to their adjunct "Letters", that needed no cloſing. 
Meaning of the word marked with <WSD> tags:  A piece of metal type used to separate words, cast lower than other type so as not to take ink, especially one that is narrower than one en (compare "quad"). (from 17thc.)