In 1818 the compositor, evidently reading this as one in a series of
journal entries, surmised that it could not follow "September 12th" and
added an integer to make it "September 19th." But, of course, what the
text intends us to understand by its idiom is, "On September 9th the ice
began to move." Since this is the date in the manuscript and it is
restored in 1831, the text has been emended here.