When Henry W. Longfellow saw that, he realized that the newspaper had left out some text. He immediately wrote to his Atlantic editor, James T. Fields (shown at left):
In “Paul Revere” as given in The Transcript I find six lines left out. I hope it is not so in the Atlantic. The lines follow immediately after “The fate of a nation rode that night,” and are rather essential, I think, to the picture. Perhaps I accidentally omitted them in copying for the press.Indeed, Longfellow had left out those lines when he wrote a copy of the poem to send to the magazine. They didn’t appear in The Atlantic Monthly, and Longfellow had to wait for the poem’s next publication to insert them.
Longfellow’s statement of where the lines should appear wasn’t precise, either. The missing stanza actually starts two lines after “The fate of a nation was riding that night.” Compare the first printed version with the eventual established text to find the additional stanza about the Mystic River.