From Elmira, where he'd gone to lecture and to court Olivia Langdon, MT wrote two letters on November 28 -- one to Mary Fairbanks, the other to Joseph Twichell. The second letter is in the Barrett Collection; the other can be seen in Wecter's Mark Twain to Mrs. Fairbanks. Both reveal the same pattern. Livy's family had accepted MT as a potential claimant for her hand, but neither they nor he wanted that news made public. He did need to share his joy with close friends, though, so he wrote the letters. The one to Twichell is boldly headed as Private:
But while the event may be "private," when MT interpolates "[Thunders and Hurricanes of applause]" into the story, he's using the same kind of bracketed references to an audience's response that appear in many accounts of his performances on the lecture circuit. The invisible audience's "Thunder" can be heard on page 2, just after MT tells Twichell that Livy's parents seem willing to let their angel leave the house as his mate:
On the letter's last page, when MT tells his friend that Livy has agreed to allow him to correspond with her from the tour, the applause reaches "Hurricane" force:
Even alone with a private event, MT was conscious of performing for an audience. There's no doubt that he loved Livy -- but in part because marriage with her would mean acceptance of the somebody he was also trying to be as a public celebrity.
(You can see the whole letter to Twichell in the "SAM CLEMENS AS MARK TWAIN section of the archive.)