In Chapter 7, Jim and Tom Redruth open a letter from Squire Trelawney addressed to Doctor Livesey. In his letter, the Squire informs them that he's found the perfect ship for their journey to Treasure Island:
The ship is bought and fitted. She lies at anchor, ready for sea. You never imagined a sweeter schooner—a child might sail her—two hundred tons; name, Hispaniola.
The repetition of the /s/ sound in the phrase "sweeter schooner" is an instance of alliteration, a figure of speech in which the first letter or syllable in a group of words is repeated. The overall sound is soft and gentle; the repeated /s/ sound gives the phrase a smooth quality, similar to a ship that moves steadily across still waters.
Stevenson uses this figure of speech as a way to both invoke specific feelings in readers and grab their attention. The phrase has a musical element that adds a lightheartedness to the Squire's words, which catches the reader's attention. The rhythmic quality of the sound of the letter "s" is especially noticeable when read or spoken aloud, and it adds a quality of playfulness to the text. All in all, this playfulness captures the thrill of the adventure that awaits Jim.