In part 4 of Gulliver's travels, swift alters the format of the novel. What is the change in format and how are the two formats similar?

In Gulliver's Travel, Swift always had this style of satire pertaining to European culture and the politics that happened at the time with a mix of nautical jargons. The fourth part of Gulliver's travel has transition of being a satire to a cynical and more dark theme of the story. Because, in the first few parts Gulliver had a peronality and his narration of his adventures had a more lighter note. Part 4 depicts that Gulliver is more in thought than in narrative.