Gulliver's explains how the Flying Island moves by giving what he calls "a philosophical account" of its movement capabilities. The explanation is quite complicated, but the movement principle is quite simple and is based upon magnetic forces in the Flying Island and in the country below (Balnibarbi). These forces, working in opposition, allow the island to move up, down, forward, backward, and sideways by means of using the attracting and repelling principles inherent in the science of magnetism. Gulliver also explains how the King uses the Flying Island to tyrannize the people of Balnibarbi. He can cut off sunshine and rain from any region on the lower island. Or, if he wishes, he can pelt it with stones. Theoretically, he could lower Laputa and crush Balnibarbian towns. Finally, Gulliver relates the story of the successful rebellion of the city of Lindalino.
Gulliver's description of the movement of the island is a parody of papers often delivered to the Royal Society. Swift is mocking the Society's fondness for concrete, technical language, and their love of mathematical and pseudo-mathematical diagrams. Gulliver's enthusiasm for the astronomical discoveries of the Laputans parodies the enthusiasm of the Royal Society for Halley's and other astronomers' observations of comets. It should be remarked, however, that Swift describes with great accuracy the two satellites of Mars. These satellites were not observed until 1877.
Swift fills his reader's mind full of reminiscences of scientific speculation with the description of the island. Then he proceeds to link these remembrances to political terrorism and tyranny. The King's attack on Balnibarbi, for example, and his policies toward Balnibarbi parallel the English crown's policies toward Ireland. Cutting off the rain and the sun refers to the royal policies that cut off Irish trade. The tall rocks in the towns of Balnibarbi seem to represent the Irish peers; the high spires represent Irish bishops, who protested Wood's scheme; and the pillars of stone probably characterize the Irish merchants.
Ireland was a rebel country and Lindalino, no doubt, represents Dublin. The towers Lindalino raised correspond to the grand jury that investigated Swift's The Drapier's Letters, the Irish privy council, and the two houses of the Irish parliament. The privy council and the parliament resisted Wood's scheme (that would debase Irish coinage), even at the cost of losing royal bribes. The lodestones installed to catch the island probably represent various quasi-legal organizations of merchants and citizens who opposed Wood's debased coinage. Swift's contemporaries seem to have recognized the many political references because the printers suppressed the Lindalino incident; it did not appear in the Travels until the nineteenth century.
adamant a hard stone or substance that was supposedly unbreakable.
packthreads strong, thick thread or twine for tying bundles, packages, etc.