what is the satire behind laputa's floating island?

Gulliver discovers that the name of the island is Laputa, which in their language means “floating island.” The island is exactly circular and consists of 10,000 acres of land. At the center there is a cave for astronomers, containing all their instruments and a lodestone six yards long. It moves the island with its magnetic force, since it has two charges that can be reversed by means of an attached control. The mineral that acts upon the magnet is large enough to allow it to move only over the country directly beneath it. When the king wants to punish a particular region of the country, he can keep the island above it, depriving the lands below of sun and rain.