At the beginning of Gulliver's third voyage, Gulliver encounters the Laputions.  He notices immediately that

Their Heads were all inclined to the Right, or the Left; one of their Eyes turned inward, and the other directly up to the Zenith.

We are immediately presented with a race of people whose configuration of eyes cannot possibly allow them to see the world as it is, and their inability to hold their heads up most likely indicates physical weakness.  The Laputians' physical being speaks to their inability to engage with the normal concerns with life--they are, at one point, too self-absorbed or, at another, looking up to an empty sky.

Swift confirms that Laputians' detachment from the world by noting that the Laputians employ servants with bladders filled with peas who get their masters' attention by tapping them on the ears or mouth to signal them to listen or speak because

the Minds of these People are so taken up with intense Speculations, that they neither can speak, or attend to the Discourses of others, without being rouzed by some external Traction upon the Organs of Speech and Hearing. . . .

We are meant to understand at this point that Swift's satire in this voyage is directed, among other things, to the scientists and projectors he lampooned in A Modest Proposal, men whose solutions to serious problems were impractical and failed to address underlying causes.

When Gulliver gets to Balnibarbi and visits the Academy of Lagado, he sees a scientist who had spent

Eight Years upon a Project for extracting Sun-Beams out of Cucumbers, which were to be put into Vials hermetically sealed, and let out to warm the Air in raw inclement Summers.

Most of the experiments Swift describes in this section are either actual or proposed experiments.

Moving through the Academy, Gulliver finds a scientist who is attempting to breed sheep that cannot grow wool.  Considering the importance of wool to the British economy, Swift's readers would find this experiment both ludicrous and frightening from an economic standpoint, but it does underscore the detachment of these scientists from the world.

Swift's purpose in Book III, similar to his purpose in A Modest Proposal, is to point up the wasteful exercise of rationality on experiments and projects that have no application to improving man's condition.  The conclusion one must reach, then, is that the problems that plague society and government cannot be solved until logic and reason are used to address real economic and social problems.