Swift’s Crater

A diagram showing the orbits of Mars' moons, Deimos and Phobos.
From Giberne’s “The story of the sun, moon, and stars” (1898) – Public Domain

On the 17th of August 1877, the search of American astronomer Asaph Hall was finally successful. He had doubted the conventional wisdom that Mars had no moon. Using the giant 26-inch refractor of the U. S. Naval Observatory in Washington, D.C., he searched close to the planet and discovered not one but two moons, travelling so close to the surface of Mars that until now they were lost in the planet’s glare. These were named Phobos and Deimos (see more about the moons on the NASA website).

This discovery had been anticipated by a fictional research organisation. In 1726, Jonathan Swift wrote Gulliver’s Travels, describing Gulliver’s visit to Balnibarbi and to Lagado, the island that floats above it where its rulers live. The intelligentsia of Lagado, though unhealthily engrossed in their studies, are advanced in astronomy:

For, although their largest telescopes do not exceed three feet, they magnify much more than those of a hundred with us, and show the stars with greater clearness. This advantage has enabled them to extend their discoveries much further than our astronomers in Europe; for they have made a catalogue of ten thousand fixed stars, whereas the largest of ours do not contain above one third part of that number. They have likewise discovered two lesser stars, or satellites, which revolve about Mars; whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost, five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars; which evidently shows them to be governed by the same law of gravitation that influences the other heavenly bodies.

So, not only did Swift suggest Mars had two moons but that they were in close orbit. Phebos orbits Mars in 7 hours 39 mins and Deimos in 30 hours.

The floating island of Laputa as described in Gulliver's Travels.
The Island of Laputa Wikimedia, Public Domain

This does not mean that Swift had some arcane knowledge we lack. Kepler had already suggested that Mars might have two moons, since Mars and Venus had none, Earth had one and Jupiter had five. Given that the century of star gazing since had not discovered them, it was plausible to think the moons would be close to Mars, thus hidden by its glare. Swift knew mathematicians who could assist in giving plausible numbers that corresponded to Newton’s theory of gravitation, such as John Arbuthnot. The technical detail links the fictional astronomers with their real-life equivalents.

The astronomers of Lagado therefore have more advanced knowledge than the Royal Society and other contemporaries who studied the skies. This sets up Swift’s satirical point. In the next chapter Gulliver visits the land beneath the floating island, Balnibarbi, and discovers houses, agriculture and clothing in a sorry state. He is told that this is due to the fact:

That about forty years ago, certain persons went up to Laputa, either upon business or diversion, and, after five months continuance, came back with a very little smattering in mathematics, but full of volatile spirits acquired in that airy region: that these persons, upon their return, began to dislike the management of every thing below, and fell into schemes of putting all arts, sciences, languages, and mechanics, upon a new foot […] whereby, as they undertake, one man shall do the work of ten; a palace may be built in a week, of materials so durable as to last for ever without repairing. All the fruits of the earth shall come to maturity at whatever season we think fit to choose, and increase a hundred fold more than they do at present; with innumerable other happy proposals. The only inconvenience is, that none of these projects are yet brought to perfection; and in the mean time, the whole country lies miserably waste, the houses in ruins, and the people without food or clothes.

Instead of using time-tested techniques that work, the projectors, bewitched by science that they do not understand, are upending everything, with harmful consequences and no regard for the effect on the people. This is the result of trusting theory over practice, an attitude Swift saw spreading and that he satirised most harshly in the 1729 Modest Proposal where logic and economics are used to argue to a repugnant conclusion.

Named features on Daimos Wikimedia, Public Domain
Named features on Deimos Wikimedia, Public Domain

One imagines Swift would be darkly amused at the accuracy of his guess. Merely being right about a scientific fact does not mean you have reached this through science. Perhaps, Swift might say, the New Philosophers should consider that established practice, though not scientific, might be correct before they ride over it roughshod. Swift’s lucky guess is commemorated by a crater named after him on the moon Deimos.

Further Reading

Project Gutenburg: Gullivers Travels

Rebekah Higgitt writing in The Guardian: Gulliver’s travels in science and satire – explores Swift’s satirical musings on the Royal Society and science.

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