One of the best illustrations of the influence of Isaac Newton, and of the intellectual capability of the eighteenth century readers, pops up in Jonathan Swift's Gulliver's Travels (1726, amended 1735). The official name is Travels into Several Remote Nations of the World, in Four Parts. By Lemuel Gulliver, First a Surgeon, and then a Captain of several Ships.
Most people have heard of Gulliver's visit to Lilliput, home of the little people. Many don't realize that gulliver travelled to several other lands, too. Swift wrote the book as a satire and condemnation of the injustices of society in the century before the great democratic revolutions. But Swift had to be careful. He couldn't just come right out and say, for example, that the king was an ass, or that the British House of Lords was composed of imbeciles, or that justices of the peace were corrupt. Doing so could have got him thrown in jail, or worse.
Instead, he had Gulliver visit lands where the king was an ass and the appointed governing body was composed of imbeciles. When challenged, he could always say that he'd written a book of fiction. He wasn't talking about home, for goodness sake.
Isaac Newton had revolutionized science. He showed that the universe runs on simple mathematical laws. He broke down the distinction between heaven and earth by showing that the same laws of physics that govern the actions of objects on Earth apply to the planets. Prior to Newton, nature was mysterious, and scientists (or natural philosophers, as they were more properly called) were limited to explaining Earthly phenomena. The Heavens were governed by their own laws, and why not? Heaven was the realm of God, and God should not be subject to the same laws that constrained the behaviours of Earthly objects.
A generation before Newton, Kepler found that the planetary orbits follow mathematical rules. The planets travel on elliptical paths at varying speed. (Their speed increases as they get closer to the sun.) And Kepler found a fascinating, but mysterious relationship: the cube of the a planet's average radius of orbit divided by the square of the planet's period of orbit is the same for all planets. In math lingo, T-squared varies directly with R-cubed.
Newton used this relationship, Kepler's elliptical orbits, and the calculus that Newton invented while on summer holidays when he was an undergrad at Cambridge University to come up with the Law of Gravity. He could demonstrate that the same force that makes apples fall keeps the planets in orbit around the sun. When he published his discoveries (some twenty years after he made them) he became an instant celebrity.
So, back to Gulliver. On his voyage, he landed at Laputa, where astronomers studied the heavenly bodies through great telescopes. In Swift's time, no moons of Mars had been discovered, so he decided to pretend that Laputian astronomers made a fascinating discovery. Read this:
They have 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.
Did you see what he said? Kepler's T-squared/R-cubed law holds for the moons of Mars, showing them to follow Newton's Law of Universal Gravitation!
I think this speaks volumes about Swift's society. Swift counted on his readers knowing Kepler's and Newton's Laws. He knew that his characters had instant credibility if they were included in Newton's great intellectual revolution.
How many authors of fiction today assume their readers would be as intellectually accomplished?