The Scientific Revolution

The earth-centred cosmos was not a superstition but a working scientific theory, and knowing how well it worked is the only way to see what replacing it cost.

Moving the earth bought no extra accuracy and no fewer circles, but it turned three arbitrary choices in Ptolemy into consequences, and it made the solar system measurable.

Better data cost a fortune, destroyed the crystalline spheres, and still failed to settle the argument, because a third system fitted everything the other two did.

Kepler threw away a model that fitted the data almost perfectly because of a discrepancy one eighth the width of the moon, and got the first exact laws in the history of astronomy.

In two years the telescope destroyed the Ptolemaic system, made the moon a place with mountains you can measure, and left the strongest rival arrangement completely untouched.

Both sides agreed that a real demonstration would settle the question, which is why the interesting fact about 1633 is that Galileo did not have one and his best argument was wrong.

Free fall is too fast to time with a seventeenth century clock, so Galileo diluted it on an inclined plane, and in doing so invented the contrived experiment.

A model earth on a bench, half an hour of arithmetic about the heart, and a programme for organising knowledge: three attempts to make a contrived case count as evidence about the world.

A question argued from texts for four centuries was closed in four years by a tube of mercury, a mountain and the first deliberate control experiment.

If the world is nothing but matter in motion, every explanation must be a push, which is what let Descartes compute the rainbow to a degree and what made gravity unthinkable.

A result obtained in a private room is not yet knowledge, and the machinery invented between 1640 and 1670 to turn one into the other mattered as much as any discovery.

The same law that makes an apple fall, weakened by the square of the distance, holds the moon in its orbit to within about one per cent, and the calculation is short enough to do here.

Universal gravitation weighed the planets, predicted the shape of the earth and the return of a comet, and to get all that Newton had to give up explaining anything.

The first direct proof that the earth moves arrived in 1728, long after everyone had accepted it, which says something important about what actually settled the question.