On a modern school protractor you cannot distinguish ten minutes of a degree, and only one astronomer before Kepler would have thought such a measurement unsatisfactory. The greatest astronomer of the ancient world, Ptolemy, had regarded ten minutes as precisely his acceptable margin of error. But Kepler had worked with Tycho Brahe, who had devised new instruments capable of measuring with unbelievable accuracy, to a single minute.
Kepler was worried about such tiny numbers because he wanted to prove that Tycho’s theoretical tools could not provide an accurate account of Mars’s movement through the heavens – Kepler’s best predictions, using traditional methods, were out by up to eight minutes. By the time Kepler had found a satisfactory way of handling this aberrant eight minutes, he had abandoned the notion that all heavenly movements are circular and introduced the idea of an orbit – the regularly repeated trajectory of an astronomical object through space….
Kepler replaced orbs with orbits (the word used in this sense was a marker of Kepler’s key innovation – previously an orbit was the track left by a wheel in the ground), replaced circles with ellipses, geometry with physics. He did so even though he came to recognize, reluctantly, that one could give a perfectly satisfactory account of his new measurements using the old apparatus of circles, eccentrics and epicycles. The problem for Kepler was that circles, eccentrics and epicycles were geometrical constructions; there was no evidence that any such gearing existed in the heavens….
Kuhn, it turns out, was wrong. His theory was that a scientific revolution is always a response to an intellectual crisis. But Copernicus neither responded to nor brought about a crisis in orthodox astronomy. In the first fifty years after the publication of his book only two competent mathematicians defended Copernicanism as a cosmology in print – Copernicus’s sole disciple, Rheticus, and the Englishman Thomas Digges. Experts read and annotated their copies of Copernicus, but the heliocentric hypothesis was in their view the least interesting part of the book. What they were interested in were the new tools that Copernicus provided for geometrical astronomy. Even Kuhn recognized that “the success of the De revolutionibus does not imply the success of its central thesis”. Astronomers were happy to employ and revise Copernicus’s tables for predicting the positions of planets in the heavens. This did not make them Copernicans; it just showed that they were keen to get their facts straight….
When Kepler published the Rudolphine tables in 1627, based on Tycho’s measurements, and named after their deceased patron, Rudolph II, no one disputed that they were superior to anything that had gone before. Thus the printing press strengthened the hand of the innovators by making it possible for them to pool information and work together. It replaced the professorial lecture, the voice of authority, with a text in whose margin you could scribble your dissent. And, by fostering a constant clash of arguments and ideas (Riccioli against Copernicus; Hobbes against Boyle), it forced each side to adapt and change. What the printing press did, quite simply, was weaken authority and strengthen evidence. One of Galileo’s opponents, Lodovico delle Colombe, protested that Galileo was undermining the monarchy of Aristotle, and with it the principle of monarchy itself – while Galileo and his supporters wrote of a republic of letters and of the learned (repubblica scienziata). Over and over again we find the new scientists adopting their motto from the second-century Platonist Alcinous, “philosophizing wants to be free”.
The printing press also fostered a sort of intellectual arms race where new weapons (the astronomical sextant, invented by Tycho; the telescope, improved by Galileo; the pendulum clock, invented by Huygens – astronomical measurements are worthless without accurate timekeeping) were constantly being brought up to the front line. It’s not surprising that Kepler’s New Astronomy is full of military metaphors – indeed he presents the whole book as a war over the motions of Mars….
Kepler did not have the word “fact” (he wrote of phenomena, observations, effects, experiments, of to hoti), but he certainly had the idea. He chose to place on the title page of his Stella nova (1606) the image of a hen pecking around in a farmyard, with the motto grana dat e fimo scrutans (“hunting about in the crap, she finds grain”). He presented himself not as a great philosopher, but as someone prepared to grub around for facts. And because he had to make his facts credible, he was obliged to adopt many of the techniques that Shapin and Schaffer think are new with Boyle – the apparently prolix recounting of irrelevant details (the glowing coal by which he read his instruments on the night of February 19, 1604), the determination to report failures (Kepler presents his war on Mars as an almost endless series of defeats) with the same care as successes, the insistence on involving the reader as if he were really present. In the Stella nova he even introduces us to his wife, as though we were visiting them at home, explaining that he had found it difficult to refute the arguments of the Epicureans, who thought the universe was the product of chance. But his wife is a more redoubtable adversary than he is:
“Yesterday, when I had grown tired of writing and my mind was full of dust motes from thinking about atoms, she called me to dinner and served me a salad. Whereupon I said to her, if one were to throw into the air the pewter plates, lettuce leaves, grains of salt, drops of oil, vinegar and water and the glorious eggs, and all these things were to remain there for eternity, then would one day this salad just fall together by chance? My beauty replied ‘But not in this presentation, nor in this order’.”
So much for what is known as the infinite monkey theorem.
– David Wootton, from his TLS review of Robert S. Westman’s The Copernican Question