"I know, I know, "Johannes said, looking at his hands. They sat in the rector's room overlooking the central courtyard of the school. It was raining. There was wind in the chimney, and balls of smoke rolled out of the fireplace and hung in the air around them, making his eyes sting. "I talk too quickly, and say things before I have had time to consider my words. Sometimes in the middle of a class I change my mind and begin to speak of some other subject, or realise that what I have been saying is imprecise and begin all over again to explain the matter in more detail. " He shut his mouth, squirming; he was making it worse. Dr Papius frowned at the fire. "You see, Herr Rector, it is my cupiditas speculandi that leads me astray."

"Yes, " the older man said mildly, scratching his chin, "there is in you perhaps too much… passion. But I would not wish to see a young man suppress his natural enthusiasm. Perhaps, Master Kepler, you were not meant for teaching?"

Johannes looked up in alarm, but the rector was regarding him only with concern, and a touch of amusement. He was a gentle, somewhat scattered person, a scholar and physician; no doubt he knew what it was to stand all day in class wishing to be elsewhere. He had always shown kindness to this strange little man from Tübingen, who at first had so appalled the more stately members of the staff with his frightful manners and disconcerting blend of friendliness, excitability and arrogance. Papius had more than once defended him to the supervisors.

"I am not a good teacher, ' 'Johannes mumbled, "I know. My gifts lie in other directions. "

"Ah yes, " said the rector, coughing; "your astronomy. " He peered at the inspectors' report on the desk before him. "You teach that well, it seems?"

"But I have no students!"

"Not your fault-Pastor Zimmermann himself says here that astronomy is not everyone's meat. He recommends that you be put to teaching arithmetic and Latin rhetoric in the upper school, until we can find more pupils eager to become astronomers."

Johannes understood that he was being laughed at, albeit gently.

"They are ignorant barbarians! " he cried suddenly, and a log fell out of the fire. "All they care for is hunting and warring and looking for fat dowries for their heirs. They hate and despise philosophy and philosophers. They they they-they do not deserve…" He broke off, pale with rage and alarm. These mad outbursts must stop.

Rector Papius smiled the ghost of a smile. "The inspectors?"

"The…?"

"I understood you to be describing our good Pastor Zimmermann and his fellow inspectors. It was of them we were speaking."

Johannes put a hand to his brow. "I-I meant of course those who will not send their sons for proper instruction. "

"Ah. But I think, you know, there are many among our noble families, and among the merchants also, who would consider astronomy not a proper subject for their sons to study. They burn at the stake poor wretches who have had less dealings with the moon than you do in your classes. I am not defending this benighted attitude to your science, you understand, but only drawing it to your attention, as it is my-"

"But-"

"-As it is my duty to do. "

They sat and eyed each other, Johannes sullen, the rector apologetically firm. Grey rain wept on the window, the smoke billowed. Johannes sighed. "You see, Herr Rector, I cannot-"

"But try, will you, Master Kepler: try?"

He tried, he tried, but how could he be calm? His brain teemed. A chaos of ideas and images churned within him. In class he fell silent more and more frequently, standing stock still, deaf to the sniggering of his students, like a crazed hiero-phant. He traipsed the streets in a daze, and more than once was nearly run down by horses. He wondered if he were ill. Yet it was more as if he were… in love! In love, that is, not with any individual object, but generally. The notion, when he hit on it, made him laugh.

At the beginning of 1595 he received a sign, if not from God himself then from a lesser deity surely, one of those whose task is to encourage the elect of this world. His post at the Stiftsschule carried with it the title of calendar maker for the province of Styria. The previous autumn, for a fee of twenty florins from the public coffers, he had drawn up an astrological calendar for the coming year, predicting great cold and an invasion by the Turks. In January there was such a frost that shepherds in the Alpine farms froze to death on the hillsides, while on the first day of the new year the Turk launched a campaign which, it was said, left the whole country from Neustadt to Vienna devastated. Johannes was charmed with this prompt vindication of his powers (and secretly astonished).  a sign, yes, surely. He set to work in earnest on the cosmic mystery.

He had not the solution, yet; he was still posing the questions. The first of these was: Why are therejust six planets in the solar system? Why not five, or seven, or a thousand for that matter? No one, so far as he knew, had ever thought to ask it before. It became for him the fundamental mystery. Even the formulation of such a question struck him as a singular achievement.

He was a Copernican. At Tübingen his teacher Michael Mästlin had introduced him to that Polish master's world system. There was for Kepler something almost holy, something redemptive almost, in that vision of an ordered clockwork of sun-centred spheres. And yet he saw, from the beginning, that there was a defect, a basic flaw in it which had forced Copernicus into all manner of small tricks and evasions. For while the idea of the system, as outlined in the first part of De revolutionibus, was self-evidently an eternal truth, there was in the working out of the theory an ever increasing accumulation of paraphernalia-the epicycles, the equant point, all that-necessitated surely by some awful original accident. It was as if the master had let fall from trembling hands his marvellous model of the world's working, and on the ground it had picked up in its spokes and the fine-spun wire of its frame bits of dirt and dead leaves and the dried husks of worn-out concepts.

Copernicus was dead fifty years, but now for Johannes he rose again, a mournful angel that must be wrestled with before he could press on to found his own system. He might sneer at the epicycles and the equant point, but they were not to be discarded easily. The Canon from Ermland had been, he suspected, a greater mathematician than ever Styria's calendar maker would be. Johannes raged against his own inadequacies. He might know there was a defect, and a grave one, in the Copernican system, but it was a different matter to find it. Nights he would start awake thinking he had heard the old man his adversary laughing at him, goading him.

And then he made a discovery. He realised that it was not so much in what he had done that Copernicus had erred: his sin had been one of omission. The great man, Johannes now understood, had been concerned only to see the nature of things demonstrated, not explained. Dissatisfied with the Ptolemaic conception of the world, Copernicus had devised a better, a more elegant system, which yet, for all its seeming radicalism, was intended only, in the schoolman's phrase, to save the phenomena, to set up a model which need not be empirically true, but only plausible according to the observations.

Then had Copernicus believed that his system was a picture of reality, or had he been satisfied that it agreed, more or less, with appearances? Or did the question arise? There was no sustained music in that old man's world, only chance airs and fragments, broken harmonies, scribbled cadences. It would be Kepler's task to draw it together, to make it sing. For truth was the missing music. He lifted his eyes to the bleak light of winter in the window and hugged himself. Was it not wonderful, the logic of things? Troubled by an inelegance in the Ptolemaic system, Copernicus had erected his great monument to the sun, in which there was embedded the flaw, the pearl, for Johannes Kepler to find.