Chapter One The Stranger

      All of a sudden Galileo felt that this moment had happened before-that he had been standing in the artisans’ Friday market outside Venice’s Arsenale and felt someone’s gaze on him, and looked up to see a man staring at him, a tall stranger with a beaky narrow face. As before (but what before?) the stranger acknowledged Galileo’s gaze with a lift of the chin, then walked toward him through the market, threading through the crowded blankets and tables and stalls spread all over the Campiello del Malvasia. The sense of repetition was strong enough to make Galileo a little dizzy, although a part of his mind was also detached enough to wonder how it might be that you could sense someone’s gaze resting on you.

      The stranger came up to Galileo, stopped and bowed stiffly, held out his right hand. Galileo bowed in return, took the offered hand and squeezed; it was narrow and long, like the man’s face.

      In guttural Latin, very strangely accented, the stranger croaked, ‘Are you Domino Signor Galileo Galilei, professor of mathematics at the University of Padua?’

      ‘I am. Who are you?’

      The man let go of his hand. ‘I am a colleague of Johannes Kepler. He and I recently examined one of your very useful military compasses.’

      ‘I am glad to hear it,’ Galileo said, surprised. ‘I have corresponded with Signor Kepler, as he probably told you, but he did not write to me about this. When and where did you meet him?’

      ‘Last year, in Prague.’

      Galileo nodded. Kepler’s places of residence had shifted through the years in ways Galileo had not tried to keep track of. In fact he had not answered Kepler’s last letter, having failed to get through the book that had accompanied it. ‘And where are you from?’

      ‘Northern Europe.’

      Alta Europa. The man’s Latin was really strange, unlike other transalpine versions Galileo had heard. He examined the man more closely, noted his extreme height and thinness, his stoop, his intent close-set eyes. He would have had a heavy beard, but he was very finely shaved. His expensive dark jacket and cloak were so clean they looked new. The hoarse voice, beaky nose, narrow face, and black hair made the man seem like a crow turned into a man. Again Galileo felt the uncanny sensation that this meeting had happened before. A crow talking to a bear-

      ‘What city, what country?’ Galileo persisted.

      ‘Echion Linea. Near Morvran.’

      ‘I don’t know those towns.’

      ‘I travel extensively.’ The man’s gaze was fixed on Galileo as if on his first meal in a week. ‘Most recently I was in the Netherlands, and there I saw an instrument that made me think of you, because of your compass, which, as I said, Kepler showed me. This Dutch device was a kind of looking glass.’

      ‘A mirror?’

      ‘No. A glass to look through. Or rather, a tube you look through, with a glass lens at each end. It makes things look bigger.’

      ‘Like a jeweller’s lens?’

      ‘Yes.’

      ‘Those only work for things that are close.’

      ‘This one worked for things that were far away.’

      ‘How could that be?’

      The man shrugged.

      This was interesting. ‘Perhaps it was because there were two lenses,’ Galileo said. ‘Were they convex or concave?’

      The