"Look how much light and heat we get from the sun," Fra Tomasso went on. "Yet, the sun appears small—I can hide it with my thumb."
Your thumb could hide four or five suns.
"Perhaps it is small," Daoud said.
"If it is as big as it must be to produce such light and heat, it must be very far away—thousands of leagues—to appear so small. But if it is that far away, it must be bigger still, for its heat and light to travel such a distance. The bigger it is, the farther away it must be—the farther away it is, the bigger it must be. Do you follow? There must be a strict rule of proportion."
Daoud told himself to ignore this nonsense and concentrate on the important thing—that Fra Tomasso badly wanted a book by this pagan philosopher Aristotle. That book might be the means of winning Fra Tomasso. Not that he could be crudely bribed, but certainly such a present would favorably dispose him to what Daoud had to say.
And he saw another way to make the point he had come to make.
"It may be, Your Reverence, that the book you want has been lost forever. When I spoke of the destruction of Baghdad the other day, I should have mentioned that the Tartars burned there a library rivaled only by the great library of Alexandria in its prime."
His flesh turned cold. That was a mistake. In his zeal he had momentarily forgotten that it was Christians who had destroyed the library of Alexandria. As the story was often told in Egypt, when the Muslim warriors took Alexandria from the Christians, they found that most of what had once been the world's greatest collection of books had been used to fuel the fires that warmed the public baths.
But, to Daoud's relief, Fra Tomasso only shut his eyes and shook his head, his cheeks quivering gently like a bowl of frumenty. "God forgive the Tartars."
"God will certainly not forgive us, Fra Tomasso, if we help the Tartars to destroy Damascus and Cairo. Or Trebizond and Constantinople."