Galileo and the Magic Numbers by Sidney Rosen

Author:Sidney Rosen
Language: eng
Format: epub
Publisher: Open Road Media
Published: 2014-05-12T00:13:46+00:00

Chapter VIII

SHORTLY after classes had ended for the summer, Galileo was invited to spend a few weeks as the guest of his friend Sagredo. The invitation was appealing, for Padua was a hot inland city in the summer. Venice, however, was cooled by the breezes of the Adriatic Sea.

Galileo was enjoying a leisurely lunch on a little outdoor terrace, when Sagredo appeared. There was a look of excitement on his face. “Ah, here you are, Galileo. I just heard the most astounding news!”

“It must have been astounding to make you late for lunch!”

“I heard about a new scientific invention this morning. It is reported that a lens grinder in Holland has invented a kind of instrument called a spyglass. It can be used to see objects at a great distance.”

“How did you come to hear about this spyglass?”

“I was at Sarpi’s home this morning for a few moments. Some of his friends were there. Everyone was talking about it! This Dutchman gave the Count of Nassau one of those spyglasses as a present. The Count has told people that he can see objects which are two miles away as clearly as though they were right in front of his eyes!”

“Describe this spyglass to me.”

“From what I heard, it seems to be simply a tube with a glass lens fixed at each end. You hold it up to your eye and—presto!—the distant becomes the near!”

“A lens fixed at each end—” Galileo sat for a moment, deep in thought. Meanwhile, Sagredo called to a passing servant to bring him some lunch. “Have you ever heard of such an instrument?” he asked, as he sat down opposite Galileo.

“No,” murmured Galileo, “never.” Suddenly he sat up, his eyes sparked by a new interest. “But there’s no reason why I can’t make one. In fact, there’s no reason why I can’t make a better one! It’s only a question of optical geometry and the laws of perspective. Let me fetch some paper and a pencil.”

“I’ll call for some—” Sagredo began, but Galileo, too impatient to wait for a servant, had already run indoors. In a moment, he returned and began to sketch some diagrams, explaining to Sagredo as he drew.

“Now, this Hollander must have just held the lenses out and moved them back and forth, until he got a sharp image. But after all, Sagredo, men’s eyes differ. There should be a way of changing the focus of the lenses. Suppose I make two tubes instead of one and have them fitted so that one will slide smoothly inside the other. Now, with a lens at each end, I could push the smaller tube in or pull it out, depending on what the position is for my eyes to see a sharp image.”

“What I don’t quite understand is how such an image appears,” put in Sagredo.

“Oh, I would have to give you a whole series of lectures on the geometry of light to make that clear!” Nevertheless, Galileo tried to show Sagredo in a simple way how a ray of light, traveling in a straight line, was bent by a lens.

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