Sunday, June 19, 2011

TELESCOPE

For years Rome remained too dangerous. Cesi’s father continued to do everything he could to block the progress of the subversive society his son had founded. Federico Cesi himself still thought of setting up their “Lynceum” in the more propitious environment of Naples. (...) But then news of the telescope and its possibilities began to reach them. Sometime in early 1609 Galileo had turned his cannochiale to the night sky; and from then on matters moved ahead with unanticipated speed.
For a start, Giovanni Battista della Porta, the sage of Naples and father figure to Cesi and the other Linceans, began snapping at Galileo’s heels. Had he not been there first? “I have seen the secret use of the eyeglass and it’s a load of balls [coglionaria],” he wrote to Cesi on August 28, 1609. “In any case, it’s taken from book 9 of my De Refractione,” he pointed out, irascibly. In the same letter he made a simple drawing of his own invention and explained that it consisted of one tube with a concave lens inserted into another with a convex lens.
Looking just with the first one will see distant things nearby [le cose lontane, vicine, a phrase that would continue to reverberate in the next few years]; but since one cannot see within the tube [i.e., at the focal point], they appear obscure and indistinct. However, if one places the other tube with the concave lens inside, it has the contrary effect, and one sees things clearly and directly. It goes in and out like a trombone, and one adjusts it according to the eyesight of the beholder, since eyesight always varies from one beholder to the other.
In other words, Della Porta had long since established the basic principle of the telescope. But by the time he wrote to Cesi it was too late. Galileo had beaten him to the post. He had made a far more refined instrument than Della Porta ever envisaged - and had actually begun to use it.

1 comment:

  1. [ David Freedberg, The eye of the lynx: Galileo, his friends, and the beginnings of modern natural history ]

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