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Page:Popular Science Monthly Volume 66.djvu/347

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Galileo in the Sidereus Nuncius (1610) gives this account of the invention of the telescope:

A report reached my ears that a Dutchman had constructed a telescope, by the aid of which visible objects, although at a great distance from the observer, were seen distinctly as if near.... A few days after, I received confirmation of the report in a letter... which finally determined me to inquire into the principle of the telescope[1] and then to consider the means by which I might compass the invention of a similar instrument, which, in a little while, I succeeded in doing, through deep study of the theory of refraction.... At length I succeeded in constructing for myself an instrument so superior that objects seen through it appeared... more than thirty times nearer than if viewed by the natural powers of sight alone.

On the title page of his book the telescope is described as 'lately invented by him.' This claim Galileo does not make, but in subsequent years it was charged by his enemies that he claimed credit not his due, and the charge perpetually reappears. The amazing discoveries of this memorable year are enumerated on the title page in question.

The Sidereal Messinger (Nuncius Sidereus), unfolding great and very wonderful spectacles and offering them to the consideration of every one, especially of philosophers and astronomers; being such as have been observed by Galileo Galilei... by the assistance of a perspective glass lately invented by him; namely, in the face of the Moon, an innumerable number of fixed stars, the Milky Way, and nebulous stars, but especially respecting four Planets that revolve about Jupiter at different intervals and periods with a wonderful celerity; which, hitherto not known to any one, the author has recently been the first to discover and has decreed to call the Medicean Stars. (Venice, 1610.)

The surface of the moon was covered with brilliant and dark areas as the peacock's tail with spots. Perhaps the moon has an atmosphere, he says. The heights of lunar mountains can be fixed by measuring their shadows. The ashy-light of the moon ('old moon in the new moon's arms') is perhaps caused by a lunar twilight. He gives Leonardo da Vinci's explanation also—the true one—that it is caused by earth-light reflected to the moon and back to us. The stars appear as points of light, the planets as small discs. The telescope brings count-

  1. Galileo uses the words perspicillum, occhiale, etc., for the instrument. The word telescope was invented to describe the new instrument by Demiscianus at the request of Prince Cesi, president of the Accademia dei Lincei about 1612. The telescope itself was invented by Hans Lippershey.