In 1609, Galileo, then Professor of Mathematics at Padua, in the service of the Venetian Republic, heard from a correspondent at Paris of the invention of a telescope, and set to work to consider how such an instrument could be made. The result was his invention of the telescope known by his name, and identical in principle with the modern opera-glass. In a maritime and warlike State, the advantages to be expected from such an invention were immediately recognised, and Galileo was rewarded with a confirmation of his Professorship for life, and a handsome stipend, in recognition of his invention and construction of the first telescope seen at Venice. In his pamphlet, The Sidereal Messenger, here translated, Galileo relates how he came to learn the value of the telescope for astronomical research; and how his observations were rewarded by numerous discoveries in rapid succession, and at In this Discussion Kepler gives reasons for accepting Galileo’s observations—although he was not able to verify them from want of a telescope—and entirely supports Galileo’s views and conclusions, adducing his own previous speculations, or pointing out, as in the case of Galileo’s idea of earth-light on the moon, the previous conception of Soon after, in 1611, Kepler published another pamphlet, his Narrative, giving an account of actual observations made in verification of Galileo’s discoveries by himself and several friends, whose names he gives, with a telescope made by Galileo, and belonging to Ernest, Elector and Archbishop of Cologne. Kepler and his friends saw the lunar mountains and three of the satellites of Jupiter, but failed to make out any signs of the ring of Saturn corresponding to the imperfect description of Galileo. Kepler had previously published a treatise on Optics (Frankfort, 1604). He now extended it to the consideration of the theory of the telescope, and explained the principle of Galileo’s telescope; he also showed another combination of lenses which would produce a similar effect. This was the principle of the common astronomical telescope, often called, from this circumstance, Kepler’s telescope, though he did not construct it. The account of In 1612 Galileo published a series of observations of solar spots, and in 1618 some observations of three comets. There exist also long series of minute observations of Jupiter and his satellites, continued to November 1619.—(Galileo’s Works; Florence, 1845.) Further astronomical researches may have been hindered by failing sight. One more astronomical discovery, however, that of the moon’s librations, was made as late as 1637, and the announcement of it is dated “dalla mia carcere di Arcetri.” Galileo died January 8, 1642. The following editions have been used for the translation:— Galileo’s Works.
Sidereus Nuncius.
Kepler’s Works, ed. C. Frisch. Frankfurt a. M., 1858-71.
THE SIDEREAL MESSENGER OF GALILEO GALILEI THE |