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16 him the greater credit, reserving an even higher meed of praise for one who deliberately invents a contrivance of great importance without any previous hint as to its possibility. The aperture of the Doge's telescope was about 1$3⁄4$ inches. It was the second instrument of its kind, but has been lost. Its magnifying power was 3 diameters, and it showed objects 22 miles distant on the earth. On his return to Padua he made a third telescope with a power of 8 diameters, soon followed by a fourth with a power of 20 diameters. This instrument he turned towards the sky, observing the moon and Jupiter, and soon found opportunity on a visit to Florence to show it to his old pupil Cosmo, now Grand Duke, since the death of Ferdinand early in the year. It is interesting to note that three weeks before Ferdinand's death Galileo had cast his horoscope at the request of the Grand Duchess, and promised many more years of life.

Early in 1610 came the fifth telescope, magnifying more than 30 diameters. With this Galileo began his series of astronomical discoveries, except that of the appearance of the moon, begun with the fourth telescope, and shown by its means to the young Grand Duke the previous year. In his tract, the "Sidereus Nuncius" (or Sidereal Messenger), printed at Venice in the same year, he announced the first fruits of his search with the new instrument; first the diversified surface of the moon, with many markings not visible to the naked eye; mountains four or five miles high, and the "earthshine," which he attributed to its true cause; next, the great number of stars revealed by the telescope in clusters, including the true structure of the Milky Way. The planets, moreover, which in his fourth telescope were seen to differ from stars, in showing discs instead of points of light, yielded fresh surprises to the fifth telescope. It was on January 7, 1610, that with this instrument directed towards Jupiter