Most people now would say that Bruno was right, but the judges of the Inquisition did not think so, and were so alarmed at his opinions that they condemned him to death. In the year 1600, just after the century closed, Bruno was burnt at the stake in Rome as an atheist, partly because he insisted on repeating that the earth is not the centre of the universe, and that there may be other inhabited worlds besides ours. ་ Chief Works consulted. —Whewell's 'Inductive Sciences;' Brewster's 'Optics;' Brewster's Martyrs of Science,' 1874; Encyclopædia Britannica,' art. Astronomy;' Drinkwater's Life of Galileo ; ' Rossiter's 'Mechanics,' 1873; Cuvier, 'Histoire de Sciences Naturelles ;' Baden Powell's Natural Philosophy.' CH. XI GALILEO. 87 CHAPTER XI. SCIENCE OF THE SEVENTEENTH CENTURY. Astronomical discoveries of Galileo-The Telescope--Galileo examines the Moon, and discovers the Earth-light upon it-Discovers Jupiter's four Moons-Distinguishes the Fixed Stars from the Planets-The phases of Venus confirm the Copernican theory--Galileo notices Saturn's Ring, but does not distinguish it clearly-Observes the spots on the Sun-The Inquisition force him to deny the movement of the Earth- Blindness and Death of Galileo. Astronomical Discoveries of Galileo, 1609–1642.-The seventeenth century was not many years old when Galileo startled the world with discoveries such as had never been heard of before. He relates that when quite a young man he was so struck with an account given by some of his companions of a lecture on the Copernican theory, that he determined to study it, and he soon became convinced of its truth. Nevertheless he saw how difficult it would be to prove that the earth moves round the sun, and not the sun round the earth. When he went to Padua he gave a great deal of time to the study of astronomy, and had already made some remarkable observations, when one day, in the year 1609, being in Venice, he heard that a Dutch spectacle-maker had invented an instrument which made distant things appear close at hand. This discovery, which Bacon and Porta had foreseen, was made at last almost by accident in Holland, by two spectacle-makers, Zacharias Jansen and Henry Lippershey. It is related that Jansen's children when playing one day with two powerful magnifying glasses, happened to place them one behind the other in such a position that the weathercock of a church opposite the house seemed to them nearer and larger than usual, and their father, when he saw this, fixed the glasses on a board and gave them as a curiosity to Prince Maurice of Nassau. Whether this story be true or not, it is certain that in the year 1609, both Jansen and Lippershey made these rough telescopes as toys, though they did not know how useful they might be. But when Galileo heard of it he saw at once what valuable help it might afford in studying the heavens; and he set to work immediately, and soon succeeded in making a useful instrument. A diagram of Galileo's telescope is given in Fig. 8. It was made on the same principle as opera-glasses are now, with one convex lens a B, which makes the rays from the object bend inwards or converge, and one concave lens C D, which makes them bend outwards or diverge before they come to a focus. In Fig. 8 one complete cone of rays is drawn coming from the point m, and the outline of another cone from the point n; there are really similar cones coming from all points along the arrow, but it is impossible to give these in a diagram. Each set of rays as they fall on the lens A B, are made to converge, so that they would end in a point or focus, if they were not caught by the lens C D. But this lens having its surfaces curved inwards makes the rays bend outwards or diverge again, so that the end of the cone m reaches the eye in parallel lines at m' m' and the cone n at n'n'. From here, as you will remember (see p. 49), we follow them out in straight lines, and see the image at the angle M o N, so that it appears greatly magnified. If you look at any object through one tube of an opera-glass, and |