less new stars to light. In the belt and sword of Orion he sees eighty stars where only seven were known before; in the Pleiades forty instead of six or seven. The Milky Way is a multitude of faint stars clustered together. The nebulæ of Orion and Praesepe are formed of stars. His discovery of the moons of Jupiter dates from January 7, 1610, when three of them were seen. They describe circular orbits about their planet. Jupiter, like each of the planets, has an atmosphere, he says. His telescope was not perfect enough to show this. It is a deduction from analogy.
New discoveries soon followed in respect to Saturn (Dec., 1610) and Venus (Jan., 1611), and they were announced in anagrams as follows:
Smaismrmilmepoetalevmibvnenvgttaviras.
Altissimvm planetam tergeminvm observavi.
(I have observed the highest planet—Saturn—to be tri-form.)
Hæc immatura à me jam feustra leguntur, O. Y.
Cynthia figuras aemulatur mater amorum.
(The mother of the loves—Venus—emulates the figure of Cynthia—the Moon.)
The latter discovery was of capital importance. If the planet Venus revolved about the sun as Copernicus had said, it must show phases like the moon. The phases, invisible to Copernicus, were revealed by the telescope. They occurred at the precise times required to demonstrate the truth of his theory. It was now no longer a theory. It was proved. From this moment no competent witness could doubt the truth of the Copernican system—Galileo less than any one.
An opportunity unique in the history of the world was presented to Galileo and he utilized it to the full. He went from triumph to triumph. The phases of Venus, the mountains of the moon, the constitution of the Milky Way, the tricorporate figure of Saturn, the solar spots, the moons of Jupiter, were death-blows to the systems of Aristotle and of Ptolemy, and were skilfully utilized to establish the system of Copernicus. That system rests, for us, not on the telescopic discoveries of Galileo, but on the working out of its details by Kepler and Newton. To the Italians of Galileo's day Kepler was all but unknown; it is even doubtful whether Galileo appreciated Kepler's splendid discoveries; it is, at any rate, certain that he never publicly mentioned them with praise.
The mere fact that the number of planets and satellites was increased by Galileo's telescope from seven to eleven was another blow to ancient superstitions. Seven was a mystic and magical number. It had relations even to Christianity, so his contemporaries thought. The seven golden candlesticks of Revelations were the seven planets. We can form some idea of the hold of certain magical numbers on the imaginations of our ancestors by remembering that when Huyghens dis-
