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a plurality of worlds received still another push forward with the invention of the telescope. In 1609, the Italian scientist Galileo Galilei (1564–1642) constructed a telescope and pointed it at the Moon. For the first time in history, the Moon was seen magnified, and more clearly detailed than was possible with the unaided eye.
    Galileo saw mountain ranges on the Moon, together with what looked like volcanic craters. He saw dark, smooth patches that looked like seas. Quite plainly and simply, he was seeing another world.
    This stimulated the further production of fictional flights to the Moon. The first was written by Johannes Kepler (1571–1630), an astronomer of the first rank * and was published posthumously in 1633. It was entitled
Somnium
because the hero reached the Moon in a dream.
    The book was remarkable in that it was the first to take into account the actual known facts about the Moon, which until then had been treated as in no way different from any Earthly piece of real estate. Kepler was aware that on the Moon the nights and days were each 14 Earth days long. However, he had air, water, and life on the Moon; there was nothing as yet to rule that out.
    In 1638, the first science fiction story in the English language that dealt with a flight to the Moon was published. It was
The Man in the Moone
by an English bishop named Francis Godwin (1562–1633). It was also published posthumously.
    Godwin’s book was the most influential of the early books of this nature, for it inspired a number of imitations. The hero of the bookwas carried to the Moon in a chariot drawn by a flock of geese (who were pictured as regularly migrating to the Moon). As usual, the Moon was populated with quite human intelligent beings.
    In the same year in which Godwin’s book was published, another English bishop, John Wilkins (1614–1672), a brother-in-law of Oliver Cromwell, produced a nonfictional equivalent. In his book
The Discovery of a World in the Moone
, he speculated on the habitability of that body. Whereas Godwin’s hero was a Spaniard (the Spaniards having been the great explorers of the previous century), Wilkins was sure it would be an Englishman who would first reach the Moon. In a way, Wilkins proved right, for the first man on the Moon was of English descent.
    Wilkins, too, assumed that air existed all the way to the Moon and indeed throughout the Universe. There was, even in 1638, no understanding that such a fact would make separate heavenly bodies impossible. If the Moon were revolving about the Earth through an infinite ocean of air, air resistance would gradually slow it and finally bring it crashing, in fragments, down on the Earth—which would similarly crash into the Sun, and so on.
WATERLESSNESS
    The notion of universal air had not long to live, however. In 1643, the Italian physicist Evangelista Torricelli (1608–1647), a student of Galileo, succeeded in balancing the weight of the atmosphere against a column of mercury, inventing the barometer. It turned out, from the weight of the column of mercury that balanced the downward pressure of air, that the atmosphere would only be 8 kilometers (5 miles) high if it were of uniform density. And if the density decreased with height, as it does in fact, it could only be a little higher than that before becoming too thin to support life.
    It was clear, for the first time, that air did not fill the Universe but was a purely local terrestrial phenomenon. The space between the heavenly bodies was empty, a “vacuum,” and this constituted, in a way, the discovery of outer space.
    Without air, human beings could not travel to the Moon by means of water spouts, or geese-drawn chariots, or by any of the usual methods that would suffice to cross a gap of air.
    The only way, in fact, that the gap between Earth and Moon could be closed was by using rockets, and this was first mentioned in 1657 by none other than the French writer and duellist Savinien de Cyrano de Bergerac