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By Root 3239 0

Jacques Badovere, which caused me to apply myself wholeheartedly to inquire into the means by which I might arrive at the invention of a similar instrument. This I did shortly afterwards, my basis being the theory of refraction. First I prepared a tube of lead, at the ends of which I fitted two glass lenses, both plane on one side while on the other side one was spherically convex and the other concave. Then placing my eye near the concave lens I perceived objects satisfactorily large and near, for they appeared three times closer and nine times larger than when seen with the naked eye alone. Next I constructed another one, more accurate, which represented objects as enlarged more than sixty times. Finally, sparing neither labor nor expense, I succeeded in constructing for myself so excellent an instrument that objects seen by means of it appeared nearly one thousand times larger and over thirty times closer than when regarded without natural vision.

It would be superfluous to enumerate the number and importance of the advantages of such an instrument at sea as well as on land. But forsaking terrestrial observations, I turned to celestial ones, and first I saw the moon from as near at hand as if it were scarcely two terrestrial radii. After that I observed often with wondering delight both the planets and the fixed stars, and since I saw these latter to be very crowded, I began to seek (and eventually found) a method by which I might measure their distances apart… .

Now let us review the observations made during the past two months, once more inviting the attention of all who are eager for true philosophy to the first steps of such important contemplations. Let us speak first of that surface of the moon which faces us. For greater clarity I distinguish two parts of this surface, a lighter and a darker; the lighter part seems to surround and to pervade the whole hemisphere, while the darker part discolors the moon’s surface like a kind of cloud, and makes it appear covered with spots… . From observation of these spots repeated many times I have been led to the opinion and conviction that the surface of the moon is not smooth, uniform, and precisely spherical as a great number of philosophers believe it (and the other heavenly bodies) to be, but is uneven, rough, and full of cavities and prominences, being not unlike the face of the earth, relieved by chains of mountains and deep valleys.

What was the significance of Galileo’s invention? What impressions did he receive of the moon? Why were his visual discoveries so stunning, and how did he go about publicizing them?

* * *

Galileo, however, never really accepted his condemnation. In 1632, he published his most famous work, Dialogue on the Two Chief World Systems: Ptolemaic and Copernican. Unlike most scholarly treatises, it was written in Italian rather than Latin, making it more widely available to the public, which no doubt alarmed the church authorities. The work took the form of a dialogue among Simplicio, a congenial but somewhat stupid supporter of Aristotle and Ptolemy; Sagredo, an open-minded layman; and Salviati, a proponent of Copernicus’s ideas. There is no question who wins the argument, and the Dialogue was quickly perceived as a defense of the Copernican system. Galileo was dragged once more before the Inquisition in 1633, found guilty of teaching the condemned Copernican system, and forced to recant his errors. Placed under house arrest on his estate near Florence, he spent the remaining eight years of his life studying mechanics, a field in which he made significant contributions.

GALILEO AND THE PROBLEM OF MOTION One of the problems that fell under the heading of mechanics was the principle of motion. The Aristotelian conception, which dominated the late medieval world, held that an object remained at rest unless a force was applied against it. If a force was constantly exerted, then the object moved at a constant rate, but if it was removed, then the object stopped. This conception encountered some difficulties, especially with a projectile thrown