Galileo’s Telescope

Such a thing as Galileo made may now be bought at a toy-shop for I suppose half a crown, and yet what a potentiality lay in that “glazed optic tube,” as Milton called it.

Continuing Galileo’s Discoveries,
our selection from Pioneers of Science by Sir Oliver Lodge published in 1893. For works benefiting from the latest research see the “More information” section at the bottom of these pages. The selection is presented in six easy 5 minute installments.

Previously in Galileo’s Discoveries.

Time: 1586-1638
Place: Padua, Italy

The earth no longer the only world to which all else in the firmament were obsequious attendants, but a mere insignificant speck among the host of heaven! Man no longer the center and cynosure of creation, but, as it were, an insect crawling on the surface of this little speck! All this not set down in crabbed Latin in dry folios for a few learned monks, as in Copernicus’ time, but promulgated and argued in rich Italian, illustrated by analogy, by experiment, and with cultured wit; taught not to a few scholars here and there in musty libraries, but proclaimed in the vernacular to the whole populace with all the energy and enthusiasm of a recent convert and a master of language! Had a bombshell been exploded among the fossilized professors it had been less disturbing.

But there was worse in store for them. A Dutch optician, Hans Lippershey by name, of Middleburg, had in his shop a curious toy, rigged up, it is said, by an apprentice, and made out of a couple of spectacle lenses, whereby, if one looked through it, the weather-cock of a neighboring church spire was seen nearer and upside down. The tale goes that the Marquis Spinola, happening to call at the shop, was struck with the toy and bought it. He showed it to Prince Maurice of Nassau, who thought of using it for military reconnoitering. All this is trivial. What is important is that some faint and inaccurate echo of this news found its way to Padua and into the ears of Galileo.

The seed fell on good soil. All that night he sat up and pondered. He knew about lenses and magnifying-glasses. He had read Kepler’s theory of the eye, and had himself lectured on optics. Could he not hit on the device and make an instrument capable of bringing the heavenly bodies nearer? Who knew what marvels he might not so perceive! By morning he had some schemes ready to try, and one of them was successful. Singularly enough it was not the same plan as the Dutch optician’s: it was another mode of achieving the same end. He took an old small organ-pipe, jammed a suitably chosen spectacle glass into either end, one convex, the other concave, and, behold! he had the half of a wretchedly bad opera-glass capable of magnifying three times. It was better than the Dutchman’s, however: it did not invert.

Such a thing as Galileo made may now be bought at a toy-shop for I suppose half a crown, and yet what a potentiality lay in that “glazed optic tube,” as Milton called it. Away he went with it to Venice and showed it to the Seigniory, to their great astonishment. “Many noblemen and senators,” says Galileo, “though of advanced age, mounted to the top of one of the highest towers to watch the ships, which were visible through my glass two hours before they were seen entering the harbor, for it makes a thing fifty miles off as near and clear as if it were only five.” Among the people, too, the instrument excited the greatest astonishment and interest, so that he was nearly mobbed. The Senate hinted to him that a present of the instrument would not be unacceptable, so Galileo took the hint and made another for them. They immediately doubled his salary at Padua, making it one thousand florins, and confirmed him in the enjoyment of it for life.

He now eagerly began the construction of a larger and better instrument. Grinding the lenses with his own hands with consummate skill, he succeeded in making a telescope magnifying thirty times. Thus equipped he was ready to begin a survey of the heavens. The first object he carefully examined was naturally the moon. He found there everything at first sight very like the earth, mountains and valleys, craters and plains, rocks, and apparently seas. You may imagine the hostility excited among the Aristotelian philosophers, especially, no doubt, those he had left behind at Pisa, on the ground of his spoiling the pure, smooth, crystalline, celestial face of the moon as they had thought it, and making it harsh and rugged, and like so vile and ignoble a body as the earth.

He went further, however, into heterodoxy than this: he not only made the moon like the earth, but he made the earth shine like the moon. The visibility of “the old moon in the new moon’s arms” he explained by earth-shine. Leonardo had given the same explanation a century before. Now, one of the many stock arguments against Copernican theory of the earth being a planet like the rest was that the earth was dull and dark and did not shine. Galileo argued that it shone just as much as the moon does, and in fact rather more — especially if it be covered with clouds. One reason of the peculiar brilliancy of Venus is that she is a very cloudy planet.[29] Seen from the moon the earth would look exactly as the moon does to us, only a little brighter and sixteen times as big — four times the diameter.

Wherever Galileo turned his telescope new stars appeared. The Milky Way, which had so puzzled the ancients, was found to be composed of stars. Stars that appeared single to the eye were some of them found to be double; and at intervals were found hazy nebulous wisps, some of which seemed to be star clusters, while others seemed only a fleecy cloud.

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