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the beginning of the 17th century, whether to cling to the oldideas of Ptolemy , which for at least fourteen centuries hadbeen almost unchallenged, or to accept the new doctrine thatthe Sun was the central ruler about which all the planetsrevolved. So violently was the ancient system maintained,that Copernicus was with difficulty persuaded to publish hisgreat work upon the “ Revolutions of the Celestial Orbs ” tenyears after it was completed, and only received the first printedcopy of it when on his death-bed ; while Galileo (see LectureV., p. 106) was forced in his old age to make a humiliatingrecantation of his belief in the movement of the Earth .
And yet there can be but little doubt that the beauty andsimplicity of the Copernican theory was such, that it must havebeen gradually commending itself to the minds of many, whowere, therefore, prepared to realize the important confirmationwhich it received from the orbital revolution of the Moons ofJupiter. We must no doubt allow, that a far more conclu-sive argument for its truth was really afforded by the view ofthe phases of Venus , which Galileo obtained in the Decemberof the same year in the beginning of which lie discovered theSatellites of Jupiter. But before the orbits of these Satellites were known, it cannot be denied that there appeared to bea certain symmetry of idea in supposing Sun, Moon , andplanets all to revolve around the Earth . Until then, the caseof the Moon would have seemed a solitary exception to ageneral rule, if it had been believed that all else circled roundthe Sun, while it alone revolved around the Earth . But eventhose who had not studied scientific matters deeply, could notbut feel that any such difficulty was removed, when Jupiter was found to have a subsidiary system of its own. And it wasa still further argument in favour of the theory of Copernicus ,that, the more complicated the general view of the Solar System thus became, the more beautifullv did that theory explain it.
It is amusing to find that there were amongst Galileo ’scontemporaries, to whom he announced his discovery, somewho denied the existence of the Satellites altogether. Someeven refused to look through his telescope, upon the plea thatit was an instrument of a Satanic nature. It is of such an