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Updated: May 8, 2025
Ptolemaic astronomy, as an explanation of planetary movements, proved its exhaustion by a liberal recourse to epicycles as the answer to all awkward objections; and philosophies show themselves moribund in an analogous way, by a monotonous pressing of some one hackneyed principle to a degree that makes common-sense revolt and fling the whole theory to the winds chaff and grain indiscriminately.
The centres of the epicycles of Mars, Jupiter, and Saturn were supposed to be further away than the sun. Mercury and Venus were supposed to revolve in their epicycles in their own periodic times and in the deferent round the earth in a year. The major planets were supposed to revolve in the deferent round the earth in their own periodic times, and in their epicycles once in a year.
Those who want an example of the general scheme of epicycles taken from the history of art need only look at the School of Sculpture which flourished in the last century under Bernini, and especially at its further cultivation in France. This school represented commonplace nature instead of antique beauty, and the manners of a French minuet instead of antique simplicity and grace.
The theories of eccentrics and epicycles accomplished the end of explaining all the known phenomena. The resolution of the apparent motions of the heavenly bodies into an assemblage of circular motions was a great triumph of genius, and was equivalent to the most recent and improved processes by which modern astronomers deal with such motions."
A system of eccentrics and epicycles has been elaborated which serves to explain the apparent motions of the heavenly bodies in a manner that may be called scientific even though it is based, as we now know, upon a false hypothesis.
The first morning at sea revealed the mystery of the little round tin box. The process of shaving, never a delightful one, is a very unpleasant and awkward piece of business when the floor on which one stands, the glass in which he looks, and he himself are all describing those complex curves which make cycles and epicycles seem like simplicity itself.
To illustrate this: imagine the progress of knowledge among mankind in the form of a planet's course. The false paths the human race soon follows after any important progress has been made represent the epicycles in the Ptolemaic system; after passing through any one of them the planet is just where it was before it entered it.
In this he had attempted to reconcile the movements of that planet to the hypothesis of eccentrics and epicycles, but eventually discovered that the orbit of a planet is not a circle but an ellipse, the sun being in one of the foci, and that the areas swept over by a line drawn from the planet to the sun are proportional to the times.
His determination of the motions of the sun and moon, and his method of predicting eclipses evince great mathematical genius. But he combined with this determination a theory of epicycles and eccentrics which modern astronomy discards. It was however a great thing to conceive of the earth as a solid sphere, and to reduce the phenomena of the heavenly bodies to uniform motions in circular orbits.
"As the real motions, both of the earth and the planets, are unequable, it was requisite to have some mode of representing their inequalities; and accordingly the ancient theory of excentrics and epicycles was retained so far as was requisite for this purpose."
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