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Updated: June 5, 2025
The same result he could obtain by assuming that the sun moved round a small circle, whose centre described a larger circle about the earth; this larger circle carrying the other was called the "deferent": so that the actual motion of the sun was in an epicycle. Of the two methods of expression Hipparchus ultimately preferred the second.
Forthright moving is in the over part of the circle that is called Epicycle, backward is in the nether part, and stinting and abiding or hoving is in the middle. The sixth book of our author deals with the conditions of man, passing in review youth and age, male and female, serf and lord. Our extracts from it fall into three groups.
All these principles are violated in the theories of the epicycle and eccentric, especially the first. For the epicycle is a sphere which changes place in the circumference of the large sphere.
Reviewing the suggestions of the ancient Greeks, he was struck by the simplification that would be introduced by reviving the idea that the annual motion should be attributed to the earth itself instead of having a separate annual epicycle for each planet and for the sun.
And upon the back of this circle in the Heaven of Venus, of which I now speak, is a little sphere, which revolves by itself in this Heaven, the circle of which Astrologers call Epicycle; and as the great sphere revolves about two poles, so does this little sphere: and so has this little sphere the equatorial circle; and so much the more noble it is in proportion as it is nearer to those: and in the arc, or rather back, of this circle is fixed the most brilliant star of Venus.
So far as the materials were concerned and the mode of representing the planetary motions, no other radical advance was made by Copernicus. Indeed, it is remarkable that he introduced an epicycle which was not considered necessary by Ptolemy in order to represent the inequalities in the motions of the planets around the sun.
The great minds, however, which really bring the race further on its course, do not accompany it on the epicycles which it makes every time. This explains why posthumous fame is got at the expense of contemporary fame, and vice vers�. We have an instance of such an epicycle in the philosophy of Fichte and Schelling, crowned by Hegel's caricature of it.
On this system the apparent motion of each planet in the epicycle was represented by a motion of the earth around the sun, and the problem of correcting the position of the planet on account of the epicycle was reduced to finding its geocentric from its heliocentric position. This was the greatest step ever taken in theoretical astronomy, yet it was but a single step.
Is it that every reported breach of her assumed uniformities is incredible, because impossible, until the possibility has been proved by some fact which is then named, erected into a class, a cause, a law, and used to explain away similar facts formerly denied, and is thus taken into that bundle of generalizations called the "laws of nature"? The ancients assumed all heavenly motion to be circular of necessity, and where facts gave against them, they patched the matter up with an epicycle or two.
To correct for these irregularities Copernicus introduced epicycle on epicycle in the lunar orbit. This is in its main features the system propounded by Copernicus. But attention must, to state the case fully, be drawn to two points to be found in his first and sixth books respectively. The first point relates to the seasons, and it shows a strange ignorance of the laws of rotating bodies.
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