deferens, bearing down), in ancient astronomy, the mean orbit of a planet, which carried the epicycle in which the planet revolved.
epicycle theory the Earth is in the center of a circle which has smaller circles rotating round its circumference.
In astronomy, the term is used in connexion with the Ptolemaic theory to denote the angular distance on the epicycle of a planet from the true apogee of the epicycle; and the "equation to the argument" is the angle subtended at the earth by the distance of a planet from the centre of the epicycle.
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