But this was no heliocentric system, since the sun moved, like the earth, in a circle around the central fire.

There is no evidence that this great astronomer supported his heliocentric theory with any geometrical proof, although Plutarch maintains that he demonstrated it.

He estimated the diameter of the sun at the seven hundred and twentieth part of the circumference of the circle which it describes in its diurnal revolution, which is not far from the truth; but in this treatise he does not allude to his heliocentric theory.

But even Ptolemy did not conceive the heliocentric theory,the sun the centre of our system.

The importance of this last discovery was of supreme value, for it confirmed the heliocentric theory.

His treatise, De Revolutionibus Orbium Caelestium, which was dedicated to Pope Paul III., appeared at Nuremberg in 1543, with a preface added to it by the preacher, Andreas Osiander, which calls the heliocentric system merely an hypothesis advanced as a basis for astronomical calculations.

The old geocentric system once shaken, the way was gradually smoothed for the heliocentric system, which Copernicus, still hampered by tradition, did not quite reach.

Heliocentric: Referred to the centre of the sun; e.g. the theory commonly called Copernican.

The error introduced by observing from some point other than that required in theory, e.g. in geocentric places because the observations are made from the surface of the earth instead of the centre, or in heliocentric places because observations are made from the earth and not from the sun.