Three centuries before Jesus Christ, Aristarchus of Samos is said by Aristotle to have composed a special work to defend the motion of the earth against the contrary opinions of philosophers. In this work, which is now lost, he laid down in the most positive manner that "the sun remains immovable, and that the Earth moves round it in a circular curve, of which that star is the centre." It would be impossible to state this in clearer terms; and what makes his meaning more clear, if possible, is that he was persecuted for it, being accused of irreligion and of troubling the repose of Vesta--"because," says Plutarch, "in order to explain the phenomena, he taught that the heavens were immovable, and that the earth accomplished a motion of translation in an oblique line, at the same time that it turned round its own axis." This is exactly the opinion that Copernicus took up, after an interval of eighteen centuries--and he too was accused of irreligion. In passing from the Greeks to the Romans, and from them to the middle ages, the doctrine of Aristarchus underwent a curious modification, assimilating it to the system of Tycho Brahe, which we shall hereafter consider, rather than to that of Copernicus. This consisted in making the planets move round the sun, while the sun itself revolved round the earth, and carried them with him, and the heavens revolved round all. Vitruvius and Macrobius both taught this doctrine. Although Cicero and Seneca, with Aristotle and the Stoics, taught the immobility of the earth in the centre of the universe, the question seemed undecided, to Seneca at least, who writes:--"It would be well to examine whether it is the universe that turns about the immovable earth, or the earth that moves, while the universe remains at rest. Indeed some men have taught that the earth is carried along, unknown to ourselves, that it is not the motion of the heavens that produces the rising and setting of the stars, but that it is we who rise and set relatively to them. It is a matter worthy of contemplation, to know in what state we are--whether we are assigned an immovable or rapidly-moving home--whether God makes all things revolve round us, or we round them."