The system of Copernicus presupposes the _fixity of the sun_, as a "conditio sine qua non." The most abstruse investigations into the "celestial mechanism" could not be made without this axiom be granted. The mathematician must have a fixed point, a fixed central point of action for his coordinates, he wants fixed invariable plains and closed curves, a radius vector describing plains, he wants axes and poles for the orbits, in order that they may describe certain figures in the heaven, and that the plains of the orbits may move,--one of the other. Naturally astronomers and men of science have never asked themselves the question, _how a heavenly body could be fixed in space_. When an astronomer asserts that the Copernician system is the only possible, he believes that it is impossible for the sun to have any motion of its own; when he at the same time asserts that all astronomy stands or falls with this system, he believes that no astronomical knowledge existed before the discovery of the Copernician system, and with the fall of the system all astronomical knowledge will cease to exist; he believes moreover true astronomy to be _that_, which men of science have imagined to be the truth regarding the heaven and the causes of the phenomena we see. If astronomers had merely presented their ideas and opinions to the world as such, and no more, no one could raise any objection; but they lay down their opinions in words and on paper as a _positive science_, they give their view as _incontroversible truths_, and _this fact_ alters the situation, for we cannot admit that science is a mere barge to be taken in tow by the imagination. The fundamental axiom of astronomical theory, such as the Copernician system, Kepler's and Newton's laws, _are not derived from a knowledge of fact_, they are the opinions, views, ideas and suppositions of individuals, which have been adapted to the heaven, and as they were generally accepted, the question was never raised whether the opinions of an organic creature--however intelligent it might be--are really and truly that which we term penetrating behind the veil of nature and compelling it to yield up its secrets. The fact of no other ideas being at hand which seemed to be better, sufficed to transform these opinions into rules and to cause them to be accepted as the only admissible and correct truths.