the star it was assumed that the solar system remained at rest. If, indeed, the solar system had a motion equal and parallel to that of the star, it would have been impossible to determine that of the latter, unless the motion of the solar system were itself known. It must, therefore, be borne in mind that the velocities with which we are at present concerned must be regarded as relative measurements conducted on the supposition that the solar system itself remained fixed.
If a star were displaced as much as a dozen times its original distance from the sun, it is obvious that a tremendous change in the apparent lustre of the star would be the consequence. If the body had moved directly away from the sun, the distance between the two objects would be increased in the proportion of thirteen to one. Had the star travelled in about the opposite direction, it would have passed comparatively near to the earth and its distance from the solar system, in the course of a million years, would be increased in the proportion of about eleven to one. On the other hand, if the star had moved in a direction perpendicular to the line from the star to the solar system, then the distance between the sun and the star would be rather more than twelve times as great as it was originally.
It is thus evident that whatever be the direction in which the star may happen to have moved, the distance between the solar system and the star will have increased during the lapse of a million years to nearly, if not quite, a dozen times as much as it was at the commencement of the same period. This leads to a remarkable conclusion with respect to the permanence of the visible heavens.
According to the laws of optics, the apparent lustre of
