In all calculations and observations relating to the Sun



SEC. XIII.] ON THE CONSTRUCTION OP TABLES. 127

and Moon, we have considered the Sun as a moving
body, and the earth as being at rest ; since all the appear-
ances are the same, whether it be the Sun, or earth that
moves. But the truth is that the Sun is at rest, and the
earth actually moves around him, once in every year, in
the plane of the ecliptic. Therefore, whatever sign and
degree of the ecliptic the earth is in at any given time,
the Sun will then appear to be in the opposite sign and
degree.
The nearer any body is to the Sun, the more it is
attracted by him, and this attraction increases, as the
square of their distances diminishes, and vice versa.
The earth's annual orbit is elliptical, and the Sun is
placed in one of its foci. The remotest point of the
earth's orbit is called the earth's aphelion, and the nearest
point of the earth's orbit to the Sun, is called the earth's
perihelion. When the earth is in its aphelion, the Sun
appears to be in its apogee ; and when the earth is in its
perihelion, the Sun appears to be in its perigee.
As the earth moves from its aphelion to its perihelion,
it is constantly more and more attracted by the Sun ;
and this attraction by conspiring in some degree with the
motion of the earth, must necessarily accelerate its
motion.
