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N.B.— The epoch for the elements in the following tables is, unless otherwise stated, the beginning of the present century.

THE SOLAR SYSTEM.

LAWS OF MOTION.

1. body continues in a state of rest or uniform rectilineal motion, unless affected by some mechanical force.

2. Every change of motion is proportionate to the force impressed, and is made in the direction of that force.

3. Action must always be equal and contrary to reaction, or the actions of two bodies on each other are always equal and directed to contrary sides.

KEPLER'S LAWS.

1. The orbit of each planet is an ellipse, of which the sun occupies one of the foci.

2. The areas described about the sun by the radius vector of the planet are proportional to the times employed in describing them.

3. The squares of the times of the sidereal revolutions of the planets are to each other as the cubes of their mean distances from the sun.

LAW OF GRAVITATION.

Any two bodies attract each other with a force proportional directly to the quantity of matter they contain, and inversely to the square of their distances.