as increased from 91,000,000 miles at the perihelion to 94,500,000.
This point of the orbit is known as its aphelion.

After rounding this point, the orbital velocity of the earth begins to
increase again, owing to the diminishing distance of the earth from the
sun, which according to the law of inverse squares (Art. 22) gives an
added intensity to the Centripetal Force.

Thus by the combination of the Laws of Motion and the Law of Gravitation
discovered by Newton, he was able to satisfactorily account for and
explain on a mathematical basis, the reason why the earth and all the
other planets move round the sun in elliptic orbits, according to
Kepler's First Law.

In the development of the physical cause of gravitation, therefore, the
same physical medium, which accounts for that law, must also give a
satisfactory explanation of the first of Kepler's Laws.

ART. 27. _Kepler's Second Law._--This law states that the Radius Vector
describes equal areas in equal times. The Radius Vector is the imaginary
straight line joining the centres of the sun and the earth or planet.
While the First Law shows us the kind of path which a planet takes in
revolving round the sun, the Second Law describes how the velocity of
the planet varies in different parts of its orbit.

If the earth's orbit were a circle, it can be readily seen that equal
areas would be traversed in equal times, as the distance from the sun
would always be the same, so that the Radius Vector being of uniform
length, the rate of motion would be uniform, and consequently equal
areas would be traversed in equal times. Take as an illustration the
earth, which describes its revolution round the sun in 365-1/4 days. Now
if the orbit of the earth were circular, then equal parts of the earth's
orbit would be traversed by the Radius Vector in equal times. So that
with a perfectly circular orbit, one half of the orbit would be
traversed by the Radius Vector in half a year, one quarter in one
quarter of a year, one-eighth in one-eighth of a year, and so on; the
area covered by the Radius Vector being always exactly proportionate to
the time.

From Kepler's First Law, however, we know that the planet's distance
does vary from the sun, and therefore the Radius Vector is sometimes
longer and sometimes shorter than when the earth is at its mean
distance; the Radius Vector being shortest at the perihelion of the
orbit, and longest at the aphelion. We learn from Kepler's Seco