t a velocity of 340 meters (1,115
feet) per second. If our atmosphere reached to the Sun, the noise of an
explosion sufficiently formidable to be heard here would only reach us
at the end of 13 years, 9 months. But the more rapid carriers, such as
the telegraph, would leap across to the orb of day in 8 minutes, 17
seconds.

Our imagination is confounded before this gulf of 93,000,000 miles,
across which we see our dazzling Sun, whose burning rays fly rapidly
through space in order to reach us.

* * * * *

And now let us see how the distances of the planets were determined.

We will leave aside the method of which we have been speaking; that now
to be employed is quite different, but equally precise in its results.

It is obvious that the revolution of a planet round the Sun will be
longer in proportion as the distance is greater, and the orbit that has
to be traveled vaster. This is simple. But the most curious thing is
that there is a geometric proportion in the relations between the
duration of the revolutions of the planets and their distances. This
proportion was discovered by Kepler, after thirty years of research,
and embodied in the following formula:

"The squares of the times of revolution of the planets round the Sun
(the periodic times) are proportional to the cubes of their mean
distances from the Sun."

This is enough to alarm the boldest reader. And yet, if we unravel this
somewhat incomprehensible phrase, we are struck with its simplicity.

What is a square? We all know this much; it is taught to children of ten
years old. But lest it has slipped your memory: a square is simply a
number multiplied by itself.

Thus: 2 x 2 = 4; 4 is the square of 2.

Four times 4 is 16; 16 is the square of 4.

And so on, indefinitely.

Now, what is a cube? It is no more difficult. It is a number multiplied
twice by itself.

For instance: 2 multiplied by 2 and again by 2 equals 8. So 8 is the
cube of 2. 3 x 3 x 3 = 27; 27 is the cube of 3, and so on.

Now let us take an example that will show the simplicity and precision
of the formula enunciated above. Let us choose a planet, no matter
which. Say, Jupiter, the giant of the worlds. He is the Lord of our
planetary group. This colossal star is five times (precisely, 5.2) as
far from us as the Sun.

Multiply this number twice by itself 5.2 x 5.2 x 5.2 = 140.

On the other hand, the revolution of Jupiter takes almost twelve year