ived to have the joy of discovering
it.

The connection is this, that if one compares the distance of the
different planets from the sun with the length of time they take to go
round him, the cube of the respective distances is proportional to the
square of the corresponding times. In other words, the ratio of r^3
to T^2 for every planet is the same. Or, again, the length of a
planet's year depends on the 3/2th power of its distance from the sun.
Or, once more, the speed of each planet in its orbit is as the inverse
square-root of its distance from the sun. The product of the distance
into the square of the speed is the same for each planet.

This (however stated) is called Kepler's third law. It welds the planets
together, and shows them to be one system. His rapture on detecting the
law was unbounded, and he breaks out into an exulting rhapsody:--

"What I prophesied two-and-twenty years ago, as soon as I discovered the
five solids among the heavenly orbits--what I firmly believed long
before I had seen Ptolemy's _Harmonies_--what I had promised my friends
in the title of this book, which I named before I was sure of my
discovery--what sixteen years ago, I urged as a thing to be sought--that
for which I joined Tycho Brahe, for which I settled in Prague, for which
I have devoted the best part of my life to astronomical contemplations,
at length I have brought to light, and recognized its truth beyond my
most sanguine expectations. It is not eighteen months since I got the
first glimpse of light, three months since the dawn, very few days since
the unveiled sun, most admirable to gaze upon, burst upon me. Nothing
holds me; I will indulge my sacred fury; I will triumph over mankind by
the honest confession that I have stolen the golden vases of the
Egyptians to build up a tabernacle for my God far away from the
confines of Egypt. If you forgive me, I rejoice; if you are angry, I can
bear it; the die is cast, the book is written, to be read either now or
by posterity, I care not which; it may well wait a century for a reader,
as God has waited six thousand years for an observer."

Soon after this great work his third book appeared: it was an epitome of
the Copernican theory, a clear and fairly popular exposition of it,
which had the honour of being at once suppressed and placed on the list
of books prohibited by the Church, side by side with the work of
Copernicus himself, _De Revolutionibus Orbium Coelestium_.

This