"proof" so confidently claimed being of the circular kind commonly known
as "begging the question". It was reserved for Newton to establish the
Laws of Motion, to find the law of force that would constrain a planet
to obey Kepler's first and second Laws, and to prove that it must
therefore also obey the third.






CHAPTER VI.

CLOSING YEARS.


Soon after its publication Kepler's "Epitome" was placed along with the
book of Copernicus, on the list of books prohibited by the Congregation
of the Index at Rome, and he feared that this might prevent the
publication or sale of his books in Austria also, but was told that
though Galileo's violence was getting him into trouble, there would be
no difficulty in obtaining permission for learned men to read any
prohibited books, and that he (Kepler) need fear nothing so long as he
remained quiet.

In his various works on Comets, he adhered to the opinion that they
travelled in straight lines with varying velocity. He suggested that
comets come from the remotest parts of ether, as whales and monsters
from the depth of the sea, and that perhaps they are something of the
nature of silkworms, and are wasted and consumed in spinning their own