other work, in 1618, entitled 'Epitome
of the Copernican Astronomy,' in which he gave a general account of his
astronomical observations and discoveries, and a summary of his opinions
with regard to the theories which in those days were the subject of
controversial discussion. Almost immediately after its publication it
was included by the Congregation of the Index, at Rome, in the list of
prohibited books. This occasioned Kepler considerable alarm, as he
imagined it might interfere with the sale of his works, or give rise to
difficulties in the issue of others. He, however, was assured by his
friend Remus that the action of the Papal authorities need cause him no
anxiety.

The Emperor Matthias died in 1619, and was succeeded by Ferdinand III.,
who not only retained Kepler in his office, but gave orders that all the
arrears of his salary should be paid, including those which accumulated
during the reign of Rudolph; he also expressed a desire that the
'Rudolphine Tables' should be published without delay and at his cost.
But other obstacles intervened, for at this time Germany was involved in
a civil and religious war, which interfered with all peaceful
vocations. Kepler's library at Linz was sealed up by order of the
Jesuits, and the city was for a time besieged by troops. This state of
public affairs necessitated a considerable delay in the publication of
the 'Tables.'

The 'Rudolphine Tables' were published at Ulm in 1627. They were
commenced by Tycho Brahe, and completed by Kepler, who made his
calculations from Tycho's observations, and based them upon his own
great discovery of the ellipticity of the orbits of the planets. They
are divided into four parts. The first and third parts contain
logarithmic and other tables for the purpose of facilitating
astronomical calculations; in the second are tables of the Sun, Moon,
and planets; and in the fourth are indicated the positions of one
thousand stars as determined by Tycho. Kepler made a special journey to
Prague in order to present the 'Tables' to the Emperor, and afterwards
the Grand Duke of Tuscany sent him a gold chain as an acknowledgment of
his appreciation of the completion of this great work.

Albert Wallenstein, Duke of Friedland, an accomplished scholar and a man
fond of scientific pursuits, made Kepler a most liberal offer if he
would take up his residence in his dominions. After duly considering
this proposal, Kepler decided to accept the Duke's offer,