hich may be regarded
as an early essay in advertising. He was fully convinced that his works
were valuable and quite worth the sums of money he asked for them; the
world was blind, perhaps wilfully, to their merits, therefore he now
determined that it should no longer be able to quote ignorance of the
author as an excuse for not buying the book. This appendix was a
notification to the learned men of Europe that the writer of the _Practice
of Arithmetic_ had in his press at home thirty-four other works in MS.
which they might read with profit, and that of these only two had been
printed, to wit the _De Malo Medendi Usu_ and a tract on _Simples_. This
advertisement had something of the character of a legal document, for it
invoked the authority of the Emperor to protect the copyright of Cardan's
books within the Duchy of Milan for ten years, and to prevent the
introduction of them from abroad.

The Arithmetic proved far superior to any other treatise extant, and
everywhere won the approval of the learned. It was from Nuremberg that its
appearance brought the most valuable fruits. Andreas Osiander,[85] a
learned humanist and a convert to Lutheranism, and Johannes Petreius, an
eminent printer, were evidently impressed by the terms of Cardan's
advertisement, for they wrote to him and offered in combination to edit
and print any of the books awaiting publication in his study at Milan. The
result of this offer was the reprinting of _De Malo Medendi_, and
subsequently of the tract on Judicial Astrology, and of the treatise _De
Consolatione_; the _Book of the Great Art_, the treatises _De Sapientia_
and _De Immortalitate Animorum_ were published in the first instance by
these same patrons from the Nuremberg press.

But Cardan, while he was hard at work on his Arithmetic, had not forgotten
a certain report which had caused no slight stir in the world of
Mathematics some three years before the issue of his book on Arithmetic,
an episode which may be most fittingly told in his own words. "At this
time[86] it happened that there came to Milan a certain Brescian named
Giovanni Colla, a man of tall stature, and very thin, pale, swarthy, and
hollow-eyed. He was of gentle manners, slow in gait, sparing of his words,
full of talent, and skilled in mathematics. His business was to bring word
to me that there had been recently discovered two new rules in Algebra for
the solution of problems dealing with cubes and numbers. I asked him who