and leisure for scientific work which he desired. Therefore he went to
Holland in 1629, and spent twenty years of quiet productivity in Amsterdam,
Franecker, Utrecht, Leeuwarden, Egmond, Harderwijk, Leyden, the palace of
Endegeest, and five other places. His work here was interrupted only by
a few journeys, but much disturbed in its later years by annoying
controversies with the theologian Gisbert Voëtius of Utrecht, with Regius,
a pupil who had deserted him, and with professors from Leyden. His
correspondence with his French friends was conducted through Père Mersenne.
In 1649 he yielded to pressing invitations from Queen Christina of Sweden
and removed to Stockholm. There his weak constitution was not adequate to
the severity of the climate, and death overtook him within a few months.

The two decades of retirement in the Netherlands were Descartes's
productive period. His motive in developing and writing out his thoughts
was, essentially, the desire not to disappoint the widely spread belief
that he was in possession of a philosophy more certain than the common one.
The work entitled _Le Monde_, begun in 1630 and almost completed, remained
unprinted, as the condemnation of Galileo (1632) frightened our philosopher
from publication; fragments of it only, and a brief summary, appeared
after the author's death. The chief works, the _Discourse on Method_, the
_Meditations on the First Philosophy_, and the _Principles of Philosophy_
appeared between 1637 and 1644,--the _Discours de la Méthode_ in 1637,
together with three dissertations (the "Dioptrics," the "Meteors," and the
"Geometry"), under the common title, _Essais Philosophiques_. To the (six)
_Meditationes de Prima Philosophia_, published in 1641, and dedicated to
the Paris Sorbonne, are appended the objections of various savants to whom
the work had been communicated in manuscript, together with Descartes's
rejoinders. He himself considered the criticisms of Arnauld, printed fourth
in order, as the most important. The Third Objections are from Hobbes, the
Fifth from Gassendi, the First, which were also the first received, from