First Journey (1619–1621), going through Bavaria, Austria, north to the shores of the Baltic and back to Holland. The greater part of these two years were spent in Bohemia, enrolled in the army of the Emperor. He was on this journey when his mental crisis occurred,—at Neuberg, in Austria, in 1619. It was then that he discovered either analytical geometry or the fundamental principle of his philosophy.
In Paris again, 1623.
Second Journey (1623–1625), to Switzerland and Italy, making a pilgrimage to the shrine of Loretto.
(3) As Writer (1629–1650).
In Holland (1629–1649). For the sake of absolute seclusion from inquisitive visitors, Descartes changed his residence in Holland twenty-four times and lived in thirteen places. All his correspondence passed through Mersenne. During these twenty years he made three journeys to France. Thus this period of absolute retirement became his period of literary production, chiefly between the years 1635 and 1644. He wrote his
Method (1635–1637).
Meditations (1629–1641).
Le Monde (1630–1632), published posthumously.
Principles (1641–1644).
Passions (1646–1649).