To avoid society, in 1629, he migrated to Holland, where he passed twenty years. He removed from town to town, hiding his actual residence from all but one or two friends. He occupied himself at first with his optics, and with the considerations which led him, in a few years, to publish his ‘Treatise on Meteors,’ as also with chemistry and anatomy. We now find him in communication with Reneri and Gassendi. He made a short voyage to England, of which nothing is recorded, except some magnetic observations made near London. About 1633, his philosophical opinions were first taught by Reneri, at Deventer. His ‘Treatise on the World,’ written about this time, was suppressed by him when he heard what had happened to Galileo in Italy; and except some meteorological observations, we find nothing to notice till 1637, when he published his ‘Principles of Philosophy,’ in which the well-known hypothesis of vortices is propounded, together with his dioptrical and meteorological theories. This publication was immediately combated in different parts by Roberval, Fromondus, Plempius, Fermat, the elder Pascal, and others. Without going into these and other now uninteresting disputes, it is only necessary to state, that Fermat, Pascal, Roberval, and several others, were soon after in friendly communication with Des Cartes. After the famous problem of the Cycloid, which was propounded about this time (1638–39), Des Cartes, as he had several times done before, renounced geometry; and his work bearing that title (but which is, in fact, his celebrated application of algebra to geometry) was not published by himself, but by his friend De Beaune, who wrote a comment on it at his desire. In the meantime, his philosophy was fast rising into repute in Holland, where, in 1639, a public panegyric was made upon it at Utrecht, on the death of Reneri. We pass over the various disputes upon it, both at Utrecht and Paris. In 1640, Des Cartes was nearly induced to take up his residence in England, under the protection of Charles I.: but the domestic troubles, which within two years broke out into civil war, interfered with the completion of this arrangement. His father died at the end of the same year; in which he also lost a child named Francina, whom he owned as his daughter, but concerning whose parentage, whether it were legitimate or not, nothing certain is known. Des Cartes was attacked at this time by the Jesuits in France, and by a party in Holland, which asserted that he himself was a Jesuit. The hostility of his Dutch opponents did not materially retard the progress of his opinions, nor could the Jesuits prevent his receiving a flattering invitation from Louis XIII. to return to France.