Meanwhile Hobbes had his thoughts too full of the political theory which the events of the last years had ripened within him to settle, even in Paris, to the orderly composition of his works. Though connected in his own mind with his view of human nature and of nature generally, the political theory, as he always declared, could stand by itself. Also, while he may have hoped at this time to be able to add much (though he never did) to the sketch of his doctrine of Man contained in the unpublished "little treatise," he might extend, but could hardly otherwise modify, the sketch he had there given of his carefully articulated theory of Body Politic. Possibly, indeed, before that sketch was written early in 1640, he may, under pressure of the political excitement, have advanced no small way in the actual composition of the treatise _De Cive_, the third section of his projected system. In any case, it was upon this section, before the others, that he set to work in Paris; and before the end of 1641 the book, as we know from the date of the dedication (November 1), was finished. Though it was forthwith printed in the course of the year 1642, he was content to circulate a limited number of copies privately[5]; and when he found his work received with applause (it was praised even by Descartes), he seems to have taken this recognition of his philosophical achievement as an additional reason for deferring publication till the earlier works of the system were completed. Accordingly, for the next three or four years, he remained steadily at work, and nothing appeared from him in public except a short treatise on optics (_Tractatus opticus, L.W._ v. 217-248) included in the collection of scientific tracts published by Mersenne under the title _Cogitata physico-mathematica_ in 1644, and a highly compressed statement of his psychological application of the doctrine of motion (_L.W._ v. 309-318), incorporated with Mersenne's _Ballistica_, published in the same year. Thus or otherwise he had become sufficiently known by 1645 to be chosen as a referee, with Descartes, Roberval and others, in the famous controversy between John Pell (q.v.) and the Dane Longomontanus (q.v.) over that problem of the squaring of the circle which was seen later on to have such a fatal charm for himself. But though about this time he had got ready all or most of the materials for his fundamental work on Body, not even now was he able to make way with its composition, and when he returned to it after a number of years, he returned a different man. Leviathan.