"As soon as his fevered imagination had cooled, he determined at once to produce his invention, and notes on the 23rd February (1620) he was thinking of finding a publisher; but presently he changed his intention; and this treatise... is by Baillet suspected to have been possibly the Olympica... Descartes had heard much of the Rosicrucians,—a hidden confraternity who were believed to have attained some mysterious key to natural knowledge apart from theology, and who were supposed to be spread all through society. A considerable literature of attack and of apology as regards this sect then occupied public interest. Baillet tells us all that was then known about them. In a MS. called Cartesii liber de studio bonœ mentis ad Musœum, Descartes confessed that he had done all he could to find out a member of the brotherhood and learn what he might of their magic secrets, but was completely and permanently unsuccessful. Nevertheless, he had talked so much about it at the time, that he found himself set down as a Rosicrucian, and had some difficulty in clearing himself of the imputation. But in the winter of 1619-20 he had not yet given up hopes of finding out this mystery, and the title of a book found among Leibnitz's transcripts gives us the clue to the lost treatise of this date. It was Polybii cosmopolitani Thesaurus mathematicus (I translate the sequel), 'in which are set forth the true means of solving all the difficulties of this science, and there is demonstrated that, as regards it, nothing further can be supplied by the human mind; with the intention of challenging the delay, and exposing the rashness of those who promise to show new marvels in all the sciences, as well as to relieve the torture (Iabores cruciabiles) of many, who, entangled in some of the s of this science, night and day spend uselessly the oil of their genius,—now offered to the learned of all the world, and especially celeberrimis in Germania Fratribus Roseœcrucis.' ... This interesting though confused title shows clearly what Descartes' inventum mirabile was... simply the solution of all geometrical problems by algebraical symbols. What agitated his mind so greatly was that the discovery would not cease there, but that by means of this new and improved calculus he could apply mathematical demonstration to all the realm of nature. ... But at this time he had only simplified his mathematics so as to make it a general method of investigation. It remained for him to likewise so simplify nature as to make it capable of submitting to his analysis. ...He ...soon turned aside to , to make trial of his new method of solving problems on Faulhaber and other mathematicians of distinction. The story of is repeated, mutatis mutandis, in the case of Faulhaber. He first despised, and then sarcastically challenged, the young inquirer, who on this occasion, however, showed considerable self-confidence, and not only solved the problems proposed, but showed general methods of doing so, and even of determining the solubility of various new problems, or the reverse. He also solved the problems proposed by Peter Roten [Roth] in reply to a challenge of Faulhaber in his algebra. These successes must have made Descartes feel assured of his inventum mirabile as far as mathematics went. But he presently suspended further study..."