 In the wake of all these pioneers, Bernoulli produced much of the results contained in Ars Conjectandi between 1684 and 1689, which he recorded in his diary Meditationes. When he began the work in 1684 at the age of 30, while intrigued by combinatorial and probabilistic problems, Bernoulli had not yet read Pascal's work on the "arithmetic triangle" nor de Witt's work on the applications of probability theory: he had earlier requested a copy of the latter from his acquaintance Gottfried Leibniz, but Leibniz failed to provide it. The latter, however, did manage to provide Pascal's and Huygen's work, and thus it is largely upon these foundations that Ars Conjectandi is constructed. Apart from these works, Bernoulli certainly possessed or at least knew the contents from secondary sources of the La Logique ou l ’ Art de Penser as well as Graunt's Bills of Mortality, as he makes explicit reference to these two works.
