The literary production of Leibnitz was enormous, consisting of some lengthy works, but mainly of correspondence (at one time with a thousand persons) and of dissertations to learned journals and societies. No one book contains his philosophy――the _Monadology_ coming the nearest to doing so. His most considerable work is his _Theodicy_. He himself published in book form only two works: his university dissertation on _Individuation_ and the _Theodicy_.[34] In spite of his many successes, the life of Leibnitz was not happy. From death or other causes his noble patrons changed, until he was left without a patron. His life went from bad to worse, and his death occurred almost unnoticed. The seventy years of Leibnitz’s life fall into four periods. That he passed through three of these periods by the time he was thirty shows the voracity and versatility of his mental powers during their formative and acquisitive state. It also reveals the unusual length of his productive period,――from his thirtieth to his seventieth year. Ten years after his productive period began, when he was forty, he had completed his philosophical theory, so that the last thirty years of his life were free for its elaboration and elucidation, and in part for his departure from it. The details of Leibnitz’s life are as follows:―― 1. _Leipsic and University Life_ (1646–1666). Leibnitz was the son of a professor of the University of Leipsic. He entered the University at the age of fifteen; received his bachelor’s degree at seventeen, and his doctor’s degree at Altdorf at the age of twenty. He was offered a professorship on account of his thesis, but he declined. He published as his bachelor’s thesis, _The Principle of Individuation_ (1663). 2. _Mainz and Diplomacy_ (1666–1672). Meeting Baron John of Boineburg, who became his patron, Leibnitz went with him to Mainz, and entered the service of the Elector of Mainz. At this time Leibnitz wrote many pamphlets at the Elector’s request, on the religious and political questions of the day. He wrote _A New Physical Hypothesis_ in 1671. 3. _Paris and Science_ (1672–1676). Leibnitz began this period with a diplomatic mission to the court of Louis XIV in 1672; but during the year both Boineburg and the Elector died, and Mainz was no longer his home nor diplomacy his interest. He remained in Paris (and London) three years longer, and spent the time in acquiring the “new science.” In Paris he met Arnauld the Cartesian, Tschirnhausen the German mathematician, logician, and most discriminating critic of Spinoza, and he studied with Huyghens the Dutch mathematician. In London he met Boyle, the chemist, Oldenburg, secretary of the Academy of Science, Collins, the mathematician, and he corresponded with Newton. On his return to Hanover he called on Spinoza, who showed him the manuscript of the _Ethics_. 4. _Hanover and Philosophy_ (1676–1716).