Much about the same time, Dupuis formed his ingenious theory with respect to the origin of the Greek months. In the course of his investigations upon this subject, he composed a long memoir on the constellations, in which he endeavoured to account for the want of any resemblance between the groups of stars in the heavens and the names by which they are known, by supposing that the zodiac was, for the people who invented it, a sort of calendar at once astronomical and rural, and that the figures chosen for the constellations were such as would naturally suggest the agricultural operations of the season. It seemed only necessary, therefore, to discover the clime and the period in which the constellation of Capricorn must have arisen with the sun on the day of the summer solstice, and the vernal equinox must have occurred under Libra. It appeared to Dupuis that this clime was Upper Egypt, and that the perfect correspondence between the signs and their significations had existed in that country at a period of between fifteen and sixteen thousand years before the present time; that it had existed only there; and that this harmony had been disturbed by the effect of the precession of the equinoxes. He therefore ascribed the invention of the signs of the zodiac to the people who then inhabited Upper Egypt or Ethiopia. This was the basis on which Dupuis established his mythological system, and endeavoured to explain the subject of fabulous history, and the whole system of the theogony and theology of the ancients.

Persuaded of the importance of his discoveries, which, however, were by no means entirely original, Dupuis published several detached parts of his system in the Journal des Savants for the months of June, October, and December 1777, and of February 1781. These he afterwards collected and published, first in Lalande’s Astronomy, and then in a separate volume in 4to, 1781, under the title of Mémoire sur l’origine des Constellations et sur V Explication de la Fable par l' Astronomie. The theory propounded in this memoir was refuted by Bailly, in the fifth volume of his History of Astronomy, but, at the same time, with a just acknowledgment of the erudition and ingenuity exhibited by the author. Condorcet proposed Dupuis to Frederick the Great of Prussia as a fit person to succeed Thiébault in the professorship of literature at Berlin; and Dupuis had accepted the invitation, when the death of the king put an end to the engagement. The chair of humanity in the college of France having at the same time become vacant by the death of Bejot, it was conferred on Dupuis; and in 1788 he became a member of the Academy of Inscriptions. He now resigned his professorship at Lisieux, and was appointed by the administrators of the department of Paris one of the four commissioners of public instruction. At the commencement of the Revolutionary troubles Dupuis sought an asylum at Evreux; and, having been chosen a member of the National Convention by the department of Seine-et-Oise, he distinguished himself by the moderation of his speeches and public conduct. In the third year of the republic he was elected secretary to the Assembly, and in the fourth he was chosen a member of the Council of Five Hundred. After the memorable 18th Brumaire he was elected by the department of Seine-et-Oise a member of the legislative body, of which he became the president. He had been proposed as a candidate for the senate when he resolved to abandon politics, devoting himself during the rest of his life to his favourite studies. He died September 29, 1809.

In 1794 he published the work by which he is best known, entitled Origine de tous les Cultes, ou lα Religion Universelle (3 vols. 4t<.>, with an atlas, or 12 vols. 12mo.) Though its circulation was small, it became the subject of much bitter controversy, and the theory it propounded as to the origin of mythology in Upper Egypt led to the expedition organized by Napoleon for the exploration of that country. In 1798 Dupuis published an abridgment of his work in one volume 8vo, which met with no better success than the original. Another abridgment of the same work, executed upon a much more methodical plan, was published by Μ. de Tracy. The other works of Dupuis consist of two memoirs on the Γelasgi, inserted in the Memoirs of the Institute; a memoir “On the Zodiac of Tentyra,” published in the Revue Philosophique for May 1806; and a Mémoire Explicatif du Zodiaque Chronologique et Mythologique published the same year, in one volume 4to. Μ. Dacier, secretary to the third class of the Institute, delivered his éloge; and an historical account of his life and writings was published by his widow.