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 324 KANT. the measure of vis viva is equal, as the Cartesians thought, to the product of the mass into the velocity, or, according to the Leibnitzians, to the product of the mass into the square of the velocity. Kant's unsatisfactory solution of the problem — the law of Descartes holds for dead, and that of Leibnitz for living forces — drew upon him the derision of Lessing, who said that he had endeavored to estimate living forces without having tested his own. A similar tendency toward compromise — this time it is a synthesis of Leibnitz and Newton — is seen in his Habilitationsschrifty Principioruni Priniorum Cognitionis Metaphysics Nova Dilu- cidatio, 1755, and in the dissertation Monadologia Physica^ 1756. The former distinguishes between ratio essendi and ratio cognoscendi, rejects the ontological argument, and de- fends determinism against Crusius on Leibnitzian grounds. In the Physical Monadology Kant gives his adherence to dynamism (matter the product of attraction and repulsion), and makes the monads or elements of body fill space with- out prejudice to their simplicity. A series of treatises is devoted to subjects in natural science: The Effect of the Tides in retarding the Earth's Rotation ; The Obsolescence of the Earth ; Fire (Inaugural Dissertation), Earthquakes, and the Theory of the Winds. The most important of these, the General Natural History aiid Theory of the Heavens, 1755, which for a long time remained unnoticed, and which was dedicated to Frederick II., developed the hypothesis (carried out forty years later by Laplace in igno- rance of Kant's work) of the mechanical origin of the uni- verse and of the motion of the planets. It presupposes merely the two forces of matter, attraction and repulsion, and its primitive chaotic condition, a world-mist with ele- ments of different density. It is noticeable that Kant acknowledges the failure of the mechanical theory at two points : it is brought to a halt at the origin of the organic world and at the origin of matter. The mechanical cosmogony is far from denying creation ; on the contrary, the proof that this well-ordered and purposive world neces- sarily arose from the regular action of material forces under law and without divine intervention, can only serve to support our assumption of a Supreme Intelligence as the I