The greatest, equally with the smallest motions of the Universe, are subjected to the rigid necessity of inevitable laws. These laws are the unknown causes of the known effects perceivable in the Universe. Their effects are the boundaries of our knowledge, their names the expressions of our ignorance. To suppose some existence beyond, or above them, is to invent a second and superfluous hypothesis to account for what has already been accounted for by the laws of motion and the properties of matter. I admit that the nature of these laws is incomprehensible, but the hypothesis of a Deity adds a gratuitous difficulty, which so far from alleviating those which it is adduced to explain, requires new hypotheses for the elucidation of its own inherent contradictions. The laws of attraction and repulsion, desire and aversion, suffice to account for every phenomenon of the moral and physical world. A precise knowledge of the properties of any object, is alone requisite to determine its manner of action. Let the mathematician be acquainted with the weight and volume of a cannon ball, together with the degree of velocity and inclination with which it is impelled, and he will accurately delineate the course it must describe, and determine the force with which it will strike an object at a given distance. Let the influencing motive, present to the mind of any person be given, and the knowledge of his consequent conduct will result. Let the bulk and velocity of a comet be discovered, and the astronomer, by the accurate estimation of the equal and contrary actions of the centripetal and centrifugal forces, will justly predict the period of its return. The anomalous motions of the heavenly bodies, their unequal velocities and frequent aberrations, are corrected by that gravitation by which they are caused. The illustrious Laplace has shewn that the approach of the Moon to the Earth, and the Earth to the Sun, is only a secular equation of a very long period, which has its maximum and minimum. The system of the Universe then is upheld solely by physical powers. The necessity of matter is the ruler of the world. It is vain philosophy which supposes more causes than are exactly adequate to explain the phenomena of things. _Hypotheses non fingo: quicquid enim ex phænomenis non deducitur, hypothesis vocanda est; et hypotheses vel metaphysicæ, vel physicæ, vel qualitatum occultarum, seu mechanicæ, in philosophiâ locum non habent._