They tell us gravely that there is no effect without a cause; they repeat to us very often that the world did not create itself. But the universe is a cause, not an effect; it is not a work, has not been made, because it was impossible that it should be made. The world has always been, its existence is necessary. It is the cause of itself. Nature, whose essence is visibly acting and producing, in order to fulfill her functions, as we see she does, needs no invisible motor far more unknown than herself. Matter moves by its own energy, by the necessary result of its heterogeneity; the diversity of its movements or of its ways of acting, constitute only the diversity of substances; we distinguish one being from another but by the diversity of the impressions or movements which they communicate to our organs. XL.--CONTINUATION. You see that everything in nature is in a state of activity, and you pretend that nature of itself is dead and without energy! You believe that all this, acting of itself, has need of a motor! Well! who is this motor? It is a spirit, that is to say, an absolutely incomprehensible and contradictory being. Conclude then, I say to you, that matter acts of itself, and cease to reason about your spiritual motor, which has nothing that is necessary to put it into motion. Return from your useless excursions; come down from an imaginary into a real world; take hold of second causes; leave to theologians their "First Cause," of which nature has no need in order to produce all the effects which you see. XLI.--OTHER PROOFS THAT MOTION IS IN THE ESSENCE OF MATTER, AND THAT IT IS NOT NECESSARY TO SUPPOSE A SPIRITUAL MOTOR.