Spirits, which the world has always talked of, and to which mankind appropriated, for a long period, a body so attenuated and shadowy, that it could scarcely be called body; but from which, at length, they have removed every shadow of body, without knowing what it was that was left. The manner in which these spirits perceive, without any embarrassment, from the five senses; in which they think, without a head; and in which they communicate their thoughts, without words and signs. Finally, God, whom we know by His works, but whom our pride impels us to define; God, whose power we feel to be immense; God, between whom and ourselves exists the abyss of infinity, and yet whose nature we dare to attempt to fathom. These are the objects of metaphysics. We might further add to these the principles of pure mathematics, points without extension, lines without width, superficies without thickness, units infinitely divisible, etc. Bayle himself considered these objects as those which were denominated "_entia rationis,_" beings of reason; they are, however, in fact, only material things considered in their masses, their superficies, their simple lengths and breadths, and the extremities of these simple lengths and breadths. All measures are precise and demonstrated. Metaphysics has nothing to do with geometry. Thus a man may be a metaphysician without being a geometrician. Metaphysics is more entertaining; it constitutes often the romance of the mind. In geometry, on the contrary, we must calculate and measure; this is a perpetual trouble, and most minds had rather dream pleasantly than fatigue themselves with hard work. MIND (LIMITS OF THE HUMAN). Newton was one day asked why he stepped forward when he was so inclined; and from what cause his arm and his hand obeyed his will? He honestly replied, that he knew nothing about the matter. But at least, said they to him, you who are so well acquainted with the gravitation of planets, will tell us why they turn one way sooner than another? Newton still avowed his ignorance. Those who teach that the ocean was salted for fear it should corrupt, and that the tides were created to conduct our ships into port, were a little ashamed when told that the Mediterranean has ports and no tide. Muschembrock himself has fallen into this error. Who has ever been able to determine precisely how a billet of wood is changed into red-hot charcoal, and by what mechanism lime is heated by cold water? The first motion of the heart in animals--is that accounted for? Has it been exactly discovered how the business of generation is arranged? Has any one divined the cause of sensation, ideas, and memory? We know no more of the essence of matter than the children who touch its superficies.