And how do we know, answered the Marchioness, that we shall always remain where we are? I begin to tremble lest we should be foolish enough to approach such an enterprizing planet as Jupiter, or that he should come to us, for the sake of drawing us into his vortex; for I can't help thinking, from your description of the agitated state of this celestial fluid, that it must move the planets irregularly, sometimes urging them nearer together, sometimes sending them to a greater distance. We may as well expect to gain as to lose by such an eccentric motion, said I; perhaps we may make a conquest of Mercury or Mars, which are smaller planets, and incapable of resisting us. However we have no occasion for either hope or fear; the planets will remain in their places; and, like the former kings of China, they are forbidden to aim at conquest. You have observed that when oil is mixed with water, the oil swims at the top. Put any substance that is extremely light on both these, and the oil will support it, so that it shall not touch the water: but put a heavier body, of a certain weight, it will pass through the oil, which is too weak to stop it, and keep falling till it meets the water, which has sufficient force to bear it up. Thus two liquors put together, being of unequal weight, will not mix, but place themselves in different situations; and neither will one rise, nor the other descend: pour on these other liquors which are of a nature to remain separate, and the same effect is still produced. In like manner the celestial matter which fills this grand vortex, is in separate strata, encircling each other, and of unequal weight, like oil and water, and some other liquors. Some planets likewise are heavier than others,[39] each therefore stops in the layer which has the degree of force necessary for supporting it, and keeping it in a state of equilibrium; and you must be convinced that it can never go beyond this stratum. [Footnote 39: The Cartesians carried their illusion so far as to believe that so solid a mass as a planet could be steadily supported by the ætherial fluid, the most subtle of all fluids.] I understand, replied the Marchioness, that the different degrees of weight are sufficient to keep them in their proper ranks. I wish with all my heart there was some such regulating power among us, that would serve to fix people in the situation most suitable to them! You have quite removed my uneasiness with regard to Jupiter. I am very glad he will let us remain quietly with our little vortex, and single moon. I feel very well contented with one attendant, and do not envy him his four.