The earth is not in the centre of the Sun's orbit nor at the centre of the universe, but in the centre of its companion elements, and united with them. And any one standing on the moon, when it and the sun are both beneath us, would see this our earth and the element of water upon it just as we see the moon, and the earth would light it as it lights us. The fundamental laws of the solar system (859-864). 859. Force arises from dearth or abundance; it is the child of physical motion, and the grand-child of spiritual motion, and the mother and origin of gravity. Gravity is limited to the elements of water and earth; but this force is unlimited, and by it infinite worlds might be moved if instruments could be made by which the force could be generated. Force, with physical motion, and gravity, with resistance are the four external powers on which all actions of mortals depend. Force has its origin in spiritual motion; and this motion, flowing through the limbs of sentient animals, enlarges their muscles. Being enlarged by this current the muscles are shrunk in length and contract the tendons which are connected with them, and this is the cause of the force of the limbs in man. The quality and quantity of the force of a man are able to give birth to other forces, which will be proportionally greater as the motions produced by them last longer. [Footnote: Only part of this passage belongs, strictly speaking, to this section. The principle laid down in the second paragraph is more directly connected with the notes given in the preceding section on Physiology.] 860. Why does not the weight _o_ remain in its place? It does not remain because it has no resistance. Where will it move to? It will move towards the centre [of gravity]. And why by no other line? Because a weight which has no support falls by the shortest road to the lowest point which is the centre of the world. And why does the weight know how to find it by so short a line? Because it is not independant and does not move about in various directions. [Footnote: This text and the sketch belonging to it, are reproduced on Pl. CXXI.] 861. Let the earth turn on which side it may the surface of the waters will never move from its spherical form, but will always remain equidistant from the centre of the globe. Granting that the earth might be removed from the centre of the globe, what would happen to the water? It would remain in a sphere round that centre equally thick, but the sphere would have a smaller diameter than when it enclosed the earth. [Footnote: Compare No. 896, lines 48-64; and No. 936.] 862. Supposing the earth at our antipodes which supports the ocean were to rise and stand uncovered, far out of the sea, but remaining almost level, by what means afterwards, in the course of time, would mountains and vallies be formed? And the rocks with their various strata? 863.