If you will take the trouble to examine a mechanic grinding cutlery on a large stone that is smooth on the sides and has a quick motion, you may observe that if a certain portion of water be poured on the perpendicular side whilst the stone is turning, it does not settle or form itself into a body round the crank or axis; nor does the gravity of the earth draw it from the surface, but forms itself on the side of the stone into something resembling concentric circles, one within another. The surface of the earth, I apprehend, revolves with much greater velocity than any grindstone; and the substances composing the spheres are much firmer than water. Most of us, I presume, have seen persons for amusement, in displaying feats of dexterity, place a full glass of wine or water on a hoop, and whirl it round their heads without spilling one drop. The centrifugal force it acquires by the revolutions overcomes the power of gravity, although nothing appears to support it but the common atmosphere. Another experiment, producing a similar effect, might be made with a cup filled with fine sand. On the surface of the sand, describe a circle nearly in the centre; it will then be apparent, on observing the cup, that the sand within the circle, provided the particles attract one another as the planets do, is as much attracted towards one verge of the cup as the other; owing to its being equally surrounded by matter or sand, and therefore it can be but very little, if any, gravitated centrewise. Hence, being in a degree suspended, only a small horizontal rotary motion is required to whirl it towards the rim or sides of the cup into a circular form; and hence it follows, that those particles of sand lying equidistant from the inner side of the circle of sand thus formed, and the outer side would be in like manner balanced, or supported, by being equally gravitated in both directions. A disposition would thus be produced to form into concentric circles, and it would therefore follow, that successive similar dispositions to subdivision should occur, gradually lessening in force and quantity. This principle applied to the earth or other planets, would cause them to be formed into concentric spheres; and would throw the matter from the axis, as well at the poles, as at the centre, and thereby constitute open poles. Another simple experiment might also be made, to illustrate that a disposition to concentric spheres does exist in nature. On a piece of paper sift a small quantity of very fine magnetic particles, such as steel or iron filings, under which hold a loadstone; and you will observe that the attractive power of the magnet will cause the filings on the paper to arrange themselves into various concentric circles, nearly regular and equidistant from each other. From what cause should this take place, rather than that the filings should be accumulated into one mass?