By virtue of the causal hierarchy of forms, the loadstone acquires its magnetic powers from the earth.[153] As the earth has its natural parts, so has the stone.[154] Although the geometrical center of a terrella is the center of the magnetic forces,[155] objects do not tend to move to the center but to its poles,[156] where the magnetic energy is most conspicuous.[157] However, in a sense, the energy is everywhere equal: the virtue is spread throughout the entire mass of the loadstone,[158] and all the parts direct the forces to the poles.[159] The poles become the "thrones" of the magnetic powers.[160] On the other hand, the directive force is stronger where coition is weaker and accordingly, verticity is most prominent at the equator.[161] [153] M: pp. 184-186, 190, 232. This is not quite the same argument as that the powers of the loadstone are identical with those of the earth. See footnote 78. [154] M: pp. 125, 180. [155] M: p. 151. [156] M: pp. 121, 150. [157] M: pp. 115, 151, 165. [158] M: pp. 106, 118, 151, 191, 205, 221, 243. [159] M: pp. 116, 117, 119, 131, 183, 188, 221. [160] M: p. 31. [161] M: pp. 116, 151, 200. The strength of a loadstone depends upon its shape and mass. A bar magnet has greater powers than a spherical one because it tends to concentrate the magnetic powers more in the ends.[162] For a given purity and shape, the heavier the loadstone, the greater its strength.[163] A loadstone has a maximum degree of magnetic force that cannot be increased.[164] However, weaker ones can be strengthened by stronger ones.[165] Similarly, the shape and weight of the iron determine the magnetic force in coition.[166] [162] M: pp. 131, 132, 153-158. [163] M: pp. 141, 152, 153, 158, 161, 191, 222. [164] M: p. 146. [165] M: p. 165. [166] M: p. 153.