Others, on the contrary, run from north to south.
The seams in the rocks indicate to us whether a vein runs from the east or from the west. For instance, if the rock seams incline toward the westward as they descend into the earth, the vein is said to run from east to west; if they incline toward the east, the vein is said to run from west to east; in a similar manner, we determine from the rock seams whether the veins run north or south.
Now miners divide each quarter of the earth into six divisions; and by this method they apportion the earth into twenty-four directions, which they divide into two parts of twelve each. The instrument which indicates these directions is thus constructed. First a circle is made; then at equal intervals on one half portion of it right through to the other, twelve straight lines called by the Greeks διάμετροι , and in the Latin dimetientes, are drawn through a central point which the Greeks call κέιτρον, so that the circle is thus divided into twenty-four divisions, all being of an equal size. Then, within the circle are inscribed three other circles, the outermost of which has cross-lines dividing it into twenty-four equal parts; the space between it and the next circle contains two sets of twelve numbers, inscribed on the lines called "diameters"; while within the innermost circle it is hollowed out to contain a magnetic needle[1] . The needle lies directly
- ↑ The endeavour to discover the origin of the compass with the Chinese, Arabs, or other Orientals having now generally ceased, together with the idea that the knowledge of the lodestone involved any acquaintance with the compass, it is permissible to take a rational
