56 BOOK III. 



Others, on the contrary, run from north to south. 



A, B, C — Vein. D, E, F — Seams in the Rocks. 



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 inchne toward the 

 westward as they descend into the earth, the vein is said to run from east 

 to west ; if they incUne 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 hnes called by the Greeks Sta^uTpoi, and in the Latin dimetientes, 

 are drawn through a central point which the Greeks call KtvTpov, 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 outer- 

 most 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 "; whUe within the innermost circle 

 it is hollowed out to contain a magnetic needle^. 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 



