THE DOCTRINE OF A ROUND EARTH 65 



known, even by tradition. Though the Phoenician traders 

 may have penetrated to the Baltic, there is little to suggest 

 that there were then dwellers or even voyagers within the Arctic 

 circle ; and lands no farther distant than Scythia were peopled 

 with the fantastic legends of the Hyperboreans, a race that 

 lived in perpetual happiness and everlasting youth. 



Bion's belief, we may conjecture, was rather one of those 

 splendid inductions which sometimes arise from a slender array 

 of facts. Travel in his day, as in ours, was the correct pro- 

 cedure of cultivated youths, and whether or no Bion had crossed 

 the seas to Egypt, we know that Democritus, his teacher, had. 

 And he who will journey no farther to the south than by the 

 breadth of the Mediterranean will note a curious change in the 

 position of the stars. The questioning eyes of the Sphinx meet 

 other constellations than those of our more northern climes ; 

 the pole-star lies lower upon the horizon. Furthermore, one 

 discovers that in the southerly regions the days and nights 

 are shorter, according as the sun has passed the summer or 

 winter solstice, than in the north. At the equator they vary 

 little throughout the year. It would be difficult to account 

 for all this if the earth were a plane. 



As the ships go out to sea, the earliest of observers must 

 have noted that they disappear piecemeal. Returning, the 

 lights of the harbour are visible from the mast-head some time 

 before they may be seen from the deck. Ascending a high 

 mountain the horizon steadily widens, and objects that from 

 the lower lands lie below it come into view. If the surface 

 of the sea and the land is curved, the earth must be a ball. 



Bion was a geometer, something of a physicist too, evidently ; 

 he understood in all its implications the geometry of light. 

 With him let us draw a circle to represent the earth, set the 

 sun at a distance, draw straight lines for its rays, and see what 

 will happen. With the sun at a certain height at noon its 

 rays will illuminate a certain area ; shift the angle and the area 

 shifts with it. 



Let us put it on paper. (See Fig. i.) 



When the sun at noon stands directly in the zenith, the 

 days and nights are of very nearly equal length twelve hours 

 day, twelve hours night. It follows therefore that, if the earth 

 is round, the sun at a given time illumines just half its surface. 

 If now the position of the sun at noon shifts, so that the days 







