ITS EARLIEST STAGES. 137 



circles ; among the rest, the equator, the tropics, and circles, at the 

 same distance from the poles a the tropics are from the equator. One 

 of the curious consequences of this division was the assumption that 

 there must be some marked difference in the stripes or zones into 

 which the earth's surface was thus divided. In going to the south, 

 Europeans found countries hotter and hotter, in going to the north, 

 colder and colder ; and it was supposed that the space between the 

 tropical circles must be uninhabitable from heat, and that within the 

 polar circles, again, uninhabitable from cold. This fancy was, as we 

 now know, entirely unfounded. But the principle of the globular 

 form of the earth, when dealt with by means of spherical geometry, 

 led to many true and important propositions concerning the lengths of 

 days and nights at different places. These propositions still form a 

 part of our Elementary Astronomy. 



Gnomonic. Another important result of the doctrine of the sphere 

 was Gnomonic or Dialling. Anaximenes is said by Pliny to have 

 first taught this art in Greece ; and both he and Anaximander are re- 

 ported to have erected the first dial at Lacedemon. Many of the 

 ancient dials remain to us ; some of these are of complex forms, and 

 must have required great ingenuity and considerable geometrical 

 knowledge in their construction. 



Measure of the Sun's Distance. The explanation of the phases of 

 the moon led to no result so remarkable as the attempt of Aristarchus 

 of Samos to obtain from this doctrine a measure of the Distance of 

 the Sun as compared with that of the Moon. If the moon was a 

 perfectly smooth sphere, when she was exactly midway between the 

 new and full in position (that is, a quadrant from the sun), she would 

 be somewhat more than a half moon ; and the place when she was 

 dichotomized, that is, was an exact semicircle, the bright part being 

 bounded by a straight line, would depend upon the sun's distance from 

 the earth. Aristarchus endeavored to fix the exact place of this 

 Dichotomy ; but the irregularity of the edge which bounds the bright 

 part of the moon, and the difficulty of measuring with accuracy, by 

 means then in use, either the precise time when the boundary was 

 most nearly a straight line, or the exact distance of the moon from the 

 sun at that time, rendered his conclusion false and valueless. He col- 

 lected that the sun is at 18 times the distance of the moon from us; 

 we now know that he is at 400 times the moon's distance. 



It would be easy to dwell longer on subjects of this kind ; but we 

 oave already perhaps entered too much in detail. We have been' 



