BOOK II. XX. 84-xxi. 86 



moon), between Mars and Jupiter half a tone, 

 between Jupiter and Saturn half a tone, between 

 Saturn and the zodiac a tone and a half : the seven 

 tones thus producing the so-called diapason," i.e. 

 a universal harmony ; in this Saturn moves in the 

 Dorian mode, Jupiter in the Phrygian, and similarly 

 with the other planets — a refinement more entertain- 

 incp than convincino^. 



XXI. A stade is equivalent to 125 Roman paces,* Heirihtofi 

 that is 625 feet. Posidonius holds that mists and 

 winds and clouds reach to a height of not less than 

 5 miles from the earth, but that from that point 

 the air is clear and liquid and perfectly himinous, but 

 that the distance between the cloudy air and the 

 moon is 250,000 miles and between the moon and 

 the sun 625,000 miles, it being due to this distance 

 that the sun's vast magnitude does not burn up the 

 earth. The majority of writers, however, have 

 stated that the clouds rise to a height of 111 miles. 

 These figures are really unascertained and impossible 

 to disentangle, but it is proper to put them forward 

 because they have been put forward already, although 

 they are matters in which the method of geometrical 

 inference, which never misleads, is the only method 

 that it is possible not to reject, were anybody 

 desirous of pursuing such questions more deeply, 

 and with the intention of establishing not precise 

 measurement (for to aspire to that would mark an 

 almost insane absorption in study) but merely a 

 conjectural calculation. For since it appears from 

 the sun's revolution that the circle through which Distanceoj 

 its orb travels extends nearly 366 degrees, and since amisk^" 

 the diameter of a circle always measures a little less 

 than ^ -^ 2~ of the circimiference, it appears that, as 



229 



