242 THE GREEK ASTRONOMY. 



later. It is an inequality of the moon's motion, 

 in virtue of which she moves quickest when she 

 is at new or full, and slowest at the first and 

 third quarter ; in consequence of this, from the 

 first quarter to the full, she is behind her mean 

 place ; at the full, she does not differ from her 

 mean place ; from the full to the third quarter, 

 she is before her true place ; and so on ; and the 

 greatest eifect of the inequality is in the octants, 

 or points half-way between the four quarters. In 

 an Almagest of Aboul Wefa, a part of which exists 

 in the Royal Library at Paris, after describing the 

 two inequalities of the moon, he has a Section ix., 

 " Of the Third Anomaly of the Moon called Mu- 

 hazal or Prosneusis." He there says, that taking 

 cases when the moon was in apogee or perigee, 

 and when, consequently, the effect of the two first 

 inequalities vanishes, he found, by observation of 

 the moon, when she was nearly in trine and in 

 sextile with the sun, that she was a degree and 

 a quarter from her calculated place. " And hence," 

 he adds, "I perceived that this anomaly exists 

 independently of the two first : and this can only 

 take place by a declination of the diameter of 

 the epicycle with respect to the center of the 

 zodiac." 



We may remark that we have here this in- 

 equality of the moon made out in a really philoso- 

 phical manner; a residual quantity in the moon's 

 longitude being detected by observation, and the 



