BOOK II. XIV. 72-74 , 



XIV. First therefore let us state the reason why OrhHs of 

 Venus never departs more than 46 degrees and ^Mer'^^, 

 Mercury never more than 23 degrees from the sun, 

 and why they often retire and return towards the sun 

 within those Umits. As situated below the sun both 

 have arcs that are the opposite of those of the other 

 planets, and as much of their circle is below the earth 

 as that of the planets mentioned before is above it ; 

 and they cannot be further from it than they are 

 because the curve of their arcs does not allow 

 greater elongation there ; consequently the edges 

 of their arcs put a hmit on a similar principle for 

 each, and compensate for the dimensions of their 

 longitude by the enlargement of their latitude. 

 But, it will be objected, why do they not reach 46 and 

 23 degrees always ? As a matter of fact they do, but 

 the explanation escapes the theorists. For it is 

 manifest that even their arcs alter, because they never 

 cross the sun ; accordingly when the edges have 

 fallen on one side or the other into the actual degree 

 of the sun, then the stars also are understood to have 

 reached their longest distances, but when the edges 

 are short of that, they themselves too are com- 

 pelled to return with proportionately greater 

 velocity, since with each of them that is always the 

 extreme limit. 



This also explains the contrary principle of their 

 motions. For the higher planets travel most quickly 

 in their evening setting, whereas these travel most 

 slowly, and the former are farthest from the earth 

 when their pace is slowest but the latter are highest 

 when their pace is quickest — the reason being that 

 with the latter the circumference of the circle 

 accelerates their pace in the same manner as 



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