jaa ESSAYS AND OBSERVATIONS 



the planet round the fun to the time the 

 planet moves from A to K : the problem 

 therefore is reduced to this, To draw the 

 line SG meeting the femicircle in G, fo that 

 the femicircle may be to the fedor ASG as 

 half the periodic time of the planet round 

 the fun to the given time. In the femicircle, 

 take the arc AB, fo that the arc ABP may be 

 to the arc AB as half the periodic time of the 

 planet round the fun to the given time. Join 

 CB ; the femicircle therefore will be to the 

 fedtor ACB as half the periodic time of the 

 planet round the fun to the given time, that 

 is, as the femicircle to the fedor ASG ; there- 

 fore the fedtors ACB, ASG, are equal ; join 

 CG. 



The angle ACB is called by Kepler the 

 mean anomaly, the angle ACG the anomaly 

 of the excentric, and the angle ASK the co- 

 equate or true anomaly. The problem there- 

 fore is reduced to this : The mean anomaly 

 of a planet being given, to find the anomaly 

 of the excentric and the coequate anomaly. 



PROP. 



