ASTRONOMY. 97 



that of the ellipsis , and if a sector a FG' be taken 

 in the circle, equal to AFG in the ellipsis, the 

 angle AFG' is called the mean anomaly. 



This angle is proportional to the time, and in- 

 creases at the rate of 59' 8". 3 daily. 



c. The angle GFG', or the difference between the 

 mean and the true anomaly, is called the Equation 

 of the Sun's Centre. 



d. If the true sun G, and the imaginary sun G', set 

 out together from A and a 9 the sectors AFG and 

 a FG', increasing at the same rate, the angles 

 AFG, and#FG', must increase unequally, and the 

 point G' must get before G, or the mean anomaly 

 must exceed the true. But when FG becomes less 

 than FG', the angle AFG will come to increase 

 faster than a FG'. At the Perigee they will 

 coincide ; and at a certain point, between A and 

 P, their difference, or the equation of the centre, 

 will be the greatest possible. This will happen, 

 when the increments of the true and of the mean 

 anomaly are equal to one another, or when the 

 sun's real angular velocity is equal to his mean, or 

 to 59' 8".3. 



Among the great number of solutions which have 

 been given of this celebrate;! problem, one dis- 

 tinguished for the simplicity of the result, pro- 

 ceeds on the supposition, that the angles at the 

 superior focus are proportional to the time, or are 

 the same with the mean anomaly ; which is not 



VOL. II, G far 



