PHYSICAL ann LITERARY. 133 
on) AP.in G, and jcin SG :. It-is evident, 
from the nature of the ellipfe and «circle, 
that the femicircle is to the fector ASG as 
the femi-ellipfe to the fector ASK ; there- 
fore the femicircle is to the fector ASG as 
half the periodic time of the planet round 
the fun to the time the’ planet moves from 
Ato 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 feCtor ASG as half the periodic 
time of the planet round the fun to the 
given time. Jn the femicircle, take the 
arc AB, {0 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 fector ACB as half the periodic 
time of the planet round the fun to the 
given time, that is, as the femicircle to 
the fector ASG; therefore the fedors 
ACB, ASG, are equal; join CG, 
Tue angle ACB is called by Kepler the 
mean anomaly, the angle ACG the ano- 
‘ maly of the excentric, and the angle ASK 
the c ppeasate or true anomaly. ‘The pro- 
. blem 
