34 s Dr. Herschel’s Account of the Changes that have happened 
No. 2. Motion of cc. When x and O are at rest, and a has a 
motion, either towards P, N, F, or S, then the effect of it, 
whatever may be the angle P a O, will be had by entering the 
following Table, with the direction of the given motion. 
Motion. 
Distance. 
Angle. 
Quadrants. 
«P 
+ 
+ 
1st and 4th 
2 3 
ccY 
+ 
+ 
to M 
1 ! 
OO 
«N 
+ 
+ 
1 2 
3 4 
aS 
+ 
+ 
1 2 
3 4 
No. 3. Motion of O. 1st case. When a and x are at rest, and 
the angle P a O is 30 degrees, a proper motion of O, towards 
either />,/, n , or s , which will be extremely small when com- 
pared with the distance of O from can have no effect on the 
apparent distance, or angle of position, of the two stars ; and 
therefore no other motion, composed of the directions we have 
mentioned, will induce a change in the comparative situation of 
cc and x. 
2d case. When the plane PNFS is oblique to the ray cc O, 
and the angle P «0 more than 90 degrees, the effect of the 
motion of O will be had by the following Table. 
