Theory of the 

 motions of the 

 ftars. 



CAUS& or tHE CHAHOES OV RELATIVE 



them, O, », X. This admits of three cafes : a motion of one o? 

 the three bodies ; another, of two ; and a third, of all the three 

 bodies together. We (hall now point out the confequences that 

 will arife in each of the cafes. 



Single Motions. 



No. 1. Motion of x. When a and O are at reft, the motion 

 of j: may be alTumed, fo as perfedlly to explain any change of 

 the diftance of the two ftars, and of their angle of pofition. 



No. 2. Motion of a. When x and O are at reft, and a has a 

 motion, either to^wards P, N, F, or S, then the effed of it, 

 whatever may be the angle P a O, will be had by entering the 

 following Table, with the dire6tion of the given motion. 



No. 3. Motion of O. 1 ft cafe. When a. and x are at reft, and 

 the angle P a O is 90 degrees, a proper motion of O, towards 

 either j!7,/, w, or «, which will be extremely fmdll when com- 

 pared with the diftance of O from », can have no effed on tiie 

 apparent diftance, or angle of pofition, of the two ftars ; and 

 therefore no other motion, compofed of the diredions we have 

 mentioned, will induce a change in the comparative fituation of 

 a and X, 



2d cafe. When the plane P N F S is oblique to the ray « O, 

 and the angle P o^ O more tlian 90 degrees, the efl^eft of th^ 

 motion of O will be had by the following Table. 



Motion 



