MOTION OF THE St7T!», 0^. 



famfe apex as the former two, its apparent motion cannot be 

 pefolved by the eWe& of parallax alone ; and this difficulty is 

 further enhanced by th« number of apices required to folve all 

 proper motions into paralla6tic ones, InGreafing, not as the 

 number of ftars admitted to have proper motions, but, when 

 their fituation is favourable, as the fum of an arithmetical 

 leries of numbers, beginning at 0, continued to as many terms 

 as there are ftars admitted. 



The author here propofes an illuftration of his fubjefl by 

 confidering the three apices, or interfering points. No. 1, 

 2, 5, in the foregoing table. 



The diftance of Ar6lurus from the apex of the folar motion Namely Ar^u- 

 is found to be 47 » 7' &', and its paraliaaic motion, which is "■"* ^"'^ ^''''^s- 

 as the fine of that diftance 2.08718'', which is the apparent 

 motion of Ar(5turus, as eftablifbed by obfervation. 



Admitting Sirius to be a very large ftar, at the diftance of 



1.6809 from us, and computing its elongation from the apex 



of the /folar motion at ISS'=> 50' 14.5'', its parallafiic motion 



<p . S 

 will be = s p =. 1.11528", which aifo agrees with the 



apparent rnotion already afcertained by obfervation as the pro- 

 per motion of Sirius. 



The diftance of Capella from the apex of the folar motion is Hence the pa- 

 80*^54'' 4-6", and admitting the velocity of the fun towards 'al'^ftic motion 

 the betbre given point, it will occafinn a paralla6tic motion of Capelu is /e^' 

 <^apella, in a direction 89*' 54' 48" fouth-following its pa-diiceJ: 

 rallel, amounting to 2.8125'''. Capella is here taken for a 

 ftar of the firfl magnitude, fuppofmg its diftance from us to 

 ibe equal to that of Ar6turus. 



By conftru6ting a triangle, the fides of which reprefent the and by refolvin'g 

 iihr«e motions of every ftar, not at reft ; one of the fides, re- '*^'^ '"'^° theap- 

 ! ,- • , • •!. . . ^ .^^-// ^1 P«'ent motion 



Iprelentjng the apparent motion, will be equal to 0.463 r' ; the and another, 



other fide, being the paral!a6iic motion, 2.8125''; and the this hft will be 

 included angle IS'' 19' 27"', from which will be obtained the Jg^y^Qf}^"^^" 

 third fide, or the real motion of the ftar, 2.3757". By the (fuppofmg the 

 given fituation of this triangle with refpeCl to the parallel <if jfy^n'^^jj" J** 

 declinati6n of Capella, the angle of the real motion will be 

 had, which is SS" 34' 1 i" north-following the parallel of this 

 ftar. A "campoftttoTJ of the paralta^ic and r^l motions in 

 the directions, will produce the .annuaL apparent motion) as 



eftabliftied by obfervation^.^ _ ^^ ..^',., .......„/ 



It is here obferved, that although the proper motion of a 



third 



