MOTION OF THE SUN. 0'7 



** tf the principle of determining the direflion of the folat- 

 ttiotion by the ftars which have the greateft proper motion, be 

 admitted", obferves the author, '* the following apex muft Apex on this laft 

 be extremely near the truth ; for, an alteration of a few mi- '^PP"""<>"* 

 mites in right afcenfion or polar diftance either vVaj, will im- 

 mediately increafe the required real motions of our ftars. Its 

 place is, right afcenfion 245° 52' SQ'\ and ilorth polar diftance 

 40° 22"'. The calculation is delineated iti Fig. 4. The furrt 

 of the leaft quantities of real motion in this experiment is 

 0.95595", lefs than the former by 0.5034.3". 



In thefe calculations the author has proceeded upon the 

 principle of obtaining the leaft poflible quantity of real motion 

 to afcertain the moft favourable fituation for a folar apex, and 

 lias proved that the fum of the obferved proper motions of the 

 fix principal ftars may be the refult of a compofition of two 

 Other motions; and that if the real motions were reduced to 

 their fmalleft poflible quantities, they vvould not exceed 0.9559. 



The Do6tor, however, feems to think that thefe real motions If the neareft 

 may not be brought down to the low quantities mentioned ; and feited^b^'^Lf" 

 proceeds to (hew that this circumftance will not affe6l the ar- lax, their pro- 

 guments he has ufedfor eftablinjing the method he has adopted; P^^ Tf^°."* 

 for, although the great proper motions of Arcturus, Procyoni more evident. 

 and Sirius, are ftrong indications of their being aff'edled by 

 parallax, it is not probable that the apparent changes of 

 their fitualions fliould be entirely owing to folar motion ; but 

 that their own real motions would have a great Ihare in 

 them; and it is evident that in paralladic motions the diftance 

 of a ftar from the fun is of material confequence ; and as this 

 cannot be afTumed at pleafure, we are not at liberty to make 

 the paralla£lic motion sp, Fig. I, equal to the lines7;i; hence 

 it follows that the real motion of the ftar cannot be from m to a, 

 but will be from p to a. If, however, //* a be a minimum, pa 

 when sp is given, will alfo be a minimum, and if all ihe ma's 

 in Fig. 4 be minima, the sp's will give the p c's as fmall as 

 poflible; which is the point defired to be eftabliflied. 



In concluding Dr. H. obferves, that as it is known that Conclufion. 



proper motions do exift, and as no folar motion can refolve Y^^ "J^C^ '*"^* 

 * ' , . . tioQor tne apex. 



them entirely into paralla6lic ones, we ought to prefer that di-. 

 reflion of the motion of the fun which will take away moft 

 real motion, and this, as has been fliewn, will be done when 

 the right afcenfion of the Apex is 215** 52' 30'', and its north 

 polar didance 40^^ 22'. 



F 2 AVw 



