COMMENTÄTIO ASTRONOMICi. 



197 



si quae differant, hypothesm eHam corrfgeiites, ut circulus nutationis ellipsi locum cedat 

 Ast haec m.nuta Iheoriae Iradit decernenda. Adjun?!! taj.ellas tres novae hy.ioll.es'i 

 adaptatas: nidical usum , quem e datis suis Iheona possLt duoere ad teUuris ß<ruram 

 delermmandam : exhibet etiam medias declinationum diiTerenfias inier nomiulla sleÜaTum 

 paria, adscensione opposita , et prope coluros sita , unde praecessionis valor medius et 

 obhquitatis echpticae , si qua fuerit, dimiimtio , inyeniatur. 



« The forementioned poinfs indee<l can be settled onJy on the supposilion, that the 

 . aiigular distanees of these stars do continue always the satne, or that (hoy have no 

 « real motion m themselres ; but are at rest in absolute space : a supposition. whioh 

 « hough usuariy made by astronomers. neverlheless seems to be founded on too uncer- 

 « tarn pnnc,ples. to be admitled in all cases. For if a judgment may be for^ed . wi.h 

 . regard to lim matter, from the result of the comparison of our best modern observa- 

 « lions, w.th sucl. as were formerly made with any talerable degrce of exaclness; ihere 

 « appears to have been a real change in the posilion of some of the &ed stars wiih 

 « respect to each olher; and such, as seems independent of any motion in our owii sy 

 « Stern and can only be referred to some motion in the stars themselves. Arctu^L 

 « afiFords a strong proof of this : for if ils present declination be compared wilh ils place 

 « as delermined either by Tycho or Flamsteed; the difference will be fonnd to be' 

 « mach greater. thaa what caa be suspected to. arise from the uncertainty of their oh. 

 ♦ servations. "^ "^ • 



«It is reasonable to expect . that other inslances of the lite kind must also occur 

 . among the great number of the visible stars: because their relative positions may be- 

 «alerd by vanons means. For if our own solar System be eonceived to chani i„ 

 « place, wah respect to absolute Space ; this might. in process of time , occasioh an 

 « apparen change m the ang.ular distanees of the fixed. .Jars; and in such a case . the 

 « places of the nearest Stars being more affecled, thnn of Ihose that nre very remole • 

 <c their re at,ve positions might seem to aller, tho' the slars themselves were really iml 

 « moveable And oa the other band, if cur own System be at res., and any of the 

 « Slars really m motion, this might litewise vary their apparent positions; and the more' 

 « so, the nearer they are to us, or the swifler their molions are, or the more proper 

 « he d.recl.on of the motion is, to be rendered perceplible by us. Since Ihen the re- 

 « at.ve places o the slars may be changed ftom such a variety of causes, considerin.^ 

 «that ama.,ns distance at which it is cerfain some of thcm are placed , it may reqt,ire 

 « the observat.ons ofmany ages, to determine the laws of the apparent changes, eyen 

 « of a smgle slar : much more difBcult- therefbre must it be, to setlle the laws relati... 

 « to all the raost remarkable stars. "^ reiau.ig: 



« Whentlxe cause,, whkh affejt the places of ,11 th. sta.. in general are Known 



^^^ ■ «.uch 



