COMMENTATIO ASTRONOMIGÄ. 205 



cundum methodos, quas esposuerit Bouguer, Traue d'Optique, Paris 1760: sed ma- 

 Yult rudiori modo ratiocinari e comparatione inter Salurnum Jovemque el solem institula. 



« Upon Ihe supposilion theu , Ihat Ihe fixed stars are of Ihe same magnitude and 

 « brighlness wilh the sun , it is no wonder, that Iheir parallax should have hithertu 

 (1 escaped Observation, since, if this is the case, it could hardly amount to two se- 

 « conds , and probably not more than one in äjvms himself ; though he had been placed 

 u in the pole of the ecliplic , and in those , that appear much less luminous, such for 

 « example as y Draconis , which is only of the thiid magnitude, it could hardly be 

 « expecled to be sensible with such instrumeuts as have hitherto been used in search 

 «of it." 



Sentit autem , quam precaria sit hypothesis aequalis splendoris nativi in sole et steilis. 

 Kihilominus iixarum splendorem nativum haud ita diversum affirmat esse quam videri. 

 Jam pergit hinc ducere sequelas de parallaxi. 



« As far as wo can guess at the parallai of the fixed stars from the principles above 

 « laid down , we may reasonably expect , that it should be exceedingly small even in 

 « those of the first magnitude; yet besides the probabilily, that some of them may be 

 « either less, or less luminous than the sun, it is not so small as to leave us aitogelher 

 « vrithout hopes, that we may sometime or olher be able to discpver it in some of 

 « them ; for I think it is not impracticable to conslruct instruments , capable of di- 

 « stinguishing even to the 20"' pari of a second , provided the air will admit of that 

 « degree of exaclness; but such instruments must be upon a plan a good deal difTerent 

 « from those hitherto made use of, as they would otherwise be not only vaslly too ex- 

 « pensiye , bul also much too great and unweildy to be of any use. " 



Qua de re accuratius si Mitchelius sentenliam explicasset , multo magis scientiae 

 profuisset hac descriptione quam ista hyjiothesium farragine. Jam vero conqueritur esi- 

 guitatem diametrorum fixarum , ne occultatione Veneris quidem mensuranda. Ergo 

 donec parallaxis et quanlitas luminis transmissi reperla sit, soIi aequiparandae erunt. 

 Interea commendat astronomis accuratam lucis stellarum cum solis luce comparalionem , 

 juxta quam reformari vult stellarum in classis distributarum calalogos. — Et jam proprias 

 observationes commemorat, Quales autem ? Rudia scilicet experimenta ; comparatione« 

 luminis Sirii cum lumine stellarum sextae maguitudinis ; unde concludit , his paraUaxin 

 2'" aut 3'" convenire. 



« I have hitherto argued about the distances of the fked stars , upon the supposition 

 « of their being of the same size and brighlness with the sun; and if this was really 

 « so, thoze which appear the brighlesl must be the nearest to us. That this is in gene- 

 tt ral the case , 1 suppose , will be Tery readily allowed ; for though it is true , that a 

 fc much greater degree of real magnilude may compensate for the grealness of distance , 



Cc 3 and 



