1 52 Royal Astronomical Society. 



numerical resultb is here, therefore, still distant." Let us hope that 

 he ■will not long leave them so. 



On the other subject to which I alluded — the parallax of the 

 fixed stars— it -would be. doing an injustice to the valuable report of 

 Mr. Main, which, as a beautiful specimen of astronomical history, 

 I hope to see ere long adorning our Transactions, if I were to avail 

 myself more largely of it on this occasion than is absolutely neces- 

 sary. It has long been understood by astronomers, that the research 

 of parallax ought not to be confined to the largest stars, but that, 

 in order to determine our choice of stars for this research, other 

 prUnd facie grounds for suspecting a proximity to our system ought 

 to be taken into consideration ; such as great proper motion, or, in 

 the case of a double star, gi-eat ajjparent dimensions of the orbits 

 described about each other. In the case of the double star 61 

 Cygni, both these indications combine to point it out as deserving 

 inquiry. In that of a Centauri they also conspire ; for it is well 

 knoAvn that this fine double star has a considerable proper motion ; 

 and my own observations prove, that the mutual orbit described by 

 its individuals about each other, is of unusually large angular di- 

 mension. The great brilliancy of the star also, and itssituation in 

 a region of the heavens in which the stars, generally speaking, 

 seem to be less remote than in others, all favour the expectation of 

 a measurable parallax being detected in it : and such Mr. Hender- 

 son, from his own observations, assigns to it. I am not about to 

 criticise this result ; on the contrary, I am disposed to attribute 

 much weight to his conclusion ; but it is only on a very long series 

 of observations of absolute places, affected as they are by instru- 

 mental error and uncertainty of refraction, that any conclusion of 

 this kind can rest Avith security. 



Bessel has attacked the question in a different way, by measuring 

 at all times of the year the angular distance of the stars composing 

 the double star 61 Cygni from two small stars visible in the same 

 field of view, and within limits adapted to secure micrometrical 

 measurement. The method is unexceptionable, the measurements 

 conducted with consummate skill, and their reduction executed 

 Avith all possible regard to every thing likely to influence the result. 

 And that result is, to assign a minute, it is true, but perfectly une- 

 quivocal amount of parallax, in a way so striking as hardly to allow 

 a doubt of its reality. Such is the impression on merely reading 

 the numerical statement; but, put in the light in which Mr. Main 

 has placed it, by the graphical projection of the measures, the con- 

 clusion seems quite irresistible : 



" Segnius irritant animos demissa per aures, 

 Quam qua; sunt oculis subjecta fidelibus, atqiie 

 Ipse sibi tradit spectator." 



It may now be reasonably asked. If all this be so, why have your 

 Council hesitated to mark this grand discovery with that distinct 

 stamp of their conviction and applause, which the award of their 

 annual medal would confer ? A problem of this difficulty and im- 

 portance solved, so long the cynosure of every astronomer's wishes 

 —the ultimate test of every observer's accuracy — the great land- 



