96 



Mr. David Gill 



[May 23, 



though less perfect, means at results like those of Henderson ; but 

 his results had been proved to be fallacious, though the causes of 

 their being so still remain somewhat inexplicable. In the case of 

 Struve's observations the weight of evidence which he produced and 

 the excellence of his method were admitted, but men were not pre- 

 pared by experience for accepting as accurate the minute changes of 

 angle which Struve had to measure ; nor was the proof afforded by 

 his series of observations so entirely convincing as that afforded by the 

 series of Bessel. Therefore, to Bessel the well-earned medal was given, 

 but the labours of Struve and Henderson received high and honour- 

 able mention. I quote from the speech of Sir John Herschel in award- 

 ing that medal. He says of Henderson's researches on a Centauri : — 



" Should a different eye, and a different circle continue to give the 

 same result, we must of course acquiesce in the conclusion ; and the 

 distinct and entire merit of the first discovery of the parallax of a 

 fixed star will rest indisputably with Mr. Henderson. At present, 

 however, we should not be justified in anticipating a decision which 

 time alone can stamp with the seal of absolute authority." 



So much for Sir John Herschel's ofiicially expressed opinion. I 

 can state now, and as Henderson's successor I do so with pride and 

 pleasure, that a different eye (that of his able and sympathetic 

 successor, Sir Thomas Maclear) fully confirmed Henderson's result 

 with another circle ; and further, that Henderson's result has been 

 still further confirmed by additional researches of which I shall 

 presently speak. 



I must now pass over briefly the history of succeeding researches, 

 and indeed it has been so admirably and so recently told within 

 these walls by Dr. Ball, that it is quite unnecessary I should enter 

 upon it in detail. The most reliable values arrived at for the 

 parallaxes of the stars of the northern hemisphere are given in the 

 following table, and to these results I shall afterwards refer : — 



Table I. — Parallaxes of Stabs which have been determined in the 

 Northern Heavens with considerable Accuracy. 



61 Cygni .. .. 

 Lalande 21185.. 

 a Tauri 



34 Groombridge 

 Lalande 21258.. 

 O. Mg. 17415 .. 

 <r Draconis 

 a Lyrso 

 jp Ophiuehi 

 o Bootis .. 

 Grooiiibrid^e 1830 

 Bradley 3077 .. 

 85 Pfxasi . . . . 



Magnitude. Proper Motion. ParaUax 



6 



n 

 I 



8 



8^ 



9 



5| 



1 



1 

 7 

 G 

 G 



