on the presentation of a Medal. 141 



element to what, after what has been said, we must now call the 

 great and conspicuous amount of a full second. Mr. Main, to whom 

 I am so largely indebted for allowing me to draw so freely on his 

 labours, has also discussed these results, and comes to the conclu- 

 sion that (as might, perhaps, be expected) the right-ascension obser- 

 vations afford a trace, but an equivocal one, of parallax, but that in 

 declination (I use his words) " The law of parallax is followed 

 remarkably well. There is scarcely an exception to the proper 

 change of sign, according to the change of sign of the coefficients 

 of parallax. This is quite as much as can reasonably be expected in 

 a series of individual results obtained from any meridional instru- 

 ment for observing zenith distances. We cannot expect to find the 

 periodical function regularly exhibited by the differences. On the 

 whole, therefore, we should say that, in addition to the claims of 

 a Centauri on our attention with relation to its parallax, arising 

 from its forming a binary system, its great proper motion, and its 

 brightness, — it derives now much additional importance, in this 

 point of view, from the investigation of Mr. Henderson. This we 

 are at least entitled to assume until some distinct reason, indepen- 

 dent of parallax, shall have been assigned for the changes in the 

 declinations. Such I do not consider impossible, having before my 

 eyes the results which Dr. Brinkley derived, in the cases of certain 

 stars, from the Dublin circle. For the present it must be considered 

 that the star well deserves a rigorous examination by all the methods 

 which the author himself has so well pointed out ; and that, in the 

 event of a parallax at all comparable with that assigned by Mr. Hen- 

 derson being found, he will deserve the merit of its first discovery, 

 and the warmest thanks of astronomers, as an extender of the know- 

 ledge which we possess of our connexion with the sidereal system." 



With this view of Mr. Henderson's labours I fully agree, and 

 await with highly excited interest the result of Mr. Maclear's larger 

 and complete series of observations on this star both with the old 

 circle and with that more perfect one with which the munificence of 

 government has recently supplied the Observatory. Should a differ- 

 ent 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 



