74 Royal Astronomical Society. 



schel, " It is only on a very long series of observations of absolute 

 places, affected, as they are, by instrumental error and uncertainty 

 of refraction, that any conclusion of this kind can rest with secu- 

 rity." But whatever the ultimate decision of astronomers may be 

 with respect to the parallax in question, there will be but one opi- 

 nion as to the merit of Mr. Henderson's investigations, and the in- 

 terest which attaches to the subject : and, in the meantime, it will 

 be remembered that this is the first determination of the parallax of 

 a star which has been confirmed by a different observer using a dif- 

 ferent instrument ; and that if future observations shall continue to 

 give similar results, which now seems a reasonable anticipation, to 

 Mr. Henderson will indisputably belong the enviable distinction of 

 having been the first who succeeded in an inquiry so often, but 

 fruitlessly, attempted by astronomers, namely, the discovery of a 

 fixed star whose distance from our system is capable of measurement 

 and expression. For these researches he was proposed to the Council 

 at the meeting in November last, as deserving the Society's gold 

 medal for the present year, but his untimely death prevented the 

 question from being entertained. 



Another attempt made by him to determine the annual parallax 

 was less successful. Sirius, the brightest star in the heavens, might 

 be supposed to be one of the least remote ; and some astronomers — 

 Cassini, Lacaille, and Piazzi — had assigned it a parallax of several 

 seconds. The Cape observations being well adapted for the inves- 

 tigation of the question, Mr. Henderson undertook the examination 

 of those made by himself, and also a series by Mr. Maclear, in order 

 to ascertain if they indicated any sensible parallax ; but in this case 

 the result amounted only to about a quarter of a second, — a quan- 

 tity not exceeding, perhaps, the probable error of the determination. 



Mr. Henderson's labours on the subject of parallax did not termi- 

 nate even here. In a letter to Mr. Main, which was read at the 

 December meeting of 1842, he gave the results of an investigation 

 of the parallaxes, as they appear from his Cape observations, of 

 twenty stars which had been observed sufficiently often to reduce 

 the errors of observation within reasonable limits. They comprehend 

 the greater number of the stars situated in the same region of the 

 heavens as a Centauri, which have been indicated by Sir John Her- 

 schel as deserving of investigation for parallax, and which, on that 

 account, are at present objects of particular attention at the Cape 

 Observatory. In a few instances considerable parallaxes appear ; in 

 the greater number of cases the results are so small as to afford little 

 hope of a measurable parallax being found, and in some they are 

 negative. The mean of the twenty parallaxes is +0""29, a result 

 which, on the whole, may be considered as affording encouragement 

 to continue the research. 



It is matter of much regret that the reduction of the entire series 

 of Mr. Henderson's Cape observations — the rich store from which 

 the above interesting results have been extracted — has not been 

 completed by him ; and that the observations must consequently be 

 deprived of the advantage of liis final revision. From the examina- 



