138 



Sir J. HerscheWs address 



rection for temperature would affect both their distances proportion- 

 ally, leaving the apparent parallactic movement still unaccounted for. 



The resulting parallax is an extremely minute quantity, only thirty- 

 one hundredths of a second ; which would place the star in question at 

 a distance from us of nearly 670,000 times that of the sun !* Such 

 is the universe in which we exist, and which we have at length found 

 the means to subject to measurement, at least in one of its members 

 probably nearer to us than the rest. 



It becomes necessary for me now to refer to two series of research- 

 es on this important subject, which have been held by your Council 

 to merit very high and honourable mention ; though neither of them, 

 separately, for reasons which I shall state, would have been consider- 

 ed as carrying that weight of probability in favour of its conclusions, 

 which would justify any immediate decision of the nature which they 

 have come to in the case of M. Bessel's. I allude to M. Struve's 

 inquiries, by the method of micrometric measures, into the parallax 

 of a Lyra : and to Mr. Henderson's, by that of meridian observati- 

 ons, on the parallax of a Centauri. 



a Lyra is accompanied by a very minute star, at the distance of 

 about 43". That this star is unconnected with a by any physical 

 relation, is clear from the fact ascertained by Sir James South and 

 myself, that it does not participate in the proper motion of the large 

 star. The mutual angular distance of these stars has been made 

 by M. Struve the subject of a very extensive series of micrometric 

 measures with the celebrated Dorpat achromatic, bearing this object 

 steadily in view, and working it out to a conclusion of the very same 

 kind, and, though materially inferior in the degree and nature of its 

 evidence to that of Bessel, yet certainly entitled to high considera- 

 tion. M. Struve's observations on this star, and for this purpose, 

 extend from Nov. 1835 to Aug. 1838, and are distributed over sixty 

 nights, averaging twenty per annum ; and from their combination, 

 according to the principle of probabilities, he concludes a parallax of 

 0"*261. Mr. Main has subjected these observations to an analysis 

 and graphical projection, precisely similar in principle to those 



* The orbit described by the two stars of 61 Cygni about each other will, there- 

 fore, be about 50 times the diameter of the earth's about the sun, or 2\ times that I 

 of Uranus. 



