140 



Sir J. Herschell's address 



a compact and consistent body of evidence drawn from two distinct 

 systems of measures mutually supporting each other, and so steadily 

 bearing on their object as to leave no more reasonable doubt of its 

 truth than in the case of many things which we look upon as, 

 humanly speaking, certain. And this conviction once obtained, reacts 

 on our belief in the other results, and induces us to receive and admit 

 it on the evidence adduced for it ; which, without such conviction so 

 obtained, we might hesitate to do until after longer corroboration 

 of the same kind. 



The other series of observations to which I must now call your 

 attention are those of Mr. Henderson, made at the Cape of Good 

 Hope, on the great star a Centauri, the third star in brightness 

 which the heavens offer to our view. It is a magnificent double 

 star consisting of two individuals, the one of a high and somewhat 

 brownish orange, the other of a fine yellow colour, and each of 

 which I consider fairly entitled to be classed in the first magnitude.* 

 Their distance is at present about 15" asunder, but it is rapidly 

 diminishing, and in no great lapse of time they will probably occult 

 one another, their angular motion being comparatively small. Their 

 apparent distance was formerly much greater : how much we cannot 

 say for want of observations, but probably the major axis of their 

 mutual orbit is little short of a minute of space. They, therefore, 

 afford strong indications of being very near our system. Add to 

 which their proper motion is very considerable, and participated in 

 by both, which proves their connexion as a binary system ; and an 

 additional presumption in favour of their proximity may be drawn 

 from their situation in what, from general aspect, I gather to be the 

 nearest region of the milky way, among an immensity of large stars. 



Mr. Henderson observed these stars with great care both in right 

 ascension and declination with the very fine transit, and (in spite of 

 certain grievous defects in the axis) the otherwise really good and 

 finely divided mural circle of the Royal Observatory in that colonv. 

 Since his return to England, he has reduced these observations with 

 a view to parallax, and the result is the apparent existence of that 



* I have seen both their images projected on a screen of three thicknesses of 

 stout paper, the eye being on the opposite side of (he screen from that on which 

 the images were depicted 



