312 Eoyal Astronomical Society : Sir J. F. W. Herschel 



which far exceeded my idea at the moment of what was its natural 

 state. Proceeding to compare it with other stars of the first magni- 

 tude (Sinus being, of course, out of the question), their arrange- 

 ment for the night was found to be as follows : 



Capella |J a Orionis | Rigel || Procyon|Jj Aldebaran | Pollux. 



" In this and subsequent arrangements of the same sort, the 

 number of vertical strokes between the names indicates the estimated 

 amount of interval, or the grades or steps of magnitude by which 

 the stars differ. Thus, the step from Capella to a Orionis is a 

 great one ; that from a Orionis to Rigel, a distinct but moderate one ; 

 from Rigel to Procyon, a great one, admitting of the easy insertion 

 of a star decidedly inferior to one, and superior to the other, between 

 them ; from Procyon to Aldebaran, a very great step, admitting, at 

 least, two such insertions of imaginary stars decidedly diverse in 

 lustre between them ; and so on. Now as I distinctly recollected 

 having, on a great many occasions, placed a Orionis nearly on a par 

 with Aldebaran, there could be no doubt of a change. Referring 

 next morning to my father's Catalogues of Comparative Brightness, 

 I find that he makes the star in question slightly inferior, or at most 

 equal, to Procyon, and much greater than Aldebaran. 



" In consequence of this observation, I proceeded forthwith to 

 draw out in order all the comparisons of a Orionis with other stars 

 made at the Cape, on the voyage homewards, and since my return. 

 In so doing, I must confess I was hardly less surprised than at the 

 sight of the star itself to find in my star-lists, containing the results 

 of a partial reduction and arrangement of my Cape observations, 

 a Orionis not merely marked as variable, but distinct entries made 

 of it in that list at its maximum and minimum, the maximum 

 being stated as above Rigel, the minimum below Aldebaran. This, 

 however, had entirely escaped my memory, but being thus recalled, 

 and so forcibly corroborated, I resolved to watch the star more nar- 

 rowly in future ; the more especially as it seemed to follow, from 

 the tenour of the observations, that its diminution of brightness 

 was likely to be rapid : and so, in fact, it has proved to be." 



The author then proceeds to give the observations on which the 

 evidence of the former changes of the star is grounded. They extend 

 over the years 183G, 1837, 1838, and 1839, and are as follows (de- 

 noting, for brevity, a Orionis by the word Orion) : 



1836. 

 March 22. Rigel, Procyon, a Crucis, Orion, Regulus, Pollux. 



Nov. 12. \ 17 - | > Procyon, Achernar, a Crucis, Aldebaran, Pollux. 

 I lu gei, J 



13. Orion = Rigel. 



26. Rigel, Orion, Achernar. 

 1837. 



Oct. 24. Orion (high), Achernar, Orion (low), Rigel, Aldebaran. 



Dec. 16. Rigel, Achernar, Orion. 



29. Rigel, Acheruar, Procyon, Orion, Aldebaran. 



