UclU. 



6. 





13. 



Feb. 



25. 



April 



14. 



1839 



Jan. 



17. 





22. 



Nov. 



26. 



on the Variability and Periodic Nature of a Ononis. 313 



1838. 



Rigel, Procyon, Achernar, Orion, Pollux, a Crucis. 

 Rigel, Procyon, Achernar, Orion, Aldebaran, a Crucis, 



Pollux. 

 Rigel, Procyon, Achernar, Orion, Aldebaran, a Crucis. 

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

 Procyon, Rigel, Orion, Aldebaran, Pollux, Regulus. 



Procyon, Aldebaran, Orion, Pollux, Regulus. 



Rigel, Procyon, Aldebaran, Orion, Pollux, Regulus. 



Orion, Rigel, Procyon, Aldebaran, Pollux. 

 On examining the above series, the general order of arrangement 

 (leaving out Orion) is found to be Rigel, Procyon, Achernar, Aide* 

 baron, a Crucis, Pollux, Regulus ; and the instances in which the 

 arrangement is different are accounted for by some peculiar circum- 

 stances connected with the observations. Thus, with respect to 

 the observation of October 24, 1837, the author states that the mis- 

 placement of Achernar is accountable for by the circumstance of the 

 two comparisons of Orion having been made (as appears by the 

 notices high and low) first when rising with Achernar then high, 

 and Rigel low ; and at a later period of the night with Rigel then 

 high, and, consequently, Achernar low. On January 2, 1838, 

 a Crucis is set down as inferior to Pollux ; but these two stars are 

 difficult of comparison, both from situation and difference in colour, 

 and from being, in fact, not very different in lustre. The trans- 

 position of Procyon and Rigel in the observation of the 14th of 

 April, 1838, is unaccountable, except from some unsuspected partial 

 haziness in that part of the sky. This observation was made at sea. 



With regard to Orion, the observations evidently show three 

 maxima, viz. in Nov. 1836, Oct. 1837, and Nov. 1839; and also 

 three minima, viz. those of March 1836, Jan. 1838, and Jan. 1839. 

 " Reasoning from this, the most obvious conclusion is that of an 

 annual, or nearly annual period. But in that case, we must admit 

 the decrease to be comparatively sudden, and the increase slow ; 

 whereas, if we admit of a period of about six months, this supposi- 

 tion will not be necessary, and as the star cannot be observed (for 

 this purpose) in the summer months, there is no primd facie reason 

 against adopting the latter period ; respecting which, however, 

 further observation will soon enlighten us." 



The observations subsequent to Nov. 26, 1839, confirmed the 

 expected decrease of the star in a very decided manner : — 



1839. Nov. 30. Rigel | Orion, Procyon || Aldebaran. 

 Dec. 11. Rigel | Orion | Procyon || Aldebaran. 



29. Rigel, Procyon, Orion, Aldebaran. 



1840. Jan. 2. Rigel || Procyon | Orion || Aldebaran. 



5. Rigel || Procyon | Orion || Aldebaran. 



6. Rigel || Procyon || Orion || Aldebaran. 



In a note to this last observation, it is stated that " the difference 

 between Orion and Aldebaran is evidently and rapidly on the de- 

 crease. The stars are all high, at nearly equal altitudes, and ad- 

 mirably arranged for comparison." 



