Colours of Stars. 437 



rison of Wega and Antares : while a more delicate and trained 

 vision, such as that of Admiral Smyth, will distinguish very 

 minute and proportionally numerous gradations of tint, and 

 detect the evidence of it even among those minute ob- 

 jects whose presence is only brought out by a patient and 

 stedfast gaze. The attention of observers was early drawn to 

 this point, Ptolemy, the Egyptian astronomer, having given 

 a catalogue of six fiery, or ruddy stars, as far back as the 

 second century. The invention and improvement of the 

 telescope did not lead to so speedy' an enlargement of our 

 knowledge in this, as in some other respects ; partly, perhaps, 

 because the value of such observations was not at first recog- 

 nized ; and partly because the man who, in other respects, was 

 the most qualified of all to give them due prominence — Sir 

 W. Herschel — had a preference for ruddy tints, arising either 

 from his eye or his specula, which rendered his results less 

 valuable as a standard of comparison. Scattered notices of 

 colour, after his day, are frequently to be met with ; but in the 

 works of Smyth and W. Struve, the subject has been treated 

 with especial accuracy, and Dembowski and other observers 

 are now following it up with close attention. It was not, how- 

 ever, till a comparatively late period that a very interesting- 

 question arising out of it attracted adequate notice, — whether 

 those colours might be subject to change ? A curious vari- 

 ation of hue had indeed been described by Tycho, in the 

 magnificent temporary star of 1572, which, having at first 

 broken out in splendid whiteness, passed, in its decrease, 

 through yellow and red, into a somewhat livid whiteness 

 again ; but the instance was altogether so extraordinary that 

 it naturally might excite no suspicion as to the possibility of a 

 similar alteration among more permanent stars. Long after, 

 but fully a century ago, Mr. Barker, of Lyndon, pointed out 

 the probability that such a change had actually taken place in 

 the most eminent possible instance, that of the resplendent 

 Sirius itself, to which the ancients ascribed a reddish tint, 

 now, as every one knows, totally imperceptible. Several of 

 the expressions in classical authors may be equivocal, but 

 we can have little hesitation as to the " rubra Canicula " of 

 Horace, and still less as to the distinct assertion of Seneca, 

 that its redness was more vivid (" acrior rubor ") than that of 

 the planet Mars ; while Ptolemy, in the list already referred 

 to, ranks it, together with Arcturus, Aldebaran, Pollux, An- 

 tares, and Betelgeuse, as 'wo/ci-ppo? — fiery-reddish. The date 

 of its change is unknown ; but it seems probable that its red- 

 ness had already become inconspicuous in the days of El-Fer- 

 gani (Alfraganus), in the middle of the tenth century, and no one 

 now would even suspect its former existence ; it may, perhaps, 



