Star Colours. 275 



fields of space, collecting knowledge as we wander from orb to 

 orb. 



If single stars of bright colonr so strongly appeal to the 

 imagination, binary, or more complex systems, in which the 

 colours are contrasted, suggest more beautiful pictures, and 

 prompt to more elaborate speculations. What, for example, 

 must be the aspect of the skies of planets that may cluster 

 round Albireo (/3 Oygni) and rejoice in the commingling- or 

 alternation of the sapphire and topaz beams. Somewhat 

 similar inquiries are suggested by stars remarkable for rapid 

 changes of hue ; such, for example, as Capella, whose vivid 

 chromatic flashings attract the most careless eye ; or the 

 strange portentous combinations and alternations of red and 

 green that gleam from Antares, in Scorpio, when that extra- 

 ordinary star is viewed through a telescope of moderate 

 size. The first question that arises is, are the colours real 

 attributes of the bodies that seem to emit them, or results of 

 our terrestrial atmosphere, or of the tendency of the eye to be 

 affected by accidental tints ? The influence of our atmosphere, 

 though in one sense a shifting quantity, is yet constant in 

 another ; and as the same star is seen at different seasons, and at 

 different hours in different parts of the heavens, and at differ- 

 ent elevations above the horizon, we can, by collating a number 

 of observations, arrive at tolerably precise results; and we 

 find that if we eliminate changes obviously belonging to the 

 stars themselves, that the star colours retain a considerable 

 amount of fixity, whether seen near the zenith, or at moderate 

 heights above the horizon, and that weather changes of greater 

 or less transparency only cause their appearances to differ, as 

 might be expected from the optical effects of air in different 

 states of dryness, moisture, motion, and homogeneity, or the 

 reverse. Thus, whether Sirius was red or not to the ancients, 

 it is a white star to us, though somewhat blueish, as M. 

 Babinet* states, in towns, through the impurities of their air. 

 Arcturus in like manner belongs to the yellow series, and Vega 

 to those of pale sapphire tint. Star colours, then, are not 

 made by our atmosphere, but only modified more or less, ac- 

 cording to its condition at the time. Some portion of their 

 colour is the result of the law of simultaneous contrast, which 

 M. Chevreul has treated in his well-known work. Thus M. 

 Babinet states that a deep blue sky has been observed to 

 make Yenus look of an orange complexion. Two stars of con- 

 trasted colours seen in the same telescopic field, and near 

 each other, will heighten or modify each other's tints according 

 to their relative intensities of the complimentary colours which 



* See an interesting letter of M. Babinet to Admiral Smyth, in Astronomical 

 Register, for April. 



VOL. VII. — NO. IV. ' T 



