Double Stars. 149 



do not afford so good a starting-point as might be desired ; and 

 it is well known that certain eyes, perfect in other respects, 

 fail, more or less, and some even altogether, in their apprecia- 

 tion of colour. These circumstances throw an unfortunate 

 impediment in the way of a curious inquiry, and one well adapted 

 for general prosecution — whether stars are liable to any change 

 of colour. The wonderful New Star of 1572 passed through 

 various tints in its diminution, and there is sufficient evidence 

 to prove that Sinus, now of so brilliant a white, was once 

 decidedly red, Seneca says even redder than Mars ; and other 

 similar suspicions have been entertained. Upon what such 

 alterations may depend, or what corresponding changes they 

 may indicate in the constitution of those far distant suns, is of 

 course wholly unknown, but they form a point of great interest. 

 It is here that a multiplication of observers may be of much 

 service, as the combination of the impressions of many eyes is 

 the most probable way of eliminating individual peculiarity, 

 and testing suspected changes ; and it is here that amateurs, 

 with eyes sensitive to colour, and provided only with telescopes 

 of adequate size, may afford assistance as effectual as could he 

 derived from all the appliances of a regular observatory. 



When a large star is of any decided hue, it may be 

 naturally expected that its feebler companions may from con- 

 trast assume the complementary colour; just as the moon, 

 viewed near, or just after, a powerful yellow artificial light, will 

 appear decidedly blue, or as Schmidt saw it, of a lively green, 

 among the ruddy clouds of volcanic smoke and steam, which 

 encompassed his observatory upon Vesuvius during the great 

 eruption of 1855. In such cases the accidental colour of the 

 smaller star will disappear when its overpowering neighbour is 

 hidden behind the edge of the field, or a thick wire introduced 

 into it. But in many instances the colours, though complemen- 

 tary, as red and green, or yellow and purple, or orange and 

 blue, are proved, by the same means, to be independent ; and 

 it is a curious and suggestive sight, to behold the whole light 

 of the spectrum thus divided in unequal proportions between 

 two companion suns. As a general rule, Struve found that, 

 when a pair of stars are not both of the same colour, the larger- 

 verges towards the red end of the spectrum, the smaller towards; 

 the blue. He gives the following result of his observations : — 

 375 pairs of the same colour and intensity; 101 of the same 

 colour, but different intensity; 120 of different colours; 295 

 both white ; 118 both yellowish or reddish ; 63 both bluish. In 

 cases of great inequality of magnitude, when the smaller star 

 is blue, he found the larger, white in 53 pairs, light yellow in 

 52, yellow or red in 52, green in 16. He assigns no colour to 

 very minute stars, but such were frequently seen by Smyth of a 



vol. i. — NO. II. m 



