62 
Sidereal Astronomy. 
[January, 
scintillation. In the luminous neighbourhood of this brilliant 
star has been discovered a little companion completely 
green, and it is not impossible that sometimes these rays, 
traversing those of Antares, mingle more or less together. 
Castor is composed of a yellow star and a second slightly 
greenish, the reflection of which sometimes modifies the 
hue of Castor seen by the naked eye. 
We may also notice, as types of beautiful coloured stars, 
the groups of o Eridan (orange and blue), 32 Eridan 
(yellow, topaz, and greenish blue), 2 of the Triangle (yellow 
and green), /3 Scorpionis (yellow and blue), 77 Persii (red and 
blue), S 163 (orange and sapphire), 35 Pisces (pale yellow 
and violet), 77 Cassiopese (pale yellow and lilac), S Orionis 
(pale yellow and blue), <J) in Taurus (red and blue), 0 Herculis 
yellow, green, and purple), a Scorpionis (copper, red, and 
clear blue), £ Pegasi (golden yellow and azure), 7 Dauphinis 
(cadmium-yellow and variable pearl gray), 95 Herculis (pale 
green and variable cerise-red), &c. All the colours of the 
rainbow are represented in the polychromatic illuminations 
of these far-off suns. Sometimes there are not only two 
stars which arrest the astonished gaze by the marvellous 
contrast of their colours, but three, four, five, six, or more ; 
the most admirable example of these masses of multi- 
coloured stars is situated near the star x of the southern 
cross ; we can there count not less than no stars collected 
together at the same spot of the heavens, sparkling in all 
colours, like a casket of precious stones. 
The contrast of colours is one of the most remarkable 
characteristics of the double stars. In 600 couples chosen 
from Struve’s great catalogue, and carefully observed, we 
find 375 in which the two stars present the same colour and 
the same degree of intensity ; 101 in which the two stars 
are also of the same colour, but with a difference of in- 
tensity : and 120 — that is to say, a fifth of the total number 
— where the colours are completely different. Of these last 
have been counted 52 where one of the two stars is red and 
the other very green or very blue ; 52 where the first is pale 
yellow and fhe second pale blue ; and 16 where one is green 
and the other blue. 
In examining the differences of magnitudes of the com- 
ponents in proportion to their differences of colour, we find 
the following proportions, which are very significant : — The 
375 stars of which the colour is the same, with the same 
intensity, give, for their average difference of magnitude, 
the number — 
0*416. 
