1876.] 
Sidereal Astronomy. 
61 
distances — AB = 11", BC = 0*7), and would only be accom- 
plished in a cycle of many thousands of years. It is pos- 
sible, then, that the fixedness of the two orange and green 
suns may be only due to the insufficiency of time for obser- 
vations ; a variation of 3 degrees would be sensible on this 
couple. The period might extend to twelve thousand years. 
One of the most magnificent of the coloured double stars 
is the star Albires, or 0 Cygni, topaz and sapphire, not less 
admirable than the preceding. To the naked eye this is 
merely a simple star, of the third magnitude. In the tele- 
scope it is a celestial couple of great beauty. The large sun 
shines with a strong and deep yellow colour ; the little star 
appears modestly at its side, of a pensive blue. The con- 
templation of this ethereal marriage brings to mind the 
Paradise of Milton, where the poet sings of male and 
female stars commingling their regards and light across the 
heavens : — 
. . . . “ Other suns, perhaps, 
With their attendant moons thou wilt descry, 
Communicating male and female light.” 
In the chromatic scale these colours are exactly comple- 
mentary ; moreover, when examined separately, they are 
real, and not due to an effedt of optical contrast. Examined 
with the spectroscope, the two components of the couple 
give two different spedtra ; that of the golden yellow sun is 
crossed by a series of black absorption lines, occupying its 
blue part ; that of its companion presents an analogous 
system, occupying its yellow and red region. These stars 
owe their colour to the nature of the vapours in their at- 
mospheres. Like 7 Andromedae, the couple /3 Cygni is 
fixed. It has been observed since 1755, and find the little 
blue star at 66° 34" from the topaz star. 
Another double star, very beautiful as to its colours, is 
t Bouvier, which is called also Pulcherrima, a star of the third 
magnitude seen with the naked eye, and composed of an 
orange star and a small brilliant emerald star. The two 
components are only 3 seconds apart, and it requires a good 
instrument to separate them. They form an orbital system 
having a slow movement. 
The star a Hercules, also of the third magnitude, may be 
equally quoted as being one of the most beautiful in the 
heavens (orange and green). It is stationary at 119 0 4". 
The brilliant star Antares, of the first magnitude, is red, 
and this colour can be observed with the naked eye. On a 
clear and transparent night the attentive eye is sometimes 
struck by some green rays which furtively mix with its 
