1876.] 
Sidereal Astronomy. 
45 
often sparkle with coloured light, offering in their strange 
couples admirable associations of contrast, in which the asto- 
nished eye sees the fire of the emerald wedded with that 
of the ruby, that of the topaz with that of the sapphire, 
the diamond with the turquoise, or the opal with the ame- 
thyst, glittering thus with all the shades of the rainbow. 
Sometimes the wonderful stars which form these celestial 
couples repose in the vault of infinity, fixed and unchange- 
able ; and for more than a century that astronomers have 
been anxiously contemplating and watching them, they have 
not varied their relative position with regard to each other : 
as the searching look of the patient William Herschel sur- 
prised them there a hundred years ago, so we find them 
to-day. Sometimes, on the contrary, the two associated 
stars gravitate round their common centre and turn round 
each other, the weakest round the strongest, rocking on 
the wing of attraction, as the moon moves round the 
earth and the earth round the sun. A certain number of 
these couples have already made many complete revolu- 
tions under the eyes of observers, the duration of these 
revolutions differing with each couple, and offering the 
greatest variety of periods, from a few years only up to 
thousands of years, and even to hundreds of centuries. Our 
small terrestrial calendar does not extend its empire to these 
far-off worlds ; our ephemeral periods, our ant-like measure- 
ments, are strangers to these grandeurs ; the earth is no 
longer the measure of creation, and our most sacred eras are 
unknown in the heavens. The study of these stellar 
systems constitutes one of the vastest and most interesting 
problems of the contemporary astronomer; it has, however, 
remained stationary, and, notwithstanding the considerable 
number of accumulated observations, no one astronomer has 
yet tried to gather up the harmony of all these systems, to 
search for differences which can exist between them, and 
(except some partial attempts) to catalogue on the one hand 
the double and multiple stars which have a certain orbital 
movement, and on the other hand those groups whose 
movement is not orbital, but rectilinear, and caused by per- 
spective, owing to the displacement of one of the stars 
situated by accident before another farther off and im- 
movable. 
Each star being a gigantic sun, shining with its own 
light, a focus of attraction, of heat, of activity, and life, the 
problem presented to the human mind by these systems of 
multiple suns is, without doubt, one of those which can 
most absorb the imagination, fire the thoughts, and affeCt 
