1876.] 
Sidereal Astronomy . 
47 
II. History of Double Stars, 
Double stars as such were not known before last century. 
However, one finds in ancient astronomical works many 
mentions of stars very near together, which they termed 
double. Ptolemy himself, in the “ Almageste,” describes 
one in roZornc (Sagittarius*), which he named Stvr \ovg, double. 
One sees it, in faCt, double to the naked eye, and it is com- 
posed of two stars very near together (v 1 and v 2 ). They are 
of the fifth magnitude, and separated by 14 minutes of arc. 
The star Mizar, or f of the Great Bear is alike described 
from the greatest antiquity as double, or rather as being 
accompanied by a little star, visible also to the naked eye to 
those with good sight. The Arabs call it Saidah, — that is 
to say, the test, because they used it to test their sight. It 
is also named Alcor, and its companion is of the fifth mag- 
nitude, and is situated at 11 minutes of arc from Mizar, 
whose brightness, which is of the second magnitude, 
eclipses the smaller from ordinary sight. The other stars 
seem equally joined two and two, and appear to the naked 
eye as apparently double. Such, also, are a 1 and a 2 of 
Capricornus, which are — the former of the first magnitude, 
the latter of the third, and distant from each other 6' 13'' ; 
good sights (that of the German astronomer Heis, among 
others) can separate them : v 1 and v 2 of the Crown, of fifth 
magnitudes, separated by 6' 19", a little more difficult to 
divide into two with the naked eye ; 0 l and 9 2 of Taurus in 
the Hyades (5' 3 y") ; it 1 and 7r 2 of Pegasus ; S 1 and S 2 of the 
Lyre ; P and e 2 of the same constellation. Another couple 
could be added to the preceding ; it is a 1 and a 2 of the 
Balance, whose separation is of 3' 4c)"; but the principal 
star being of the third magnitude, and the second of the 
sixth, I doubt whether it can be divided with the naked eye, 
and I know nobody who can do so. Do these apparent 
couples constitute themselves true binary systems ? This 
is not probable. In general double stars are incomparably 
closer. However, it must not be affirmed that their con- 
nection is only accidental, and due only to chance and to 
perspective. We shall find farther on examples of true 
common movements : we are justified in thinking that these 
stars may be associated together, although they may be 
more removed still from others on the celestial sphere. 
The study of these double stars only dates from telescopic 
investigations. By a curious chance the first star separated 
* In a Latin translation which I possess of the “ Almageste ” (Venice, 
1828) this star is thus described: — “ Quae in oculo est nebulosa et bina.” 
