48 Sidereal Astronomy. [January, 
by the telescope is that which was most remarkable to the 
naked eye, as being apparently double, — Mizar, — which is 
not only accompanied by Alcor, but is itself double. It is 
composed of two stars, separated by 14 seconds of arc from 
each other ; the brightest is of the second magnitude, and 
its companion is of the third. This star was recognised as 
double for the first time by Riccioli, in the middle of the 
seventeenth century. In 1700 Gottfried Kirch and his 
learned wife Maria Margareta described it, and again 
drew the attention of astronomers to it. Bradley, Mayer, 
and Herschel observed it afterwards. In comparing the 
observations made during two centuries, we find that the 
two stars have hardly changed position with regard to each 
other. The angle increases slowly. William Herschel had 
concluded that it was diminishing, but this is an error of 
the illustrious astronomer. It is possible that the three 
stars (the double and Alcor) form a triple system. They 
are all three animated by one common movement in space. 
The second star separated with the telescope is Mezartim, 
7 of the Whale, which was separated by Hook when observing 
the comet of 1664. The principal star is of the \\ magni- 
tude, the other of the fifth ; their distance apart is 9 seconds. 
Their relative position has not varied since the earliest 
observations. 
The third star separated is that which has since become 
one of the most interesting, on account of its parallax — 
our neighbour a Centauri. It was described in 1709 by 
Feuillee, at Lima. Its two components turn rapidly round 
each other, following a much elongated ellipse, half the 
principal axis of which measures 14". Since the time of its 
discovery there have been more than two revolutions ac- 
complished. We give farther on the elements of this 
magnificent orbital system, of which the distance from the 
earth is eight trillions three hundred and seventy-six mil- 
liards of leagues. 
In proportion as the attention of astronomers has deve- 
loped and has carried them nearer to the stars, till then 
unknown and looked upon as simple points of light, they 
commenced to discover these stellar groups which had been 
so long unexplained. The double star 7 Virginis was 
separated in 1718 by Bradley ; Castor, a Gemini, in 1719 ; 
61 Cygni in 1753, ft Cygni in 1755. Then followed 7 An- 
dromedse, e Lyrse, 70 p. Ophiuchi, f of Cancer, ft of the 
Scorpion, 6 and ? of Orion, 1 of the Great Bear, &c. Their 
numbers gradually augmented up to the time of Flam- 
steed, who employed a rudimentary micrometer, until the 
