Sidereal Astronomy. [January, 
Names. 
Magni- 
tude. 
Half- 
Major 
Axis. 
Periods. 
Years. 
Colours. 
Calculators. 
X Ophiuchi . . 
• • 4 — 5 '5 
1*20 
250 + | 
White ' 
and ashy 
Capt. Jacob, ’58 
/i 2 in Bouvier 
00 
1 
00 
Ln 
1*50 
290*00 
Green 
Orange ) 
Doberck, 1875 
36 / ndromedae 
. . 6 — 7 
i -54 
349*00 -j 
and 1 
yellow J 
Doberck, 1875 
y Lion ' 
2—4 
2*00 
40200 
Yellow 
Doberck, 1875 
6 of 9 Hydra. . 
•• 3—4 
3*00 
490 ±- 
' Yellow 
and 
k purple 
Admiral Smyth. 
i860 
H in the Dragon . . 
• • 4 4"5 
3*00 
600 + 
White 
f White 1 
Hind, 1865 
49 in the Serpent. . 
. . 6—6*5 
3*00 
600 + ■ 
and 
yellow 
r Klinkerfues, 1870 
12 2 in Lynx . . 
.. 6-6*5 
1*50 
, r White 
7 °° i { an d re d 
Maelder, 1850 
y Coronae 
. . 6 — 6*5 
6*oo 
0 ( White 
8 43 -°° { & ashy 
| Doberck, 1875 
Castor 
• • 2*3—3 
774 
gg 6 *oo 
Yellow 
Yellow 
Thiele, 1872 
« z Lyrae . . 
.. 5-6-5 
3*00 
1000 + 
and 
[ Maelder, 1850 
orange 
) 
S in Versian. . 
• • 4 — 4-5 
7‘64 
1578*00 
White 
Doberck, 1875 
£ 2 Lyrae 
• • 5 — 5-5 
2*90 
2000 + 
White 
Maelder, 1850. 
We see in this table that there is a great variety of periods, 
and although those which are inscribed here extend over 
2000 years, there are much longer periods which are still only 
vaguely estimated. We may remark that the colours of the 
stars in rapid orbital movement do not offer the beautiful 
contrasts of which we were speaking before. This is a 
surprising fadt, and one which has greatly astonished me ; 
the most beautifully -coloured stars turn only very slowly round 
each other . There is not a single contrast in the thirty-one 
systems of this table ; a Cygni only seems to offer an 
exception ; but its colours are undecided and variable. One 
can remark, also, that amongst these movements some are 
diredl, that is to say accomplishing in the direction east, 
south, west, north, and whilst others go backward (west, 
south, east, and north), one of the orbits, that of l Scorpionis, 
is very inclined on our visual ray ; this makes the orbit 
appear very elongated. Another, that of 42 Capella, lies 
entirely in the plain of the visual ray, so that we only see a 
waving movement of it. As can be easily verified, the greatest 
variety reigns in these stellar systems. 
VIII. Masses of Double Stars — How we Weigh a Star. 
The double stars are not only immense suns shining with 
their proper light in the depths of the heavens, but we know 
now that they are heavy, bulky, ponderous, and incom- 
