Pore.—On the Southern Stars and other Celestial Objects. 171 
y Crucis.—It has been customary for astronomers to catalogue this 
star—the “ Head of the Cross "—as a double star; but the proper motion 
of the large orange-coloured star is rapidly carrying it away from its five- 
. and-a-half-magnitude blue companion, The spectrum of y Crucis is perhaps 
the finest of all stellar spectra. The groups of lines are so numerous and 
so well marked that this spectrum may be observed under almost any at- 
mospherie conditions, if the star can be seen at all. y Crucis is a typical 
star of Secchi’s third class, which are all orange colour verging towards red. 
In their spectra there are numerous, easily-seen, close groups of lines; but 
the hydrogen lines are either very indistinct or altogether absent. a Orionis 
and a Herculis are good specimens of the two principal subdivisions of this 
class. In the spectrum of y Crucis there are at least eight broad groups of 
lines, and some of these occupy the parts of the spectrum at which sodium, 
iron, magnesium, and calcium lines are found in the solar spectrum. 
But, because they are groups, it is much more diffieult to say whether they 
contain the lines belonging to those elements or not, than it is in the case 
of a first or second-class spectrum. Still, I anticipate that careful measure- 
ments will confirm my opinion that iron and magnesium lines, especially 
the latter, are present in the spectrum of this star; the sodium line is pro- 
bably there too. There is, also, a fine line just at the part where the green 
merges into the blue of the spectrum. This is possibly the F. hydrogen 
line. 
There is one very significant feature in this spectrum, so at least it seems 
tome. It is well known that when the Sun is near the horizon, especially 
in damp weather, his spectrum contains certain groups of lines which are 
due to the aqueous vapour in our own atmosphere, and that, as he reaches 
a greater altitude, these lines become faint or disappear. Now, two at 
least of the groups in the spectrum of y Crucis appear to occupy the same 
position as two of the principal groups of atmospheric lines. Now this 
being verified, important conclusions might follow. Secchi, on grounds of 
this sort, infers the existence of aqueous vapours in the neighbourhood of 
sun-spots. The spectroscope knows nothing, so to speak, about distance, 
except indeed where motion of approach or recession is concerned. If 
these aqueous vapour-lines are produced in spots on the sun, may they not 
be produced in much the same way in y Crucis, the principal difference being 
that on the distant star the cause is more general and the effect greater than 
it is onourown Sun. If I am not mistaken, the existence of these s 
lines should enable us to read a certain portion of the ‘‘life history” of a 
star 
This history might be something like this: Let us suppose that, count- 
less ages ago, y Crucis was a white star, like Sirius, It was then far more 
