168 Transactions.—M iscellaneous. 
of Sirius. ‘There ave a great many very fine lines in the spectrum of 
Canopus, but these are not generally visible. It is only when the atmos- 
phere is very steady and clear that they can be plainly seen. A fine line, 
however, or rather a small group of lines, in all probability that called 6, 
and due to the presence of magnesium in the photosphere of the star, can 
generally be made out in moderately fine weather. 
x Argus.—This is a wide telescopic double-star, forming, with a very 
distant companion of about the fifth magnitude, another double, easily 
visible as such with the naked eye. The colour of the large third-magni- 
tude star is a strongly-marked orange; the other two are indigo-blue. It is 
a well-known fact, that a large yellow or orange-coloured star has frequently 
a distant companion of a blue or green colour. It is generally supposed 
that this is a sort of prima facie evidence that the two stars are in some way 
physically connected. It seems to me that the existence of these comple- 
mentary colours in apparently neighbouring stars in no way indicates per se 
that they are physically connected. I am inclined to think that, given a 
large bright orange star, with a smaller star naturally very white and nearly 
in the line of sight, this latter must appear greenish or bluish. The light 
of the bright orange star fatigues the eye as far as its power of receiving the 
impressions which we call red, orange, and yellow is concerned. Now, 
when the eye is directed to the smaller star, the less refrangible portion of 
the light coming from this fainter object is unable to act with its normal 
effect, while the green, the blue, and the violet rays, by which the 
eye has not been fatigued at all, produce their ordinary impression. 
It is commonly said that this explanation may be true enough in a few 
cases; but that, if the bright star is hidden behind a thick bar placed across 
the field of the telescope, and the smaller star still appears blue or green, it 
is a proof that the light of the smaller star is really blue or green, and that 
its colour cannot be the effect of mere contrast. This is, I feel sure, fal- 
lacious. I have often tried the experiment and at first it was very dis- 
appointing, for one would naturally expect that a star, which appeared 
coloured in the presence of a very bright companion, would show its colour 
still more distinctly when that companion was hidden from view. But 
this never happened, the more completely the light of the larger star was 
removed, the less was colour in the companion observable. I feel per- 
suaded that, if the light of the larger star could be entirely cut off, which 
by-the-by is impossible, the blue colour would entirely disappear. It is 
worth noting, too, that the longer one looks at a blue star, its com- 
panion being hidden, the more completely does the blue colour disap- 
pear; that is, I take it, as the eye recovers its normal condition, after 
being exposed to a severe strain from the light of the large star, so does 
