66 Sidereal Astronomy. [January, 
21. Vega Bluish-white. 
22. Altair . ,, 
23. S in the Great Bear ... ,, 
24. Saturn Yellowish-green. 
What astonished me most in these researches was to find 
Mars less red than a gas-flame. I have renewed the 
experiment more than thirty times before being convinced 
of this. 
By combining the first stars with the last I have formed 
couples which reproduce, nearly in all their intensity, the 
double stars red and green, yellow and blue, described 
above, such as 7 Andromedae, /3 Cygni, &c. Must we there- 
fore say that it is necessary to suppress all the green, blue, 
or violet colours of the double stars, and to attribute these 
colours only to the effedl of optical contrast ? Undoubtedly 
no ; but we must be sure that these stars are extremely 
rare, that many of them have their intensity increased by 
contrast, and that a very large number only owe their hue 
to the effedb of contrast. 
In these comparisons it is not only the tint of the stars 
which produces these contrasts, but the different inten- 
sities of the lights play a part which is far from insig- 
nificant. 
In summing up, therefore, although contrast increases 
the difference of the colours of the multiple stars, these 
colours really exist, and all the tints of the spedtrum are 
represented in the illumination of the suns of the universe. 
But the colours at the red extremity of the spedlrum are 
much more frequent than those at the blue extremity. From 
the point of view of the effedfs produced on the unknown 
worlds which gravitate round these many-coloured suns, we 
may remark, moreover, that the effedts of contrast may 
augment the real colours, when two or more of these suns 
appear together above the same horizon. This is what I 
purpose contemplating in the following chapter. 
VI. Worlds Governed and Illuminated by many Suns. 
Ought we to suppose with a learned contemporary astro- 
nomer — M. Faye, Member of the Academy of Sciences, and 
President of the Bureau des Longitudes — that the idea of the 
plurality of worlds is a mediocre idea (“ Year-Book ” for 
1874, p. 477) ; that in all our planetery systems there is only 
Mars which is habitable ; and again (Id., p. 487), that the 
double and multiple suns are incapable of governing in- 
habited planets (Id., v. 484); and that for a world to be 
