TRANSLATIONS AND SELECTED ARTICLES. 311 
centre of gravity in periods of sufficiently short duration, which have 
already in certain cases admitted of determination. Observing that 
‘these double stars are of colors very unlike, our thoughts would 
naturally be carried to the inhabitants of the planetary bodies, non- 
luminous and turning about their own axes, which to all appearance 
‘revolve about these suns, and we should remark, not without a real 
anxiety for the works of the painters im these distant worlds, that to 
a day illuminated by a red light there succeeds, not indeed a night, 
but another day, of equal brilliancy, only illuminated by a green light. 
The comparisons of the positions of the stars determined at different 
epochs would prove to us that they are very improperly denominated 
fixed ; that in fact they are in motion in space in different directions, 
so that in the course of time, the form of the actual constellations 
will be completely changed; that the absolute velocities of these stars 
are unequal, but that the velocity in one of the cases which have been 
determined with entire certainty is at the rate of twenty leagues a 
second ; lastly that the sun, like all the other stars in this respect, is 
not stationary, and carries in his train the family of planets with 
which he is surrounded. We should be struck by the unequal distri- 
bution of the stars in the celestial sphere. In one place, we should 
see more than twenty thousand in an area equal to the tenth part of the 
moon’s apparent surface. In another, in an area of the same extent, 
not a single luminous point would be visible, even with the best tele- 
Scopes. ; 
After having cast an attentive glance at the luminous matter scat- 
tered over immense spaces, which, by its agglomeration continued. 
through centuries, seems capable of giving birth to new stars, we 
should discuss the noble conceptions of Wright, Kant, Lambert, and 
W. Herschel, on the constitution and dimensions of the milky way. 
Finally, some steps further in conjectural astronomy—that is to say, 
in that branch of the science which rests only on imposing probabilities 
and natural generalisations, there would be unveiled to us phenomena, 
which by their nature, or the enormity of the numbers which measure 
them, would cast the strongest minds into a sort of vertigo. 
But let us leave these speculations, however worthy of admiration 
they be, to return to the main question which I proposed to treat in 
this note, and to try, if it is possible, to establish some connexion 
between the physical nature of the stars and that of our sun. 
We have succeeded, by aid of the polariscope, in determining the 
nature of the substance which composes the solar photosphere, because, 
