It is not so difficult, after all, then, to believe that there are
immense collections of shadowy gases and meteoric dust whose presence
is only manifested when they intercept the light coming from shining
bodies behind them.
This would account for the apparent extinguishment of light in open
space, which is indicated by the falling off in relative number of
telescopic stars below the tenth magnitude. Even as things are, the
amount of light coming to us from stars too faint to be seen with the
naked eye is so great that the statement of it generally surprises
persons who are unfamiliar with the inner facts of astronomy. It has
been calculated that on a clear night the total starlight from the
entire celestial sphere amounts to one-sixtieth of the light of the
full moon; but of this less than one-twenty-fifth is due to stars
separately distinguished by the eye. If there were no obscuring medium
in space, it is probable that the amount of starlight would be
noticeably and perhaps enormously increased.
But while it seems certain that some of the obscure spots in the Milky
Way are due to the presence of ``dark nebul?,'' or concealing veils of
one kind or another, it is equally certain that there are many which
are true apertures, however they may have been formed, and by whatever
forces they may be maintained.
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