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POPULAR SCIENCE REVIEW. 
difficulty, to which the inquiring mind is naturally led by the 
partial success which has attended inquiries into the origin of 
our own solar system. We recognise so clearly within our 
solar system such motions and such laws of distribution 
as suggest a process of evolution, that the mind is led to 
inquire whether the motion of the stars and their arrangement 
throughout space may not indicate the action of a yet higher 
order of evolution. If the genesis of a solar system has been 
or is being revealed to us, may not the genesis of a galaxy be 
one day revealed in like manner ? 
But I merely point to such inquiries as these, in passing, by 
way of indicating the class of questions to which such phe- 
nomena as I am about to consider may eventually lead. 
Let us now turn simply to the discussion of those observed 
facts which seem to show that the stars in certain regions have 
been gathered into streams. 
If we consider the stars according to their various orders of. 
apparent magnitude, we are, in fact, treating the problem pre- 
cisely as though the celestial vault were studied by means of 
telescopes progressively increasing in power. Nor need we, in so 
doing, make any assumption as to the real magnitudes of the 
stars. We know quite certainly that whatever telescopic power 
we use, or even when we study the heavens with the naked 
eye, we have to deal with objects lying at different distances, 
and that, therefore, we are exposed to the possibility of error 
arising from the fact that orbs which seem to be associated 
may in reality be in no way connected. But if we keep this 
possibility of error very carefully in view, and if we apply to 
the various cases which come under our notice such laws of 
reasoning as may best serve to eliminate such error, then, al- 
though we may not be sure that in all instances the error in 
question has been obviated, we shall yet have done much to 
obtain at least probable evidence respecting the laws of stellar 
distribution. 
As an illustration of my meaning, I will take an instance 
belonging to the more general law of stellar arrangement, of 
which stream- formation is but an instance. The reader is 
aware that the six stars which ordinary powers of sight recognise 
in the Pleiades, are but a few among a very large number which 
are seemingly collected towards one particular region of the 
heavens in this place. Now, if we consider only two stars of 
the Pleiades, considerably unequal in magnitude, it must be 
regarded as not only possible, but (on a priori considerations) 
highly probable, that these two orbs lie at very different dis- 
tances from the earth, and are not physically associated. But 
we are not free to extend this reasoning, which is admissible in 
the case of two stars, to the whole group of the Pleiades, and to 
