STAR STREAMS AND STAR SPRAYS. 
405 
beyond all possibility of question the existence of some real 
cause which has led to a drifting of the stars towards certain 
regions. As regards such peculiarities of arrangement as would 
fall more particularly under the head of my present subject, I 
think it is almost equally impossible to feel any doubt. If 
some of the streams and reticulations which can be recognised 
in the isographic chart added to the second edition, be due to 
chance distribution, the coincidence is very much more remark- 
able than the theory of star streams which I am at present ad- 
vocating. It is truer to say, however, that the laws of proba- 
bility as at present understood will not permit us to regard 
such singular configurations as accidental. 
It would be desirable that we should have equal-surface 
charts of the heavens to include stars down to the seventh, 
eighth, and ninth magnitude severally ; because it is only by 
thus considering the separate stages of space-penetration that we 
can obtain complete recognition of the laws of st ellar distribution 
throughout space. We owe, I think, to the elder Struve the 
first recognition of the importance of such graduated advances 
within the star-depths ; though he dwelt rather on the impor- 
tance of star-gauging (and that, also, according to averages) than 
on the value of star-charts capable of revealing to the eye the 
statistics of stellar distribution. It will not be difficult to con- 
struct charts including stars down to the seventh, and eighth, 
and ninth orders of magnitude ; because as soon as the com- 
plete survey of the heavens has been effected after the plan 
already extended by Argelander to the northern hemisphere, 
the charts forming the survey, if carefully drawn,* will enable 
us to construct charts of complete hemispheres including stars 
down to the seventh, eighth, and ninth magnitudes severally 
inclusive. 
At present, however, for want of such intermediate charts 
(so to speak) I pass from my equal-surface projection of all the 
stars down to the sixth magnitude inclusive, to an equal-sur- 
face projection which I have just completed, in which all stars 
in Argelander’s series of forty northern maps have been marked 
in with careful reference as well to their arrangement as to 
their magnitude. In these forty charts, as many of my readers 
* It is important that the size of the discs used to indicate the several 
magnitudes should remain unchanged during the whole process of engraving, 
and also that the several charts forming the series should he printed with 
exactly the same degree of fulness. In Argelander’s splendid series of forty 
charts, in which all the northern stars down to the magnitude intermediate 
between the ninth and tenth are included, slight changes have taken place 
during the progress of the work, which creates some degree of doubt as to 
the orders to which the stars belong in some of the charts. 
VOL. X. — NO. XLI. E E 
