Jan. 1, 1886.] 



KNOWLEDGE ♦ 



83 



Jlilky W;.y. I thiuk too that we are bound to look on 

 the stars composiug the Milky Way as really minute in 

 comparison with Aldebaran and its like. Projecting the 

 Milky Way to the distance due to the apparent smallncss of 

 its component str.rs r.ssumed nearly equal to lucid stars, 

 1 cannot understand the mi'.ny singular correspondences 

 between its arrangement and that of the brighter stars. 

 But looking on it as a stream swayed by the leading stars, 

 one seems to get a general conception of its nature 

 according satisfactorily with observed appearances. 



Have you ever noticed the singular contrast between 

 the poverty of the heavens (in lucid stars) from Cen- 

 taurns to Monoceros on one side of the Milky Way, and 

 the extreme richness from Crux to Orion on the other 

 side ? [See map on p. K9, drawn since above was in type.] 



Your suggestion that the Galaxy contains within itself 

 miniatures of itself, is very beautiful, and doubtless points 

 to a great truth, as yet but dimly seen. — Yours very 

 truly, R. A. Proctor. 



stone]* maybe distributed in space, so as to appear to our 

 eyes and telescopes just as our Milky Way and sidereal 

 firmament does, I sec no distinct reason for or against a 

 spiral, discoid, annular, or cellular arrangement.^ As 

 regards the openings in the form of '' Coal-sacks, ' I do 

 not quite see that what you say (" Other Worlds than 

 Ours,'' 1st Edition, p. 2.5G) as to a channel having a 

 particular direction and perfectly straight, is necessarj-. 



Imagine, for instance, such a form (not merely plane, but 

 tridimensional) as^Aif(Fig. 5) forthestar-groupsandgalactic 

 masses. This would le.we quite as good a passage for the 

 visual ray otit into space as the neatest cut chimney.f 



Collingwood, April 1, 1870. 

 I have been examinLug my star-gauges in reference to 

 the very curious and interesting statistical relations your 

 letter communicates [these are given in my essay on a 

 novel way of gauging the star-depths, "Essays on Astro- 

 nomy."-— R. P.] ; but I see that in so far as the relation 



THE UNIVERSE OF STARS. 



EXTRACTS FROil 



LETTERS TO FJCHAKD A. PKOCTuK. 



Bv Sib Johx Heeschei,. 



ColliH(/ivood, AtKj. 20, 18G9. 

 NE of the arguments ad- 

 vanced in favour of spatial 

 extinction of light was 



that if 

 lieavens 

 blaze of 

 mitting 

 because it 



not the whole 

 ought to be one 

 solar light — ad- 

 the universe to 

 was contended 



Fig. o. — showing liuw a ' 



uoal-saek " in the Milky Way may be explaincil. 



lie infinite, 



that there could then be no direction in space in which 

 the visuil ray would not encounter a star — i.e.. a sun. 

 This argument is fallacious ; for it is easy to imagine a 

 constitution of a universe literally infinite which would 

 allow of any amount of such directions of penetration as 

 niit to encounter a star : - 



Granting that it i-iiusists of sj-.stems subordinated 

 according to the law that every higher order of bodies 

 in it should be immensely more distant from the centre 

 than the next inferior order, this would happen. Thus 

 — in our own — the moon is very near the earth and the 

 satellites to their primaries. These primaries are 

 immense]}- more distant from the sun, tlieir centre. The 

 fixed stars again still more immensely more remote from 

 the sun. Suppose our system to terminate with the 

 visible fixed stars. Then imagine a system of such 

 systems as remote from each other in comparison with 

 their own dinicnsions, as the distance of the fixed stars in 

 comparison with the diameter of the solar system. Such 

 systems seen from each other would subtend no greater 

 angle thr.n a star seen from the sun,* and so on. 



May 11, 1870. 



Among the innumerable waj-s in which an almost 

 infinite multitude of luminaries of all sizes and bright- 

 nesses, from riO,000 suns] down to [an ounce of red-hot 



of the grouping to the plane of the Milky Way is con- 

 cerned, the results there arrived at [that is in Sir J. 

 Herschel's star-gauges] are applicable only for stars 

 below 8 rnacr., and for stars 8 mag. and upward those 

 gatiges afford no ground for any conclusion one way or 

 other. — i.e., in Hie moilo in whirli they are there 

 grouped. 



It would perhaps be worth while to regroup them [be 

 it under.stood that Sir John Herschel is here referring to 

 his own o-p,uges] for the regions within nnd without your 

 boundary-line which — if I understand you right — divides 

 the globe of stars 6 mag. r,nd upwards into two very 

 unequal segments — a rich and a poor one — having to 

 each other the radii of about 5 to 2 in area, with no 

 reference to the Milky Way, but ctitting straight across 

 it ! — certainly a very startling fact, and none the less so 

 that it should hiive the Nuhccida Major for its centre. 

 Still it seems almost too sudden to jump to a conclusion 

 as to a real concentricity resulting from a phj-sical con- 

 nection — the more especially as the B. A. Catalogue can 



* Wherefore it follows, we may note in passing, tliat the nebulie 

 which subtend much larger angles than this are utterly unlike the 

 neighbouring galaxies as analogy would lead us to expect; hat 

 these would appear to us — that is as mere points in apparent size, 

 and as also exceedingly faint in apparent intrinsic lustre.— E. P. 



* The brackets here are used as in mathematics. Sir John 

 intended me to understand that each luminary might be anything 

 from a group of lo.uOO suns down to an ounce of red-hot stone. 

 Without the first pair of brackets, I might have understood him to 

 represent a multitude of luminaries, instead of a single luminary, by 

 the 10,000 suns. The second pair of brackets was rendered neces- 

 sary— logically— by the use of tlie former pair which could not be 

 avoided.' This condensed way of writing is very convenient and 

 useful wlien the writer knows that his correspondent will not mis- 

 understand him ; but of course it would be very unsuitable in address- 

 ing the general public on scientific subjects.— R. P. 



t The only objection is that the overlapping star-clouds would 

 give marked variations of brightness around a " coal-sack," whereas 

 a general uniformity is observed.— E. P. 



