i;o 



A'A TURE 



[June 1 1, 1908 



to penetrate the mystery that concoals Us destiny, 

 will nut be abandoned on account of the difficulty of 

 the problem or the dearth of pertinent facts. There 

 may be little hope that our observations and those of 

 our predecessors will prove Adequate to the task of 

 reading- the riddle, but the human mind needs very 

 little information to tempt it to form conjectures con- 

 cerning the order of creation in its widest extent. In 

 this department of science, history unfortunately 

 bears witness rather to the richness of our imagina- 

 tion than to our skill in securing facts. But in recent 

 times, as the contents of the two works under notice 

 show, the tendency has been to limit our excursions 

 into the unknown, and to substitute exact inquiry 

 directed to a definite end, in place of the loose, but 

 possibly plausible, suggestions that did duty for critical 

 examination. In the first-mentioned work M. Stroo- 

 bant is content to count the stars the positions of which 

 have been recorded in connection with the scheme 

 for the construction of the photographic chart 

 of the heavens. Such work is no doubt tedious and 

 unheroic, but it is eminently useful, and more wel- 

 come than any random speculations, however brilliant 

 or startling they might be. The object the author had 

 in view in undertaking this wearisome task was to 

 determine the law of stellar distribution, both on the 

 chart and in the catalogue, according to variation of 

 galactic latitude. For the present the research is 

 limited to the stars in the zones taken at the obser- 

 vatories of Paris, Bordeaux, Toulouse, Algiers, and 

 .San Fernando. Of the star charts 879 have been used, 

 containing the total of 985,430 images; and of the 

 catalogue negatives 535, which show the places of 

 163,009 stars. The celestial surface scrutinised con- 

 tains 4126 square degrees, approximately one-tenth 

 of the entire surface of the sphere. 



One of the by-products of the research is to indi- 

 cate that the mean magnitude of the faintest stars 

 recorded on the catalogue plates is ii'5 mag., and 

 that of the faintest stars on the chart i3'5 mag., or 

 taking into account the loss of images, unavoidable in 

 reproduction, 137 mag. These figures show, so far 

 as this inquiry is trustworthy, that the original pro- 

 posals for the construction of the international chart 

 have been adhered to very faithfully, h further con- 

 clusion is that the total number of stars we may 

 expect to find in the complete catalogue is 2,676,000, 

 and on the chart 9,854,000. These totals are more 

 modest than early and less informed estimates, and 

 M. Stroobant gives reason to think that these numbers 

 will be exceeded when some of the unpublished charts 

 become available. The data supplied from each obser- 

 vatory are discussed separately and fully, but space 

 will not permit more than the reproduction of the final 

 result, which exhibits the conclusions drawn from the 

 whole material under discussion : — • 



Stellar density 



Chart Catalosue 



0'14 ... 019 



0-13 ... 018 



021 .. O'jO 



0-51 ... 0-57 



I 'OO ... I '00 



052 ... 0-52 



0'20 ... 0'25 



o'i7 ... 0T5 



The want of exact regularity in the change of these 

 numbers with the latitude is doubtless due to in- 

 sufficient data, but considering the number of stars 

 involved and the care taken to secure vmiformitv, the 

 result is probably more trustworthy than that drawn 

 from Herschel's gauges, which indicate a much more 

 rapid increase in stellar density as the latitude 



NO. 2015, VOL. 78] 



diminishes. Further examination shows that the 

 number of stars on the chart increases uniformly in 

 both hemispheres, but that if the faintest stars be e.\- 

 cluded and the research limited to those that appear 

 in the catalogue, the density is more marked in the 

 northern than in the southern hemisphere. It is not 

 possible to make any complete inquiry as to the varia- 

 tion of density depending on galactic longitude, but 

 from a preliminary investigation of those regions of 

 the Milky Way where it cuts the celestial equator, 

 M. Stroobant shows that at the ascending node of the 

 Galaxv, the northern border is richer in stars than 

 the southern, and that at the descending node this 

 relation is reversed. It is further pointed out that 

 the increase in the number of stars on the photo- 

 graphic chart does not correspond with the contour 

 lines drawn in naked-eye representations of the Milky 

 Way, and in conclusion the author directs attention 

 to regions of the sky which are very rich in stars, 

 though fairly remote from the central line of the 

 Milky Way, to the pole of which are assigned the 

 coordinates a = i2h. 46m., 5 ±28°. 



Prof. Max Wolf addresses himself to a scientific con- 

 gress, mainlv composed of medical men, and neces- 

 sarily his paper is of a more popular character. He 

 franklv admits that we have but very little knowledge 

 of the true construction of the Milky Way, and that 

 speculation has supplied the place of exact information. 

 By means of e.xcellent photographs he shows the 

 great variety of structure running throughout the 

 Galactic Belt, and indicates the difficulties which any 

 theory of the Milky Wav has to surmount. Prof. Max 

 Wolf is intimately acquainted with the literature of 

 the subject, knows the strength and the weakness of 

 the various hypotheses that have been advanced, and 

 treats the many problems that arise in a luminous and 

 interesting manner. 



He glances at the various studies that have 

 been made to solve the problem of the possible geo- 

 metrical form of the Gala.xy, from the time when 

 Herschel began his laborious task of counting the 

 stars visible in the field of his telescope, down to that 

 later period when the resources of photography have 

 supplied more information, but at the same time re- 

 vealed a more complex structure, offering fresh diffi- 

 culties for solution. Of the different attempts that 

 have been made to represent its true shape, concealed 

 as it is by the curious bifurcations, rifts, condensa- 

 tions, and lacunje, that suggested by Dr. Easton, of 

 .Amsterdam, meets with the greatest favour. In this 

 scheme the Spiral Nebula in Ursa Major has ad- 

 mittedly supplied the model. K nucleus is placed in 

 the constellation Cygnus, and from this central con- 

 densation radiate streamers, which can be arbitrarily 

 arranged so that the combined effect can be made to 

 resemble the general aspect of the Milky Way. 

 The objection the autiior raises to the scheme is that 

 Cygnus does not present that close agglomeration of 

 stars which such an hypothesis requires. It might 

 further be added that in the sketch given, the sun 

 occupies too much the place of a detached spectator, 

 and is apparently quite disconnected from the system. 



A feature of great prominence in many photographs 

 of nebulae is the comparative scarcity of stars in the 

 immediate neighbourhood of the nebula, and Dr. Max 

 Wolf discusses the probable physical connection be- 

 tween the dark lacunae and the brilliant condensations 

 adjoining. This effect is real, and not dtie to con- 

 trast, for by counting the stars on a photograph within 

 a definite area, and shading the different parts of that 

 area according to the number of images impressed on 

 the film, it is possible to exhibit statistically the re- 

 lative density of stars surrounding the different 

 nebulae. This plan has been adopted with great sue- 



