ISO 



KNOWLEDGE 



[August 1, 1899. 



that our figures are much under rather than over the 

 mark. Mr. JMaunder remarks* it is hard to understand 

 how we can have gaseous masses of such enormous extent. 

 They beggar our solar system in dimensions, and instead 

 of a very few bodies of comparatively small size and con- 

 densed nature, must occupy an amount of solid space 

 which we are quite unable to grasp. 



The second feature to which I would call attention, and 

 which Dr. Roberts in his description of the photographs 

 specially refers to, is that of the dark rifts or lanes 

 occurring in the nebula, especially the N.P. portion. 

 They are sharply defined and clearly cut. How are we 

 going to explain these dark rifts, which Mr. Maunder and 

 others have alluded to ? The breadth of one of these 

 sharp rifts is about 1 mm., which on Dr. Roberts' 

 scale = 24". If the nebula is homogeneous and with a 

 thickness in the line of sight approximately the same as 

 that perpendicular to it, we are driven to the conclusion 

 that this rift must be a hole, perforating the nebula from 

 one side to another, with a length which must exceed its 

 breadth by at least fifty times. This, as in the case of a 

 bullet hole in the case of a terrestrial object, we might 

 perhaps allow, if the aperture were circular ; but when we 

 come to have several of these rifts with an irregular, yet 

 sharply-defined outline, the probabiUty is very enormous 

 against then- being apertures extending through the 

 nebulous matter to an extent corresponding to that of the 

 whole system, in the line of sight. 



I believe it has been suggested that such a phenomenon 

 as these rifts may be due to the interposition of solid dark 

 masses of matter between us and the nebula. But in the 

 present state of our knowledge, and on scrutinizing the 

 photograph under consideration, I cannot bring myself to 

 believe that this is the correct explanation. The rifts do, to 

 me, certainly appear as real vacuities, showing the black- 

 ness of space between or amongst the nebulous matter. 



I can only account for them by the infinitely complicated 

 character of this nebula. I suppose it to consist of streams 

 and wisps, and projections of gas, bending, twisting in all 

 directions, and by no means homogeneous when considered 

 over the whole angular space which the nebula seems to 

 occupy. In that case, a hole or rift is not so difficult to 

 understand when we consider that it pierces a portion of 

 nebula small in comparison to the whole system. Some 

 cause or other, at present totally unknown to us, may tend 

 to draw away or attract the nebulous fluid from certain 

 definite but comparatively small localities and produce 

 these gaps. The explanation, I fear, is a lame one to a 

 certain extent, but who can ofi'er a better ? Those who 

 have studied the writings of Proctor on this subject will 

 probably trace his influence in this attempted explanation. 

 He it was who said that " the constitution of the sidereal 

 universe is too complex to be at present ascertained," and I 

 think this remark would apply very largely to the particular 

 nebula I have been considering. We must not think this 

 nebula to be of the same nature as the regular spherical or 

 elliptical ones, or the globular clusters of stars. In such 

 I do not think such a thing as a dark vacuity exists. 



It is possible that photographs taken at some future time, 

 on a much larger scale, when the art has been greatly 

 improved, may show these gaps or rifts to be partially 

 occupied with, perhaps, comparatively tenuous nebular 

 matter, just as increase in magnifying power of a (visual) 

 telescope brings out details unexpected before. Meanwhile 

 the rifts must remain a very remarkable feature, showing, 

 I think, the very complicated nature of the detail which go 



» Knowledge, February, 18S6, p. 38. 



to make up one of these irregular nebulre. The cnrdhngs 

 and streaks, etc., in the great nebula in Orion are, I think, 

 a phenomenon of an analogous order, although the general 

 character of that nebula may difl'er from the one particularly 

 under consideration. 



E. E. Makkwick, Col. 



THE ORIGIN OP FLINT. 



To the Editors of Knowledge. 



Sirs, — I find that, in an article on " Flint" in KNO\^xEDGE 

 for June, 1899, 1 have omitted mention of a comprehensive 

 paper by Prof. Rupert Jones, f.r.s., on " Quartz, 

 Chalcedony, Agate, Flint, Chert, Jasper," in the 

 Proceedings of the Geologists Association, Volume IV. 

 (1876), p. 439. Prof. Rupert Jones provides an admirable 

 historical account of the various opinions that had been 

 held as to the origin of ilint, and strongly supports the 

 view (p. 450) that the silica is deposited as a pseudomorph 

 of hmestone. So much had been written on the subject in 

 a more or less extravagant vein, that this paper, twenty- 

 three years ago, produced a very salutary impression. 



Gkenville a. J. Cole. 



THE DISTRIBUTION OF STARS IN SPACE. 

 To the Editors of Knowledge. 



Sirs, — With reference to Dr. Burns' interesting paper 

 on this subject in the July number of Knowledge, I find, 

 in going through the recently pubUshed volume of measures 

 made with the photometer at Potsdam Observatory 

 (zone +20^ to -f 40°), about one hundred eases in which 

 the photometric magnitudes difl'er from those in the 

 DurchmustermKj by one magnitude and over. With only 

 one exception in the hundred, the magnitudes given in the 

 Durchmustiritng are brighter than those found by the photo- 

 meter. Thus, a 7-0 magnitude in the Thtrchmusterung is 

 80 or less in the Potsdam Catalogue, a 7'3 magnitude in 

 the Ihirchmusterung is 8'3 or less, and a 7'5 magnitude 

 star in the Burchmusterung is only So or less when measured 

 with the photometer. This tends to confirm Dr. Burns' 

 opinion that the fainter stars in the Durchmusttiung are 

 estimated too bright. Only stars down to 7-5 magnitude 

 in the Thtrchmusterung were, however, measured at Potsdam. 



With reference to the stars composing the Milky Way, 

 it seems very improbable, I think, that the faintest stars 

 lie at the distance indicated by their magnitude. For, 

 taking stars of the Kith magnitude, their distance would 

 be one thousand times — (1-585)''' — that of an average star 

 of the 1st magnitude, and with Dr. Elkin's mean parallax 

 of 0089" for stars of the 1st magnitude, the parallax of a 

 loth magnitude star would be only 0-0000s9", or a " light 

 journey" of about 36,600 years ! Placed at this distance 

 our sun would be reduced in brightness to a star of magni- 

 tude 19-8, which no telescope yet constructed would show. 

 I find by Pogson's formula that to glimpse a star of 19-8 

 magnitude, a telescope of 132 inches, or 11 feet, in aperture 

 would be required. 



To reduce the sun to a star of the 16 th magnitude it 

 should be removed to a distance of 398,100,000 times its 

 present distance from the earth. This would imply a 

 parallax of 0'000518 ', and a "light journey " of over 

 0000 years ! But the stars composing the Milky A^'ay 

 may very possibly be much smaller than the sun and 

 intrinsically brighter (Sirian type), and, therefore, much 

 nearer to us than the above calculation would indicate. 



Dublin, July 10th. 



J. E. Gore. 



