November 1, 1899.] 



KNOWLEDGE. 



240 



of some attracting mass, would ultimately fall therein, the 

 particles of highest initial velocity deferring this common 

 fate the longest. The extraneous comets and meteors that 

 visit the solar system must be considered as a few scat- 

 tered fragments that have avoided capture. The light 

 intercepted by the small bodies that still wander in space 

 unattached to an attracting centre we may look upon as a 

 negligible quantity. 



4. There remains the hypothesis — the only natural and 

 obvious one — that the stars do really thin out and ultimately 

 cease as their distance from us increases. On the supposition 

 that the stars are infinite in number, it follows that a 

 straight line drawn in any direction from the eye of an 

 observer on the earth will ultimately meet a star. Now, 

 it is a well-known law in optics that the brightness of a 

 body is independent of the distance, and that the quantity 

 of light received from a sphere of constant brightness only 

 depends on the area of its apparent disc ; consequently the 

 total light received from a number of stars is proportional 

 to the total area of their apparent discs ; but, if the number 

 of stars were infinite, this area would be simply that of 

 the whole sky ; hence we should have the whole sky one 

 blaze of light ! Therefore the number of stars must be 

 finite. 



It does not, however, absolutely follow that the stellar 

 universe is finite. We may escape from this conclusion by 

 imagining that outside the luminous stars there is an 

 infinite number of dark bodies that are never seen, and 

 that the visible universe is bounded by clouds of cosmical 

 dust which conceal everything beyond ; but this is un- 

 supported by evidence. 



A reference to popular works on astronomy will show 

 that there is a great reluctance to adopt the view here 

 presented. " We cannot imagine such a thing to be 

 possible " is the argument put forward. What any person 

 thinks possible or impossible depends on his mental 

 constitution. 



(irauting that the universe is finite in space it follows 

 that it is finite in time, for the quantity of matter and of 

 energy it contains are both finite ; the energy is being 

 steadily dissipated in the form of radiant heat ; this 

 constant loss of heat cannot have persisted for an infinity 

 of time past, and it must end in the future. 



But if we adopt the hypothesis of a finite universe, we 

 at once meet with a number of questions which it is im- 

 possible to answer. What, for instance, is the destination 

 of 1618 Groombridge, with its velocity of two hundred and 

 thirty miles per second ? It has been calculated that this 

 star must pass out of the stellar universe altogether, there 

 being no known force sufficient to restrain it. Are there 

 other universes constructed on different principles from 

 ours '.' Is the ether finite ? and what becomes of the heat 

 constantly radiated into space '? Perhaps the real solution 

 of the difficulties thus presented by a finite universe is 

 metaphysical. The human intellect is so framed that it 

 can only conceive space as infinite, and yet can form no 

 conception of infinite space. Possibly space without limit 

 is a mental illusion. 



The only satisfactory method of dealing with such a 

 question as the limits of the stellar universe is by inference 

 from observed facts. 



[We fear Mr. Burns' handling of this subject is scarcely 

 conclusive. We have no means for experimenting on the 

 first of his four hypotheses. Mr. Burns' second argument 

 proves too much. It would follow that the existence of 

 matter in the gaseous state is impossible in interstellar 

 space, a conclusion which the existence of gaseous nebulae 

 of enormous tenuity and extent appears to controvert. 

 Under the third head he supposes that the particles of 



cosmical dust would all soon fall in to some attracting 

 body ; whereas they would revolve round it in nearly all 

 cases. Whilst the assumption that if the stars were 

 infinite in number, " the whole sky would be one blaze of 

 light," supposes something as to their distribution. We 

 see that the earth is small as compared with its distance 

 from the nearest other planet, and that the solar system 

 is small as compared with the distance separating it from 

 the nearest star. If the snme rule prevails on the larger 

 scale ; if the dimensions of star systems are small as 

 compared with the distances between them, then " a 

 straight line drawn in any direction from the eye of an 

 observer on the earth, will," in most cases never " meet a 

 star." — E. W.iiTER Maunder.] 



PHOTOGRAPH OF NEBULA SURROUNDING 

 THE STAR D.M. NO. 1848 MONOCEROTIS. 



By Isaac Egberts, d.sc, f.r.s. 



THE photograph annexed is of the region in the sky 

 comprised between R.A. 6h. o7m. 53'5s. and R.A. 

 7b. 2m. 52-7s., and in declination between south 

 11- 9-!) and 9° 81'-1. The area, therefore, is 

 4m. 5!)'2s. in extent from foUoning to precedinr/, 

 and 1° 35''8 in south declination. Scale, one millimetre 

 to twenty-four seconds of arc. 



Co-ordinates of the fiducial stars marked with dots for 

 the epoch 1900. 



Star (.) D.M. Schonfcld No. 1818 Zono -&° E.A. 6h. o9m. 12-9s. 



Bee. S. 9° 58'-6. Mag. (5-3. 

 Star (..) D.M. No. 1862 Zoue -10° R.A. 7h. Ini. G-3s. Dec. 



S. 10° 30' -o. Mag. 7 0. 

 Star (•.•) D.M. No. 1854 Zone -9° R.A. 7.i. 2m. 36 7s. Dee. 



S. 9° 49'-7. Mils. 7-3. 



The nebulae I assume to be new to science, for they are 

 not referred to in the catalogues, and by referring to the 

 nebula N.(r.C. 2237-9 iMonocerotis, a photograph of which 

 was published in the number of Knowledge for .June last, 

 it will be seen that the three nebulas are in near proximity 

 to each other. 



The photograph was taken with the twenty-inch reflector, 

 and exposure of the plate during 2h. ■47m., on the 9th of 

 March, 1899, and it shows the brighter nebula to be of a 

 flocculent character with some faint star-like condensations 

 involved, and the star D.M. 1848, which is north preceding 

 the centre, seems to be on the margin of a dark sinuous 

 vacancy, or rift, in the nebula, through which we can see 

 into the starless vacancy of space beyond it. Sharply- 

 defined zig-zag dark rifts have been shown on other photo- 

 graphs of cloud-like extensive nebulse which have been 

 published in Knowledge, notably that designated N.G.C. 

 2237-9 Monocerotis, and in a less striking manner, N.G.C. 

 1499 Persei. I;l V. 37 Cygni, I^I V. 14 Cygni, the Great 

 Nebula in Orion, and others. The " keyhole " in the 

 nebula round ij Argiia greatly resembles that shown in 

 this nebula. 



These vacancies are most conspicuously seen where the 

 surrounding nebulosity is dense, though they are also 

 visible in some parts where it is relatively faint. The 

 margins of the vacancies are often sharply defined and 

 suggestive of the idea that in consequence of some internal 

 strain, operating from opposite directions, the nebula was 

 rent asunder and the parts separated from each other. 

 We could also imagine that another nebula, of smaller area 

 than this, moving in space at nearly right angles, and 

 being edgewise to it, rushed through carrying along in its 

 course so much of the material of this nebula as would ^be 

 represented by the sectional area of the other, and thus 



