THE LIGHT OF THE STARS 293 



which blots out the light of the more distant stars; and (2) the misty 

 matter associated with the more condensed star-groups may obscure the 

 light of external galaxies which therefore are better seen through the 

 thinner places in our own stellar mass. Either of these causes would 

 account for the stellar voids which Sir William Herschel describes as 

 even a warning of the proximity of nebulas; but it will be seen that 

 there is no foundation for the inference which Mr. Herbert Spencer 

 has built upon the supposed fact, namely, that none of the nebulas can 

 be external galaxies, because " thousands of nebulas . . . agree in their 

 visible positions with the thin places in our own Galaxy," and that they 

 are necessarily most intimately linked with its structure. The connec- 

 tion, if established, will in no wise invalidate the wider generalization 

 that external galaxies must appear to be most numerous in those regions 

 where the mists or gaseous masses attendant on our Galaxy thin out 

 and permit the light from the outside to penetrate the starry walls. 



Mr. Eoberts bears this testimony to the fact that the larger part of 

 the nebulas are situated beyond the confines of the Galaxy: There are 

 " to be seen," he says, " stars apparently in a complete state of develop- 

 ment, scattered over the surfaces of the most prominent of the nebulas, 

 but it will be observed that they do not conform with the trends of the 

 spirals nor with the curves of the nebulous stars [or stellar condensa- 

 tions 8 ?] involved in them. This fact I apprehend to be strong evi- 

 dence that they are independent of the nebulas — that they are not in 

 any way involved in the nebulosity, but are seen by us either in front, 

 or else in space beyond the nebulas. If they were beyond them, their 

 light would have to penetrate through the nebulosity, and we should 

 therefore expect it to be duller in character and the margins of the 

 stars to be surrounded by more or less dense nebulous rings; but these 

 effects are not traceable in the photo-images, and we are consequently 

 led to adopt the alternative inference that they are between us and the 

 nebulas. If they were involved in the nebulosity, they would conform 

 with the trends of the convolutions and appear like nebulous stars." 9 



The dark lanes in the Milky Way are sometimes called " rifts," a 

 term which implies that the stars are distributed in a relatively thin 

 sheet which can be rent asunder. Moreover, the word is not used in a 

 merely metaphorical or descriptive sense, but in its full significance, as 

 in the following quotation from " Worlds in the Making " by Svante 

 Arrhenius (p. 173) : "The presumption that these rifts represent the 

 tracks of large celestial bodies which have cut their way through widely 

 expanded nebular masses has been entertained for a long time." And 



8 Of the larger spiral nebulse, Professor G. W. Ritchey says (Astrophys. J., 

 Vol. 32, p. 32, July, 1910) : "All of these contain great numbers of soft star-like 

 condensations which I shall call nebulous stars. ' ' It appears not improbable that 

 these represent irresolvable stellar groups. 



9 ' ' Photographs of Stars, Star Clusters and Nebula?, ' ' Vol. 2, pp. 23-24. 



