Knowledge. 



With which is incorporated Hardwicke's Science Gossip, and the Ilhistratcd Scientific Xews. 



A Monthly Record of Science. 



Conducted by Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 



DECEMr.i:K, 1911. 



THE NEW ASTRONOMY. 



IV.— THE GAL.AXV AND AN IMMORTAL C()SMO.S. 



By PROFESSOR A. W. BICKEKTOX. 



Thi^- more \\e study the stars, the more we are 

 impressed w ith the fact that the stellar s\stem is not 

 a chance distribution, but on the contrar}-. that 

 almost the entire content of the celestial \ault 

 that we can see, whether it be nebulae or stars, 

 is a single organized s}stem and has a definite 

 boundary. 



Whiti.-. planetary and diffused nebulae ; star 

 clusters • temporarw variable and double stars, each 

 and all occup\' definite positions, every one of w hich 

 offers striking evidence of a s\'stem of evolution 

 as consistently simple as it is conclusively 

 demonstrated. 



Taken roughly as a whole, the Galactic Universe 

 consists of a belt of stars, containing lateral streams, 

 dense aggregations in parts, and equally striking 

 defects of illumination in other parts. This rough 

 ring or belt is possibh' i>f a double spiral character : 

 this opinion is ver\' firmh' held b_\' Professor See and 

 a number of other able astronomers. This belt of 

 stars, which varies from some ten to twent}' degrees 

 in width, is almost exactly bisected by a great circle 

 of the heavens. Leaving the margins of this stellar 

 belt, we come upon two belts of the celestial sphere 

 that are sornewhat sparsely inhabited. Then, as we 

 ajjproach the two poles, we meet with an increasing 

 number of nebulae. These seem to have their 

 maximum density in both hemispheres in a position 

 approximately that of the poles of the great circle 

 of the Galax}'. (See Figure 1.) It is well to 

 hiok upon this great circle as the equatorial 

 plane of the Sidereal Universe. A vast number 



of these nebulae are, as described in our last 

 article, of a double spiral character. The\- 

 are, as a rule, what are called White Nebulae, 

 that give continuous spectra, suggesting that 

 the\' are dust swarms. There are comparatively 

 few stars in the polar regions of the heavens. 

 Stars are mostlv confined to the equatorial belt, 

 and it is in this same belt that we find nearly 

 all the gaseous nebulae of the heavens. These \ast 

 masses of diffused gas are of two kinds, the one the 

 planetarv nebulae, already described. Usually, 

 although ver\- rare, these are extremely definite. 

 The other class of gaseous nebulae, such as 

 the great nebula in Orion (see Figure 4), is 

 of extreme irregularit\', usually quite devoid of 

 an\- s\"mmetr\- of form, vet exhibiting marked 

 structure that often seems to suggest drifting 

 motion. In this same Milk\' Way belt, in addition 

 to gaseous nebulae, are to be found most of the 

 beautiful star clusters. Nearly all the temporary 

 stars have blazed out in this belt, and it is in this 

 same belt that we find most of the variable, or 

 wonder stars, most of the telescopic double stars, and 

 spectroscopic binaries, and here also, although some- 

 what singularly situated, we find the Wolf-Rayet 

 stars. But very few White Nebulae are found in 

 the belt of the Milky Way. (See Figure 2.) 



Indki'knoent Sii)i-:kiiAi. Systems. 



In addition to all that has been described, that 

 seem to be parts of one consistent whole, we have 

 other s\-stems which it is not certain belong to our 

 Galactic Universe at all. It is the opinion of Sir 



453 



