

PROGRESS OF MODERN ASTRONOMY 



greater reflector resolved others that would not yield to 

 Herschel's largest mirror. It seemed a fair inference 

 that with sufficient power, perhaps some day to be at- 

 tained, all nebulas would yield, hence that all are in 

 reality what Herschel had at first thought them- 

 vastly distant "island universes," composed of aggre- 

 gations of stars, comparable to our own galactic system. 



But the inference was wrong ; for when the spectro- 

 scope was first applied to a nebula in 1864, by Dr. Hug- 

 gins, it clearly showed the spectrum not of discrete 

 stars, but of a great mass of glowing gases, hydrogen 

 among others. More extended studies showed, it is 

 true, that some nebulae give the continuous spectrum 

 of solids or liquids, but the different types intermingle 

 and grade into one another. Also, the closest affinity 

 is shown between nebulae and stars. Some nebulae are 

 found to contain stars, singly or in groups, in their 

 actual midst; certain condensed "planetary" nebulae 

 are scarcely to be distinguished from stars of the gas- 

 eous type; and recently the photographic film has 

 shown the presence of nebulous matter about stars 

 that to telescopic vision differ in no respect from the 

 generality of their fellows in the galaxy. The familiar 

 stars of the Pleiades cluster, for example, appear on the 

 negative immersed in a hazy blur of light. All in all, 

 the accumulated impressions of the photographic film 

 reveal a prodigality of nebulous matter in the stellar 

 system not hitherto even conjectured. 



And so, of course, all question of "island universes" 

 vanishes, and the nebulae are relegated to their true po- 

 sition as component parts of the one stellar system the 

 one universe that is open to present human inspection. 



