THE STORY OF NINETEENTH-CENTURY SCIENCE 



process of condensation to form stars, was generally 

 accepted for almost half a century. But in 1844, when 

 Lord Rosse's great six-foot reflector the largest tele- 

 scope ever yet constructed was turned on the nebulae, 

 it made this hypothesis seem very doubtful. Just as 

 Galileo's first lens had resolved the Milky Way into 

 stars, just as Herschel had resolved nebulae that resisted 

 all instruments but his own, so Lord Rosse's even greater 

 reflector resolved others that would not yield to Her- 

 schel's largest mirror. It seemed a fair inference that 

 with sufficient power, perhaps some day to be attained, 

 all nebulae would yield, hence that all are in reality 

 what Herschel had at first thought them vastly distant 

 " island universes," composed of aggregations 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 be- 

 tween nebulae and stars. Some nebulae are found to 

 contain stars, singly or in groups, in their actual midst; 

 certain condensed "planetary" nebulas are scarcely to 

 be distinguished from stars of the gaseous type; and re- 

 cently the photographic film has shown the presence of 

 nebulous matter about stars that to telescopic vision dif- 

 fer 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 



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