ISLAND GALAXIES ' 



By A. ViBEET Douglas, M. B. E., Pn.U. 

 McGill XJnivers'ity, Montreal 



[With five plates] 



The knowledge that the heavens contain bodies that are neither 

 planets nor stars is age old, for the keen eyes of the stargazers of 

 civilizations long since gone did not fail to detect such objects as 

 the nebu,losity in the constellation of Orion and the small, hazy 

 patch in Andromeda. But the significance of these objects remained 

 a mystery for many centuries. 



With the invention of the refracting telescope by Galileo about 

 1600, many of the apparently nebulous regions in the Milky Way 

 were found to be resolvable into separate stars. These are so closely 

 strewn in the sky that to the unaided eye their light is completely 

 merged and blended. Toward the end of the seventeenth century the 

 second great type of telescope was devised by Sir Isaac Newton, 

 namely, the i-eflecting telescope, in wdiich the starlight is brought to 

 a focus not by a lens but by a mirror. About 150 years later, when the 

 small pif)neer telescopes of Galileo and Newton had given place to 

 large and i)owerful insti'unients. Lord Rosse discovered that a cer- 

 tain nebulous region in the constellation Cannes Venatici when 

 viewed through his gieat telescope was not merely a random, hap- 

 hazard agglomeration, but a cluster of many stars distinctly grouped 

 in the configuration of a spiral. (PL 5.) Thereafter the search 

 for and discovery of other spiral nebuloe became one of the most 

 fruitful tasks of the astronomer. From that time to the present, as 

 a result of ever-increasingly powerful instruments, together with the 

 introduction of photographic methods, many hundreds of spiral 

 nebulae have been found, and it is estimated that a thorough search of 

 the entire heavens would disclose hundreds of thousands of them. 



Speculation was at once begun. Could it be that all the nebulas 

 were in reality close assemblages of stars requiring only yet more 

 powerful telescopes to show each star separately? 



1 Reprinted by permission, with alterations, from Discovery, Vol. IX, No. 99, March, 

 1028. 



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