Photography of the Skies 



of stars of nearly equal magnitude ; some of faint 

 stars, also of nearly equal magnitude; while the 

 distances between the stars are remarkably 

 regular. Passing from these characteristics of 

 stellar arrangement to photographs of spiral 

 nebulas, Dr. Roberts points out that the nebulous 

 matter in the spirals is broken up into star-like 

 loci, which in the regularity of their distribution 

 resemble the curves and combinations of stars 

 exhibited by photographs upon which no trace of 

 nebulosity is visible. It seems, therefore, that 

 the curvilinear grouping of stars of nearly equal 

 magnitude gives evidence that the stars have been 

 evolved from attenuated matter in space by the. 

 action of vortical motions and by gravitation. 

 Exactly how the vortical motions were caused, 

 or what has brought about the distributions of 

 nebulosity in the spiral nebulae, cannot be an- 

 swered; but the marvellous pictures of Dr. Rob- 

 erts establish the reality of the grouping, and 

 furnish students of celestial mechanics with rich 

 food for contemplation."* 



"As Professor Bond drew the nebula of Andro- 

 meda with his eye at the best telescope he could 

 command, he depicted dark lanes which come out 

 in a photograph as divisions between zones of 



* Nature, March 3, 1898. 



A second volume of Dr. Roberts's "Photographs of Stars, 

 Star Clusters, and Nebulae" was published in December, 

 1899, by Witherby & Co., 326 High Holborn, London. It 

 contains seventy-two photographs printed in collotype from 

 the original negatives, with descriptive and explanatory 

 letterpress. 



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