468 



KNOWLEDGE & SCIENTIFIC NEWS. 



(July, igo6. 



are sharp and well defined in the midst of dense 

 nebulosity. They are as clearly cut as we see the 

 canyons of great rivers, but the-r width may in reality 

 be millions of miles, for we have no reason to assume 

 that the nebula is nearer to the earth than the stars. 

 It is, indeed, possible that the stars which dot the sur- 

 face are nearer to us than the nebula." 



About 3 degrees north-east of the star t* Canis 

 Majoris is another nebula of irregular shape. Dr. 



defined, and suggestive of the idea that in consequence 

 of some internal strain, operating from opposite direc- 

 tions, the nebula was rent asunder, and the parts separ- 

 ated from each other." 



In another nebula in Monoceros, photographed by Dr. 

 Roberts, a little west of the triple star 15 Monocerotis, 

 there is a remarkable vacuity or hole. Dr. Roberts 

 calls it a dark tortuous rift, and says : " The rifts prove 

 that the nebulje are not globular, but are like clouds 



Great Nebula near p Ophiuchi. 



{From a ;<lio(of)rii;)/l by Prof. E. E. Barnard, nj the Lick Obscrrntorij .) 



Roberts says that the star D.M. 1848 '"is on the mar- 

 gin of a dark sinuous vacancy or rift in the nebula, 

 through which we see into the starless vacancy of space 

 beyond it." This opening closely resembles the " key- 

 hole " opening in the great nebula in Argus. Dr. Roberts 

 adds : ' ' These vacancies are most conspicuously seen 

 where the surrounding nebulosity is dense, though 

 they are also visible in some parts whore it is relatively 

 faint. The margins of the vacancies- are often sharply 



with relatively small depths, and that we can see 

 through them into the darkness of space beyond." 

 There are also very noticeable areas devoid of stars in 

 the region surrounding the nebula. 



On July 12, 1891, Professor Max Wolf, of the 

 Astrophvsical Observatory of Heidelberg, discovered 

 three dark markings in the Milky \\'ay, about lA 

 degrees west of the star 7 .4quilEe. He calls them the 

 " Triple Caves," and they certainly present a very re- 



