May 25, 1917] 



SCIENCE 



529 



Pig. 18. The Milky Way iu Ophiuehus showing apparent absorption or obstruction effects; 

 photographed by Barnard with the 10-inch Bruce telescope of the Yerkes Observatory. 



were able to see this material only as the 

 very strong wave of light which left the 

 star at maximum brightness made the ma- 

 terial luminous in passing. 



We can scarcely doubt, in view of all 

 these facts, that there is a stupendous 

 amount of obstructing material scattered 

 throvighout our stellar system. This may 

 eventually be condensed into stars ; but the 

 point I wish to emphasize is that the mate- 

 rial is there, and is evidentlj' obstructing 

 the passage of light. The efficiency of the 

 obstructing material is no doubt the greater 

 in the long dimensions of the system ; in the 

 direction of the Milky Way. 



Let us now consider the nebulte which are 

 not in or near the Galaxy. The overwhelm- 

 ing majority of the stars are in the galactic 

 zone of the sky. If we call this zone 30° 

 wide, which makes it a shade over one 

 fourth the entire sky, we may say that this 

 fourth-area contains certainly three fourths 

 of all the stars known to exist in our stellar 

 sj'stem. The remaining three fourths of 

 the sky do not show more than one fourth 

 of all the stars. Of about 15,000 nebulae 

 recorded probably not over 300,'* certainly 



5 It is not practicable to state the number more 

 definitely. To illustrate the difBculty, we mention 

 the fact that several small adjoining nebul» re- 



