EVOLUTION OF THE ST MIS 225 



read that the nebulae in general abhor the Milky Way. In the northern 

 hemisphere they cluster most densely in the neighborhood of the pole 

 of the galaxy. In the southern hemisphere they show the same tend- 

 ency, but not so strongly. There are nebulae in the Milky Way, but 



Southern Hemisphere. Northern Hemisphere. 



Fig. 5. Distribution of Nebul.e (and Star Clusters). According to Proctor. 



Nebulae are marked by dots ; clusters by crosses. 



they are relatively few. HerschePs and Proctor's conclusions related 

 only to the brighter nebula?, which had been discovered by visual 

 methods. 



Before Keeler began to photograph nebulae with the Crossley re- 

 flector, in 1898, some 10,000 of these bodies had been discovered and 

 catalogued. A few plates exposed by Keeler here and there over the 

 northern sky recorded several hundred additional nebula?. Using his 

 photographs of small areas of the sky as samples, he estimated con- 

 servatively that at least 120,000 nebula? are discoverable with the Cross- 

 ley reflector. Further observations by Perrine with the same instru- 

 ment and by Fath with the 60-inch Mount Wilson reflector have shown 

 that the number discoverable with fairly short exposures is considerably 

 greater than 120,000. Path's plates, uniformly distributed over the 

 northern sky from the North Pole to declination 22°. 5 south of the 

 Equator, recorded 86-1 nebula? previously unseen. The numbers on the 

 individual plates are set down in the corresponding area. The curve 

 drawn across the chart represents the central line of the Milky Way. 

 The north pole of the galaxy is at N\ The distribution of these faint 

 nebula? is seen to be patchy, but the fact is in evidence that the faint 

 nebulae, like those bright enough to be discovered by visual methods, 

 abhor the Milky Way. 



VOL. LXXXVII. — 16. 



