October 1, 1891.] 



KNOWLEDGE. 



189 



exception of the letters and numbers upon them they are 

 absolutely untouched. Fig. 2 very nearly corresponds 

 with the region comprised in the large plate, and it will 

 enable our readers to recognize on the heavens the chief 

 patches of light and the brighter stars shown in the 



Vm. 1. index map, niiide from Dr. Ma 

 showing tlie jjrincipal stars about « Cygni. 



Wolf's photograph, 



photographs. They are at present very conveniently 

 situated for evening observation. The brighter stars in 

 the curious circle of stars to the right hand, or preceding 

 side of the line joining ; and X. Cygni, will at once be 

 recognized with an opera glass. 



On Dr. Max Wolf's photographs the region within and 



just around this little circle of stars is darker than the rest 

 of the field, and it is connected with a dark channel which 

 passes across the nebulous area close to ; Cygni. It seems 

 to be part of a dark branching structure which springs 

 from the darker region on the preceding side of ; Cygni. 



Fig. 2. Index map, made from Dr. Max "Wolfs photogrskph, 

 sho^iTng the principal stars about a Cygni. 



A similar dark branching structure is well shown on om- 

 large plate a little to the north of a Cygni, and it is 

 traceable running northward to near the top of the plate, 

 and again branching. This is due to no photographic 

 defect, for it is clearly visible on three different photo- 

 graphs of this region which have been sent me by 



Circle 



l-'n,. :i. Zinc iiliolu-ctrlii 



1)1' a iiart of (lie £ Cygui photogniph. on ilonblc the scale of the plate 



