MOUNT WILSON OBSERVATORY. 251 



Direct photographs of the following galactic nebulse and nebulous 

 stars have been made with the two reflectors: 



These galactic nebulse usually show a marked obscuration of stars 

 lying within or beyond them. Another general impression gained from 

 inspection of these plates and others is that the forms and structure 

 of galactic nebulse are influenced largely, if not chiefly, by repulsive 

 forces emanating from involved or associated stars ; at least, the forms 

 are interpreted more readily on a basis of repulsion than on one of 

 attraction. 



The 10-inch Cooke astrographic lens and the small cameras have 

 been used to study the distribution of extended nebulae and areas of 

 obscuration. A double distribution of these objects has definitely been 

 established. They condense about two planes — the galactic circle 

 and the belt of bright helium stars. This fact supports the hypothesis 

 of a local cluster and emphasizes its similarity with the Milky Way 

 clouds. 



Three small patches of obscuration have been located in galactic 

 latitudes as high as 30° to 37°. Additional evidence confirms Mr. 

 Hubble's former conclusion that the division in the Milky Way in the 

 Aquila-Ophiuchus region is due to great clouds of dark nebulosity. 



Polarization tests have been made on several nebulse with the appa- 

 ratus employed by Mr. Babcock in his work on the polarization of the 

 night sky. Positive indications were obtained in the case of the 

 Merope nebulosity, but certain questionable points make it desirable 

 to repeat the observations with a new grating in front of the calcite 

 crystal before final conclusions are formulated. 



A neodymium-chloride filter prepared by Mr. Anderson has given 

 promising preliminary results with objective prism spectra. This 



