MOUNT WILSON OBSERVATORY. 273 



of the dwarf class, are not distributed in the same way as the stars of 

 normal speed, but show a very asymmetrical distribution, their cen- 

 troid moving towards a point in the galaxy of galactic longitude about 

 250°. The same result was found previously by Adams and Joy 

 from a smaller number of stars of large radial velocity. 



Spectra of Nebulous Stars. 



The investigation of the spectra of stars involved in nebulosity has 

 been carried on by Mr. Hubble with the aid of the Cassegrain spec- 

 trographs and a small slitless instrument which may be used at the 

 primary focus of either of the telescopes. With the latter instrument 

 the spectra of about 150 stars ranging in magnitude from 10.5 to 14.0 

 have been classified. 



The spectra of 85 stars have been photographed with the Casse- 

 grain spectrographs. The stars involved in extended nebulae giving 

 an emission spectrum are nearly all of tyipes OeS and BO. Those 

 in extended nebulse giving an absorption spectrum are Bl or later, 

 averaging about B4. The following six stars of types later than A3 

 are found to be involved in nebulosity: 



B. D. +31° 597 K2 giant 



4h i4m^ ^28° 5' (1920) K8 dwarf 



T Tauri Gp with bright lines 



B. D. +28° 645 F8 



B. D. -19° 4357 G5 giant 



R Coronse Australia Gp with bright lines 



The central stars of all the large planetary nebulse so far observed, 

 N. G. C. 246, 1514, 3587, 6853, 7293, and 7635, with mean diameters 

 exceeding 2', have spectra intermediate between the Wolf-Rayet 

 type and Oe5. 



The bearing of these results on the nature of the spectra of the 

 nebulse with which the stars are connected is discussed in another sec- 

 tion of this report (p. 254). 



Miscellaneous Investigations. 



1. Observations of o Ceti were continued as far as its minimum of 

 light, and show a repetition of the remarkable changes in its spectrum 

 which were first seen at the preceding minimum. A curious longitu- 

 dinal asymmetry in the bright hydrogen lines and the bright regions 

 adjoining the heads of the titanium-oxide bands was observed. The 

 components of the hydrogen lines were displaced with reference to 

 each other by an amount which would correspond to an angular dis- 

 tance of 0''2 in the sources producing the lines. 



2. The spectrum of R Scuti was observed on April 17 to have strong 

 M-type bands which disappeared by May 24. The spectrum was 

 estimated as G5 on June 11. Strong, sharp enhanced lines are very 

 prominent in the spectrum. No bright lines were found. 



