10 



7520 Lists. 



Catalog-ues. 



Colours of Double Stars. 



Spectroscopic Binary Systems. {See. 8600). 



Spectroscopic Observations of Visual Binary Systems. 

 {See 8560). 



Invisible Companions. 

 7530 Discussion of Orbits. 



Dimensions, Mass and Distance of Binary Systems. 



7600 Variable Stars, including New Stars. 



Observations, Light Curves. 



Lists, Catalogues. 



Classificatiou. 'IVpes of Variable Stars. 



Spectrum {see 8300). 



7700 Star Clusters. 



Position. 



Triangulations. 



Variable Stars in clusters. 



7800 Nebulae. 



Observations (form, brightness, position). 

 Variations in Nebulae. 

 Diffused Nebulosity {e.g. Pleiades, Orion). 

 Planetary Nebulae. 

 Distribution in sky. 

 Nebiilfe and clusters. 



Photographs, Maps, Drawings (published repro- 

 ductions). 



7900 Milky Way. 



8000 Stellar Spectroscopy (Stars, Nebulae, Clusters). 



General. (Books, treatises). 

 8010 Stars. 



8020 Wavelengths of lines for individual stars. 



8040 Comparison of wavelengths, intensity and width, 



in different stars. 

 8050 Identification of Elements. 



8070 Distribution of Energy in Spectrum. 



8080 Physical Constitution (Pressure, Temperature). 



8100 Classification. 



8120 Study of special types of Spectra. 



8140 Distribution of types of Spectra in the Heavens. 



8200 Nebulai and Clusters. 



(With divisions as for Stars). 

 8300 Variable Stars, including New Stars. 



(With divisions as for Stars). 

 8400 Peculiar Spectra. 



8450 Photographs of Spectra (published reproductions). 



Drawings and Maps of Spectra. 



