General Reduction and Rectification of Observations. 

 3000 Adjustment of litstnnnenis. 



3010 Equatorial^, including; Clock Eate and Refraction. 



3020 Transit Circle. 



3040 Other Meridian Instruments, 



3050 Altazimuth. 



3060 Almucantar. 



3070 Other Extra-uieridian Instrumeuta. 



3080 Heliometer. 



3100 Micrometer, "Visual and Photographic. 



Refraction, Aberration. 

 3200 Personal Equations. 



3220 Errors of Screws, Circles, etc.. Flexure. 



3240 Photog-raphic Materials and Processes. 



Plates, Development, Fading of Images. 



Determination of Astronomical Constants by 

 Observation. 

 3300 General. 



3310 Constant of Aberration. {See also 0250). 



3320 Constant of Precession and Nutation. {See also 0260, 



1710). 

 3350 Miscellaneous. Refraction. 



DESCRIPTIVE ASTRONOMY AND ASTRO- 

 PHYSICS. OBSERVATIONS. 



SOLAR SYSTEM. 



4000 General. 

 4010 Sun. General. 

 4020 Observations of Position. 



4030 Constants (Dimensions, Mass, Density, etc.). 



4050 Solar Parallax. 



4060 Rotation {see also 4640 for Spectroscopic Determi- 



nation). 

 4070 Spots, Faculte, Atmosphere, Chromosphere and Corona 



without Eclipse. 

 4100 Periodic Phenomena of Surface (Sun-spot Cycle, etc.). 



4110 Connection of Solar Processes with Terrestrial 



Phenomena. {See also F 04 60). 

 4200 Temperature, Brightness, Radiation Constant, Rolo- 



meti-Y. {See also F 0930, 0940 ; C 4210). 

 4210 Eclipses. {See also 0350). 



4220 Predictions, Ephemerides, Maps of Shadow Track. 



4230 Times of Contact (Observations). 



4240 Corona. General. 



Form 



Brightness and Law of Brightness. 



Spectrum {see below, 4660). 



Polarization. 



Thermal Effects. 



Periodic Changes. 



Photographs, Drawings. 



