General Reduction and Rectification of Observations. 



3000 A djustment of Instrnments. 



3010 Equatorial?', including- Clock Rate and Refraction. 



3020 Transit Circle. 



3040 Other Meridian Instruments, 



3050 Altazimuth. 



3060 Almucantar. 



3070 Other Extra-meridian Instrumenta. 



3080 Heliometer. 



3100 Micrometer, "Visual and Photographic. 



Refraction, Aberration. 



3200 Personal Equations. 



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



3240 Photographic Materials and Processes. 



Plates, Development, Fading- of Imag-es. 



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, FacultV, 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 0460). 

 4200 Temperature, Brightness, Radiation Constant, Bolo- 



metry, {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 (^ee below, 4660), 



Polarization, 



Thermal Effects, 



Periodic Changes, 



Pliotographs, Drawings. 



