PHI LOSOPHICAL T R ANSACTIONS. 
I. The Solar and Lunar Diurnal Variations of Terrestrial Magnetism. 
By S. Chapman, M.A., D.Sc., Fellow and Lecturer of Trinity College, Cambridge , 
and Chief Assistant at the Royal Observatory, Greenwich. 
Communicated by Sir F. W. Dyson, Astronomer Royal, F.R.S. 
Received March 12,-—Read March 22, 1917. 
Contents. 
§ 1. Introduction 
Page 
o 
Part I.—The Present State of the Problem. 
§2. Schuster’s first investigation (1889). 6 
§ 3. Fritsche’s investigations of the solar diurnal magnetic variations. 9 
§4. G. W. Walker’s investigation (1913). 11 
§5. van Bemmelen’s study of the lunar and solar semi-diurnal magnetic variations (1912) . 12 
§6. Schuster’s second memoir (1907). 14 
Part II.—A New Analysis of the Solar Diurnal Magnetic Variation. 
§ 7. Description of the data. 16 
§ 8. General outline of the analysis of the data. 18 
§9. The harmonic representation of the magnetic variation held.. 21 
§ 1-0. Comparison with previous harmonic analyses of the solar diurnal magnetic variation . . 23 
§11. The separation of the external and internal solar diurnal variation fields.26 
Part III.— A New Analysis of the Lunar Diurnal Magnetic Variation. 
§12. Description of the data and of the method of analysis .28 
§13. Results of the analysis of the lunar diurnal magnetic variation.30 
§14. Compai-ison with van Bemmelen’s data.31 
Part IV.—The Connection between the External and Internal Magnetic 
Variation Fields. 
§ 15. The observed values of the amplitude ratios and phase differences.34 
§16. The hypothesis of a uniformly conducting earth. 36 
§17. The hypothesis of a non-uniformly conducting earth. 38 
§ 18. The electrical conductivity of the earth as deduced from the diurnal magnetic variations . 41 
YOL. CCXVIII.-A 561, B [Published February 5, 1919. 
