Dr. C. Chree. Observations on Atmospheric 



" Observations on Atmospheric Electricity at the Kew Observa- 

 tory." By C. CHREE, Sc.D., Superintendent. Communi- 

 cated by Professor G. CAREY FOSTER, F.R.S. Received 

 May 11, Read June 4, 1896. 



TABLE OF CONTENTS. 



PAET I. 

 The Measurement of Potential in Theory and Practice. 



PAGE 



1 Historical and descriptive , 96 



2 3 Interpretation of electrograph records 98 



4 Selection of stations , 99 



5 6 Comparison of results at the different stations 100 



7 9 Eatio of readings at different stations, at different times, and under 



different meteorological conditions 102 



10 Comparison of water-dropper and portable electrometer 106 



11 Defects in instruments 108 



12 Checks recommended 109 



PAET II. 



Application of Results to Theories of Atmospheric Electricity. , 



1315 Theories of Exner and of Elster and G-eitel 110 



16 Method of treating Kew observations 112 



17 19 Anticipation of some objections : want of uniformity in conditions as 



to wind, and cloudiness; proximity to London 112 



20 Tables of results, including particulars as to potential, vapour density, 



humidity, sunshine, temperature, barometric pressure, and wind 



velocity 114 



21 Analysis of preceding tables according to voltages at base station .... 123 



22 Further tables, each containing analysis according to magnitude of 



some one meteorological element. . . . , 125 



23 Discussion of possible influence of vapour density 128 



24 relative humidity 128 



25 sunshine 128 



26 temperature 129 



27 barometric pressure 129 



28 wind velocity 129 



29 30 General summary of bearing of results on theory 130 



PAET I. 



The Measurement of Potential in Theory and Practice. 



1. An electrograph belonging to the Meteorological Office has 

 been in operation at Kew Observatory, with interruptions, since 1861. 

 The results obtained in the early years of its existence were dis- 



