282 Mr. E. H. Nichols on the Diurnal 



remarkable that the law of equipartition of energy of the kinetic 

 theory of gases gives an angular velocity of the same order. 

 In fact, taking for the mean translational velocity of iodine 

 molecules at 0° C. the value 1*64 . 10 4 cm. /sec. and for the 

 molecular radius 2 . 10 ~ 8 cm., and attributing to the molecules 

 two exchangeable rotational momentoids, against three trans- 

 itional ones, I find for the average angular velocity 



« = 1-59.10 12 , 



which is well comparable with the above value. 



I gladly take the opportunity of expressing my thanks to 

 Professor R. W. Wood, who has drawn my attention to 

 these beautiful phenomena and has encouraged me to take 

 up the subject of resonance-spectra from the theoretical 

 standpoint. 



July 27, 1916. 



XXXIII. The Diurnal Variation of Atmospheric Electrical 

 Quantities. By E. H. Nichols, B.Sc, A.R.C.Sc* 



THE diurnal variation of the electrical conductivity has 

 been investigated recently by Kahler t and Dorno J 

 by means of a continuously recording dissipation apparatus, 

 while Gockel § has obtained eye observations of conductivity 

 and electric charge. For the investigations here detailed, 

 two Ebert Electrometers || have been used to record the 

 respective positive and negative electric charges, while 

 the Wilson Compensating Gold Leaf Electroscope *|[ 

 measured the conductivity and air-earth current, the 

 potential being obtained from a Kelvin Water-Dropper 

 apparatus. The method employed for the Wilson instru- 

 ment was a variation of the original method adopted by 

 C. T. R. Wilson. There are three operations involved : — 



(a) The charge on the test-plate is first found by removing 

 the cap, and replacing it quickly after momentarily earthing 



* Communicated by the Director of the Meteorological Office. 



t Ergebnisse der Met. Beob. im Potsdam, 1909, 1911. 



X " Studie iiber Licht und Luft des Hochgebirges," 1911 (Davos). 



§ Mache u. von Schweidler, Atmosphdrische Elektrizitat, 1909, p. 90; 

 A. Gockel, Met. Zeit. xxiii. pp. 53, 339 (1906); xxv. p. 9 (1908); 

 Archives des Sc. phys. et nat., Sept. 1913. 



|| Phys. Zeit. viii. 8. p. 246 ; viii. 16. p. 527 : x. 8. p. 251. 



it Proc. Camb. Phil. Soc. xiii. p. 184 (1906). M. O. Geophvs. Mem. 

 No. 7. 



