Journal of the Asiatic Society of Bengal. [N.S., XII, 



the ratio of Potential difference to pressure remains constant both in air 

 and in hydrogen. The Potential difference goes on decreasing as pressure 

 decreases up to a certain point, but after that, it increases with decreased 



pressure. 



The paper dealt with a mathematical theory which explained all 



these features. 



The curve connecting current and pressure showed similar pecularities. 



but that connecting current and potential difference (exhibited on the 



screen) was very complicated, showing one nodal point. 



On the Radio-activity of some of the Mysore Rocks. — By 



W. F. Smbeth and H. E. Watson. 



Determinations have been made of the amount of radium in a num- 

 ber of rocks collected from different parts of Mysore. The geological 

 history of these rocks is known with some accuracy, and it is shown that 

 certain geological groups contain similar amounts of radium. 



On the Cathode fall from various, metals. — By 



H. E. Watson and G. Paranjpb. 



The cathode fall from as many metals as possible is being measured 

 in the inactive gases. There appears to be a definite relation between 

 the cathode fall and the position in the periodic table of the metal used 

 as cathode. 



The Contribution of Arabs to Astronomy and Trigonometry 

 with Special Reference to El-Biruni and his Kanoon 



Masudi.— By Zia-Ud-Din Ahmad, CLE. 



A New Method of observing the Zeeman Effect.— By 



Wali Mohammad. 



The Potential Gradient at Patna. — By V. H. Jackson, M.A-, 



and S. K. Mitra, B.Sc. 



Continuous records of the potential gradient were commenced in 

 January 1914, absolute values being obtained in the manner recommended 

 by Simpson (Phys. Zeitschr. XIV, January 1913) by attaching a radium 

 collector to the centre of a long insulated wire stretched horizontally 2*5 

 metres above a lawn. For satisfactory insulation under all weather con- 

 ditions the surfaces of the sulphur insulators used have to be protected 

 and electrically warmed. Preliminary results are as follows : — Harmonic 

 analysis of the daily range for the whole year gives P = 125 + 70 sin 

 (6 + 131) + 43 sin (20 + 195) + 125 sin (36 + 260) + 11 sin (46 + 348). 

 The mean gradient is lowest, about 75, in May, and reaches a maximum, 

 about 200, in November. The diurnal variation shows an unusually 

 marked double oscillation in all months, particularly in the cold weather, 

 November to February, when the evening maximum about 9 p.m often 

 exceeds 400 v/m. A second record of the gradient over a flat roof 12*8 

 metres above the ground, commenced in October 1915, leads to the con- 

 clusion that at this level the diurnal oscillations are much less marked, 

 e.g., analysis for December 1915 gives — 



At ground-level P= 207-4 + 121-5 sin (6 + 136) + 90*8 sin (20 + 197) 



+ 2(i-7 sin (30 + 303) 

 At roof-level P=153-3 + 05-6 sin (0 + 125) 4- 45-6 sin (20 + 190) 



+ 6-5 sin (30 + 318) 



