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V. Electric Discharge in a Transverse Magnetic Field. 

 By Prof. D. N. Mallik, B.A., Sc.D., F.B.S.E., and 

 A. B. Das, M.Sc* 



[Plate II.] 



N a paper in the Philosophical Magazine, Oct. 1U08, 

 one of us (D. N. M.) considered the behaviour of 

 an electric discharge in a tube of De La Rive's pattern, under 

 gradually decreasing pressure. It was there shown that, 

 starting with a pressure inside the tube equal to that of the 

 atmosphere, the discharge is at first in the nature of a 

 shower of sparks, filling the whole tube ; that these various 

 streams combine into a single band or single thick stream, 

 when the pressure is sufficiently low ; that only when the dis- 

 charge is of this kind is there rotation under the action of a 

 magnetic field, as in the usual De La Rive apparatus. It 

 was also noted that, as the pressure is further reduced, the 

 band is gradually changed into a shower again and the 

 rotation ceases. 



2. In a subsequent paper (Oct. 1912) a theoretical ex- 

 planation of the various phenomena was attempted, and it 

 was shown that they are connected with the fact that the 

 relative number of positive and negative ions present in the 

 tube varied at these different stages. 



3. The object of the present paper is to discuss, in detail, 

 the behaviour of the discharge when the rotatory stage is 

 passed. It results both from theory and experiment that 

 the phenomena are dependent on (1) the voltage of the 

 primary of the induction-coil, (2) the nature of the coil, 

 (3) the difference of potential between the electrodes of the 

 discharge-tube, (4) their distance, (5) and (6) the pressure 

 and the nature of the gas or vapour in the tube, and (7) the 

 nature of the electrodes. 



It has been our object to investigate the manner in which 

 the phenomena are severally dependent on them. 



4. That the variation in the character of the discharge 

 depends on the induction-coil used to produce the discharge 

 and the distance between the electrodes in the discharge- 

 tube is clearly seen from the photographs (PI. II. figs. 1, 

 2, 3, 4). 



* Communicated by the Authors. Paper based on brief notes com- 

 municated to the second and the third All-India Science Congresses 

 (1915 and 1916). 



