233 



An Investigation of a Point Discharge in a Magnetic 



Field. 



By Oscar William Silvey. 



Since the announcement of the magnetic deflection of the electric arc 

 and of the path of the particles of a vacuum tube discharge, there has 

 been some investigation of the electric discharge in a magnetic field at 

 atmospheric pressure. 



Among the first of these investigations was that of Precht, 1 who found 

 that when a spark passed transverse to the lines of force in a magnetic 

 field, between a point anode and a blunt cathode, there was a deviation 

 of the path of the spark, especially from the middle portion of the spark 

 gap to the cathode, the spark increased in brightness, and there was a 

 decrease in the fall of potential between the electrodes. Also, if the elec- 

 trodes were separated farther until a brush discharge existed between 

 tbein, the stream showed a deflection, the potential between the points 

 decreased, and the brush often changed into a spark discharge, when the 

 electro-magnets producing the field were excited. In case of the glow dis- 

 charge, where there existed a small brush at the anode and a bright spot 

 on the cathode, with the intervening space dark, the spot moved up or 

 down according to the electrodynamic laws, when the field was mag- 

 netized first in one direction and then in the other. 



In case a point cathode was used with a blunt anode, the spark was 

 deflected and the potential raised, when the magnet was excited the spark 

 discharge being often changed to a brush. 



2 H. E. Schaeffer has recently studied the effect of the magnetic field 

 on the spark discharge of an induction coil in each of the following types 

 of spark : 



"1. The spark obtained when neither capacity nor self-induction had 

 been introduced into the secondary circuit of the induction coil. 



"2. The spark obtained when a capacity of 0.005 to 0.012 microfarads 

 had been introduced into the secondary circuit. 



1 3. Precht, Wied. Annalen (66-4, pp. 676, 697), 1898. 



2 H. E. Schaeffer, Astro-Physical Journal (28, pp. 121-149), Sept., 1908. 



