An INVESTIGATION OF A Potrnt DiscHARGE IN A MAGNETIC 
FIELD. 
By Oscar WILLIAM SILVEY. 
Since the announcement of the magnetic deflection of the electric are 
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,t 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 
them, 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. 
"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. 
1J. Precht, Wied. Annalen (66-4, pp. 676, 697), 1898. 
°H. E. Schaeffer, Astro-Physical Journal (28, pp. 121-149), Sept., 1908. 
