636 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



velocity of rotation as the pressure of air in the tube was diminished. The 

 effect of the magnetic field is to separate the discharge from the cathode 

 into two discharges, one a violet glow, the other a plume-like orange 

 light, which seems to extend across both cathode dark space and Fara- 

 day space. Its presence is shown by the flaring light on the spires of 



the helix of the photograph. The effect of the field at the anode also is 

 to separate the discharge into a plume-like rose discharge and a smaller 

 plume-like violet discharge. These discharges also rotate about the 

 pole. 



7. The electro-magnet was placed with its core at right angles to the 

 line of discharge at the anode. The discharge was thrown up or down, 



