Trowbridge — Electric Discharges through Hydrogen. 345 



paratively high exhaustions this latter portion of the cathode 

 beam ceases to ionize the gas ; the current ceases and the 

 potential between A and D rises to the full potential of the 

 battery, indicating an open circuit. When, however, D' is 

 made the cathode, the current is immediately re-established and 

 the cathode beam from D' ionizes the 

 gas between D 7 and A. The tube 

 acts as a rectifier ; for when D is 

 made the anode and A the cathode a 

 current passes ; on reversal of the cur- 

 rent, as I have said, no current passes 

 in the opposite direction. 



It is interesting to observe the effect 

 of a transverse magnetic field on the 

 discharge in this tube when A is 

 made a cathode and D' an anode and 

 striae appear in the portion DD\ 

 The magnetic field placed near A 

 diverts the cathode beam and striae 

 advance in the portion DD f . While 

 this field is still on, another trans- 

 verse magnetic field placed near D' 

 diverts the striae independently of the 

 action of the field at A. This indi- 

 cates the well-known fall of potential 

 from striae to striae. 



The rectification observed under proper conditions in the 

 tube fig. 6 suggests other forms of tubes by which rectification 

 can be produced. Even with a straight cylindrical tube the 



Fig. 7. 



current can be stopped at high exhaustions by touching the 

 outside of the tube with the finger, thus diverting the cathode 



