394 ELECTRICAL MACHINERY 



live with respect to H, current will flow through the battery 

 and tube by the anode B. The current through the battery 

 will therefore have the form given in Fig. 259. 



lonization of Gas Necessary for the Operation. In order 

 to operate as described above it is necessary that the tube 

 be filled with ionized mercury vapor. If the mercury vapor 

 is once ionized the current flowing through the tube will 

 maintain the ionization but if the current ceases for a 

 fraction of a second the vapor immediately becomes non- 

 ionized and will not carry current. Hence a tube as repre- 

 sented in Fig. 259 would not maintain its ionization because 

 at times 1, 2, 3, 4, etc., the current reaches zero value. 



Time > 



FIG. 260. By Inserting Inductance in the Circuit the Current Form is 

 Changed as Shown Here. Compare with Fig. 260. 



Maintenance of Ionization. If, however, the trans- 

 former supplying the power to the tube is designed with 

 considerable leakage (giving it self-induction) the current 

 is changed from the form given in Fig. 259 to that given in 

 Fig. 260; this current never reaches a zero value after the 

 tube starts to operate, hence if the ionization in the tube 

 is started by some method the current itself will maintain 

 the ionization. 



Use of Starting Anode. To start the ionization an 

 additional anode, called the starting anode is provided. 

 This consists of a pool of mercury close to the cathode as 

 shown at D in Fig. 261. When the tube is tipped slightly 

 the mercury of D runs over and makes contact with C. 



