578 Mr. A. E. Garrett on Positive Electrification 



alteration in the pressure produces also an alteration in the 

 current, yet on bringing both temperature and pressure to 

 their former values, the same steady current is obtained. 



III. Attempts to increase the Activity. 



Richardson ** found that a platinum wire which is heated 

 to such a temperature that an excess of positive ions are given 

 off, gradually becomes less and less active in this respect until 

 a more or less steady state is reached. When the wire 

 reaches this state he found that it could be rendered much 

 more active by passing, for about a minute, an electric dis- 

 charge through the tube containing the wire, and he further 

 showed that this regained activity persisted for a considerable 

 time after the discharge had ceased. 



It was thought that a discharge might have a similar effect 

 upon the heated phosphate when it had reached the steady 

 state. The heating-current was therefore cut off and a dis- 

 charge from a Ruhmkorff coil sent through the tube. This 

 increased the current temporarily. If the coil was again 

 applied less effect was produced until, after several repeti- 

 tions, the coil produced no effect. 



The actual period during which the discharge lasted was 

 gradually increased, and it was found that the maximum 

 effect was attained when the discharge continued for -J minute. 

 On no occasion did it require more than 20 minutes again to 

 reach the original steady state after discontinuing the dis- 

 charge. In order to ascertain whether the temporary 

 increase in current was due to the effect which the discharge 

 produced upon the salt itself, or upon the residual gas, a 

 fresh supply of G0 2 was admitted when the state at which 

 the coil discharge produced no effect was reached, and the 

 tube pumped down to0"12 cm. pressure. The coil discharge 

 again caused a temporary increase. The direction of the coil 

 discharge did not influence the result. 



The extra current therefore appears to be due to an effect 

 produced by the action of the discharge upon the surrounding 



IV. Action of Heat in the absence of Electrostatic Field. 



When the electrode e was insulated while the heating was 

 continued an abnormally large current was obtained so soon 

 as the field was put on between e and E (fig. 1). This current 

 gradually decayed, but it was some 2 or 3 minutes before it 



* Phil. Mag. [6] pp. 93 et seq., 1903, 



