in the Uniform Positive Column in Air, 183 



These results are also shown in fig. 2. When the current 



Fig. 2. 



1 



r-o/e- I , „ 









/-"" 







'^ 



0-445 











f 



t \ 



^e> 





p^-o.e^s^^ 





N;* 



r\^ . 



^ ^K ^ *-¥^ 









/ 





^'^-^^^-o^^. 







f 









■*- 

















400 500 _ 600 



is very small thejintensity rises very rapidly with the current, 

 but the rate of rise falls off as the current increases. When 

 the current is greater than a certain value the discharge 

 becomes unstable and generally breaks down into an inter- 

 mittent discharge in which the intensity is much smaller 

 than in the steady discharge. A telephone was included in 

 the circuit through the side tube by means of which the rate 

 o£ intermittence could be estimated. The period of inter- 

 mittence diminishes as the current is increased. At the 

 upper end of the curves for the intermittent discharge 

 the rate of intermittence is so slow that the successive dis- 

 charges can be seen to follow each other at regular intervals 

 of about one to two seconds, and the electrometer and gal- 

 vanometer needles both oscillate. The electrometer shows 

 that in between the discharges the intensity has the larger 

 value corresponding to the steady discharge, and its deflexion 

 drops at each discharge. The intermittent discharge conse- 

 quently consists of a small steady current with momentary 

 discharges superposed on it at regular intervals. When the 

 current was increased sufficiently the electric intensity in 

 the intermittent discharge became nearly independent of the 

 current and was given by the formula X = 35v^p. 



As the current is increased the rate of intermittence in- 

 creases, and the note emitted by the telephone rises until it 

 becomes of very high pitch. With slightly more current the 

 telephone becomes silent again, and the discharge seems to 

 be perfectly steady. It was at this stage that the previous 

 measurements {loc. cit.) were made. 



