422 Dr. Tyndall and Mr. Hughes on Cathode 



about 320-330 volts. It will be seen from the curves 6*15 

 and 3*08 m.a. that the rate of disintegration at this value 

 of " V " is exceedingly small but not zero. However, until 

 more accurate experiments have been carried out in this 

 region, it may be assumed that the rate of disintegration is 

 zero at or not much below the normal cathode-fall. 



f* 



Ct 



rRVES 2. 



Current 





(A) 6-J5 ma. 





(B) 4--I0 - 





(C) 3-08 " 





(Q) 2-10 » 





(E) 1-05 . 





./ 



400 500 600 700 800 



UrfKcnU, $a/l of PeGbrdml \ (uv VcCto) 



In order to prove that the form of curves obtained was 

 not due to the particular shape of cathode and discharge- 

 tube used, some of the experiments were repeated with 

 (1) a plate cathode backed by mica as used by Holborn and 

 Austin, and (2) a discharge-tube of spherical form which 

 was a replica of that used by Kohlschutter. The results did 

 not materially differ from those above cited. In the case 

 of the plate cathode, the actual values of disintegration 

 differed from corresponding experiments with wire cathodes 

 by a few per cent., but this difference is easily accounted for 

 by non-uniformity of discharge introduced by the edge of 

 the plate. 



Effect of Current Density. 



The conclusion arrived at by Granqvist that the disinte- 

 gration for a given cathode is proportional to the square of 

 the current has been somewhat widely quoted. GranqA r ist, 



