at the Electrodes in Vacuum-Tube Discharge, 635 



and increasing the current-density at the anode sufficiently, 

 we should, if like conditions hold at the two electrodes, obtain 

 similar results, namely, an increase in the anode drop with 

 increased current and decreased gas-pressure. 



Variation in Drop of Potential at Anode with Current- 

 density. 



An experiment was performed with the aforesaid purpose in 

 view. A steel disk-anode, similar to that serving as cathode 

 in previous experiments, but having an area of 0*25 sq. cm., 

 was used as upper electrode in fig. 1. To prevent its drop 

 being affected by the cathode stream, a guttapercha cap was 

 placed over the upper surface of the lower electrode, thus 

 forcing the cathode discharge to take place down the tube 

 away from the anode. Observations made on the anode drop 

 under these conditions are given in Tables VIII. & IX. With a 

 gas-pressure of 1*2 mm., Table VIII., the drop first decreases, 



Table VIII. 



Variation in Drop of Potential at Anode with Current-density. 



Pressure of Gas, 1*2 mm. Area of Electrode, 0*25 sq. cm. 



Current 

 (Milliamps.). 



Current-density 



(Milliamps. per 



sq. cm.). 



Drop at Anode 



(Volts). 



10 

 1-5 

 20 

 25 

 3-0 

 3-5 

 40 



4 

 6 



8 

 10 

 12 

 14 

 16 



27 



237 



24 



26 

 28 

 29-5 

 30 



then increases slightly with increasing current. The decrease 

 is probably due to the slight decrease in the potential gradient 

 in the positive column as the current increases. The observa- 

 tions in Table IX. are plotted in fig. 6 (p. 636). The curves are 

 slightly concave to the axis of abscissas, while for the cathode 

 they are straight lines. I have noticed, however, that, under 

 some conditions there is the same tendency at the cathode, 

 as may be seen from the observations at a gas-pressure of 

 1 mm. in fig. 3. The maximum inclination of the lower 

 curve in fig. 6, compared with the cathode drop, gives 

 c = 0'7, while under the same conditions at the cathode, 

 c = 24*4. The drop increases then thirty-five times as rapidly 

 at the cathode as at the anode. 



