Experiments on Delta Rays. 539 



14. When hydrogen was substituted for air, still more 

 strange results were obtained. In this case, the current 

 proved not to be proportional to the pressure for any finite 

 range at low pressures. The addition of a very small quantity 

 of gas to the previously exhausted vessel did not increase 

 the current at all; in some cases it appears even to decrease it. 

 But the most remarkable feature occurred when the relation 

 between the current and the P.D. was examined for these low 

 pressures. In Table III., column 1 gives the relation for a 



Table III. 





! 



Current. 





P.D. 











i. 



2. 



3. 



50 



1201 



711 



49;> 



30 



1043 



7i3 



330 



20 



937 



713 



224 



10 



812 



699 



113 



8 



771 



084 



87 



6 



720 



(552 



68 



5 



592 



633 



59 



4 



054 



598 



56 



3 



596 



545 



51 



2 



510 



405 



51 



1 



399 



325 



74 



















pressure of 1*1 mm. and a distance between the electrodes of 

 about 1-^ mm., column 2 gives the relation for a pressure zero, 

 and column 3, which is the difference between 1 and 2, the 

 relation for the part of the current which would be expected 

 to be due to the gas only. It will be observed that for a 

 certain range of low potentials the current seems to decrease 

 with an increase of potential. Xo explanation is offered at 

 present of this result, which is typical of those obtained with 

 hydrogen, or of the results with air; they are recorded 

 merely in order to show that there are many things connected 

 with conduction through ionized gases which still wait to bo 

 explained. 



Summary and Conclusions. 

 2-4. It is shown that, in the case of a current carried by 

 delta rays from metals, the relation between the current and 

 the P.D. is independent of the temperature of the electrodes; 

 also that the current is determined rather by the P.D. between 

 the electrodes than by the electric field in the space between 

 them. It is concluded that the delta rays must be emitted 

 originally with a finite velocity and that the velocity which 



