Specific Velocities of Ions in the Discharge from Points. 95 



which do not occur with positive discharge — furnish another 

 instance *. 



So also does the gradual and permanent increase in the 

 strength of this field when the point is discharged from for 

 long periods ; an increase which is not shared by the field for 

 positive discharge from the same point*. 



If, then, we may assume that the starting-place of the 

 positive discharge is in the gas surrounding the point, while 

 that of the negative is at or just below the surface of the 

 metal, it may quite well happen that while the positive ions 

 are all formed of hydrogen, some of the negative ions consist 

 of gases other than hydrogen occluded in or condensed on the 

 point, which, by occurring in greater or less numbers, give 

 rise to the fluctuations observed in V. Our value of V — 

 for hydrogen may thus be too low. 



Summary of Results. 



In the following table are collected the most reliable of our 

 values for V; the results of Rutherford f and of Townsend J 

 being added for comparison. Numbers in square brackets 

 are for wet gases. The velocities are in centimetres per second 

 in a field of 1 volt per centimetre. The value of V— for 

 hydrogen may be too high or too low for one or other of the 

 reasons already given. 



Substance. 



V. 



V-/V4-. 



Rutherford. 



Townsend. 



Point- 

 Discharge. 



Townsend. 



Point- 

 Discharge. 



Hydrogen 



520 

 1-07 

 1-60 

 1-40 



6-60 

 [5-40] 



0-98 

 [1-00] 



1-39 

 [1-34] 



1-29 

 [1-29] 



641 

 88 

 i'55 



[i-5tq 



1-57 



<;6obl4 



1-54 

 [Ml] 



M3 

 [1-04] 



1-54 

 [1-09] 



1-58 

 [1-24] 



1-38 



111 



1-36 



[1-21] 



1-42 



1-15 



Carbon Dioxide... 



Air 



Oxygen 



Turpentine 



Apropos of the fact that our values of V— /V+ lie between 

 those for dry and wet gases, we may mention that in the cases 

 of air and carbon dioxide we quadrupled the length of P 2 5 - 

 tubes, with the only result that the ratio fell a trifle lower. 



* Chattock, Phil. Mag. Sept. 1891, p. 295. 

 t Rutherford, Phil. Mag. Nov. 1897. 

 X Townsend, Phil. Trans, vol. 193, 1899. 



