80 Prof. Chattock, Miss Walker, and Mr. Dixon on the 



In the following tables these specific velocities (V+ and 

 V — ) are given for the positive and negative ions in centi- 

 metres per second in a field of one volt per centimetre ; c 

 being the current from the point in microamperes, n the 

 number of values for which V is the mean, Z\ z 2 the distances 

 in centimetres from point to ring used in the " double position " 

 method (I.e. p. 413), and V the mean of V + and V — . 



Hydrogen. 



c. 



n. 



v+. 



V-. 



V. 



V-/V + 



. z v z 2 . 



i 



4-4 



12 



5-3 



73 



63 



1-38 



80 30 



Tube A. 



22 



11 



5-1 



73 



62 



1-43 



>> >» 



>> ,, 



32 



3 



5-6 



8-5 



7-0 



1-67 



Curves. 



Tube B. I. 



3-2 



19 



5-6 



7-9 



6-8 



1-41 



9-2 37 



Tube B. II. 



1-6 



19 



53 



7'2 



6-3 



1-36 



,, ,, 



>> ») 



0-8 



19 



52 



6-8 



6-0 



1-31 



,, ,, 



,, >? 



32 



19 





7-8 







„ ,, 



Tube B. III. 



1-6 



19 





7-2 







,, „ 



,, ,, 



3-2 



7 



5-4 









Curves. 



Tube B. IV. 



32 



7 





7-6 







Curves. 



Tube B. V. 



20 





5-40 



7 43 



641 



1-38... 



Weighted means 



for Tube B only. 



Tube A in all the tables is the tube used in the original 

 experiments on air. Its length was 34 centimetres, and its 

 internal diameter 6'3 centimetres. Owing to the high values 

 of the ionic velocities in hydrogen, it was necessary to use 

 greater distances between point and ring than in other gases 

 to obtain measurable pressures. This brought the discharge 

 region so near the ends of the tube, that it became doubtful 

 whether it was safe to assume that the ends were at an 

 infinite distance from the wind. For this reason a second 

 tube B of ebonite, 55 centimetres long and 5*6 centimetres 

 internal diameter, was used in the later work ; the decrease 

 in diameter possessing the twofold advantage of decreasing 

 the convection-currents in the gas and of increasing the 

 pressures to be measured. 



In the experiments with Tube A the readings were all 

 taken under the same conditions, as the positive and negative 

 discharges for the larger current were sandwiched both with 

 each other and with those for the smaller current. All these 

 values are therefore comparable. The same is true of each 

 of the separate groups of experiments with Tube B, marked 

 respectively I., II., III.; and the remark applies to the tables 

 for the other gases as well as for hydrogen. 



