214 * 
MR. J. ZELENY ON THE VELOCITY OF THE IONS 
7'64 
v =5-118 ———r—r = 1‘63 centims. per second. 
2-60 x 9’21 1 
T = — = ‘34 second. 
A summary of the results obtained for dry air for both the positive and the 
negative ions is given in Table VI. 
Table VI.—Dry Air. Summary of Results. 
Reference 
X. 
U. 
A. 
T. 
Tempera- 
Gas 
Ionic velocity. 
number. 
ture. 
pressure. 
Negative. 
Positive. 
1 
2-60 
7-64 
- 9-21 
•34 
°C. 
15-8 
76-2 
1-63 
2 
2-60 
7-64 
+ 12-0 
•34 
15-8 
76-2 
— 
1-25 
3 
2-60 
7-64 
+ 12-2 
■34 
16-3 
75-8 
— 
1-23 
4 
2-60 
7-57 
- 9-31 
•34 
16-3 
75-8 
1-60 
— 
5 
2-60 
7-28 
- 9-15 
•36 
12-2 
76-6 
1-58 
— 
6 
2-60 
7-23 
+ 12T5 
•36 
12-2 
76-6 
— 
1T8 
7 
2-60 
15-8 
- 18-3 
•16 
13-8 
76-6 
1-71 
— 
8 
2-60 
15-9 
+ 24-8 
T6 
13-8 
76-6 
1-27 
9 
2-60 
15-9 
- 18.1 
T6 
13-8 
76-6 
1-74 
— 
10 
2-60 
15-9 
- 18-3 
T6 
13-8 
76-6 
1-725 
— 
11 
2-60 
16-6 
- 18-65 
T6 
14-6 
75-8 
1-75 
— 
12 
2-60 
16-3 
- 18-22 
•16 
14 
76-8 
T78 
— 
13 
2-60 
15-5 
+ 24-8 
T7 
12-5 
76-7 
— 
1-25 
14 
2-60 
15-5 
+ 23-7 
T7 
10-7 
77-6 
— 
1-31 
15 
2-60 
15-6 
-18-1 
T7 
10-7 
77-6 
1-72 
— 
16 
5-15 
8-65 
+ 7-76 
•60 
11-4 
77-3 
— 
M3 
17 
5-15 
8-62 
- 5-9 
•60 
11-4 
77-3 
1-47 
— 
18 
5-15 
15-6 
- 9-31 
•33 
11-4 
77-6 
1-67 
— 
19 
5-15 
15-7 
+ 12-6 
•33 
11-4 
77-6 
— 
1-26 
20 
5-15 
8-58 
+ 7-64 
•60 
11-7 
77-5 
— 
1-14 
21 
5T5 
8-58 
- 5-88 
•60 
11-7 
77-5 
1-48 
— 
At No. 7 the drying apparatus was changed, and at No. 12 the Crookes’ tube 
was replaced by a new one. 
The results are represented in fig. 8, excluding the points marked by squares. 
The final values thus obtained for dry air when the 2 per cent, correction men¬ 
tioned in § 4(15) has been added, give the velocity of the negative ions — 1‘87 centims. 
per second, and of the positive ions = 1‘3G centims. per second. 
The temperature varied several degrees between the different observations, but 
was on the average about 13° C. 
Most of the tests to which the method used in these experiments was subjected 
by changes of experimental conditions, were tried with dry air. Among these was 
tried the effect of changes in the intensity of the rays. By interposing aluminium 
plates the rays were diminished so that the conductivities produced by them changed 
