208 
MR. J. ZELENY ON THE VELOCITY OF THE IONS 
§ 7. Moist Air. 
The following is an example of a set of readings taken for the positive ions in air 
saturated with aqueous vapour. 
Letters refer to corresponding quantities in formula (9). 
Temperature = 14’5° C. X = 2'60 centims. a = '50 centims. b = 
2'555 centims. 
Width of beam of rays = '20 centim. Barometer = 75'4 centims. 
Excess pressure inside gasometer — 1*56 centims. of mercury. 
,, ,, in apparatus = '59 centim. of mercury. 
20 cells = 42'6 volts. 
Table I.—Moist Air. Positive Ions. 
Voltage of outer 
cylinder. 
Electrometer deflection 
in 30 seconds. 
Descent of gasometer 
in 40 seconds. 
Cells. 
Divisions. 
Centims. 
+ 10 
145 
6-77 
+ 12 
105-5 
6-79 
+ 14 
68-5 
6-78 
+ 10 
29-5 
6-72 
+ 18 
12 
6-70 
+ 19 
7 
6-83 
+ 17 
19 
6-81 
+ 15 
52-5 
6-78 
+ 13 
87 
6-77 
+ 11 
128 
6-76 
In the middle of the observations the gasometer was refilled from the gas bag. 
The sectional area of the gasometer was 2904 sq. centims., and the area between the 
two cylinders was 19'73 sq. centims., so the average rate of descent of the gasometer 
above indicates an average velocity in the apparatus of 2 5'2 centims. per second, 
when corrected for the difference in pressure between the gasometer and the 
apparatus. 
The voltages and their corresponding deflections are represented graphically in 
curve I. of fig. 5. The set of readings here given, and most of those which are to 
follow as examples, have been selected from among the best obtained. 
It is seen that the curve at first approaches the axis of abscissas in nearly a straight 
line, but becomes convex when near to it. Had readings been taken for voltages 
smaller than those used, that part of the curve would have been concave to the axis 
of abscissas. 
It has been explained in § 4 (3), why there is a nearly straight portion in the 
curve, while the width of the beam of rays and the various causes tending to spread 
