MEASUREMENT OF ATMOSPHERIC ELECTRICITY 
current (1), semi-saturation current (11), and saturation 
current (III); see Fig. 5. 
To attain clearer experimental conditions, it is now 
a general practice to employ the aspiration condenser 
in connection with the so-called method of perpendicular 
velocities as follows: When air containing ions flows 
through a condenser to which an electric field has 
been applied, the trajectory of an ion is found to be 
the resultant of the two mutually perpendicular forces, 
namely, that of the air current and that of the field. 
If M is the aspirated quantity of air in cubic centi- 
meters per second, C is the condenser capacitance (C = 
L/{2 In (R/r)] for cylindrical condensers having radii 
R and r and length L), and V is the potential in volts, 
the expression 
ky = M/4aCV (7) 
represents the limiting mobility of the condenser and 
states that all ions whose mobility is greater than, or 
al 
(b) Kg 
Fic. 6.—Schematic diagram of the current-potential char- 
acteristic in the aspiration condenser (a) in the presence of 
one type of ion, (b) in the presence of several types of ions. 
at least equal to, this mobility are deposited. Of those 
ions, whose mobility & is smaller, only the percentage 
k/k, is deposited. 
It is evident that, in the foregoing, the characteristic 
relationship between current and potential in the con- 
denser will be a broken linear curve. This curve will 
resemble Fig. 6a when but one type of ion is present, 
and assume the form of Fig. 6b when several types of 
ions occur. From the preceding statement, the following 
conditions are found for the measurement of ions: 
Conductivity: 17 must be chosen so great or V so 
small that operations take place in the first segment 
of the curve that rises from the origin of the coordinate 
system. 
Jon Counts: Determined from the saturation current. 
Jon Mobility: Hach break in the curve yields, accord- 
ing to equation (7), the mobility of a corresponding 
type of ion. 
147 
Ton Spectrum (numerical distribution on the basis 
of the individual mobilities): The number pertaining 
to a given mobility results from the magnitude of the 
change in slope of the characteristic; expressed in terms 
of differentials, the ion spectrum is determined by the 
second differential quotient of the characteristic. 
Additional methodological details are given else- 
where [54, 56, 57]. With respect to ‘‘edge disturbances” 
(effect of the inhomogeneity of the field at the edge of 
the condenser), see Itiwara [73], Israél [56], and others. 
For special designs, that homogenize the field of cylin- 
drical condensers. refer to Becker [8], Swann [137], and 
Scholz [115]. 
Well-known instruments that are easy to manipulate 
include the Gerdien aspirator [39, 40] for measurements 
of conductivity; the Ebert ion counter [32, 33, 35] and 
the Weger aspirator [58, 142] for measurements of the 
concentration and mobility of small ions (see references 
[6, 41, 42, 142] for errors of the Ebert instrument), and 
the Israél ion counter [55] for counts of medium and 
larger ions. 
Mobility measurements by means of divided con- 
densers are described in the literature [18; 19; 29; 54, 
pp. 179 ff.]; a differential method of very great resolving 
power had been proposed by Benndorf (e.g., see [54, 
56, 57]). Recording devices for conductivity measure- 
ments are also described in the literature [82, 108, 115, 
116, 138]; recording instruments for counting ions have 
been devised by Nordmann [94-96], Leckie [82], Lange- 
vin [81], Hogg [52, 53], and others. 
Schering’s method [110, 111] for recording conduc- 
tivity, which is still used occasionally, is somewhat 
different. A wire from 10 to 20 m long is freely sus- 
pended and surrounded by a cylindrical wire net having 
a radius of approximately 1 m. The wire is charged at 
certain time intervals and its voltage drop is recorded, 
for instance, by a Benndorf electrometer. 
Rates of Ion Formation and Recombination; Mean 
Life of Ions. Under conditions of equilibrium, the rate 
of ion production g and the numbers n, N, and No of 
the small ions, large ions, and uncharged suspensions, 
respectively, have the following relationship: 
q = an? + mnN + mnNo + n3NNo + mN? (8) 
where 
a = recombination coefficient between small ions, 
m = recombination coefficient between small and 
large ions, 
n2 = recombination coefficient between small ions 
and uncharged particles, 
n; = recombination coefficient between large ions 
and uncharged particles, 
ns = recombination coefficient between large ions. 
The last two terms of equation (8) are insignificant as 
compared to the others, because 7; and 7 are smaller 
than the other coefficients by several orders of magni- 
tude. 
In order to determine the individual recombination 
coefficients, synchronous measurements of all partici- 
pating constituents are necessary [92, 93]. Owing to 
the prerequisite of ionization equilibrium, such meas- 
