148 
urements are very difficult [60, 63]. However, according 
to von Schweidler [121-123], the following visualizable 
approximation can be made: Under natural conditions 
near the ground where moderate to high values of N 
and Np prevail, we can write instead of equation (8) 
g = an? + Bn = B'n, (9) 
since the quadratic term becomes less important in 
comparison to the linear one, as the concentration of 
large ions in the air becomes greater. The coefficient 
6’, which has the unit of sec, is designated as the 
vanishing constant. Tis reciprocal then is the mean life 
of small cons, in analogy to radioactive phenomena. 
In practice, the air is introduced into an ionization 
chamber (condenser, sealed on all sides). By applying 
a high voltage, the value of n present is determined, 
and then the characteristic current-potential relation- 
ship is recorded. The values for g and n are determined 
by means of Method I (ohmic current), or g and @ are 
found by Method II (semisaturation current); for more 
details, see the references previously cited. 
Condensation Nuclei and Dust Particles. Aside trom 
the hydrometeors (fog, clouds, and precipitation), the 
atmospheric content of suspended particles is some- 
what arbitrarily divided into condensation nuclei and 
dust particles. Condensation nuclei, hygroscopic par- 
ticles whose radius is approximately 10° cm or less, 
are counted by producing condensation upon them in 
supersaturated air and determining the number of re- 
sulting droplets. Two types of such nuclei counters are 
well known. One was developed by Aitken [1] and the 
other by Scholz [117, 118]. For details, see these papers 
as well as others [23, 71, 80]. 
The measurement of dust particles is made by means 
of the Owens counter [9] and the Konimeter.* 
The Electric Field of the Atmosphere 
If an uncharged conductor of any given shape is 
introduced into the earth’s field, a separation of electric 
charges is found on this conductor, due to electrostatic 
induction. The conductor assumes the potential V,, 
which is the potential of a given equipotential layer in 
the earth’s field. This layer intersects orthogonally the 
electrically neutral line nn of the conductor’s surface. 
It is the potential of the reference point B (see Fig. 7). 
The following possibilities exist for measurements of 
the electric field. 
1. The body is temporarily grounded in the position 
shown in Fig. 7. Under such conditions it assumes the 
zero potential of the earth and takes on a charge Q = 
—CVz (where C = capacitance) from which, when it 
is troduced into a field-free space (‘‘shielding’”’), the 
difference in potential of V; with respect to the ground 
can be determined (electrostatic induction method). 
Variations of the method illustrated in Fig. 7 include: 
a. The body is grounded, then insulated, and trans- 
ferred to another point in the field. In this way its 
electrostatic induction is changed. Measurement of this 
“free induction charge” furnishes a measure of the dif- 
3. Described in the Zeiss catalogue, Jena. 
ATMOSPHERIC ELECTRICITY 
ference in potential of the reference points of both posi- 
tions. (For the principle of the movable conductor see 
[2; 7; 108; 137, p. 182]). 
b. If after temporary grounding the body remains 
in position, its changes in electrostatic induction give 
a measure of the variation of the field; by means of 
high-ohmie leaks, the arrangement is converted into a 
field variometer [59]. 
c. If a metal plate is mounted flush with the earth’s 
surface, grounded and exposed to the field, and there- 
upon shielded agaist the latter in an insulated state, 
it furnishes the surface density of the electrostatic m- 
ductance charge and thus the field intensity at the 
ground level (Wilson test-plate [146-149]). Rhythmical 
exposure to and shielding from the field produces an 
a-e current [87, 89-91, 124]. 
2. If provisions are made for the removal of the 
induction charge at a pomt P not situated on the neu- 
tral line of the conductor, a new neutral line is pro- 
duced to which a different equipotential surface V, 
YU 
YUE 
Fra. 7.—Electric field conditions produced by an uncharged 
conductor. 
CALA 
Af ff 7 
“4 
orthogonally connects (see Fig. 8). A connected meas- 
uring instrument indicates the potential of the reference 
point R with respect to the ground. Discharge of the 
electrostatic induction is attained by so-called collectors 
as enumerated herewith: 
a. Point collector, based on the point discharge flow 
(no longer in use). 
b. Flame collector, utilizmg the ionization of the 
gases of combustion to conduct the charge away; a 
variant is the glow collector. 
c. Water-dropper collector, operating by capacitive 
charge separation and discharge. 
d. Radioactive collector, which provides for discharge 
by ionization of its environment. 
The discharge proceeds according to an exponential 
law: 
Wie anew. (10) 
where U;, is the potential difference at the time ¢, Uo 
the potential difference at the time zero, C’ the capaci- 
tance, and « the discharge constant. The discharge con- 
stant « or its reciprocal, the “apparent” or “transition” 
