150 
Investigations of Thunderstorm Electricity 
Field. Measurements of atmospheric electricity in 
conjunction with electrical storms require a very rapid 
response of the equipment. This requirement elim- 
inates collector measurements. The measurements are 
based on the application of electrostatic induction tech- 
niques of field measurement (Wilson test-plate, Wilson 
elevated sphere, mechanical collectors, antennas) in 
combination with high-speed recording instruments in- 
cluding cathode-ray oscillographs. 
Current. The vertical current can be determined with 
the aid of the Wilson test-plate in connection with a 
galvanometer or a capillary electrometer [148] or by 
recording the current through a point collector mounted 
in an exposed position [148, 150]. 
Precipitation Charge. Precipitation is collected in an 
insulated vessel. Splashing of the drops is prevented by 
lining the bottom with velvet, brushes, etc. Records 
are obtained either by the accumulation technique or 
by the ‘“‘current-circuit method.” For charge measure- 
ments on individual drops see Chalmers and Pasquill 
[25], Gschwend [43], and Gunn [44]. 
Investigations of Lightning Discharges.* The following 
methods can be employed: The optical method involves 
photography, using, for example, the Boys camera [20, 
21]. 
In the electrical method the Klydonograph is used 
for the direct measurement of peak voltages in the 
lightning discharge by means of Lichtenberg figures; 
the measuring range is approximately 2-18 ky [83]. 
The magnetic method is based on the magnetization 
of small steel rods by currents flowing through light- 
ning rods of various types [88] as, for example, the 
Fulchronograph [140, 141], or on the measurement of 
the magnetic field of the lightning discharge channel, 
and on numerous other special methods some of which 
are used in combination with high-tension lines [84, 
99, 100, 144]. 
Radio Interferences. The electromagnetic pulses (at- 
mospheric) originating from electric discharges in the 
atmosphere are investigated with respect to their num- 
ber, direction of incidence, place of origin, and pattern. 
Excitation of an oscillating circuit coupled to a non- 
directional antenna gives the number; use of rotating 
loop antennas gives the directional distribution; ranging 
with cathode-ray direction finders furnishes a bearing 
on the point of origin; finally, the pattern of the dis- 
turbance is established by use of aperiodic d-c ampli- 
fiers. For literature of the foregoing see: Appleton and 
collaborators [4, 5], Bureau [24], Lugeon [88], Norinder 
[98, 101], Schindelhauer [112, 113], and numerous others. 
Measurements in the Free Atmosphere 
The methods used for determination of the individual 
factors of electricity i the free atmosphere are funda- 
mentally the same as those used at ground level. They 
must, however, be properly modified to allow for the 
special operational conditions obtaining in either the 
4. Consult “The Lightning Discharge” by J. H. Hagenguth, 
pp. 1386-148 in this Compendium. 
ATMOSPHERIC ELECTRICITY 
free-flying or captive carriers of the measuring instru- 
ments, such as manned free balloons, gliders, motor- 
driven aircraft, dirigibles and blimps, automatic re- 
cording balloons, captive balloons, and kites. For a 
summary of older and more recent aerological methods 
of atmospheric electricity see Israél [65]. 
Problems of Present-Day Research in Atmospheric 
Electricity 
In concluding this discussion of equipment and 
methods, a few ideas may be presented on the most 
urgent problems of modern research in atmospheric 
electricity. 
Although measurements have been made for almost 
two hundred years, the phenomena of atmospheric 
electricity have been considered a discrete part of the 
physics of the atmosphere; it is only recently that cer- 
tain fundamental relationships to other atmospheric 
phenomena have been uncovered. Through the gradual 
detection of the inner relationships between atmos- 
pheric-electric and meteorological processes, new light 
is being shed on many of the electric phenomena that 
hitherto have been unexplained. Moreover, the possi- 
bility arises of immediate application of the knowledge 
gained in atmospheric electricity to meteorology and 
aerology. 
As has recently been pointed out [68], the funda- 
mental concepts of atmospheric-electric phenomena 
have undergone a mutation in that the tendency for — 
segregation of electric from meteorological processes is 
slowly disappearing and is giving way to a trend toward 
correlating them. The stimulus for this development 
has been primarily the knowledge gained through the 
ocean expeditions sponsored by the Carnegie Institu- 
tion. These cruises have revealed the world-wide syn- 
chronous component of the electric field, the coupling 
of this field with the world-wide weather, and the in- 
creasingly clear relationships between the local varia- 
tions and the vertical mass exchange. 
This last correlation, in particular, may furnish the 
key to the major portion of the relationship between 
atmospheric-electric and meteorological phenomena and, 
thus, simultaneously indicate the direction im which 
further research should proceed. 
A primary requirement is the extension of the meas- 
urements to more than a single atmospheric-electric 
element, because the prevalent practice of recording the 
potential gradient alone permits only very limited con- 
clusions. The three fundamental quantities of field in- 
tensity (potential gradient) H, conductivity A, and ver- 
tical current density 7, are interrelated in Ohm’s law: 
EA = 1. 
Any statements regarding processes taking place in the 
atmospheric-electric circuit under equilibrium condi- 
tions require that two of these fundamental quantities 
be known. If we are to include the nonstationary 
(“switching-on”’) processes, all three quantities must 
be measured. It would be most desirable if this prac- 
tice, now followed by the large atmospheric-electric 
