INSTRUMENTS AND METHODS FOR THE MEASUREMENT OF 
ATMOSPHERIC ELECTRICITY* 
By H. ISRAEL 
Institute for Atmospheric Electric Research of Buchau a. F. 
System of Units 
Various systems of units are used in electricity. Each 
of these is an entity in itself and is built up on a 
definite fundamental physical relationship: 
1. The “electrostatic cgs system” is based on Cou- 
lomb’s law of the force effects of interacting electrical 
charges and arbitrarily takes the proportionality factor 
to be nondimensional and equal to unity. 
2. The “electromagnetic cgs system” is based on the 
Biot-Savart law of the forces between an electric cur- 
rent and a magnetic pole, and again the proportionality 
factor is set equal to unity. 
3. Giorgi’s “natural m-sec-v-amp system” assumes 
voltage and amperage as fundamental quantities, with 
the second (sec) as the time unit and the meter (m) 
as the length unit. 
In the first two systems the electrical quantities are 
reduced to the mechanical units, em, g, and sec (egs), 
which appear in complicated, nonvisualizable com- 
binations. The third system of units is more suitable 
to the scope of physics in general; therefore, its adop- 
tion for consistent use in the field of atmospheric elec- 
tricity is recommended. In this system, the interna- 
tional standards for volt, ampere, etc., are employed. 
Auxiliary Equipment and Practical Suggestions 
The atmospheric electrical problems of measurement 
consist predominantly of the measurement of potential 
differences of medium magnitude and of minute elec- 
trostatic charges. They belong, therefore, to the do- 
main of electrometry proper. Although increasing use 
is bemg made of ‘‘vacuum tube electrometers” (d-c 
current amplifiers or d-c voltage amplifiers), thorough 
familiarity with the electrometer is a prerequisite for 
work in atmospheric electricity. 
All electrometers are based on the principle of elec- 
trostatic attraction or repulsion. An exception is the 
capillary electrometer which utilizes the change in the 
surface tension of mercury when traversed by an elec- 
tric current. Therefore, strictly speaking, the capillary 
electrometer represents a type of galvanometer [103]. 
Quadrant electrometers have long oscillation periods 
and are therefore suited chiefly for the measurement of 
constant potential differences, whereas filament elec- 
trometers adjust themselves aperiodically and almost 
instantaneously at sensitivities that are not excessively 
high. The highest sensitivities are attained with the 
modern modifications of the quadrant electrometer. 
Figure 1 shows schematically the well-known prin- 
ciple of the quadrant electrometer. Special electrometer 
types are: the model developed by Elster and Geitel 
* Translated from the original German. 
144 
[37], particularly suited to photographic recording; the 
Dolezalek electrometer [80, 31] for high sensitivities; a 
special design by Schultze [119]; the ‘“Binanten”’ elec- 
trometer [49] and the ‘“‘Duanten” electrometer of Hoff- 
mann [48, 50, 51]; the Benndorf electrometer [11, 12], 
the familiar, low sensitivity quadrant electrometer for 
mechanical recording of potential gradients. 
Figures 2 and 3 are sectional drawings of the bifilar 
electrometer without auxiliary potential and of the 
unifilar electrometer with auxiliary potential according 
to Wulf’s design [152]. More modern designs for attain- 
ing the highest sensitivites include those of Lindemann 
and Keeley [85], Compton [26, 27], Shimizu [127], Swann 
[139] and Perucea [104, 105]. 
The development of the so-called electrometer tubes 
with their characteristically high insulation of the con- 
trol grid and very low grid current (10~! amp and less) 
has resulted in the substitution of vacuum-tube elec- 
trometers for the ordinary electrometers. Many types 
of electrometer tubes are now commercially available. 
During contimuous operation, maintenance of a con- 
stant zero point is sometimes difficult; some ameliora- 
tion can be provided by using oversized filament bat- 
teries and by the use of selected pairs of tubesin a bridge 
circuit (for further details see, for example, [22, 28, 36, 
46, 47, 69, 77, 82, 106, 109, 114]). 
There are several types of circuits available for use 
with quadrant and filament electrometers provided with 
auxiliary potentials: In the zdiostatic cirewit the needle 
(lemniscate or electrometer filament) and one pair of 
quadrants (knife edge) are grounded; the unknown 
voltage is applied to the other pair of quadrants (knife 
edge). The deflection is proportional to the square of 
the unknown voltage, thus making possible a-c meas- 
urement. In the quadrant circwt the needle is at a fixed 
high voltage; one pair of quadrants is grounded, and 
the unknown voltage applied to the other. Deflection 
is proportional to the unknown voltage. The hetero- 
static or needle circuit has both pairs of quadrants con- 
nected to a fixed auxiliary voltage of opposite sign and 
the unknown voltage applied to the needle. This is the 
most frequently used and most sensitive circuit, and 
has the lowest capacitance. In the current circuit the 
voltage measurement is made at the terminals of a re- 
sistor which is usually of the high-ohmic type. 
Measurements of atmospheric electricity are almost 
exclusively electrostatic measurements and therefore 
call for high quality of the dielectric materials. The 
best insulating materials are the natural products, am- 
ber and sulfur. Good substitutes melude high quality 
plastic dielectric materials such as hard rubber (ebon- 
ite), plexiglass, and Trolitul. Meticulous surface treat- 
