146 
can be prevented by double insulation separated by a 
grounded metal plate. In all cases, when working with 
maximal sensitivities, it is judicious to protect the in- 
sulators against either direct or indirect influence of 
electric fields by shielding them. 
On many occasions, especially when working with 
movable parts such as rotary collectors, unwelcome 
concomitant phenomena are possible as a result of the 
Volta effect. The latter must be determined and cor- 
rected for by check tests. 
In electrostatic work, the almost universal contam- 
ination of rooms by a-c fields produced by the electric 
light network is a source of serious disturbance. Its 
effect can, in general, be easily recognized and elim- 
inated when working with electrometers. When am- 
plifiers are used such a-c fields may easily lead to errors 
of measurement and misinterpretation (apparent at- 
mospheric electrical potential gradient in rooms) be- 
cause of unintended and undetectable rectifier action. 
Batteries are preferable to rectified a-c lines as sources 
of constant potential, especially in electrometric work. 
Portable high-voltage sources for counting-tube meas- 
urements in open country are described elsewhere 
{133, 136]. 
High ohmic resistors up to about 10'* ohms are fab- 
ricated commercially by evaporation of thin platinum 
films on quartz or amber. For homemade high ohmic 
fluid resistors, radioactive (Bronson) resistors, and other 
possibilities, see von Angerer [3]. 
Ions and Other Atmospheric Suspensions 
Tonizers of the Atmosphere. The ionization of the 
lower atmospheric layers, aside from occasional local 
ionizers of subordinate significance (waterfall effect, 
combustion gases), is caused by the a, 8, and y radia- 
tion of radioactive substances and by cosmic radiation. 
The special methods for measuring radioactive sub- 
stances and cosmic radiation are treated elsewhere in 
this Compendium. 
The ionization in a sealed chamber is due to radia- 
tion from the chamber walls (mathematical determin- 
ation according to von Schweidler [120], experimental 
determination in mines [17]), radiation from the earth, 
radiation from the atmosphere, and cosmic radiation. 
The mathematical estimation of the radiation from the 
earth and the atmosphere is made as follows: 
Tf pearth and pair are the concentrations of radium, or 
of its RaC-equivalent, in a cubic centimeter of earth 
or Of air, Mearth ANA pair the absorption coefficients of 
the corresponding y-radiation in earth or in air, and if 
K is the “Eve number” (4.0 < 10° in the absence of 
secondary radiation, approximately 5 to 6 X 10° in 
thick-walled ionization chambers), the ion production 
q (z.e., number of ion pairs formed per cubic centimeter 
per second) is given by 
Radiation instru- (1) 
earth (0) = ZrpearthK/pearth, ment directly on the 
earth’s surface 
1. Consult ‘Radioactivity in the Atmosphere” by H. Israél, 
pp. 155-161. 
ATMOSPHERIC ELECTRICITY 
Radiation instru- (2) 
ment in the ground 
(caves, tunnels, etc.) 
earth = AT pearthls / earths 
Radiation instru- (3) 
ment at an altitude 
h above the earth’s 
surface 
earth (h) = earth (0) (hutair), 
wherein 
Radiation instru- 
ment on the surface 
of the earth 
Qair (0) = QmpoirK / Mair, (4) 
Qair = AmpairK / pair. For great altitudes (5) 
Portable radiation devices, which are convenient to 
manipulate, have been described elsewhere [78, 79, 
151], as have counting-tube instruments for field work 
[133, 136]. 
Conductivity, Concentration of Ions, and Ion Mobility. 
Tf an electric potential is applied to two electrodes in 
an ionized gas, a weak current begins to flow. Corre- 
sponding to the two oppositely flowing ionic currents, 
the current density is the combination of two terms: 
1 = e(kyny + Kons) EH = AE, (6) 
where ¢ is the charge of the ion and equal to 1.6 X 
10-9 amp sec, EF is the field intensity, n1 and m2 denote 
the number of positive and negative ions, and hk; and 
ke represent the mobility of the positive and negative 
ions, respectively. The expression e(kym1 + keno) = A 
is designated as the (total) conductivity of the gas. 
The terms 
M = kyne and No = konze 
are the positive and negative polar conductivities of 
the ionic conductor. 
~--~—.. 
CURRENT 
\ 
XN 
| POTENTIAL 
I I I Ww 
Fic. 5.—Schematic curve of the current-potential relationship 
(characteristic) in an ionized gas at rest. 
If the voltage is increased starting from zero, a 
gradual decrease in ion content results; the current 
does not rise in proportion to the voltage and remains 
constant after a given value of voltage has been at- 
tained. Accordingly a distinction is made between ohmic 
2. For a tabulation of this function, see [86]. 
