UNIVERSAL ASPECTS OF ATMOSPHERIC ELECTRICITY 
The earth and the ionosphere, or possibly the upper 
stratosphere, serve as the inner element and the outer 
element, respectively, of a spherical electrical condenser. 
Because the air between the inner and outer elements is 
conductive this condenser has a “leakage”’ resistance A. 
A difference of potential V between the elements is 
maintained by the supply current. The leakage current 
I is V/R, and for steady conditions this is also the 
magnitude of the supply current. For J = 1800 amp 
and R = 200 ohms (values based on observations), V 
= 360,000 v. A somewhat lower value of V is obtained 
from measurements of potential gradient made on bal- 
loon flights at altitudes ranging from sea, level to about 
10 km (see equation (4)). 
Apparently J and V are the chief variables in this 
relation and of these V is regarded as the independent 
variable. No appreciable variation in F is indicated by 
the data now available. Although the average con- 
ductivity measured on Cruise VII of the Carnegie (mean 
epoch, 1929) was only 74 per cent of that for Cruise 
VI (mean epoch, 1921), the average air-earth current 
density did not differ significantly, that for Cruise VII 
being 107 per cent of the value for Cruise VI. This 
indicates that 7, and consequently V/R, was essentially 
the same for these two epochs. This fact does not neces- 
sarily exclude the possibility that V and R were related 
as dependent and independent variables, respectively, 
because if R had increased but the supply current had 
remained constant, V would have varied directly as R. 
But there are no grounds for thinking that R varies ap- 
preciably owing to variation throughout the atmosphere 
in the rate of ionization, the chief factor. The chief 
ionizer, the cosmic radiation, seldom varies by more 
than a few per cent of the mean; variations in ampli- 
tude as great as 3 to 4 per cent occur infrequently, 
usually during magnetic storms, and last only from a 
few hours to a day or two. On only four occasions in 
more than a decade have increases of more than 10 
per cent of normal (at sea level) been observed [12]. 
Perhaps on these occasions a detectible decrease in R 
occurred. This should be revealed by a simultaneous 
increase of \ at widely distributed stations and a cor- 
responding decrease of H. No such world-wide changes 
of X and # have yet been definitely detected, but a 
special examination should be made of the four cases 
just mentioned. 
Apparently the only possible source of world-wide 
changes in X, amounting to more than a few per cent 
and continuing for long periods, is corresponding 
changes in the pollution of air with nuclei which serve 
for the formation of large ions. Even if such extensive 
changes do occur near the earth’s surface, there would 
be no comparable change in F& unless the change in ) 
occurs throughout most of the troposphere. A decrease 
of \ from the surface to a considerable altitude appar- 
ently does occur over limited areas especially in the 
vicinity of cities or industrial centers where there is 
notable pollution of the atmosphere. The extent of this 
is such that the columnar resistance r appears to be 
increased severalfold but the total area involved is 
doubtless such a small part of the earth’s surface that 
107 
only immeasurable effects in R may be expected. Pe- 
riodic changes in 7, such as diurnal variations, are also 
in evidence at some places, but these depend mainly 
upon local circumstances and apparently do not affect 
R appreciably. 
These statements about variations in r are based on 
information obtained by an indirect method which de- 
pends upon the assumption that 77 = V is the same 
everywhere on the earth at a given instant. If 7 is 
measured simultaneously at two places, then according 
to this condition the ratio of the value of r at one place 
to that at the other place is equal to the inverse ratio 
of corresponding values of 7. The efficacy of this method 
of analyzing such data also depends upon the circum- 
stance that at some places, notably over the oceans, r 
seems to be much more nearly constant than at some 
places on land. This device has been used chiefly for 
estimating the average diurnal variation of r [21, 22]. 
The results are at least plausible. 
That the more prominent variations of \ occur chiefly 
in the lower part of the atmosphere is indicated by the 
reciprocal relation, frequently found, between \ and 
(electric field strength), namely, \H = 7 where 7 is 
approximately constant. This mdicates that in these 
cases r is not modified much by the changes in A, and 
that accordingly the vertical extent of the changes in 
and F# is relatively small. The height of the air stratum 
involved has been estimated in several ways. At Paris a 
height of 200 m or less was indicated by the observa- 
tion that variations of H# near the top of the Hiffel 
Tower were chiefly of the universal type, whereas at a 
nearby ground station the variations were much more 
complex. Heights for the region of abnormal conductiv- 
ity of the order of one to two kilometers have been 
estimated for other situations, in which r is appreciably 
modified. 
Of the features of air conductivity discussed here, 
those of chief importance for the broader aspects of 
atmospheric electricity are (1) electrical conductivity of 
air is a universal property, (2) this property imcreases 
with altitude and at some altitude, probably less than 
60 km above sea level, is so great that at a given instant 
the electric potential at that level is essentially the same 
everywhere over the earth, and (3) the electrical con- 
ductance between the earth and the high atmosphere, 
or the reciprocal of this, the resistance #, probably is 
not subject to appreciable variation. 
THE ELECTRIC FIELD OF THE ATMOS- 
PHERE IN FAIR WEATHER 
Many observations of the electric field in the atmos- 
phere have been made during the nearly two hundred 
years since Franklin made his famous kite experiment 
in 1752 and Lemonier, later in that year, first observed 
an electric field in the atmosphere during clear weather. 
Before the end of the eighteenth century a number of 
the characteristics of the electric field were correctly 
inferred from qualitative observations made chiefly in 
Europe. Quantitative measurements of the electric field 
strength came into vogue after Sir William Thomson 
in 1860 stressed the need of measurements which could 
