110 
ductivity, because of the electrode effect previously dis- 
cussed. A characteristic of that effect is that a low 
value of negative conductivity and a normal value of 
positive conductivity should accompany a large posi- 
tive potential gradient, while for a large negative gradi- 
ent the roles of positive and negative conductivity 
should be interchanged. There is abundant evidence as 
well as a rational basis for this rule, but such evidence 
is not clearly shown in Figs. 4 and 6 during periods of 
greater activity because the original gradient trace was 
very dim when rapid changes of gradient occurred and 
was ‘‘off scale” for considerable periods. However, the 
reader doubtless can see evidence of trends of this char- 
acter in these figures. 
RAINFALL IN INCH 0.02 
AUGUST 6, 1936 
SEM : 
pos VE ¢ DUCTIVIT 
120° EAST MERIDIAN HOURS 
ATMOSPHERIC ELECTRICITY 
charge-cloud does not necessarily coincide with a visi- 
ble cloud. Ten such charge-clouds are indicated by the 
record for the latter storm. So many alternations of 
potential gradient in one series (barring changes which 
accompany lightning discharges and which are of too 
short duration to register with the apparatus used here) 
is somewhat unusual. They appear more frequently in 
records for the Huancayo station than in any other 
records available to the author. 
The suggestion that such a series of changes in gradi- 
ent may be attributed to a number of charge-clouds 
drifting by in tandem array may be an oversimplifica- 
tion. The only model of this sort which could account 
for the abrupt change of sig¢n—within about one minute 
“Th 
if 
ny ae a 
| 
| POTENTIAL sR 
iNT 
With the aid of this rule one can readily see that dur- 
ing the periods when intense electric fields prevail the 
sign of the gradient varies. The record shown in Fig. 6 
covers two storms in a 24-hr period: one in the interval 
20 to 22, approximately, on March 17, the other be- 
ginning about 14" March 18 and lasting more than three 
hours. During the former period, a negative gradient 
was recorded for more than one hour but an intense posi- 
tive gradient for only 10 min is indicated. Durimg the 
latter storm an intense positive gradient prevailed dur- 
ing the first 75 min. This was followed by an intense 
negative gradient which continued about 15 min. In 
the next hour and three-quarters, eight abrupt reversals 
of sign occurred. 
Such characteristics of potential gradient must be 
attributed to considerable masses of electric charge or 
“charge-clouds” in the vicmity of the observatory—a 
—and the intense field, continuing for 10-15 min or 
more between reversals, is one in which the charge- 
clouds are at an elevation which is small compared with 
their lateral dimension, and the array of clouds, charged 
alternately positive and negative, is closely packed. It 
is doubtful whether such a model is compatible with 
several physical conditions which seem to be required 
to maintain the charge of such clouds. Any further dis- 
cussion of phenomena of which this case is representa- 
tive should come under the category of the thunder- 
storm electric field, a topic which is discussed very 
briefly in this article. 
Another example of a field change of type (a) is 
shown on the trace for potential gradient in Fig. 5, just 
before 14550™. This is a characteristic “dust whirl’ or 
“dust devil” effect. The sign of the field change indi- 
