304 
fect under the conditions when the electric field 
is quite low, I question that the process he de- 
scribes is usually the dominant one. He ascribes 
the field changes primarily to the discharge of 
electrified rain when it falls on the ground. It 
appears to me that a serious objection to this 
idea is the general fact that the current density 
resulting from the falling rain is usually only a 
fraction of that measured for point discharge. 
Accordingly, since field changes are the result of 
current flow, it would appear that the precipita- 
tion current plays a secondary role. Another ob- 
jection to this postulated mechanism is our ob- 
servation that the changes of the electric field 
associated with the falling of precipitation often 
begin a minute or more before any precipita- 
tion has reached the ground. 
Dr. James P. Lodge (communicated)—Dr. 
Vonnegut has noted, as numerous previous in- 
vestigators have done, that an energetic light- 
ning discharge is frequently followed by a 
marked increase in rainfall intensity. He asso- 
ciates this as, respectively, cause and effect. Is 
it not more likely that the cause and effect are 
instead reversed, that in fact the lightning dis- 
charge simply used the descending rain sheet as 
a low resistance path to the ground so that the 
lightning flash merely appears to precede the 
rain because the final air gap is bridged while 
the rain is still a few hundred meters above the 
ground? It seems to me that the increased rain 
DISCUSSION 
usually arrives only seconds after the hghtning 
flash, which is much too short a time for in- 
creased rain to be generated as a result of the 
lightning stroke and to fall all the way from the 
cloud. 
Dr. Vonnegut (communicated)—The gush of 
rain frequently observed after a lightning stroke 
is probably quite a complicated phenomenon 
that may arise from several different causes. The 
alternative suggestion proposed by Dr. Lodge 
seems quite reasonable and may indeed account 
for some observations of this kind. I believe 
there may be some question concerning the 
validity of Dr. Lodge’s main premise that the 
lightning uses the descending rain sheet as a 
low resistance path. My own observations of 
thunderstorms lead me to doubt that lightning 
prefers the rain sheet. I have frequently been 
struck by the fact that the lightning often de- 
scends from the cloud base through clear air 
where no rain is falling even though a heavy rain 
sheet is nearby. The lightning appears to have 
little affinity for the rain and seldom either fol- 
lows a path through or terminates in the rain 
sheet. Quite possibly Dr. Lodge may have in 
mind a situation that is somewhat different from 
the sort we have discussed, for the rain gush 
that we observed followed the lightning by a 
minute or two instead of only seconds after the 
lightning flash, as Lodge describes. 
