290 
one half to two minutes earlier a cloud-to-ground 
stroke had come out of the cloud base.” 
In our observations on Mt. Withington, New 
Mexico we observed a similar sequence repeated 
six times on one day in which heavy rain with 3 
mm drops appeared on the summit about two 
minutes after nearby cloud to ground strokes. 
On this oceasion the cloud base was well below 
the summit. The time that elapses between the 
stroke and the appearance of the rain appears to 
be sufficiently large that the phenomenon could 
be explained on the basis of accelerated coales- 
cence. Alternatively it is possible that the rain 
gushes that were observed may have been the 
cause of the hghtning. 
Measurements made at close range with a 
sensitive radar to determine whether or not an 
increase in reflectivity precedes or follows the 
stroke should determine which of these possible 
explanations is correct. If such observations show 
that the lightning occurs first they will indicate 
that the stroke is effective in promoting pre- 
cipitation formation. Whether or not this hap- 
pens in the way that is proposed or by some 
other mechanism will require sufficient detailed 
knowledge of the nature of the discharge and 
the electric fields and ion densities that it pro- 
duces so that quantitative calculations can be 
carried out. 
It is worth noting in this discussion of the pos- 
sible effects of lightning in thunderstorms that 
a possibly related phenomenon has been ob- 
served in connection with volcanic electricity. 
In describing the electrical discharges that some- 
times accompany voleanic eruptions, Guest 
[1939] references Beyersdorfer [1922] and Boning 
[1927] and states, “These dark clouds of finely 
divided particles of ejected matter are often 
brightened by vivid flashes of lightning dis- 
VONNEGUT AND MOORE 
charging through the cloud to the rim of the 
crater. At such times a sudden agglomeration 
and precipitation of dust may follow... .” 
Laboratory experiments are another approach 
that may shed some light on the possible effects 
of lightning in promoting particle growth. It 
should be possible to produce high voltage spark 
discharges in aerosols that simulate conditions 
in the thundercloud and to determine what ef- 
fects occur. 
Conclusions—It is concluded that the sudden 
redistribution of electric charge caused by light- 
ning in a cloud may significantly accelerate the 
formation of precipitation. In order to evaluate 
this effect, radar measurements, laboratory ex- 
periments, and investigations of the lightning 
discharge are required. 
Acknowledgment—This work was made pos- 
sible by the support of the Office of Naval Re- 
search, Bureau of Aeronautics and the Atomic 
Energy Commission under Contract Nonr 
1684(00). We wish to thank High Voltage En- 
gineering Corp. of Burlington, Massachusetts, 
which organization irradiated the plastic blocks 
for us. 
REFERENCES 
Arxinson, P. (translator), Ganot’s Physics, Wil- 
lam Wood & Co., New York 1255 pp., 1887. 
Bryersporrer, P., Sugar-dust explosions, Zs. Ver. 
Deut. Zucker, Inc., 72, 475-523, 1922. 
Bontna, P., Dust electricity, possible explanations, 
Zs. Tech. Phys., 8, 385-398, 1927. 
Gross, B., Irradiation effects in plexiglas, J. Poly- 
mer Sci., 27, 135-143, 1958. 
Guest, P. G., Static electricity in nature and in- 
dustry, Bul. 368 U. S. Bureau of Mines, 98 pp., 
1939. 
WerckMann, H., Precipitation in Cumulonimbus, 
Thunderstorm Electricity, (H. R. Byers, ed.) 
Univ. Chicago Press, 345 pp., 1953. 
Discussion 
(Note: Discussion of this paper is combined with that following the next paper.) 
