DISCUSSION 
399 
Discussion 
Mr. W. A. Mordy—lI lived for a number of 
years in Hawaii. In the process of harvesting 
sugar cane in the Islands they set fire to the 
fields to get rid of the leaves and waste ma- 
terial before they harvest the cane. They burn 
15 to 20 acres of cane at a time. Frequently a 
cloud forms over these fires. At the appearance 
of these clouds such as we have seen in Dr. 
Dessens’ slides, we have occassionally made time- 
lapse movies. When I first went to the Islands, 
I heard a report that such a cloud had in fact 
yielded a half an inch of rain on one occasion. 
This, of course, was interesting to us, since these 
clouds were very frequent. They could be seen 
about fifty times a year. It therefore became a 
pastime of mine to follow up on these whenever 
possible. As I traveled around the Islands I did 
this. And I was very interested to see if I could 
find another instance when a cloud had, in fact, 
formed rain. I never found another instance, and 
I could not confirm the first report either. In ten 
years we found not a single case when one of these 
clouds produced rain. 
Dr. H, Dessens—It is necessary to start the 
fire under favorable meteorological conditions; 
these are latent instability and no wind. Both 
conditions occur in our equatorial regions. Rain 
has been obtained by us in the first experiments 
but it was light rain, amounting to less than one 
millimeter. 
Dr. Tor Bergeron—l have in fact another 
project for getting more precipitation in central 
and northern Africa: the main thing is that one 
should not let the waters of the Rivers Congo 
and Nile run out into the sea, but one should use 
any available source of energy for keeping them 
inland, and especially within the regions where 
there is already some vegetation. The second 
point is that the water should certainly not be 
used for irrigation in the northern part of the 
Sahara or lower Egypt, because it will be evapo- 
rated into dry air without clouds to a great ex- 
tent. But further south, of course, the project of 
Dr. Dessens would probably come in very handy. 
I just wonder if these two projects could not 
go hand in hand and help each other, and I hope, 
in fact, we shall have an opportunity to do so, 
but then I have one question about the possible 
cost. 
Dr. Dessens—From the economic point of 
view this project seems to me more useful than 
the project of sending rockets to the Moon. 
Dr. C. E. Junge—I think it is a very good 
idea to start making use of the huge amounts of 
energy which are available in an unstable atmos- 
phere just by initiating the vertical convection 
by means of bringing in some heat. I think this 
may really be the first step in a quite new direc- 
tion of weather modification which should be 
much more exploited. 
Major C. Downie—We should also look into 
the chemistry of this process. Fuel oil during 
combustion produces about one and one-quarter 
(14%) pounds of water per pound of fuel, de- 
pending on the particular hydrocarbon mixture 
involved. Thus an appreciable amount of mois- 
ture, in addition to the heat energy, is released 
into the atmosphere. That both of these factors 
are important is borne out by the Geophysics 
Research Directorate study of aircraft condensa- 
tion trails, another example of artificially pro- 
duced clouds. 
Mr. Mordy—We did make estimates on the 
basis that one adds very much water. One would 
expect the cloud base in these eases would be 
different from other clouds in that area. But if 
you compare the effect of the added water and 
the effect of released heat, you find the energy 
added makes the difference. It is not the water. 
Actually, there are three possible variables: the 
nuclei, the water, and the energy. 
Dr. Bernard Vonnegut—In his comments a 
few minutes ago, Dr. Bergeron hinted at some 
ideas he had on the control of climate, and he 
has consented to give us a brief, but more ex- 
tensive outline of this. 
Dr. Bergeron—As you know, there are great 
plans for buildmg a new dam at Aswan, in 
Egypt. For immediate needs, this dam will be 
very useful, but not for more far-sighted plan- 
ning of water resources. In fact, the irrigation 
water spent in the arid northeast trade region 
will only be utilized by vegetation to a very 
small percentage. Part of it will go through 
plants and be useful once, and then never more. 
But the rest of it will not even go through plants 
once; it will go directly up in the air and from 
there, anywhere. It will not come down again 
in North Africa, because there are no clouds 
there. True enough, we should not allow the 
