forecasting for periods less than an hour may be 
a delicate matter, but various methods are al- 
ready envisaged to make it more objective. Such 
methods might include the observation of ‘sfer- 
ics,’ the use of radiosondes at the critical mo- 
ments and the study of the intensity of diffused 
light from the zenith. 
When the operation started, the experiment 
will consist of observing low-level conditions, 
how long it would be possible to go on localizing 
the convection over the experimental area, and 
how long it would be possible to continue influ- 
encing the precipitation over the area. 
Possible future development of artificial con- 
vection—From the foregoing discussion, it ap- 
pears that our first objective would be to try to 
concentrate the rainfall over a cultivated area, 
possibly at the expense of a slight deficit of rain- 
falls over surrounding regions. For example, if 
we succeeded in increasing the rainfall over 
500 km? of cultivated area by 30%, it is possible 
that we will cause a decrease of 38% over 5000 
km*, which we assume will be relatively wild, 
that is to say forest or savanna. This decrease 
in the rainfall on the surrounding regions could 
have no economic disadvantage because it is not 
cultivated. 
Before finishing this exposition of this project, 
I would like to discuss some of the future per- 
spectives which the artificial convection opens 
to us and which have much wider application 
than this that we considered so far. 
(1) In tropical regions, during the dry sea- 
son, it is commonly found that the humid air at 
ground level, is overlain by dry air. It sometimes 
occurs that this humid layer is not sufficiently 
deep to permit the natural formation of Cumulo- 
nimbus. In this ease the artificial impulse given 
by the burning of fuel, may provoke a local 
deepening of the humid air layer and thus the 
very local formation of cloud. In this case, it is 
possible to imagine, when during a dry season, 
the cloud formation is not general, that local 
cloud and precipitation may be produced. We 
have already succeeded in Africa, by brush fires, 
in producing some local light rainfall (1 mm) in 
situations when no natural rainfall occurred in 
the region. 
(2) In temperate regions, in situations where 
instability occurs along a chain of mountains 
such as the Pyrenees, our intervention at criti- 
cal moments might result in a concentration of 
HENRI DESSENS 
stormy precipitation at higher areas useful to 
hydroelectric installations. 
(3) From a study of the very heavy storm 
rainfall in southern France, sometimes accom- 
panied by devastating hail storms, this phe- 
nomenon results from the coupling of the ther- 
mal energy of low air with the kinetic energy of 
the jet stream, through quite stable and localized 
ascending air currents. By analogy, some cou- 
pling effect might be obtained, in situation with 
strong jet-stream, with artificially stimulated 
convection. There would be advantage that, m 
this case, the location is controlled by the choice 
of place for the experiments. 
The ‘solar meteotron—The first experiments 
have to be made with a ‘fuel meteotron’ because 
its cost is relatively low, less than $100,000, while 
the preparation of the surface for the differential 
heating by the Sun with the proper materials 
will require a very much higher expenditure. I 
hope, nevertheless, that some participants at 
this Second Conference at Woods Hole, will agree 
that, in the end, it will certainly be necessary to 
consider either the ‘solar meteotron’ or a ‘mixed 
meteotron’ in which both solar energy and fuel 
are used. The real domestication of solar energy 
will come only with the use of a ‘meteotron’ to 
provide a rain-giving cloud. 
REFERENCES 
Dessens, H., Essai de formation artificielle de 
Cumulus par utilisation exclusive de l’énergie 
solaire, Bul. Obs. Puy de Déme, pp. 113-125, 
1956. 
Dessens, H. ann J. Dessens, La formation arti- 
ficielle de grands Cumulus producteurs de pluie, 
C.-R. Acad. Sci., 243, 814-817, 1956; Etude pré- 
liminaire des Cumulus et des pluies obtenus par 
convection provoquée, Bul. Obs. Puy de Déme, 
pp. 47-60, 1957. 
Dessens, J., Niveau de congélation des nuages con- 
vectifs équatoriaux, Bul. Obs. Puy de Dome, pp. 
73-80, 1959. 
Dessouiers, H., Refoulement dw Sahara, Ch. Beé- 
ranger, Edit., Paris, 158 pp., 1930. 
Espey, J. P., The philosophy of storms, Boston 
(Ch. GC. Little and James Brown), 552 p., 1841. 
Goréa, H. anp Rové, A., Kisérlet mesterséges esd 
eloallitasara. Idéjaras, 14, 2-9, 1938. 
Scuarrer, V. J., Cloud explorations over Africa, 
Trans. New York Acad. Sci., ser. I, 20, 535-540, 
1958. 
Soutacr, G., Réponse A la note de Bigg, E. K., 
Freezing nuclei in the atmosphere, Bul. Obs. Puy 
de Déme, pp. 80-85, 1956. 
