Page 173 - James Rodger Fleming - Fixing the sky

In his insightful autobiographical memoir, Sverre Petterssen, a leader in the
field of weather analysis and forecasting, reviewed his involvement with Lang-
muir in the 1950s. Petterssen was trained in the Bergen School of meteorology,
chaired the Department of Meteorology at MIT, and served in Norwegian uni-
form in World War II, preparing forecasts for bombing raids by the British Royal
Air Force, the Anzio landing, and, notably, the D-day invasion of Normandy.
After World War II, Petterssen served as head of the Norwegian Forecasting Ser-
vice, scientific director for the U.S. Air Force Weather Service, and professor and
chair of the Department of Meteorology (later Geophysics) at the University of
Chicago. He explained the situation:

About 1947 Irving Langmuir, a Nobel Prize laureate in chemistry, and his group
working at the General Electric Laboratories had discovered that silver iodide had
a structure similar to small ice crystals. Since natural clouds, even at very low tem-
peratures, are generally deficient in ice crystals while silver iodide can readily be
produced, it seemed possible to supply silver iodide dust to cold clouds, hoping
that the clouds might be “fooled into believing” that natural ice crystals were pres-
ent. Thus, if the clouds could be so misled (and few doubted it) weather modifica-
tion (or control) would not be much of a problem.
Langmuir was unlucky and became a victim of one of the many pitfalls that
nature so generously provides for scientists who venture too far outside their own
field of specialization. Though a leading authority on the chemistry of crystal
points and surfaces, a philosopher, and a polyhistor in general science, Langmuir
did not appreciate the complexity of meteorology as a science. In the atmosphere,
processes of vastly different spatial scales and life spans exist together and interact;
impulses and energy are shuttled through the whole spectrum of phenomena—all
the way from molecular processes to global circulations and the changes in the
atmosphere as a whole. No chemist, physicist, or mathematician who has not lived
with and learned to understand this peculiar nature of meteorology can pass valid
judgment on how the atmosphere will react if one interferes with the details of
the natural processes. Moreover, to determine whether or not the atmosphere has
responded to outside interference, it is necessary to predict what would have hap-
pened had it been left alone.
As I have just said, Langmuir was unlucky. For no profound reason he had left
a silver-iodide generator somewhere in New Mexico and made arrangements with
a local person to “burn” the generator on a weekly schedule. Using a set of read-
ily available weather reports, Langmuir found that the rainfall had begun to vary
in a weekly rhythm. The amazing thing was that the response was not just local;
it was nationwide and might well be of hemispheric proportions. Langmuir, and

156 | PatHoloGiCal SCienCe