Langmuir's Claim
of a Seven-Day Periodicity
Caused by Cloud Seeding

Copyright 2002 by Ronald B. Standler


In November/December 2002, while reading meteorology journals from the early 1950s on cloud seeding, I came across an apparently fantastic claim by Irving Langmuir that cloud seeding during 1949-51 had modified the weather more than 1000 kilometers downwind.

The specific project was conducted by Dr. Irving Langmuir's research group (including Dr. Bernard Vonnegut) at the General Electric Company, under contract to the U.S. Military. As part of this project, Dr. Vonnegut released AgI from a generator on the ground at Socorro, NM on Tuesday, Wednesday, and Thursday of each week during 6 Nov 1949 to 27 April 1950. (Langmuir's Collected Works, Vol. 11, p. 217)

Langmuir claimed that this release of AgI modified the weather, not only in the state of New Mexico, but also more than 1000 kilometers downwind. Langmuir's evidence was a seven-day periodicity found in meteorological records in the Ohio River Valley, the Wabash River Valley, as well as in New England.

Annotated Bibliography

Langmuir made a few public presentations of his claims at meetings of various scientific societies, and brief versions of his claims were published at:

Criticism of Langmuir's Claims

Langmuir's claims were rejected by the meteorological community, because Langmuir's published evidence was inadequate. The following is a partial list of publications that disagree with Langmuir's claims:

Langmuir's Reaction

Instead of publish adequate evidence, Langmuir appears to have ceased publishing in journals of professional scientific societies. I can think of two reasons for this sudden cessation of publications by Langmuir:
  1. Perhaps Langmuir was annoyed by the harsh criticism by meteorologists.
  2. Perhaps Langmuir was censored by managers and attorneys for General Electric Company who were trying to avoid tort liability for flooding near Kansas City in July 1951. Langmuir had earlier said that AgI release by Vonnegut in New Mexico had caused rain in Kansas, and General Electric was releasing AgI in New Mexico during June and July 1951.
Of these two reasons, the second appears more likely to me. Vonnegut, who was a prolific author of scientific papers, apparently never published any discussion of why he chose a weekly periodic release of AgI, and apparently never published any discussion of the results of his periodic release. Given General Electric's careful assignment of all cloud seeding from airplanes to the U.S. Military (i.e., with General Electric's employees only as observers), Vonnegut's release of AgI smoke from the ground seems to me to have violated General Electric's policy of having only the U.S. Military make decisions when and where to release AgI.

Langmuir's detailed evidence was given in a tediously long technical report issued by General Electric company as part of the research project sponsored by the U.S. Military. (Final Report of Project Cirrus, Part II, General Electric Research Laboratory Report RL-785, May 1953.) This report was initially classified by the U.S. Military, but later declassified and published in 1961 in The Collected Works of Irving Langmuir, volume 11. The important thing to note here is that Langmuir's critics (with the possible exception of Brier) probably had not seen the then classified report.


My opinion is that there was a naturally occurring seven-day periodicity in the weather in the central and eastern USA at that time, and it is purely coincidence that Vonnegut operated his AgI generator on a weekly cycle. Further, Langmuir never publicly published adequate evidence for his conclusions that (1) AgI release caused rainfall far from the point of release or (2) periodic AgI release caused periodicities in meteorological variables.

Langmuir's controversial and fantastic claims are now only a small detail in the history of science and technology, which is why I have written about them in a separate essay from my other essays on the law and technology of weather modification. If one were interested in evaluating the long-range effects of AgI release, it would be better to do a new experiment than to re-examine Langmuir's old data. A new experiment could take advantage of modern technology, including use of tracers (e.g., SF6) to follow the AgI in the atmosphere.

Prof. Byers made the following tantalizing remark:
One has only to ask that someone in the Southwest [USA] repeat this ridiculously simple experiment to see what vindication can be found for Langmuir.
Horace R. Byers, foreword to The Collected Works of Irving Langmuir, volume 11, p. xx, 1961.

this document is at
revised 23 Dec 2002

Return to my essay on History and Problems in Weather Modification.

Go to my homepage.