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C.T.R. Wilson versus G.C. Simpson:Fifty Years of Controversy in

Atmospheric Electricity

Earle Williams

MIT

International Conference on Atmospheric Electricity Beijing, China

August 2007

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Research Notebooks of C.T.R. Wilson

• Fifty research notebooks were bequeathed to the library of the Royal Society in London in the early 1960s by the Wilson family

• All notebooks were microfilmed in 2002 and provided to the Niels Bohr Library of the American Institute of Physics in College, Park Maryland.– Notebooks A1-A21 Condensation and the Cloud Chamber– Notebooks B1-B29 Atmospheric Electricity

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Setting the stage for the controversy about the polarity of thunderclouds

• Time frame is the turn of the century (~1900)

• Wilson (31 years old) has already invented the cloud chamber– Documented condensation on small ions– Discovered the continuous ionization of the atmosphere

• The Earth has sustained negative charge (a point of widespread agreement) but what maintains this charge against dissipation in conductive atmosphere?

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1899-1902, Wilson tooling up for career in atmospheric electricity

• Notebooks are filled with background investigation of atmospheric electricity with ideas to test and things to try

• 1903 Nature paper on “Atmospheric Electricity” sets forth basic idea about the global circuit:

“In regions enjoying fine weather there will be a dominant electric current; there must then be a compensating current accompanying precipitation, negative electricity being brought down in the rain and the positive charge being left behind in the atmosphere.  There is reason to believe that an excess of negative charge is brought down to the Earth's surface as rain.”

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George Clarke Simpson wants to answer this “fundamental question” of

atmospheric electricity

• 1903, In his first scientific paper, he found evidence against the idea of Elster and Geitel that the Earth is negatively charged because of the asymmetry in ion mobilities

• 1904, Simpson travels to Lapland to make continuous measurements of atmospheric electricity for an entire year

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Simpson in Lapland 1904

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1907, Simpson in Simla, India to measure the charge on rain

• Key finding: Rain is predominantly positively charged

• Interpretation: Breaking drop theory makes a negative dipole (negative over positive charge)

• Crucial uninterpreted finding: Documented prevalence of negative potential gradients at the ground under electrified storms

• Wilson’s notebook assessment of Simpson (1909): “Rather long-winded”

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Sketches of Negative Dipoles (Wilson Notebook B6)

(1) (2)

(3)

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Wilson initiates thunderstorm studies at the Solar Physics

Observatory (1913)

• Goals in notebooks clearly set forth: – (1) Measure the charge on rain– (2) Measure the field changes due to lightning

• Simpson (1909) has had an impact on Wilson:– All notebook sketches in this period are negative dipoles

(negative over positive charge)

• Wilson (1916) pioneers the electrostatic method for inferring thunderstorm charge structure but is still not affirming the positive dipole

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1917-1919, Kite-balloon work in electrified conditions

• Growing awareness of magnitude of point discharge current

• Charge on rain is the result rather than the cause of the storm electrification

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Wilson’s interest in point discharge currents (1917-1920)

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1920, Wilson breaks with Simpson

• Wilson now has completely different hypothesis for the positive charge on rain

• Thunderstorms AND electrified shower clouds are positive dipoles and batteries for the global circuit

• All notebook sketches are positive dipoles from this stage onward.

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Two Face-to-Face Discussions

• 1922 Discussion session on “The Maintenance of the Earth’s Electric Charge” at the Royal Astronomical Society Wilson acknowledges positive charge on rain but this observation “does not exclude the possibility of precipitation being the source of the Earth’s negative charge”

• 1924 Symposium on “Ionization in the atmosphere and its influence on the propagation of wireless signals” at Imperial College Simpson is “unable to accept Mr. Wilson’s explanation for the origin of the normal negative charge on the Earth”

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Simpson’s Argument about Branching of Lightning

• Based on laboratory studies, Simpson (1926) postulates that only the positive end of lightning can branch Downwardly branched lightning below the cloud is therefore evidence for a negative thunderstorm dipole Jensen (1930, 1933) refutes Simpson (1926) in Nebraska observations

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Wilson's response to Simpson's claim about branching of lightning

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Classical analysis by Whipple (1929)

• Cornerstone of atmospheric electricity

• Support for Wilson's positive thunderstorm dipole

• Simpson continues his objection:– "In my opinion, there is no physical support to Wilson's

hypothesis. I have over and over again discussed this point and have shown that all evidence which Wilson adduces from clouds of positive polarity can be interpreted just as well by my theory in which the cloud is not of pronounced positive polarity."

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Simpson and Scrase (1937)Simpson and Robinson (1940)

• Balloon soundings of electrified clouds at Kew Observatory Development of alti-electrograph for obtaining electric field structure

• Emergence of the tripole concept, a resolution of the argument over charge structure

• Simpson continues to defend the breaking drop theory as origin of lower positive charge

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Gish and Wait (1950)

• Aircraft overflights of thunderstorms in central US showed clear evidence for dominantpositive charge in the tops

• Clinching evidence for Wilson's positive dipole

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Retrospectives on their debate

• Simpson (1942)– "I shall try not to be argumentative, but to state the pros and

cons in as objective and impartial way as is possible for one who for thirty years has been in the midst of the controversy-- a controversy which, I am pleased to say, has been good tempered and always conducted in a truly scientific spirit.“

• Wilson (1956)– In his last scientific paper, no mention of Simpson or his

work at all

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1965, Richard Feynman Summary in “Lectures on Physics”

• The top of a thunderstorm has a positive charge and the bottom a negative one, except for a small region of positive charge in the bottom of the cloud.  No one seems to know why it is there, how important it is--whether it is a secondary effect of the positive rain coming down or whether it is an essential part of the machinery.  Things would be much simpler if it weren't there

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The Wilson-Vonnegut ConnectionFebruary 9, 1956

Dear Mr Vonnegut Many thanks for your letter which I received yesterday, and for the accompanying paper. I have read the paper with great interest. Our ideas about the nature of the mechanism of the thundercloud as an electrical machine seem to be essentially much alike. I have recently brought to completion a paper with is the result of very many years work and am now just getting it into its final form for publication. As I am now within a week of entering my eighty-eighth year you will understand that I am trying to get the paper off my hands without any further delay and hope shortly to send you a copy! I am interested to find that our methods of approach to the subject and the details of the mechanisms suggested are not at all alike. It is a great pleasure for me to get into touch with someone who delights as I do in contemplating the workings of the thundercloud.

Yours sincerelyC.T.R. Wilson

Sketch from notebook B10

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The contemporary perspective on

inverted polarity of clouds :

We are arguing about this again

today.