At the end of the XIXth century Édouard Branly discovered that the conductivity of a filings-full resistive tube was greatly enhanced when a spark radio-emitter was turned on in its vicinity. Oliver Lodge developed the coherer, the first "sensitive" radio detector, based on this effect, and the coherer was used by Guglielmo Marconi in the first radio transmission experiments. This effect never received a satisfactory physical explanation.
This article proposes to understand Branly's effect as a consequence of the induced tunneling effect theoretically discovered by François Bardou and Dominique Boosé. (D. Boosé and F. Bardou, “A quantum evaporation effect,” Europhys. Lett., 53, 1-7 (2001)) This effect has been checked experimentally by Benjamin Thomas et al. (Ch. Hirlimann, B. Thomas, D. Boosé, Induced optical tunneling, Europhys. Lett. 69, 48-54
(2005)).
This is interesting. We are writing a textbook on electrodynamics. This might make a nice problem somewhere .. hmm ... thanks.
Hello,
I have asked myself that same question. I wrote a thesis on this question in 1993, and it is available on ResearchGate. It contains historical information about coherers and the STM that is not generally known. The thesis is titled "Coherers, a review". It is several hundred pages long.
Regards,
Tom Cuff
Dear Thomas,
I apologize for the long delay.
All along year 2015 I have had a long mail discussion about Branly's effect with Chris Maness who was @CSU Fullerton working on early radio-electricity.
The result of this long discussion is that there might be enough energy in the incoming em waves impinging onto a coherer to have the electrons pass above the potential barriers that separate the filings. He made the point that even on long transatlantic distances the attenuation of em in the frequency range of the time (~100 kHz) is not as large as one can think it is because of the guiding of the waves between see and ionosphere.
Specific experiments should be performed to assess the role of induced tunnelling involvement in Branly's effect.
I just downloaded your thesis and will certainly read it.
Hello,
I just realized that the page references in the various Tables of Content in my thesis "Coherers, a review" are wrong. I apologize. The computer I am using does not have Microsoft Office 2007, and so I had to use Open Office to convert the Word file to pdf. Unfortunately, Open Office changed the pagination. When I return home, I will use Word 2007 to create the pdf file and post it on ResearchGate. Again, I apologize - I should have checked.
Regards,
Tom Cuff
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