Talk:Heinrich Hertz/Archive 2

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Archive 1

Archive 2

Removal of paragraph on radio wave/light analogy

Latest comment: 7 years ago9 comments4 people in discussion

I added a paragraph to the article helping to explain why Hertz did not realize the potential practical uses of radio waves

Part of the reason for this was that Hertz's insight was limited by the analogy between radio waves and light. He believed that like light, radio waves only traveled in straight lines, and so their use as a communication medium would be limited by the horizon to a few miles.

This was recently removed by an editor with the edit comment: "it's not an analogy, they are exactly the same and do travel in straight lines -- I think you mean "didn't anticipate ionospheric reflection"

The first over-the-horizon transmission was by ground waves, not skywaves. Today we are used to the idea that radio waves can propagate beyond the horizon by two methods, ground waves which follow the contour of the Earth, and skywaves which reflect from the ionosphere. But the waves Hertz generated were in the VHF and UHF bands, which did not propagate by these methods, only line-of-sight. Even if he had generated lower frequencies, they wouldn't have traveled much beyond the horizon because he was using horizontal dipole antennas. Ground waves require vertically polarized antennas. Over-the-horizon radio propagation was only achieved by Marconi after he invented the monopole antenna in 1895.

The belief that radio waves traveled in straight lines, originating from the radio wave/light analogy, was held by the first generation of radio scientists: Hertz, FitzGerald, Lodge until Marconi proved them wrong (they even called the first radio receivers "artificial eyes"). In the late 1800s there were already light wave communication methods being used, semaphore and Bell's photophone, which did not require complicated circuits and used the sensitive human eye as a receiver. If radio waves were limited by the horizon like light, as these scientists believed, radio would have no advantage over these simpler communication methods. That's the context of Hertz's comment. @LaurentianShield: The paragraph I added was unsourced; I'll try to find some sources on this. --Chetvorno^TALK 21:26, 13 February 2017 (UTC)

My edit summary that you quote above is from when I restored your paragraph that LaurentianShield removed. I think your point is about right, but I don't find a good source to directly support it. See also the discussion that LaurentianShield started on my talk page (I don't know why he didn't start it here where it belongs). Dicklyon (talk) 21:57, 13 February 2017 (UTC)

OK, I see you've changed it now to his edit summary, and that you've also found the discussion on my page. Dicklyon (talk) 22:14, 13 February 2017 (UTC)

Thanks for catching my error! I think the optical analogy is in The Maxwellians, a great book about the first generation of radio researchers: Hertz, Oliver Lodge, George FitzGerald. Earnest Rutherford, but not much of the text is visible in Google Books. But the role of the optical analogy in limiting innovation is definitely in Hong. It doesn't say specifically that Hertz believed that radio waves were limited by the horizon, but it does say "...the Maxwellian physicists' adherence to optics obscured a telegraphic application of Hertzian waves."(p.7). Marconi, who was not a scientist but an entrepreneur, was inspired by ground-return telegraph systems of the time to try grounding one side of his transmitter (p.21), which enabled him to transmit long distances. "The emphasis on telegraphy separates Marconi from the other physicists and engineers that were working on Hertzian waves; all the others were preoccupied by optical analogies." (p.22) --Chetvorno^TALK 23:26, 13 February 2017 (UTC)

I can check my copy of The Maxwellians on Thursday or so. Dicklyon (talk) 00:11, 15 February 2017 (UTC)

I have a source I cited on Dicklyon's page, which says that the primary reason Hertz did not believe radio was viable for communication was not the line-of-sight issue, but rather because he did not think the waves would have the strength. In order for him to cause the spark to jump in his receiver, he had to focus his waves using what he called "mirrors". There is a fairly clear direct quote, I just don't have it right now. My main concern in any case was to call radio waves an "analogy" with light. In free space they are identical and both travel is straight lines orthogonal to the E-M fields. Quasi-guided waves (such as around the earth) can "bend" of course, from a variety of factors. I would like to see any wording not muddle this point to new readers who might not understand the subtlety. Meanwhile, when I find the quote I am referring to, I will provide it. LaurentianShield (talk) 23:40, 13 February 2017 (UTC)

Here is the quote by Harold I. Sharlin, in The Making of the Electrical Age who further goes on to quote Hertz:

Hertz was asked if his discovery could be used for telegraphy. "If you could construct a mirror as large as a continent, you might succeed with suche experiments," he answered, "but it is impracticable to do anything with ordinary mirrors, as there would not be the least effect observable." He mistakenly believed that waves had to be focused to travel any distance.

Sharlin cites Rupert W. Maclaurin, Invention and Innovation in the Radio Industry as his source. Note that Sharlin interprets Hertz to be speaking about strength (distance), an interpretation which I assume he arrives at from Maclaurin.

With respect to the line-of-site issue, if it is worthy of mention I hope it is obvious that I agree radio EM propagation at RF is different that optical frequency propagation in and around media, I would just like to be more precise about it one way or the other -- light after all bends when it is guided, even on the Earth. My guess is Marconi anticipated that RF somehow does something similar, or else he would not have dared with the trans-Atlantic transmission.

LaurentianShield (talk) 00:47, 14 February 2017 (UTC)

Its interesting to see Hertz did say something about wireless telegraphy, didn't know that and it should probably be added to the article. Beyond Hertz (may be off topic) - the reason not to develop radio-telegraphy before Marconi was "wire was cheap". Radio waves could not be detected over 1/2 mile (according to Lodge), they required expensive and delicate lab equipment to even detect them, and since they could only send a signal to something at a short visual range, why not just lay wire, or use a signal light or flag if it was a ship at sea. The only real use they could see for adapting such an arcane laboratory experiment to telegraphy was, "what if you had a ship lost in fog looking for a lighthouse, can't use a wire and can't use a visual signal. Yep, maybe that is an occasion it would be worthwhile to have radio based communication" (Hong, page 8 and 17). Fountains of Bryn Mawr (talk) 20:32, 14 February 2017 (UTC)

All of those applications you mention are short range, within the visual horizon. The background assumption of all these educated physicists was that of course radio waves couldn't propagate much beyond the horizon regardless of their power, because they travel in straight lines, because light does. So there wasn't much incentive to increase the power. If Hertz or his contemporaries had the slightest inkling in 1887 that radio waves could travel transatlantic distances, they would have been all over it. But they missed it, because they were hung up on the optical analogy, where Marconi wasn't. Yes, if it was limited to line-of-sight, radio was not much of an improvement over wire. But if it can travel 3000 miles around the curve of the Earth? BIG improvement. --Chetvorno^TALK 23:11, 14 February 2017 (UTC)

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