When Maxwell realized in 1862 that light consists of waves in the electromagnetic field, why didn't anyone try to use electricity to make such waves right away? Why did Hertz succeed only 24 years later?
According to 𝘛𝘩𝘦 𝘔𝘢𝘹𝘸𝘦𝘭𝘭𝘪𝘢𝘯𝘴:
"Since he regarded the production of light as an essentially molecular and mechanical process, prior, in a sense, to electromagnetic laws, Maxwell could elaborate an electromagnetic account of the propagation of light without ever supposing that ether waves were produced purely electromagnetically."
In 1879, a physicist named Lodge realized that in theory one could make "electromagnetic light". But he didn't think of creating waves of lower frequency:
"Send through the helix an intermittent current (best alternately reversed) but the alternations must be very rapid, several billion per sec."
He mentioned this idea to Fitzgerald, who believed he could prove it was impossible. Unfortunately Fitzgerald managed to convince Lodge. But later he realized his mistake:
"It was FitzGerald himself who found the flaws in his "proofs." He then proceeded to put the subject on a sound theoretical basis, so that by 1883 he understood quite clearly how electromagnetic waves could be produced and what their characteristics would be. But the waves remained inaccessible; FitzGerald, along with everyone else, was stymied by the lack of any way to detect them."
In 1883, Fitzgerald gave a talk called "On a Method of Producing Electromagnetic Disturbances of Comparatively Short Wavelengths". But he couldn't figure out how to 𝘥𝘦𝘵𝘦𝘤𝘵 these waves. Hertz figured that out in 1886.
@johncarlosbaez A bit of waiting for equipment to catch up and be serendipitously able to stimulate ideas?
Things like having reasonable vacuums and dependable higher voltages available in the lab. Or, outside the lab, advancing telegraphy.
Not to mention the difficulties in detecting something you don’t fully understand. iirc, Hertz had a lot of trouble until he realised the room he was working in was affecting his detection.
The "experience" of Herz was a mere chance observation. Here is a schema (1:45) What he observed was that every time there was a spark in the emitter, there was also a spark in the receptor. But he understood that it validated the transmission of electromagnetic fields and then Maxwell's ideas.
(You can activate the subtitling and the translation in the video but it is not always correct.)
@fl wrote: "The "experience" of Hertz was a mere chance observation."
Wikipedia:
"During Hertz's studies in 1879 Helmholtz suggested that Hertz's doctoral dissertation be on testing Maxwell's theory. Helmholtz had also proposed the "Berlin Prize" problem that year at the Prussian Academy of Sciences for anyone who could experimentally prove an electromagnetic effect in the polarization and depolarization of insulators, something predicted by Maxwell's theory. Helmholtz was sure Hertz was the most likely candidate to win it. Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, and worked on electromagnetic induction instead. Hertz did produce an analysis of Maxwell's equations during his time at Kiel, showing they did have more validity than the then prevalent "action at a distance" theories.
In the autumn of 1886, after Hertz received his professorship at Karlsruhe, he was experimenting with a pair of Riess spirals when he noticed that discharging a Leyden jar into one of these coils produced a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to proceed with the "Berlin Prize" problem of 1879 on proving Maxwell's theory (although the actual prize had expired uncollected in 1882). He used a dipole antenna consisting of two collinear one-meter wires with a spark gap between their inner ends, and zinc spheres attached to the outer ends for capacitance, as a radiator. The antenna was excited by pulses of high voltage of about 30 kilovolts applied between the two sides from a Ruhmkorff coil. He received the waves with a resonant single-loop antenna with a micrometer spark gap between the ends."
@johncarlosbaez@BashStKid "Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, and worked on electromagnetic induction instead."
He'd given up. But it explains why he knew Maxwell's theories so intimately.
@johncarlosbaez@BashStKid "he was experimenting with a pair of Riess spirals when he noticed that discharging a Leyden jar into one of these coils produced a spark in the other coil. With an idea on how to build an apparatus"
It looks like the "chance observation" I described. Except that it doesn't use the equipment in the diagram.
@johncarlosbaez@BashStKid "The antenna was excited by pulses of high voltage of about 30 kilovolts applied between the two sides from a Ruhmkorff coil. He received the waves with a resonant single-loop antenna with a micrometer spark gap between the ends."
This time it corresponds to the diagram but it's an experiment set up after the involuntary observation described in the message above.
@johncarlosbaez@BashStKid "Hertz did produce an analysis of Maxwell's equations during his time at Kiel, showing they did have more validity than the then prevalent "action at a distance" theories."
It was what I thought tonight: was it a "action at a distance" or a "transport"?
@johncarlosbaez I am thinking how you could demonstrate radio waves with 19th century means. With home made coils and capacitors, the frequencies would be low, and the wavelength huge.
According to Wikipedia, Hertz used high voltage discharge to generate high frequency radio waves, which he detected using a "spark micrometer".
@johncarlosbaez The 1st issue of "Electric Experimenter" feautures an article on the history of producing and detecting radio waves. Another Maxwellian played a major role: J.A. Flemming, the inventor of the vacuum tube, was his student.
WikiPedia:<He was among the "two or perhaps three University students who attended Maxwell's last Course". Maxwell's lectures, he admitted, were difficult to follow. Maxwell, he said, often appeared obscure and had "a paradoxical and allusive way of speaking">
@tg9541 - neat! There's so much I want to learn about the early history of electronics. I'd never heard of Flemming or thought about who invented the vacuum tube.
Add comment