23 votes
Accepted

How did scientists plot complicated graphs in the 19th century?

I do not know how exactly was this picture made, but there are at least two methods. The first one is to compute this potential (which is not too difficult), plot sufficiently many points and connect ...
Alexandre Eremenko's user avatar
18 votes

How did scientists plot complicated graphs in the 19th century?

Adding to Alexandre's answer. My father, educated in the 1930s, used a set of "French curves" like this Secondly ... perhaps the picture in the post was not drawn by Maxwell himself, but by a ...
Gerald Edgar's user avatar
  • 10.3k
12 votes
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Was it suspected that the speed of electricity was equal to the speed of light?

For a long time it was not only believed but even ascertained that electric signals moved not just as fast but faster than light, even "instantaneously". The original experiments involving ...
Conifold's user avatar
  • 75.2k
11 votes
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Did Maxwell originally write his equations using quaternions?

I read somewhere, some time ago that Maxwell originally wrote his eponymous equations using the formalism of quaternions ... Is this true? It seems that the answer is "Not quite". Maxwell originally ...
Peter Taylor's user avatar
10 votes

How did early scientists know if a current was changing direction? (AC vs. DC)

Daniel Sank is correct; with a magnetized needle on a pivot and a coil of wire you can make a device called a galvanometer with which you can watch current change direction, at least for low ...
niels nielsen's user avatar
9 votes

Electromagnetic constants and the speed of light

The relation of the speed of light $c$ to electrodynamics was known before Maxwell. In 1846, Weber derived his force law between point charges:1 $$F=\frac{ee'}{r^2}\left[1-\frac{1}{2c^2}\left(\frac{...
Geremia's user avatar
  • 5,289
9 votes

How did Stern or Gerlach, of Stern-Gerlach experiment, create individual silver atoms? How were they accelerated?

Atomic spectroscopy was very advanced 100 years ago (1920s) and we must appreciate their intelligence. If a metal like silver is being heated to the extent of boiling in high vacuum, all you get is ...
AChem's user avatar
  • 4,049
8 votes
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Is it thought that Maxwell used Green's Theorem to derive his equations?

Of course Maxwell knew Green's theorem, by the time he was writing this was the common knowledge. Maxwell's book has a mathematical preliminary chapter (chapter 2) where he explains mathematical tools ...
Alexandre Eremenko's user avatar
8 votes

Who originally derived the general force law equation of force between current elements?

Ampère did. Ampère's force law (not to be confused with one of Maxwell's equations, "Ampère"'s circuital law, which Ampère never wrote down, as Ampère didn't deal with the field concept), written in ...
Geremia's user avatar
  • 5,289
7 votes
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Was the telegraph system of 1859 powered by AC or DC and how extensive was it?

Google really is your friend. history.com says E.W. Culgan, a telegraph manager in Pittsburgh, reported that the resulting currents flowing through the wires were so powerful that platinum ...
Carl Witthoft's user avatar
7 votes

How did Henry Cavendish deduce the inverse square law in electrostatics from his experiment in 1772?

Newton proved that if the attraction obeys the inverse square law, then the force inside a uniformly charged sphere is zero. It follows from the description that you give that Cavendish used the ...
Alexandre Eremenko's user avatar
7 votes
Accepted

Historical origin of magnetic monopoles

The modern concept of magnetic monopole (as a real isolated charge) is due to Dirac in 1931, although Curie speculated about the possibility earlier. Even electric charges, as in particles, only ...
Conifold's user avatar
  • 75.2k
7 votes
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Names of the electromagnetic units in SI

Actually, the farad was the term used for a unit of charge by Latimer Clark and Charles Bright in 1861 in honour of Michael Faraday. But by 1873, it had become the unit of capacitance and was adopted ...
Mozibur Ullah's user avatar
7 votes
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Whatever happened to parageometrical optics of diffraction?

There was nothing wrong with parageometrical optics mathematically, it just did not take. It happens. Compare Google ngram for parageometrical to the ngram for nomography. And nomography had ...
Conifold's user avatar
  • 75.2k
7 votes

How and by whom was the magnetic term in the Hamiltonian first derived?

Lorentz derived the Lagrangian and the Lorentz force formula with the magnetic term in his Versuch einer Theorie der electrischen und optischen Erscheinungen in bewegten Körpern (1895). There were ...
Conifold's user avatar
  • 75.2k
6 votes

Who discovered the magnetic vector potential, $\vec{A}$?

Franz Ernst Neumann was the first¹ to write down the magnetic vector potential in his 1845 paper "General laws of induced electrical currents." He used it to write the equation summarizing Faraday's ...
Geremia's user avatar
  • 5,289
6 votes
Accepted

What did Einstein learn in his university electricity and magnetism courses?

Einstein's physics teacher, H. F. Weber, apparently did not teach him any Helmholtz, as Einstein wrote in a 10 August 1899 letter to Mileva Marić: I returned the Helmholtz volume* and am at present ...
Geremia's user avatar
  • 5,289
6 votes
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What is the idea behind Maxwell's "displacement current" in electromagnetism?

Maxwell did not think of the displacement current as a continuation of the conduction current, and his motivations are generally entwined with his mechanical models of ether. But the naming itself ...
Conifold's user avatar
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6 votes
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Where exactly did George Brown publish the first paper about Turnstile antennas?

Electronics, (subtitled 'radio, communication, industrial applications of electron tubes ... engineering and manufacture') was published by McGraw Hill. Not a journal per se, more of an industry ...
Jon Custer's user avatar
  • 1,197
6 votes

How did physicists deal with the variance of electromagnetism before special relativity?

There certainly WERE formulae that correctly described parts of the electromagnetic puzzle, including Fitzgerald-Lorentz contraction of distance, and even some medium-drag light delay experiments with ...
Whit3rd's user avatar
  • 161
6 votes
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"Équation de Maxwell-Thomson"

In French, physical laws are not always named the same as in English (usually some Frenchman is added) Snell's law $\to$ loi de Snell-Descartes Gauss' theorem $\to$ théorème de Ostrogradski-Gauss WKB ...
Mauricio's user avatar
  • 3,344
5 votes

Why do Maxwell's equations bear his name?

Ampère never wrote down what is confusingly called "Ampère's circuital law," not even the form without the displacement current term, as Ampère never dealt with the field concept.* Maxwell derived $$\...
Geremia's user avatar
  • 5,289
5 votes

Historically how it was discovered that we need fields to describe matter?

The Wikipedia coverage of the history is pretty spot on, and there is hardly a point in exactly dating the incremental formal developments of the second quantization picture of Dirac, Jordan, Wigner, ...
Cosmas Zachos's user avatar
5 votes

High voltage / current sources in 19th century cathode ray experiments

In order to obtain a nonpulsating power source some early investigators used Wimshurst or similar static electricity generators, or batteries of many small storage cells. (The discovery of the ...
jkien's user avatar
  • 1,901
5 votes
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Origin of the Heaviside function?

"Oliver Heaviside ... what he was doing, why he developed his step function"? A short answer is that Heaviside was interested, as a practical electrical engineer, in transient effects in complex ...
terry-s's user avatar
  • 4,375
5 votes
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How did Henry Cavendish deduce the inverse square law in electrostatics from his experiment in 1772?

Alexandre Eremenko's answer is great, but I figure the page could benefit from an explanation of the method in general. Cavendish's Experiment The question Cavendish was facing was this: Given that ...
Sam Gallagher's user avatar
5 votes

How was (non-instantaneous) electric current first discovered?

I will assume "non-instantaneous" means something other than electric discharge in the atmosphere, from animals like eels and torpedo fishes, or electrostatic generators like the Leyden jar or the van ...
Conifold's user avatar
  • 75.2k
5 votes
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Why is wave guide theory developed so long after Maxwell's work was published?

This is not an answer but a viewpoint to examine: EM theory as we now know it was largely developed by Oliver Heaviside in the 1880s and 1890s from Maxwell's somewhat awkward formulation (it's tedious)...
Chris Ison's user avatar
5 votes

Why is electric potential denoted by $\phi$?

This is not an answer, but is I think closer to an answer than some of the comments. The symbol $V$ was used by Laplace to denote the gravitational potential in Mécanique Céleste (1798, see e.g. book ...
Sam Gallagher's user avatar
4 votes

What is Heaviside's version of Maxwell's equations?

Are we all talking about the same "Heaviside" who wrote "On the Forces, Stresses, and Fluxes of Energy in the Electromagnetic Field", received 1891-06-09, read 1891-06-18, that you ...
NinjaDarth's user avatar

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