23 votes
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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 ...
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17 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 ...
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  • 8,625
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 ...
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9 votes

Were there serious attempts to model the photoelectric effect classically?

"Serious" in the OP sense is probably too high a bar. In 1900-s the situation was very much in flux as to what classical physics could and could not explain. Even Planck's and Einstein's ...
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9 votes
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How did gyromagnetic ratio come up before quantum mechanics, and who introduced it?

This is a very good question, I wish it got more attention. My answer will only be partial for I had difficulty finding early details on gyromagnetic effect and ratio. The concept comes up every time ...
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  • 67.1k
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{...
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  • 5,051
9 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 ...
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9 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 ...
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  • 67.1k
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 ...
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  • 3,009
8 votes

Why do Maxwell's equations bear his name?

As you noticed, separate equations have other names as well. Maxwell's adding the displacement term made the system complete, with all important consequences, in particular, existing of ...
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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 ...
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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 ...
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  • 5,051
7 votes

How did Maxwell conclude that light is an electromagnetic wave?

Maxwell had at least three arguments in favor of the conjecture on electromagnetic nature of light. The first one was philosophical (Chap. XX, section 781). He could not imagine waves propagating in ...
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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 ...
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7 votes
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What was the real need of divergence and curl operators?

These operations arose from the study of quaternions see e.g. Thomson and Tait's Treatise on Natural Philosophy, that should probably have information on the sort of math. Stokes's theorem originated ...
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7 votes
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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 ...
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6 votes

Why are microwaves called "microwaves", when they are much longer than a micrometer?

The micro- in micro-waves, as far as I know, comes from the way that we produced electromagnetic waves at the time: following Hertz, people generally used currents cycling through antennas. Generally ...
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  • 386
6 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 ...
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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 ...
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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 ...
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  • 161
5 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 ...
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  • 5,051
5 votes
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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 ...
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  • 5,051
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 $$\...
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  • 5,051
5 votes
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What is Heaviside's version of Maxwell's equations?

This gives the four equations in the form Heaviside came up with: $$\varepsilon E = \rho$$ $$\nabla \times E = - \mu \frac{\partial H}{\partial t}$$ $$\nabla \cdot \mu H = 0$$ $$\nabla \times H = k E +...
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  • 8,122
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 ...
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  • 1,799
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 ...
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  • 3,044
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 ...
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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 ...
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  • 67.1k
5 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 ...
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5 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 ...
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