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Basically the title, I found it weird that we use two different names for each fields. What were the reasons for doing so, historically speaking?

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  • $\begingroup$ Are you asking why these names were chosen, or why they are different? The latter should be obvious: they represent different things. $\endgroup$ – Carl Witthoft Apr 16 at 11:14
  • $\begingroup$ In what sense do you mean different things? They both are constants which go along with the expressions you use to evaluate the fields, why call it permeability for one field and permitivitty for the other? @CarlWitthoft. $\endgroup$ – Buraian Apr 16 at 11:18
  • $\begingroup$ They are totally different things, they are orthogonal their values are different, the question is disturbing in that it is like the difference between pressure and density of water they must be separated. Maxwell derived these two constants and then proceeded to calculated the speed of light by math that includes both these constants. $\endgroup$ – Barry Apr 19 at 15:06
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Whilst we now call it electromagnetism, it was originally electricity and magnetism. They were seen as two separate phenomena. Hence the terms permeability and permittivity arose from two distinct fields of study that were only later unified.

It was Oersted in 1820 who first published a link between the two. He had discovered that a magnetic compass needle was deflected by a nearby electric current. This motivated research into electrodynamics, and, forty years later, in 1862, Maxwell published his equations that unified electricity and magnetism. It was one of the earliest unifications. Incidentally, Oersted is often said to gave discovered the link accidentally. This is simply myth. The truth is he was researching for a link between electricity and magnetism for around two years before he made the above discovery.

Whilst one could argue that the two terms - permeability and permittivity - should be unified into a single term, the terms remained as they were, as they had already been established for some time. In fact, recently standards organisations have moved to calling them the electric and magnetic constants.

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