Re: Magnetic N and S poles

["John S. Denker" <jsd@MONMOUTH.COM>]

Ludwik Kowalski wrote:
> I know that Ampere speculated that all magnetic fields are due
> to currents.

OK.  He might have been right.  Or not.

> But the prevailing explanation of magnetic fields,
> at that time, was in terms of so-called magnetic charges.

What's the evidence for that?

> "Physics for Students of Science & Engineering", 1937.
> H is defined as a force per unit pole.

That can be made to sound less shocking by restating it
as "energy per unit dipole" rather than "force per unit
pole".

> Many textbooks published in this century still presented
> magnetostatic in the same way in which they presented
> electrostatics. The only difference was the recognition that
> a magnetic dipole could not be cut into two monopoles.

What's wrong with that?  As Feynman was fond of saying, the
same equations have the same solutions.  The equations of
electrostatics are essentially the same as the equations of
magnetostatics.  And elastic drumheads.  And the flow of
dry water.  So why not present them the same way?

> Did
> Gauss believe in the reality of N (plus) and S (minus)
> magnetic charges?

Do you believe in the reality thereof?  If not, can you
explain why not?  Can you prove it?

> When did the new definition of B (via
> F=q*v x B) start to appear in textbooks?

That question seems based on multiple questionable
assumptions.  First of all, I'm not sure the magnetic
field was _ever_ "defined" in the "old" or "new" ways
suggested above.  We have a multitude of operational
methods for measuring B, including
 -- Force = q v cross B
 -- Energy = dipole dot B
 -- Force = q d/dt B
 -- Energy density = B^2

and it's not at all clear to me which (if any) of these
facts deserves to be annointed as the definition.
Physics does not have, and has never had, a structure
analogous to Euclidean geometry, where everything is
derived from a handful of axioms and definitions.

Similarly, knowing one fact about magnetism is
not inconsistent with  knowing one or more of the
other facts.

Thirdly, if one wants to speak of the origin of an idea,
it is traditional to cite the time when it was discovered,
not the time when it became common in textbooks.  The
textbooks, to their shame, are often many decades behind
the professional literature.

The Lorentz force law (F = q v cross B) was promulgated
by H. A. Lorentz.  It might have been in his thesis (1875)
but more likely was a bit later.  It was certainly well
before 1902.
  http://www.nobel.se/physics/laureates/1902/lorentz-bio.html