Re: Magnetic N and S poles

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

The question about Gauss would be hard to answer, unless
we have a historian of science on this list. But the second
question, "when did the new definition of B (via F=q*v x B)
start to appear in textbooks?" can be answered by those of us
have old physics textbooks at homes or libraries. Look into
what you can find and tell us what you see. I have one old
book; here my little contribution:

"Physics for Students of Science & Engineering", 1937.
The section on E&M was written by R.J. Stephenson.

The Coulomb's Law for magnetic masses is presented.
H is defined as a force per unit pole. The values of H,
in different locations, are calculated from Coulomb's Law.
They can also be compared experimentally by measuring
periods of oscillation of a small magnetic needle (magnetic
dipole whose moment is M=m*L and not I*A). B is
introduced later as magnetic field inside iron.

The magnetic effects of currents are discussed. But H
is not redefined in this section. The Biot Savart formula
for dH (called Ampere Law in this text) is used to calculate
H theoretically for a given setup, for example, a solenoid.
The "force on a current" section does show that the

dF=B*I*dl*sin(TET)

but it is not used as a definition of B. No cross product
formalism is used. But the illustration (Figure 332) of
the direction of dF is consistent with the cross product.
It is interesting that this formula is derived in terms of a
magnetic mass of unit length. Unless this particular book
was an exception, I would conclude that magnetic masses
were still in used to explain magnetic phenomena in late
1930s. Can this be confirmed by those who have access
to other textbooks from that period? What is the oldest
textbbok in which B is DEFINED BY the F=q*(v x B)
formula?

Ludwik Kowalski wrote:

> CORRECTED (sorry, I forgot we are in the 21st century).
>
> I know that Ampere speculated that all magnetic fields are due
> to currents. But the prevailing explanation of magnetic fields,
> at that time, was in terms of so-called magnetic charges. (In
> that model B was defined as F acting on the N pole, per unit
> pole.) Many textbooks published in the 20th 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.
> Did Gauss believe in the reality of N (plus) and S (minus)
> magnetic charges? When did the new definition of B (via
> F=q*v x B) start to appear in textbooks?
> Ludwik Kowalski