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Re: Influence machine



I came into this late. There are/were a variety of induction machines. =20
One that was very common in Europe in the last century was a Holtz=20
machine. It differs in appearance from the Wimshurst since it has only=20
one rotating plate.

cheers

On Thu, 10 Apr 1997, Leigh Palmer wrote:

Why? could you be more explicit. I mean, I do not know
this symetry argument. How symetry makes friction
irrelevant?
=20
Asymmetric electrostatic generation by friction: rub A on B and A
always becomes positively charged while B becomes negatively charged.
=20
Symmetric electrostatic generation by friction: rub A on A and A
sometimes becomes slightly positively charged and sometimes
negatively charged.
=20
What is the nature of this fluctuations? I believe you mean
that plates may get charged from the surrounding air, which
always contains some charged ions.
=20
The generator may be biased initially by charging one terminal
with a cat fur rubbed hard rubber rod. That terminal will become
the negative terminal when a symmetric machine is started up.
Otherwise some small asymmetry will determine the polarity.
=20
electrophorus (and some Van de Graaffs) is an induction machine
in which the polarity may be determined by triboelectricity, but
the sustained operation of which depends solely on induction.

I agree, altough it doesn't seems to me this device has
trivial explanation. I would like to show it to the students,
but I still don't know how to derive the charge distribution
that appears on the disks, or how does the effectivity depends
on the angle between the two opposite cupper brushes.
Any hint?
=20
Roughly it works by charging capacitor plates by induction and then
disconnecting them from their charge sources and pulling them apart
while they are disconnected.
=20
You should cosult a source for an explanation. "Trait=E9 =E9l=E9mentaire
d'=E9lectricit=E9" by Joubert, or its translation, "Elementary Treatise
on Electricity and Magnetism" by G.C. Foster and A.W. Porter, 2ed,
Longmans, Green & Co. (1903), section 78, p 110, or "The Elements of
Electricity and Magnetism" by Franklin and MacNutt, Macmillan (1908)
are the books that come readily to hand in my office. Descriptions
of Wimshurst's machine seem to be missing from most modern texts,
but as has been mentioned they were the workhorses before the
invention of the Van de Graaff generator.
=20
The latter text also has some nice description of the transmission
and propagation of electromagnetic waves according to the Maxwellian
ether mechanism, complete with drawings of gears, three years after
Einstein's publication of the special theory,
=20
Leigh
=20
=20
=20