Faraday, Thames, Tyndall, Hall.

[brian whatcott <inet@INTELLISYS.NET>]

At 01:16 1/24/99 -0500, you wrote:

> > This is reminiscent of Faraday's attempt to measure a current flowing
> > transverse to the River Thames from wires dipped into each side of
> > that river.
>
> Is this similar to the Hall Effect where we find a potential
> difference across the sides of a current carrying conductor
> in a magnetic field?
>
> By the way.... was Faraday's attempt successful??
>
> Herb Gottlieb


Faraday had demonstrated the production of electric current between the
pivot and a fixed point on the periphery of a copper disk. He believed he
should
find a comparable electric current from electrodes immersed in moving water.
 (He apparently thought the Earth's motion might provide the requisite motion)
His attempt apparently failed owing to the feeble nature of this current.

This does not foreshadow the elegant effect investigated by Hall and his
professor.

 I offer here, an excerpt from John Tyndall's, "Faraday as a Discoverer"
5th Ed. Longman's, Green 1894:
------------------------------------------------------------------------
He went to the round lake near Kensington Palace, and stretched 480 feet of
copper wire, north and south, over the lake, causing plates soldered to the
wire at its ends to dip into the water. The copper wire was severed at
the middle, and the severed ends connected with a galvanometer. No effect
whatever was observed.
But though quiescent water gave no effect, moving water might. He therefore
worked at London Bridge for three days during the ebb and flow of the tide,
but without any satisfactory result. Still he urges, 'Theoretically it
seems a necessary consequence, that where water is flowing there electric
currents should be formed. If a line be imagined passing from Dover to
Calais through the sea, and returning through the land, beneath the water,
to Dover, it traces out a circuit of conducting matter one part of which,
when the water moves up or down the channel, is cutting the magnetic curves
of the earth, whilst the other is relatively at rest.... There is every
reason to believe that currents do run in the general direction of the
circuit described, either one way or the other, according as the passage of
the waters is up or down the channel.' This was written before the
submarine cable was thought of, and he once informed me that actual
observation upon that cable had been found to be in
accordance with his theoretic deduction.
----------------------------------------------------------------------

Brian
brian whatcott <inet@intellisys.net>
Altus OK