Re: Slightly off topic- Van DeGraff Generator / other E&M experiments

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<DR.RESONANCE-at-next-wave-dot-net>

> On the upward run of the belt remove the charge with a screen on both
> outside and inside of the belt.  It seems most of the charge ions end up on
> the inside of the belt (consider the charing belt as it passes the screen,
> belt (dielectric), and grounded pulley to be a capacitor and it makes more
> sense.

I tried to take charge from the outer side of the belt with a comb while
the belt is touching the metallic pulley. With the comb and the pulley
in electric contact, this should take charge from both sides.

> Now the "spray down" part.  Attach a wire and a 10 - 20 meg Ohm 50 kV rated
> resistor to the dome (dome must be well insulated from the pulley and
> bearing assemblies) and this terminates on an insulated (1-2 inch high PE
> rod stock) which feeds an insulated spray down screen.  The resistor makes
> the dome "live" electrically with respect to the pulley and causes the spray
> down screen to dump equal and opposite charge on the downward run of the
> belt.  Grounded screen on the bottom removes it as does the lower pulley
> itself.

Ok, but why the resistor? Maybe to prevent sparks tracking over the
belt?
In the old papers describing the large double machine built in the
1930's
that is now at a science museum in Boston there are several descriptions
of elaborate charging systems involving current doublers. The basic idea
was as D. C. described, with combs taking charge from both sides of the
belt and charging the pulley. But a resistor was added in series with
the
down-spray comb (at the top of the pulley) only as part of a complicated
system for voltage regulation.  

Antonio Carlos M. de Queiroz