Re: very long sparks

To: tesla-at-pupman-dot-com
Subject: Re: very long sparks
From: Stan <sdarling-at-columbus.rr-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sun, 09 Jan 2000 03:54:56 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
Bert: Did you use descreening on your scanner when you scanned this
photo in?  I notice some print screening in the photo....

For what I talk about below refer to:

http://users.better-dot-org/sdarling/longspark/longarc.gif - I drew on the
original image in red and black
http://users.better-dot-org/sdarling/longspark/longarc_inverted.gif - same
image, just inverted to show detail

I agree that when I first looked at the photo I sort of scratched my
head.  I agree the discharge path seems awfully circuitous.  Perhaps if
the arc duration were long enough there could have been a rising
heat/jacob's ladder effect?  Its general shape looks like the arc you
get from a NST HV terminal to ground.  
If you look closely, it appears there might be a short rod sticking off
the top of the tower.  Notice how the first fraction of the spark is
very straight and much thinner than the rest?

Also, what the HECK is that big ball of light at the top of the left
power line tower?  It seems too bright to be ordinary glare or
relfection.

As for the shadows--yes they do seem odd.  I think it might be a daytime
shot taken with infrared film.  The shot is taken from a building and
the sun is behind the building.  I think the sky being black (a classic
signature of infrared film) tricks your eyes into thinking it's night,
thus making the shadowing appear very weird.  The strangest thing I see
re shadowing is abotu 2/5 of the way from right side of the picture. 
Notice the three parallel slightly curved lines/shadows going at about
135 degress (to the back left of the picture)?  It seems these could be
shadows from the power lines.  Of course, this shoots down the sun
behind a building theory unless there are very bright artificial light
sources.

As for determining scale, the best indicator I see is at the bottom
right of the transmitting tower. There appears to be a one-story
entrance/lobby to the base of the round tower.  If one figures it would
be about 12 feet tall, then one can estimate the height of the tower
fairly accurately.  I show about 8.5 x or 8.5 x 12 feet or almost
exactly 100 ft.  The straight line distance from the spark start on the
tower to where the spark goes off the photo is 2x the tower height, or
about 200 ft.  Assuming the spark really did hit the power lines, and
extending the fence off the edge of the photo, and assuming the lines
run parallel to it, there is about 50 ft of spark not caught in the
photo.  So total estimated spark length is about 250ft.  Of course this
is assuming the spark is at a 90deg angle.  If it's more or less than
that, the spark length is higher.

Comments welcome.

-Stan


Tesla List wrote:
> 
> Original Poster: Mark Finnis <mefinnis-at-medicine.adelaide.edu.au>
> 
> At 08:40  06/01/2000 -0700, Bert Hickman wrote:
> 
> >Certainly! I've scanned in a jpeg of the picture and you can see it at
> >http://people.ce.mediaone-dot-net/bert-hickman/frames/longarc.htm
> 
> Couple of comments:
> 
> 1.  Having taken a look at the discharge, what amazes me is the path taken.
> 
> The discharge terminal at top of the building (you couldn't refer to
> something this size as a "coil") is of comparatively small dimension and
> the e-field should be such that the ground would have been a "better"
> target long before the transmission tower ? 100m away.
> 
> Seems odd.  I bet if we built a coil to a scale of this and placed a
> grounded tower equidistant as per the photo we would be waiting 'till hell
> freezes over before the tower was hit.
> 
> 2.  I think it is hard to ascertain the true distance of this
> discharge.  Granted it is large (and I'd be bloody pleased if it were my
> coil !) but the perspective of the photo is "optimized" to make it look
> larger.  Look at the fence leading to the towers, they are in fact well in
> the distance and we don't see the actual tower hit (which appears to be
> back towards the viewer).
> 
> 3.  The other thing which is strange is some of the shadowing in the
> photo.  Seems to be lit from above ???   I would be interested to get an
> expert photographic opinion !
> 
> Bert ...... I am just a little skeptical of this shot :-(
> 
> What do you & others think ??
> 
> Cheers
> 
> Mark