The disappearance of darkness

On 2013.05.27 18:56 , Eric Stevens wrote:
On Mon, 27 May 2013 16:48:50 -0400, Alan Browne
wrote:

On 2013.05.26 23:33 , Eric Stevens wrote:
On Sun, 26 May 2013 17:32:55 -0400, Alan Browne
wrote:

On 2013.05.24 20:48 , Eric Stevens wrote:
On Fri, 24 May 2013 16:10:07 -0400, Alan Browne
wrote:

On 2013.05.24 00:30 , Eric Stevens wrote:
On Thu, 23 May 2013 21:56:27 -0400, wrote:

On Thu, 23 May 2013 15:26:32 +1200, Eric Stevens wrote:

On Wed, 22 May 2013 21:19:48 -0400, wrote:

On Wed, 22 May 2013 18:34:32 -0400, nospam wrote:

Next time you're near a hydro tower, listen to the hum of the wires and tower...

What is a 'hydro tower'?

Wires hum without electricity. It's just the wind.

Right, a 60hz or 120hz or 180hz wind...

Listen kid, get back to your day care center before they put out an Amber Alert
on you!

I'm not saying that you can't hear corona losses.

I'm saying you can get vibrations induced from vortex shedding of the
wind. http://en.wikipedia.org/wiki/Vortex_shedding "This vibration is
the cause of the "singing" of overhead power line wires in a wind, ...
"

The hum is most audible in dead still air. No wind needed.

Dry air - Corona discharge - no hum - more like white noise

Humid air - hum @ 120 Hz (100Hz if 50 Hz base)

See my other post.

And if really fond of wikipedia, see the article:
https://en.wikipedia.org/wiki/Mains_hum

"Around high-voltage power lines, hum _may_ be produced by corona
discharge." (empasis added).

But I'd add that the core of transmission lines is steel. And that will
move v. the magnetic field - it hums.

It doesn't have to be steel to interact with a magnetic field. It only
has to be a conductor carrying electricity.

Again there are two forms.

Corona discharge has a 'crackling' sound. (dry air).

Magnetic effect has a humming noise. (humid air)

'Two forms' of humming I presume.

No. The crackling sound is not all like a hum.

There is a third: vortex shedding induced by wind.

We were addressing the electrical form of noise - most often heard when
the air is still. If it makes you feel warm and fuzzy nobody denies
that wind can make wires hum.

This all started when BobF wrote:

Next time you're near a hydro tower, listen to the hum of the wires and tower...

... and I replied

What is a 'hydro tower'?

Wires hum without electricity. It's just the wind.

So we weren't just addressing the electrical form of noise. We were
discussing the humming of power lines.

I didn't write that phrase so don't attribute it to me.


What is the source of the magnetic field in your "Magnetic Effect"
with which the current interacts and why is it only present when the
air is humid?

When the air is humid there is something to make noise (water droplets
moving around). The magnetic field is generally present at all times.
Think about it. Let your compass guide you.

I thought you would be relying on the earth's magnetic field. This
shouldn't be affected by humidity.

But the character of the noise would be. Again, the character of the
noise very is different in humid and dry conditions.

Nor should the water droplets be
affected by magnetism.

Never said they would. But pause on that point. Water droplets can
indeed carry a charge (either positive or negative) and with such a
charge would be induced to oscillate in the field generated by the
wires. No confirmation on this but it's possible.

They do however produce a leakage path which
reduces the dielectric strength of the air.

Certainly.

Anyway, you may have the last word.

--
"A Canadian is someone who knows how to have sex in a canoe."
-Pierre Berton

On 2013.05.28 06:17 , Whisky-dave wrote:
On Thursday, May 23, 2013 9:55:50 PM UTC+1, Alan Browne wrote:
On 2013.05.22 23:26 , Eric Stevens wrote:

On Wed, 22 May 2013 21:19:48 -0400, wrote:



Next time you're near a hydro tower, listen to the hum of the wires and tower...



What is a 'hydro tower'?



In Quebec 98% or so of power is hydro derived - the utility is called

"Hydro Quebec" so we say "hydro tower" (poles, service, lines, ...)



This is common in several areas in North America.





Wires hum without electricity. It's just the wind.



Not at all. Power lines have an audible 120 Hz hum esp. when it is

humid. (would be 100 Hz in places with 50 Hz service). One place I ski

has 315 VAC power lines go right over the area immediately before the

chair lift and on very humid days it is quite loud.



The space between the wires and the ground is a dielectric - it is being

charged and discharged continuously (a power waste that does not occur

with HVDC). While the lines are aluminum they have a stainless steel

core and that vibrates with the continuous charge/discharge from the

line to the ground. (Or perhaps water droplets get charged and then

react to the field charging and discharging).



When it is really dry there is a crackling sound. (Corona discharge).

So it's not really the wires that are making the noise/hum or crackling it's the molecules in the air producing changes in pressure.
I don;t think you can hear current flowing through a wire if it were in a vacumm or in space :-)

Whether the noise is the wire vibrating or the air vibrating, eventually
molecules do need to move to transmit noise (pressure waves).

I seem to remmeber some definition of current from school physics in that a curretn of 1 amp flowing through two parelle conductors 1 metre apart in a vacumm produces as for of 1 X 10^-7 newtons of force.
This rapid changing of force is what makes the 'noise' by dispacing the air.

As I stated elsewhere, the noise is very different depending on the
humidity. In dry air a 'crackling' sound, in humid, more of a hum.

Currents cause a force where there is a magnetic field (the definition
you put up above). In turn this can make a noise. (That's how
loudspeakers work).

Voltage causes sparking and discharges.

--
"A Canadian is someone who knows how to have sex in a canoe."
-Pierre Berton

On 2013-05-28 16:18:14 -0700, Alan Browne
said:

Given some of the current (forgive me for that) power line discussion,
I thought you might find this Sunday morning event interesting.

http://www.sfgate.com/bayarea/articl...00-4550070.php


--
Regards,

Savageduck

On Tue, 28 May 2013 16:57:31 -0700, Savageduck
wrote:

On 2013-05-28 16:18:14 -0700, Alan Browne
said:

Given some of the current (forgive me for that) power line discussion,
I thought you might find this Sunday morning event interesting.

http://www.sfgate.com/bayarea/articl...00-4550070.php

It wouldn't be mud on the power lines which was the problem. It would
be mud on the insulators.
--

Regards,

Eric Stevens

On 2013-05-28 17:24:22 -0700, Eric Stevens said:

On Tue, 28 May 2013 16:57:31 -0700, Savageduck
wrote:

On 2013-05-28 16:18:14 -0700, Alan Browne
said:

Given some of the current (forgive me for that) power line discussion,
I thought you might find this Sunday morning event interesting.

http://www.sfgate.com/bayarea/articl...00-4550070.php

It

wouldn't be mud on the power lines which was the problem. It would
be mud on the insulators.

Perhaps, but that is the report, and today's reporters are known to be
confused from time to time.

--
Regards,

Savageduck

"Chris Malcolm" wrote in message
...
obvious "evidence-based" scientific experiments if you haven't taken
the care to make explicit the underlying assumptions and made sure
that the implied models hold.

An obvious contradiction.

The problem is that this is only obvious at first glance.

And second, and third... to a real scientist anyway.
(They are in short supply these days with funding often relying on vested
outcomes :-(


An experiment is *not* "evidence based" if it
relies on unproven assumptions and models.
That's how psuedo science works of course.

In that case a great deal of public medical policy is pseudo
science.

Unfortunately true, especially when it comes to big Pharma.


It's also well known to be the case that in periods of what Kuhn
called "normal science" (in "The Structure of Scientific Revolutions")
the assumptions and models are usually not made explicit.

And deliberately so when trying to mislead for vested interests.


Plus the
assumptions and models underlying a specific scientific paradigm are
only provisionally proved by the ongoing success of the paradigm. As
Popper pointed out what is often taken to have been scientifically
proved is in fact really only so far not disproved.

Right, but it's usually often to disprove something at least, than it is to
ever prove anything for all possible conditions.

Trevor.

In article , ozcvgtt02
@sneakemail.com says...

J. Clarke wrote:

Would you be kind enough to provide an example of an experiment in which
"assumptions and models" affect the outcome?

Experiment as in "the measured raw results" or as in "the
results after evaluating the measurements"?

As in the published paper.

In rec.photo.digital Wolfgang Weisselberg wrote:
J. Clarke wrote:

Would you be kind enough to provide an example of an experiment in which
"assumptions and models" affect the outcome?

Experiment as in "the measured raw results" or as in "the
results after evaluating the measurements"?

You've got it!

--
Chris Malcolm

In rec.photo.digital J. Clarke wrote:
In article , ozcvgtt02
@sneakemail.com says...

J. Clarke wrote:

Would you be kind enough to provide an example of an experiment in which
"assumptions and models" affect the outcome?

Experiment as in "the measured raw results" or as in "the
results after evaluating the measurements"?

As in the published paper.

Do those published papers count in which the authors later revised the
conclusions they originally drew from their experimental results? Or
those in which later reviewers, not the original authors, did the same
thing?

--
Chris Malcolm

In article ,
says...

In rec.photo.digital J. Clarke wrote:
In article , ozcvgtt02
@sneakemail.com says...

J. Clarke wrote:

Would you be kind enough to provide an example of an experiment in which
"assumptions and models" affect the outcome?

Experiment as in "the measured raw results" or as in "the
results after evaluating the measurements"?

As in the published paper.

Do those published papers count in which the authors later revised the
conclusions they originally drew from their experimental results? Or
those in which later reviewers, not the original authors, did the same
thing?

Give us your example if you have one.