SPARKS IN AIR (fwd)

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Date: Sun, 28 Oct 2007 14:00:52 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: SPARKS IN AIR

    Ionized oxygen emits blue light, ionized nitrogen emits orange/red 
light.  In an spark excited by AC the result is usually a purplish 
color.  Same thing happens with a discharge in air at low pressure.

    With a DC spark the colors are somewhat different.  A spark from a 
positive terminal to a negative one appears to exhibit blue color near 
the positive end and purplish near the negative end.  At least that's my 
experience playing with static electric generators.  I have a small Van 
de Graaf generator which generates sparks up to about 8 inches in 
length.  The appearance of many [but not all] sparks in the dark is very 
interesting.  When the sparks are from the top [+] terminal to the 
ground terminal roughly the first half of the spark is usually bright 
blue but somewhere beyond that the spark color can either turn to purple 
or, more interestingly, the single blue spark terminates in a bunch of 
purplish sparks which branch out into a number of different streamers.  
Really spectacular and spooky to watch in really black conditions.  
There has been discussion here recently of sparks "into the air" and I 
observe the same phenomenon with the VDG.  Sometimes the sparks from the 
top ARE into the air and they usually show the same characteristic - 
blue line into a bundle of purple streamers.

    I also have a small "dirod" generator which will produce 1-1/2" 
sparks between 2" diameter spheres.  These sparks don't break into 
streamers but do show blue at one end and purple at the other.  With 
this particular machine the polarity reverses on every discharge so, 
when the sparking rate is low, it's possible to see alternate blue and 
purple sparks coming from each terminal.

    The discharge of an induction coil appears to be similar.  Usually 
the secondary voltage consists of a spike of high amplitude and one 
polarity followed by a broader but much lower reverse voltage.  As a 
result, depending on the polarity of the primary voltage it's common to 
see sparks which are blue and one end and purple at the other although 
the colors don't seem as saturated as with DC.

    My experience with TC's is same as in all of the pictures I see of 
other guys coils.  The streamers are usually purple [both oxygen and 
nitrogen ions in the same place] but when I draw an arc to a metal 
object the color is usually white.  May be a matter of the intensity and 
the response of the eye but I'm not sure.

    Is there a physicist in the crowd with a better explanation?  How 
about Antonio who seems wise in all such matters?

Fun topic,

Ed