Found this thing at Radio Shack today (Dec. 21 2001) for less than $30.00.
It consists of a hollow, handblown glass ball that has a light dusting of green & blue glowing phosphors on its inner surface. All the air is sucked out and a little bit of argon and krypton
gas is put in. It sits on a base holding a small high voltage inverter; this ionizes the gas mixture inside and makes these plasma streamers swirl around inside.
The phosphor intensifies the glow somewhat, so this lamp can be enjoyed day or night.
The ball is handmade and looks like the earth. The phosphors are applied inside so that most of the blue ends up in the "water" areas and the green on the "land" areas.
The dusting of phosphors is very light, so the blue glass ball is still transparent and the plasma streamers inside aren't hidden.
Placing your hand on the ball intensifies the streamers and causes a surface glow where your hand rests; this behavior is similar to how ordinary plasma globes act under similar conditions.
A version of this device is also available using a purplish glass CUBE, and uses additional phosphors to complement the colors.. I have not yet seen one in action, but I'll
see if I can get the guy at the store to set a demo unit out.
Who needs a demo when you can have the real thing?
The cube uses 3 different phosphors and is much more colorful.
The arc appears to have the same basic color as the earth shaped lamp; all of the extra coloration comes
from a mixture of several different phosphors (blue, green, and red) and from the tinted glass of the lamp itself.