Measuring voltage output of a Wimshurst machine I see that there are a few variables that effect the voltage output of the Wimshurst machine. For one the size of the disk, the amount of conductive strips on the disk, and obviously the spark gap itself. 
Heres my question : if air breakdown voltage is 3000v per mm then if a spark jumps 50mm (2") is it 150,000v? Or is the electrostatic build up around the two electrodes what allows the spark to jump easily? If i am right yay. If i am wrong, what must be taken into the equation of figuring out its output voltage? 
And this is less important but i still would like to know, how can I calculate how much max power my Wimshurst machine will have based on the disk size, conductive plates, and Leyden jars?
 A: Your disk size and how many conductive strips you have affect 2 things, depending on how close together the strips are, and how many there are will determine whether you need to self start the machine or not. It will also determine how much voltage can be produced. The gauge of the wire will tell you how much voltage can be carried over it, so use a thick wire. The most important thing is the leyden jar. This will determine how much voltage you can hold before a spark, or before you ruin your leydfen jars.
A: No.  On Wimshurst and Bonneti Machines (All of the so-called "Influence Machines") you typically have a small 1/2" to .75" ball or smaller attached to a larger ball on both discharge electrodes.  Anyone who knows these machines knows if the small ball on the positive side of the machine is angled up towards the large on the negative polarized side you get sparks MUCH MUCH MUCH larger, typically in dry air at regular atmospheric pressure 30,000 volts per inch, ball plane gaps (with the plane negative) even more.  On my Youtube channel Mister Bonetti you can see my 12" Quadruple Bonetti machine making 17 - 20 cm sparks, I tested voltage using a homemade voltage divider 100,000 volts maximum peak voltage on each side so 200 kV total, not what the 170 mm spark would suggest.   Using spark gaps to measure voltage (besides humidity and barometric pressure factors) requires two equal-sized electrodes that are both equal in size and shape.  The size and shape matter, and there are charts that will tell you the voltage with different electrode combinations. Although you cannot get a Wimshurst or Bonetti to start with a pointed gap physically connected, two sharp points will typically massively outperform any other electrode shape in spark length.  The 30 kV per cm does not apply at all in that case, as 30 kV between two sharp points can jump nearly 2". If you are interested in voltage or current measurements from your machine see my youtube channel videos on the subject!
