There are 3 variables you can play with: size of the spark gap, angle of the neutralizing bars, and switching of the Leyden jars in and out of circuit.
Start with the spark gap set to about 1", the neutralizers at 45° to the collector combs (90° to each other), and the Leyden jars disconnected. Turn the crank smoothly at a moderate speed. The electrodes should produce a thin blue spark. Look closely and you’ll notice that one end is brighter; this is your positive electrode.
Stop cranking and engage the Leyden jars. These can hold a charge for days. From this point on, consider the machine “hot” until you short the electrodes by simultaneously touching both with the tip of a screwdriver. Also be warned that Leyden jars can acquire charge just sitting there, so you need to discharge them this way each and every time before you touch the electrodes.
Turn the crank again. After several revolutions you’ll hear the neutralizing brushes crackle, you’ll smell the fresh scent of ozone, and — CRACK! — a strong blue spark will jump the gap.
Short the electrodes and reposition them a little farther apart. Crank some more and you’ll see a bigger spark. Repeat this procedure until you see multiple small sparks jump from one of the collectors, across several sectors, to a neutralizing brush. You’ve reached your maximum spark length.
After you find the maximum gap, you can adjust the neutralizing bars. Narrowing their angle from 90° to about 60° will increase the maximum voltage at the expense of a small decrease in current.
Your machine should require little maintenance, but may require periodic replacement of the belts and cleaning of the disks. Use only water to clean them, or rubbing alcohol if you suspect there is oil on them.
The Electric Kiss (and Other Entertaiments)
Wimshurst machines had a place in Victorian entertainment. After a fine meal, guests might adjourn to the parlor for games, discussion, and scientific demonstrations. One can imagine the visceral impact of the Wimshurst machine, with its spinning glass disks, electrical discharges, and the loud report of 6" sparks.
For the adventurous, in the right company, there was a demonstration known as the electric kiss. Two volunteers would stand on insulating surfaces. Each would touch one of the 2 charge collectors and then they’d slowly, without any other part of their bodies touching, bring their lips together for the inevitable “tingle” of electricity.
CAUTION: Demonstrate the electric kiss only with the Leyden jars taken out of the circuit, to avoid a painful jolt.
Ford, R.A., Homemade Lightning: Creative Experiments in Electricity, 2001
Francis, G.W., Electrostatic Experiments: An Encyclopedia of Early Electrostatic Experiments, Demonstrations, Devices, and Apparatus, 2005
See the Wimshurst machine in action on Make: television, Episode 103, at makezine.tv/episodes.
This project first appeared in MAKE Volume 17, page 94.