Editing Wimshurst machine (section)

==Description==
These machines belong to a class of electrostatic generators called [[influence machine]]s, which separate [[electric charge]]s through [[electrostatic induction]], or ''influence'', not depending on friction for their operation. Earlier machines in this class were developed by [[Wilhelm Holtz]] (1865 and 1867), [[August Toepler]] (1865), J.&nbsp;Robert Voss (1880), and others. The older machines are less efficient and exhibit an unpredictable tendency to switch their polarity, while the Wimshurst machine has neither defect.

In a Wimshurst machine, the two insulated discs and their metal sectors rotate in opposite directions passing the crossed metal neutralizer bars and their brushes. An imbalance of charges is induced, amplified, and collected by two pairs of brushes or metal combs with points placed near the surfaces of each disc. These collectors are mounted on insulating supports and connected to the output terminals. The positive feedback increases the accumulating charges exponentially until the dielectric breakdown voltage of the air is reached and an [[electric spark]] jumps across the gap.

The machine is theoretically not self-starting, meaning that if none of the sectors on the discs has any electrical charge, there is nothing to induce charges on other sectors. In practice, even a small residual charge on any sector is enough to start the process going once the discs start to rotate. The machine will work satisfactorily only in a dry atmosphere. It requires mechanical [[power (physics)|power]] to turn the disks against the electric field, and it is this energy that the machine converts into the electric power of the spark. The insulation and size of the machine determine the maximal output voltage that can be reached. The accumulated spark energy can be increased by adding a pair of [[Leyden jar]]s, an early type of [[capacitor]] suitable for high voltages, with the jars’ inner plates independently connected to each of the output terminals and the jars’ outer plates interconnected. A typical Wimshurst machine can produce sparks that are about a third of the disc's diameter in length and several tens of microamperes.

Wimshurst machines were used during the 19th century in physics research. They were also occasionally used to generate high voltage to power the first-generation Crookes [[X-ray tube]]s during the first two decades of the 20th century, although [[Electrostatic generator#Holtz machine|Holtz machines]] and [[induction coil]]s were more commonly used. Today they are used only in science museums and education to demonstrate the principles of electrostatics.