The Wimshurst Machine by Jacques Charrier Send email to Jacques Charrier Preparation Nantes CAPES Visit Jacques Charrier’s personal page Visit the original French version of this page (This English version was translated using The Altavista Babelfish, and the translation was then edited and adapted by Jon Singer, of the Joss Research Institute.)

J.Ch  &  Y.C., with minor corrections by J.S.

The animated figure above is a simplified representation of the operation of a Wimshurst machine. The primary principle underlying the operation of this type of generator is that of electrostatic induction or “influence”; the translator has provided a brief explanation of induction at the end of this page, for those who are not already familiar with it.

Two insulating discs (often made of Plexiglas™) turn in opposite directions. Conducting sectors are attached to the outer faces of the discs. For simplicity, only two sectors are represented on each disc in the figure. The sectors drawn with dotted lines are on the rear disc; the sectors in solid lines are on the front disc. Red represents positive charge, cyan represents negative charge, and gray represents a discharged or neutral sector.

Four brushes (these form “X”-shaped item in the middle of the diagram) are connected to each other (and, in this case, to earth/ground). Notice that one pair faces the front disc and the other pair, at about a right angle (though they are usually built so the angle is adjustable), faces the rear disc.

The points of a collector comb facing a positively-charged sector take on a negative charge by induction; micro-discharges from the points then neutralize the charge of the sector. (This is effectively as if the positive charge were being collected by the points.) Likewise, the points of a collector comb facing a negatively-charged sector take on a positive charge by induction, and effectively collect the negative charge from the sector.

The two Leyden jars, the inner conductors of which are connected to the collector combs, store the collected charges. Note that their outer conductors are interconnected and grounded (earthed).

Let’s follow the rotation of a sector on the rear disc (in the usual direction, which for the rear disc is counterclockwise), starting as the sector leaves the upper edge of the collector comb array on the right-hand side. I have indicated the relative positions in increments of 45 degrees, with 0° referring to the comb array on the right (at 3 o’clock) because that is where the description begins; 90° straight up, at 12 o’clock; and 180° referring to the comb array on the left, at 9 o’clock. The rear-disc sectors are drawn with dashed lines, as are the rear-disk neutralizer brushes.

• 0°   The initial charge of the sector is null or nearly so after it passes in front of the teeth of the collector comb.
  
  
• 45°   During its contact with the upper rear brush, the sector takes on a positive charge by induction from a negative sector of the front disc. (Refer to the description of induction, below, if necessary.)
  
  
• 90°   (Nothing important happens here.)
  
  
• 135°   A sector of the front disc takes on a negative charge during its contact with a front brush, by influence from the sector we’re following, which now carries a positive charge.
  
  
• 180°   The positive charge on the sector is neutralized by the negative charges it induces in the points of the comb on the left. (That is, the comb on the left effectively picks up the positive charge from the sector, and delivers it to the Leyden jar.)
  
  
• 225°   During its contact with the rear brush, the sector we are following takes on a negative charge, by induction from a positive sector of the front disc.
  
  
• 270°   (Nothing important happens here.)
  
  
• 315°   A sector of the front disc takes on a positive charge during its contact with a front brush, by influence from the sector we are following.
  
  
• 360° / 0°   The negative charge on the rear sector is neutralized by micro-discharges from the points of the comb on the right (again, the comb on the right effectively picks up the negative charge from the sector, and delivers it to the Leyden jar), and the cycle begins again.

Note: on a real machine, the charge actually acquired by the sector in contact with a brush is always higher than that of the [main] influencing sector because there is additional influence from the adjacent sectors, which are not represented on this simplified machine.

Now let us try rotating the machine in the opposite direction.

• One needs a rotation of 3/8 of a turn for the same sector to reach the brush, instead of 1/8.
  
• The sector arriving opposite has just left the combs, and is not charged.
  
• Thus, the machine does not function!

To start the machine so that it negatively charges the condenser on the right-hand side (on the advice of F Bossert):

• Discharge the condensers by making contact between the balls of the spark-gap. (It may help to rotate the disks at least once while the condensers are short-circuited; this will empty the sectors of charge.)
  
• Present a positively charged rod near the rear brush on the right-hand side. (Prof. Charrier suggests Plexiglas for this.)
  
• The rear sectors that pass under this brush charge negatively by influence from the rod.
  
• Withdraw the rod when the machine is started.

Conversely, to once again cause the machine to charge negatively on the left:

• Discharge the machine as above.
  
• Position the positively charged rod near the front brush on the left until the machine has started.

The operation of the machine appears ideal, but a question still arises: In steady operation, the twin sector diametrically opposite the one we are watching (but on the same disk) always carries a charge of the opposite sign from that of the one we’re observing. The reverse, however, could equally well occur: at the outset, the diametrically opposed sector could have the same charge as the studied one. In that case, the machine would not take charge. This does not occur, so the charges must, in general, be opposed. Some authors justify the appearance of these opposed charges by suggesting that the rear brushes (for example) constitute only one insulated driver. On our actual machine, however, all of the brushes are connected to each other through the metal frame of the machine. For more certainty on the potentials, we connected this frame and the external conductors of the Leyden jars to earth ground. Our machine functions very well this way.

The initial figure was created with CABRI Géomètre software. This figure, which can also be animated, requires the use of many conditional points. Without the assistance of my colleague Yves Cortial, I would never have managed to build it. The successive images of animation were captured with Paint Shop Pro, and the final animated GIF was assembled with GIF Construction Set.

To download  or launch the CABRI file:  wimjc_yc.figcback or  wimjc_yc_w.figWindows

The most complete site about electrostatic machines is that of Professor Antonio Carlos M. de Queiroz, in Brazil.

[Unfortunately, the next three links appear to be dead.]

The machine of Wimshurst of the Virtual Museum of Daniel Giroux

The homepage of Daniel Giroux.

We await a photograph of the Wimshurst machine of Jean Marie Laborde, the person in charge of project IMAG CABRI-GEOMETRICIAN

This page presents a simulation with a virtual machine. It will help you to understand the way the machine operates, but nothing replaces actual experience with a real Wimshurst machine. If you do not own one of them and do not have the opportunity to buy one, you can build it. François BOSSERT, of the Lycée Louis Couffignal, Strasbourg, has built several; he has provided technical information and plans in an article that was published in the Bulletin of the Union of Professors of Physics and Chemistry, Volume 696, July-August-September 1987, p.881, and is also available on the Web:

The Machine of Wimshurst: Principles and Construction (very simple and very economic) by François Bossert [Translator’s note: this mailto may be out of date. If so, use the one given in the text in the above paragraph.]

[The next link appears to be dead, but the following two are okay.]

College Louis Couffignal, Strasbourg

UDP Strasbourg