History of the Capacitor – The Pioneering Years

The history of capacitors starts in the pioneering days of electricity. I liken it to the pioneering days of aviation when you made your own planes out of wood and canvas and struggled to leap into the air, not understanding enough about aerodynamics to know how to stay there. Electricity had a similar period. At the time of the discovery of the capacitor our understanding was so primitive that electricity was thought to be a fluid and that it came in two forms, vitreous electricity and resinous electricity. As you’ll see below, it was during the capacitor’s early years that all this changed.

The history starts in 1745. At the time, one way of generating electricity was to use a friction machine. This consisted of a glass globe rotated at a few hundred RPM while you stroked it with the palms of your hands. This generated electricity on the glass which could then be discharged. Today we call the effect taking place the triboelectric effect, which you can see demonstrated here powering an LCD screen.

Discovery of the Leyden jar
Discovery of the Leyden jar

In 1745 Ewald Georg von Kleist in Pomerania, Germany tried to store electricity in alcohol thinking that he could lead the electricity along a wire from the friction machine to alcohol in a glass medicine bottle. Since electricity was considered a fluid it was a reasonable approach. He reasoned that the glass would act as an obstacle to the escape of the electrical “fluid” from the alcohol. He did this similarly to how it’s shown in the illustration, by putting a nail through a cork and into the alcohol and while holding the glass bottle in one hand. He wasn’t aware at the time of the important part played by his hand. Von Kleist found that he would get a spark if he touched the wire, a more powerful spark than he’d normally get from the friction machine alone.

He communicated his discovery to a group of German scientists in late 1745 and the news made its way to Leyden University in the Netherlands, but in a confused form. In 1746 Pieter van Musschenbroek and his student Andreas Cunaeus at Leyden University succeeded in doing the same experiment but with water. Musschenbroek then informed the wider French scientific community of the experiment. It’s considered that von Kleist and Musschenbroek independently discovered it. But as you can see below, this was only the beginning.

Abbé Nollet, a French experimenter, gave the jar its name, Leyden jar, and sold it as a special type of flask to scientifically curious, wealthy men.

It was realized also at Leyden University that it worked only if the glass container was held in your hand and not if it was supported by an insulating material.

Today we realize that the alcohol or water in contact with the glass was acting as one plate of the capacitor and the hand was acting as the other while the glass was the dielectric. The high voltage source was the friction machine and the hand and body provided a ground.

Daniel Gralath, a physicist and the mayor of Danzig, Poland was the first to connect multiple jars in parallel to increase the quantity of stored charge. In the 1740s and 1750s Benjamin Franklin, in what was to later become the United States of America, also experimented with Leyden jars and called this collection of multiple Leyden jars a battery, due to its similarity with a battery of cannon.

Franklin did a lot of experiments with both water filled Leyden jars and foil lined Leyden jars and concluded that the charge was stored on the glass and not in the volume of water. He did this by working with dissectible Leyden jars (see the photos above), ones where the outer and inner foils could be removed from the glass. This was later proven to be incorrect. Franklin worked with soda glass which is hygroscopic. As the foils were removed from the glass, charge was transferred via corona to moisture on the glass. When a jar of paraffin wax or baked glass is used instead, the charge remains on the metal plates. There is another weaker effect called dielectric absorption which involves the dipoles within the glass, or dielectric, and allows capacitors to retain some of their charge after the plates are shorted.

Franklin subsequently worked with flat glass plates with foil on either side, described connected in series in one letter.

It was around this same time that Franklin, in experiments not involving capacitors, showed that electricity had just one charge carrier, though he considered it a ‘subtle fluid’, the discovery of the electron having to wait until the late 1800s. He found that a charged object either had an excess of this fluid or a deficiency. This disproved the idea of the two types of electricity, vitreous electricity and resinous electricity.

In 1776 Alessandro Volta, working with different methods to measure electrical potential (voltage, V) and charge (Q) discovered that for a given object, V and Q are proportional, i.e. the law of capacitance, though it was not called that at the time. It was for this work that the unit volt was named after him.

The term ‘capacitor’ didn’t start being used until sometime in the 1920s. For a long time they were referred to as condensers and still are for some applications and in some countries. The term ‘condenser’ was first coined by Volta in 1782, deriving it from the Italian condensatore, due to its ability to store a higher density of charge than an isolated conductor.

Faraday's specific inductive capacity apparatus
Faraday’s specific inductive capacity apparatus

In the 1830s Michael Faraday did experiments which determined that the material in between the capacitor’s plates had an effect on the quantity of charge on the capacitor’s plates. He did these experiments with spherical capacitors, basically two concentric metal spheres in between which he could have air, glass, wax, shellac or other materials. Using a Coulomb’s torsion-balance he effectively measured the charge on the capacitor when the gap between the spheres was filled with air. Keeping the potential difference constant he then measured the charge when the gap was filled with other materials. He found that the charge was greater with the other materials than it was with air. He called it the specific inductive capacity and it was for this work that the unit for capacitance is called the farad.

The term ‘dielectric’ was first used in a letter from William Whewell to Faraday where he speculated that Faraday had coined the term dimagnetic in analogy to dielectric and that perhaps Faraday should have used diamagnetic but that it wouldn’t work as well for diaelectric, given that the two vowels are together.

Wimshurst machine with Leyden jars
Wimshurst machine with Leyden jars

Leyden jars and capacitors made of flat glass plates with foil remained in use for spark gap transmitters and medical electrotherapy equipment until the late 1800s. With the invention of wireless (radio) capacitors began to take their modern form, partly due to the need for lower inductance to work with higher frequencies. Smaller capacitors were made using flexible dielectric sheets, such as oiled paper, often rolled with foil on either side. But the history of modern capacitors is a large topic for another post.

One fun thing about the early history of capacitors is that they have a very DIY feel to them, many having been homemade. In fact, Leyden jars are still used today by high-voltage hackers, as in this 3D printed Wimshurst machine and for pure fun as in this Leyden jar of doom. Do you make Leyden jars or any other types of capacitors for any things you build? Also, are there instances where you use, or see used, the term condenser instead of capacitor? We’d love to know about it. Let us know in the comments below.

30 thoughts on “History of the Capacitor – The Pioneering Years

  1. The term condenser is still used sometimes with small engines that still have points-condenser type ignition. Walk into a small engine shop and ask for an ignition capacitor and you’ll get funny looks.

    I’ve built a number of capacitors over the years, mostly high voltage caps for use with a Tesla coil. These were built with aluminum foil and plate glass, about as simple as they come.

    1. I recall a boy making caps using wax paper and aluminum foil. And discovering that applying too much voltage would cause them to explode with a loud bang. Mom hated when I did that.

  2. I have a vague memory of a Crystal Set Construction project shown in my Cub Scout manual, back in the 1940s. In it they showed how to make a capacitor from, “dad’s cigarette pack”. The cellophane wrapper was cut into squares and the inner foil wrap was cut into smaller squares. Alternating squares of foil were somehow connected together to become the plates of the capacitor and the poles of the capacitor. I also vaguely remember winding several coils on toilet paper tubes and one on an oatmeal box. That was about as far as I got. My dad saw my efforts and went to a local TV shop and asked if they could order a built crystal set. It arrived in about a week, and all thoughts of completing the project went out the window. I strung wire out a window to our garage and was able to pick up several local Detroit AM radio stations. Quite a thrill for a nine year old!

  3. My first Tesla coil was a spark gap type, and the tank capacitor was a number of glass bottles filled with salt water brine, and wrapped in aluminum foil. A little mineral oil over the brine helped suppress corona inside the bottle, but the foil would still have some corona discharge. 1/4″ bolts were inserted through the top of the bottle down into the brine and hot glued in place, the bottles were all set on a sheet of metal for the other terminal. I want to say I determined that the bottles each provided around 6 nF capacitance.

  4. Here in Czech Rep., we use „kondenzátor“ (plural „kondenzátory“), or in EE slang „kond“ or „kondík“, pl. „kondy“, „kondíky“ (= cap, caps).

  5. Cool article and some stuff I didn’t know.

    “Franklin did a lot of experiments with both water filled Leyden jars and foil lined Leyden jars and concluded that the charge was stored on the glass and not in the volume of water.”… “This was later proven to be incorrect.”

    I think that could do with some clarification. Most of the charge displacement in a capacitor with a good dielectric is ‘stored’ as polarisation of the dielectric.

  6. Incomplete. The history of electricity goes back well beyond 2000 years ago.
    The first known capacitors were based on citrus juice and copper wire for gold plating.
    If ancients could plate other items with simple low voltage capacitors,
    What else did they do?

    Theory and conjecture: the rate, speed and accuracy of the pyramids build: each block was cut. In one strike no less, by a radial arm saw that was over 5 meters in diameter. How is this possible? The proof is in the test cuts!

    So if our wisdom of electricity is so inspired, why was Maxwell’s theory of electricity dumbed down to vector theory analysis?

    Why is our historical time line incomplete and missing massive amounts of data?

    Why is Antoine Priore and his theory of rotational plasma fields not taught in school?

    Why is the symbiotic relationship of shared electricity with the universe accepted but any positive results discounted?

    This is the beginning of our knowledge. We are still at the start line. In over 60 years we have uncovered a grain of sands worth of data in a star ocean of universe of data. We know nothing. Now we can start learning.

    1. My god you are right. So many English live in Europe when they retire but they stay still, and so many Europeans come over to England to work and move! It’s the right hand rule!! The force pushed us out of Europe!!! Brexit is electromagnetism!!!!! Brelextromagnetism!!!!!! And England was earthed by it’s land and Iceland were insulated by their Ice and the force pushed us out of the Europian cup!!!!!!! It all makes sense now!!!!!!!!

    2. good possibility a lot of knowledge was lost through ignorance when a country was conquered and libraries destroyed because they didn’t fit with prevailing religious belief (sound familiar? it’s still happening)

      1. They already found in Baghdad some ancient jars that with added electrolyte [vinegar] produced some electric power. If you read the Illiad, Achilles ‘s armor was made out of layers of bronze, leather and copper, but he used leather sandals for insulation (therefore not properly protected). When he hit an enemy, it was said that he was shocked. I don’t know if that is true, but it integrates well with the heel vulnerability.

        1. I think you’re referring to the Baghdad battery: https://en.wikipedia.org/wiki/Baghdad_Battery. Hmm… looks like the current interpretation according to that article has changed from what I remember. Looks like the battery interpretation is no longer the current one.
          Regarding Achilles giving shocks, sounds like some rubbing was going on with his clothing and he was becoming charged via the triboelectric effect. That’s the same effect that give you a shock when you rub your socks on carpet and then touch a doorknob.

  7. To me capacitor seems to be more fitting than condenser. When i hear the term condenser i relate that to a device/apparatus to change the state of matter (condense) a gas into a liquid (opposite of evaporation).

  8. a few weeks ago i experimented with DIY supercapacitors. i grinded some active charcoal to dust, mixed it with clear paint and painted it onto tome metal mesh. Soldered wires onto the two plates and made a sandwich of Aluminium Foil and My “electrodes” , and submerged it into salt water. I could hold about 0.6-0.8V. Graphene would be better than charcoal, but it costs more. There are some really good videos on youtube about a teacher, that is building MegaFarad condensators in his Kitchen.

  9. I learned to call them “condensers” when I first got interested in radio in 1950. I also learned about “cycles”, too. Now at age 77, I wonder what the point of this post is.

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