How did gold lead to the first rules of electricity? And, why is it ½ correct? What is correct and what was incorrect? Well, I’ll tell you and along the way, I’ll talk about how static electricity works, why it doesn’t work on humid days, and why it often flows away and confuses us.
Table of Contents
Gray’s Article
Du Fay’s Discovery
Experimenting with Gold
Why Electrical Experiments only work on Dry Days
Why Du Fay was only 1/2 Correct
Gray’s Article
In 1731, an Englishman named Stephan Gray published a letter in the royal society about how electricity conducts. It was almost universally ignored. Most people were still fascinated with the revolutionary ideas from Isaac Newton’s theory of gravity and forces.
A poor merchant talking about moving little pieces of fluff seemed trivial and unimportant. However, it was read by a 33 yr old incredibly wealthy Frenchman named Charles-François de Cisternay Du Fay.
Du Fay came from a long line of wealthy diplomats and generals. In fact, he became a soldier at the tender age of fourteen but retired early to focus on his true love: science. Du Fay was interested in basically everything scientific: Chemistry, Anatomy, Botany, Geometry, Astronomy, Engineering, and Physics, and in all, he “shone with unusual brilliancy.”
When Du Fay read that article from Stephan Gray that electricity flows, Du Fay wondered if everything had electricity but people didn’t notice it with the materials that let the electricity easily flow out of them. [See, at the time, “electric” meant that small objects would be attracted to it if it was rubbed.]
Du Fay’s Discovery
Before Du Fay people thought that metal objects weren’t “electric” as if you rubbed them nothing stuck to them. Du Fay thought that maybe the metal was becoming electric but then the electricity just flowed out of the metal and into the person’s hand.
Therefore, he rubbed a metal object without touching it with his bare hand and put it on an insulating stand, or a stand that would not let the “electrical fire” flow out. (He used wax, I am using cotton pot holders). This way, metal objects could attract feathers just as glass or wax does.
In this manner, Du Fay found that every solid object he experimented with attracted small objects by rubbing them. In other words, Du Fay demonstrated that electricity is in all objects – it is everywhere and in everything!
Du Fay then read all the literature about electric forces (which didn’t take long). He learned that 65 years earlier a German man named Otto Von Guericke had found that after feathers were electrically attracted to a smelly ball of sulpher, the feather would fall off and be repulsed by the ball.
Du Fay tried it with other (less smelly) objects and found that if he waited, all objects would electrically attract small objects and then after a time electrically repel the same objects.]
Experimenting with Gold
This is when he started to use pieces of gold. See, scientists love using gold if they have the money as it is conductive but also so malleable that you can make very thin light pieces of gold, lighter even than feathers. Du Fay had the money to play with gold.
When he charged up a tube of glass and put a piece of gold near it, [the gold would jump to the glass and then bounce off and stick to the floor. Then, it would often jump back up to the tube. On a dry day he could make the gold dance.]
This is where Du Fay came up with his first “simple principle” to explain how electricity works, a theory that we still think is correct over 280 years later! In his own words: “electric bodies attract all those that are not so, and repel them as soon as they become electric by contact with the electric body.”
[In other words, the neutral feather or piece of gold or aluminum foil ball was attracted to the charged rod. When it touched the glass tube it gets some of the charges and was repelled. Then, when it touched the ground it lost its charge and became neutral and could be attracted again.
The Gold Leaf Experiment
This explains why electrical experiments only work well on dry days. On humid days, the water in the air is attracted to the charged object, but once in contact, the water becomes charged and then is repelled, taking some of the charge with it. This continues with multiple water droplets until the charged object loses all of its charge so that no electrical experiments can be conducted.
Du Fay had an ingenious method of verifying his theory. He took two tubes and charged them both by separately by rubbing them. He then placed a gold leaf near one of the tubes and watched it get attracted and repelled. In his theory, the gold leaf is repelled because it has taken some of the “electricity” from the tube.
Therefore, the second tube should repel the gold leaf too. He was flabbergasted when he tried the experiment and the gold leaf was repelled by the first tube but strongly attracted to the second. He determined that it was because one tube was made of glass and another of sealing wax.
In other words, there is more then one type of electricity! [You can see this process more easily (as well as cheaply) with feathers instead of gold foil. He named one type of electricity vitreous electricity for glass-like electricity and one type of electricity resinous electricity for wax like electricity.
The Basic Laws of Electricity
After exhaustive experimentation, Du Fay found that every object would fit into one of these two categories. He also found that if objects had the same charge they would repel and different charges they would attract.]
Du Fey had created the basic law of electrics: “opposites attract, like repel, and charged attracts neutral”. That is completely correct! So, what did he get wrong? Something subtle but important. Du Fay thought that by rubbing things he was creating electricity and different types of material created different electricities.
He didn’t realize that electricity isn’t created it is only moved. When he rubbed the glass it gained electrons from his hand (and became negatively charged) and when he rubbed the wax it lost electrons to his hand (and became positively charged). Electricity always has symmetry although because it can flow to the ground it is often hard to see.
This seems like a minor mistake, but it is vital to understanding electricity especially in circuits.
Du Fay wrote seventeen additional papers on electricity in just 5 years. His work was cut short when he died from smallpox at the age of 41 in the summer of 1739. Now that a wealthy scientist had written about it more people in Europe began playing with electricity. By far the most influential not to mention flamboyant was a German “wizard” named Matthais Bose.
Bose took Du Fay’s scholarly work and added a man named Hauksbee’s electricity machine to make the most dramatic electrical experiments the world had ever seen. Soon, everyone was shocking each other at fashionable electricity parties. Bose started an electrical craze! His story, and his bad poetry, are next time on the “secret history of electricity”