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History

The First Electrical Machines

From rubbed amber to electricity that could be generated, detected, and carried

For thousands of years, static attraction had been a curiosity: rub amber or another suitable material and it might attract bits of straw, hair, or dust. Around the beginning of the seventeenth century, investigators began turning that curiosity into a repeatable subject of study.

This is an important change in the story:
electricity was no longer only something that happened in nature. It was becoming something an experimenter could make on demand, test with an instrument, move from one place to another, and compare from one material to another.

William Gilbert — electricity becomes a subject of investigation

In 1600 the English physician and natural philosopher William Gilbert published De Magnete, a major study of magnetism. Gilbert also investigated the attraction produced when materials such as amber were rubbed.

He used the Latin word electricus, derived from the Greek word for amber, to describe this amber-like attractive effect. The English words electric and electricity developed from this terminology.

Gilbert also made an extremely simple detector called a versorium: a light pointer or needle balanced so that it could turn freely. Bring an electrified material near it and the pointer would move toward the charged object.

A primitive electrical instrument — but an important one

The versorium did not tell Gilbert how many volts were present or how much charge existed. Those ideas did not yet exist. But it did something fundamental:

it made a weak invisible effect visible;
it allowed materials to be compared;
and it gave the experimenter something more objective than simply feeling a spark.

Measurement trail 2 — before a unit, first make the effect reproducible

Gilbert had no voltmeter and no agreed electrical unit. The versorium could answer simpler questions: Is an electrical effect present? Is one material more strongly electrified than another? Does the effect reach this detector?

That is an important stage in measurement. Before scientists can assign trustworthy numbers, they first need an effect that can be repeatedly detected, compared, and reproduced. The volt, ampere, coulomb, and ohm were still far in the future.

Static charge by hand was useful — but inconvenient

Rubbing a small object worked, but it was difficult to produce large and repeatable amounts of charge. The obvious next step was mechanical: instead of rubbing a little piece of material by hand, why not make a large surface move continuously while it was being rubbed?

Otto von Guericke — the rotating sulfur globe

In the middle of the seventeenth century, Otto von Guericke built a machine using a large ball of sulfur mounted so that it could rotate. As the globe turned, a hand rubbed against its surface and generated static charge.

This is commonly regarded as the first rotary electrostatic generator. It was not a generator of continuous electric current in the later battery-or-dynamo sense. It was a machine for repeatedly producing static charge by friction.

Rubbed amber: rub a small object by hand → Rotating globe: keep a larger surface moving and keep generating charge.

The significance was enormous. A laboratory could now have a source of static electricity that could be operated again and again for demonstrations and experiments.

Glass replaces sulfur

Later experimenters improved the idea by using rotating glass globes. Around the beginning of the eighteenth century, Francis Hauksbee built effective glass-globe electrical machines and demonstrated them before the Royal Society.

A glass globe could be rotated rapidly while being rubbed by the experimenter's hand or by another material. The generated charge could produce attraction, repulsion, sparks, and striking glowing effects under suitable conditions.

The early machine was not yet the familiar hand-cranked plate generator of later physics laboratories, but the basic idea was already there: mechanical motion + friction = a repeatable source of static charge.

But could electricity travel?

At first, many electrical demonstrations involved the object that had itself been rubbed. A major question was whether the electrical effect could be transferred somewhere else.

This led directly to one of the most important discoveries in early electrical science: some materials allow charge to move through them much more readily than others.

Stephen Gray — conductors and insulators

In experiments reported beginning in 1729, the English investigator Stephen Gray showed that electrification could be carried considerable distances through suitable materials.

The details of his experiments were revealing. A line of material could carry the electrical effect, but if that line was supported in the wrong way the charge disappeared into the supports and the surroundings. Silk supports worked much better because they did not let the charge escape easily.

Material or arrangement	What the experimenter discovered	Modern idea
Metal, moist thread, the human body, and other suitable paths	Electrical effects could be carried from the charged source to another location.	Conduction
Silk, glass, and other poor conducting supports	Charge could remain on the intended object instead of leaking away through the support.	Insulation
Connection to Earth or a large conducting body	Charge could disappear from the experimental object.	Grounding or a path for charge to move away

The modern words conductor and insulator came later, but Gray's work made the distinction experimentally clear.

Why the support mattered

Imagine charging a metal rod while holding it directly in your hand. Your body and surroundings provide a path through which charge can move away. Now support the same rod on a material such as glass or dry silk. The charge has a much poorer path to escape.

This is the beginning of a lesson that remains important in electronics today: the circuit includes every available path, not just the path you intended.

Electricity could attract — and repel

As stronger machines and better insulated conductors became available, experimenters could do more than watch bits of material jump toward a charged object. They could charge separate objects and observe how those objects acted on one another.

This revealed that electrical effects were not all alike.

Charles du Fay — two kinds of electrification

In the 1730s, the French investigator Charles François de Cisternay du Fay concluded that there were two kinds of electricity. He called them vitreous electricity, associated with rubbed glass, and resinous electricity, associated with materials such as amber or resin.

Du Fay observed the important pattern that similarly electrified objects repel one another while differently electrified objects attract.

In modern language we use positive and negative charge rather than vitreous and resinous electricity. But the underlying observation was already becoming clear:

like charges repel; unlike charges attract.

A new problem: the charge would not wait around

By the 1730s and 1740s, experimenters had learned how to generate stronger static charges, carry them along conductors, prevent them from leaking away with insulators, and compare different forms of electrification.

But static charge was still inconvenient. It could leak away into the air, through damp surfaces, through a person's body, or through a poorly insulated support.

If electrical science was going to advance, experimenters needed some way to accumulate a larger charge and keep it available until they wanted to discharge it.

That problem leads directly to one of the most important early electrical devices: the Leyden jar — the ancestor of the modern capacitor.

< The World Before Electrical Science | Storing Electricity — The Leyden Jar >