From Franklin to Faraday

The Electrical Century: 1745–1831

10.1 Benjamin Franklin (1706–1790)

Benjamin Franklin was a self-made polymath — printer, publisher, diplomat, inventor, and one of the Founding Fathers of the United States. His electrical experiments, conducted in Philadelphia in the 1740s and 1750s, transformed electricity from a parlour curiosity into a branch of natural philosophy.

The Leyden Jar & Electrical Fluid

The Leyden jar (1745), invented independently by Pieter van Musschenbroek in Leiden and Ewald Georg von Kleist in Pomerania, was the first device capable of storing electric charge. Franklin studied it intensively and made a crucial conceptual advance: he proposed that electricity is a single fluid, not two separate fluids as most European electricians believed.

A body with an excess of this fluid is “positively” charged; a body with a deficit is “negatively” charged. This convention — which Franklin chose arbitrarily — is still used today, even though we now know that it is the negative electrons that flow in a wire. Franklin also recognized that charge is conserved: it cannot be created or destroyed, only transferred.

The Kite Experiment (1752)

In June 1752, Franklin performed his most famous experiment. He flew a kite in a thunderstorm with a metal key attached to the string. Sparks jumped from the key, demonstrating that lightning is an electrical discharge — the same phenomenon as the sparks from a Leyden jar, only vastly more powerful.

This had immediate practical consequences. Franklin invented the lightning rod — a pointed metal conductor that safely channels lightning to the ground. Within a decade, lightning rods were installed on buildings across Europe and America, saving countless lives and structures. It was one of the first applications of pure science to technology.

10.2 Coulomb's Law (1785)

Charles-Augustin de Coulomb (1736–1806), a French military engineer, used an exquisitely sensitive torsion balance of his own invention to measure the force between electric charges. His result, published in 1785, established the inverse-square law for electrostatics:

The force is attractive for opposite charges, repulsive for like charges, and exactly proportional to the product of the charges divided by the square of their separation — the same mathematical form as Newton's law of gravitation.

Coulomb also measured magnetic forces and found they obey the same inverse-square law. However, he drew a firm conclusion: electricity and magnetism are completely independent phenomena. This belief, dominant among French physicists, would persist until Ørsted's bombshell of 1820.

The Torsion Balance

Coulomb's torsion balance was a masterpiece of experimental technique. A thin silver wire suspended a horizontal arm with a charged pith ball at one end. When another charged ball was brought near, the arm rotated until the electrostatic torque balanced the restoring torque of the wire. By measuring the angle and knowing the wire's torsion constant, Coulomb could determine the force with unprecedented precision.

The same instrument was later adapted by Cavendish to measure gravitational attraction between masses (the “Cavendish experiment” that determined \(G\)), demonstrating the deep parallel between electrical and gravitational forces.

10.3 Volta's Pile (1800)

Alessandro Volta (1745–1827) settled a fierce debate with Luigi Galvani about “animal electricity” by showing that the source of electrical effects was not in frog legs but in the contact between dissimilar metals in a moist environment.

In 1800, Volta announced his voltaic pile — the first true electric battery. It consisted of alternating discs of zinc and copper separated by cardboard soaked in brine. For the first time, a steady, continuous flow of electricity could be produced, rather than the momentary discharge of a Leyden jar.

The impact was immediate and revolutionary. Within weeks of the announcement:

• • William Nicholson and Anthony Carlisle used the pile to decompose water into hydrogen and oxygen (electrolysis)
• • Humphry Davy used ever-larger batteries to isolate new elements: sodium, potassium, calcium, barium, magnesium, and strontium
• • Napoleon invited Volta to demonstrate the pile at the Institut de France, awarding him a gold medal

The voltaic pile transformed chemistry, enabled all the electrical experiments of the 19th century, and ultimately made the telegraph, electroplating, and the entire electrical industry possible. The unit of electric potential, the volt, honours his name.

10.4 Ørsted's Discovery (1820)

Hans Christian Ørsted (1777–1851), a Danish physicist and natural philosopher, had long believed in the unity of natural forces — influenced by the German Romantic philosophy of Naturphilosophie. He searched for years for a connection between electricity and magnetism.

In the spring of 1820, while preparing a lecture demonstration, Ørsted noticed that a compass needle was deflected when placed near a wire carrying an electric current from a voltaic pile. The needle swung to orient itself perpendicular to the wire — a completely unexpected direction.

This was revolutionary for two reasons:

Ørsted published his results in a four-page Latin pamphlet that spread across Europe like wildfire. It triggered Ampère's creation of electrodynamics (see next chapter), Faraday's lifelong research programme, and ultimately Maxwell's electromagnetic theory.

10.5 Michael Faraday (1791–1867)

Michael Faraday is one of the greatest experimental scientists in history. Born into poverty as the son of a blacksmith, apprenticed to a bookbinder at age 14, he educated himself by reading the books he was binding — especially Jane Marcet's Conversations on Chemistry.

In 1812, a customer gave Faraday tickets to attend Humphry Davy's lectures at the Royal Institution. Faraday took meticulous notes, bound them, and sent them to Davy as a job application. Davy hired him as a laboratory assistant. Within a decade, the former bookbinder's apprentice had surpassed his master.

Electromagnetic Rotation (1821)

Following Ørsted's discovery, Faraday built the first device that converted electrical energy into continuous mechanical motion: a wire carrying current that rotated continuously around a magnet. This was the first electric motor, however primitive.

Electromagnetic Induction (1831)

On 29 August 1831, Faraday made his most important discovery. He wound two coils of wire on opposite sides of an iron ring. When he connected one coil to a battery, a brief pulse of current appeared in the other coil — but only at the moment of connection or disconnection. A changing magnetic field produces an electric current.

This discovery is the basis of all modern electrical power generation. Every generator, transformer, and dynamo in the world works on the principle Faraday discovered that August day.

The Field Concept

Faraday's greatest conceptual contribution was the idea of the electromagnetic field. Where Newton, Coulomb, and Ampère thought in terms of forces acting instantaneously at a distance between particles, Faraday imagined lines of force filling space — a physical entity that exists everywhere, mediating interactions between charges and magnets.

He made these lines visible by sprinkling iron filings around magnets, watching them arrange themselves into beautiful patterns. For Faraday, these patterns were not merely a visualization tool — the lines of force were real. Space was not empty; it was filled with the electromagnetic field.

This was a radical departure. Most Continental physicists dismissed Faraday's field concept as the unsophisticated intuition of a man who knew no mathematics. But James Clerk Maxwell recognized its genius and would translate it into the mathematical framework that unified electricity, magnetism, and light.

Other Discoveries

“Nothing is too wonderful to be true, if it be consistent with the laws of nature.”— Michael Faraday, diary entry, 19 March 1849

The Stage Set for Maxwell

By 1850, the experimental discoveries were in place:

What was missing was a mathematical unification. Faraday had the physical intuition but not the mathematical language. The next chapter tells how James Clerk Maxwell would translate Faraday's lines of force into four equations that unified electricity, magnetism, and light — and predicted the existence of electromagnetic waves.