Sir Charles Wheatstone ( / ˈ w iː t s t ə n / ; 6 February 1802 – 19 October 1875) was an English physicist and inventor. He is most famous for his work on the Wheatstone bridge, a tool that helps measure unknown electrical resistance. This device was first created by Samuel Hunter Christie. Wheatstone also played a key role in creating telegraphy, which is the system for sending messages over long distances using electrical signals. Other inventions linked to him include the English concertina, the stereoscope, which shows 3D images, and the Playfair cipher, a method for hiding messages.

Life

Charles Wheatstone was born in Westgate, Gloucester, and was baptized at St. Mary de Lode. Later, a biography mistakenly claimed he was born at his grandmother’s home in Barnwood, Gloucestershire. His father, W. Wheatstone, was a cobbler and music seller in the town. His mother came from a family connected to the lord of a nearby village and had ties to London society. Four years after Charles was born, his father moved to 128 Pall Mall, London, where he taught the flute to members of royalty. Charles, the second son, stayed with his grandparents and attended a village school in Barnwood before studying at several schools in London. One of these schools was in Kennington, run by Mrs. Castlemaine, who was impressed by his quick learning. At another school, he ran away but was found near Windsor, close to where he later worked on his practical telegraph. As a child, he was shy and often spent time alone in an attic, thinking deeply about things.

At about fourteen years old, Charles became an apprentice to his uncle, who sold musical instruments in London. However, he preferred reading books over working with tools or selling goods. His father supported his interest in learning and eventually removed him from his uncle’s care.

At fifteen, Wheatstone translated French poetry and wrote two songs. One of these songs was given to his uncle, who published it without knowing it was his nephew’s work. Some of his writings about the lyre were used as a motto on an engraving by Bartolozzi. He often visited a bookstall near Pall Mall, which was a poorly maintained street. He spent most of his money on books, including fairy tales, history, and science.

One day, he wanted to buy a book about Volta’s discoveries in electricity but could not afford it. He saved his coins to purchase the book, which was written in French. He then bought a dictionary to understand it. With his older brother, William, he repeated the experiments in the book using a homemade battery made in the scullery behind his father’s house. They needed copper plates for the battery but only had a few coins. Charles suggested using the coins themselves, and the battery was completed.

On February 12, 1847, Wheatstone married Emma West at Christchurch, Marylebone. Emma was the daughter of a tradesman from Taunton and was described as attractive. She died in 1866, leaving five young children for Wheatstone to care for. His personal life was quiet and uneventful.

Although he was quiet in public, Wheatstone spoke clearly and enthusiastically about his favorite subjects in private. He was small in size but energetic and intelligent. Sir Henry Taylor once saw him at a party in Oxford, where he explained the telegraph to Lord Palmerston. Palmerston was surprised and asked Lord Westbury to keep Wheatstone talking so he could leave. This event may have inspired Palmerston to imagine a future where a minister could ask Parliament if war had started in India and reply, “Wait a minute; I’ll just telegraph the Governor-General.”

In 1868, Wheatstone was knighted after completing the automatic telegraph. He had previously been honored as a member of the Legion of Honour. He received many awards from scientific societies, including being a Fellow of the Royal Society since 1836. In 1859, he became a foreign member of the Royal Swedish Academy of Sciences, and in 1873, he was named a Foreign Associate of the French Academy of Sciences. That same year, he received the Ampere Medal from a French organization. In 1875, he was made an honorary member of the Institution of Civil Engineers. He held degrees from Oxford and Cambridge.

During a visit to Paris in 1875, Wheatstone worked on improving a device for underwater telegraph cables. He caught a cold that led to a lung infection. He died in Paris on October 19, 1875, at age 73. A memorial service was held at an Anglican chapel in Paris, attended by members of the academy. His body was returned to London and buried in Kensal Green Cemetery. A blue plaque now marks his former home at Park Crescent.

Music instruments and acoustics

In September 1821, Charles Wheatstone gained public attention by displaying the 'Enchanted Lyre,' also called the 'Acoucryptophone,' at a music shop in Pall Mall and at the Adelaide Gallery. The device appeared to be a lyre hanging from the ceiling by a cord, producing sounds from instruments like the piano, harp, and dulcimer. In reality, it was a simple box that made sound. The cord was actually a steel rod that carried the vibrations of the music from hidden instruments. At this time, Wheatstone conducted many experiments on sound and how it travels. Some of his findings were published in Thomson's Annals of Philosophy in 1823.

He understood that sound moves through waves or vibrations in the air, similar to how light was thought to travel through waves in the luminiferous ether. He found that water and solid materials, such as glass, metal, or wood, carry sound very quickly. He proposed using these materials to send sound signals, music, or speech over long distances. He estimated that sound could travel 200 miles per second (320 km/s) through solid rods and suggested using this method to send messages from London to Edinburgh. He even called his system a 'telephone.'

In 1667, Robert Hooke wrote in his book Micrographia that he could send sound over long distances using a stretched wire. He noted that the wire did not need to be straight—it could be bent. This idea became the basis for a mechanical device called the 'lover's telephone,' which was reportedly known in China centuries earlier. Hooke also thought about ways to improve human hearing.

A writer in the Repository of Arts on September 1, 1821, described how the 'Enchanted Lyre' could allow an opera performance at the King’s Theatre to be heard in places like the Hanover Square Rooms or the Horns Tavern in Kennington. The vibrations would travel through underground pipes, like gas flowing through tubes.

In addition to sending sound over long distances, Wheatstone created a simple tool to amplify weak sounds, which he named the 'Microphone.' It used two thin rods to carry vibrations to both ears. This device is different from the electrical microphone later made by Professor Hughes.

In 1823, Wheatstone’s uncle, a maker of musical instruments, died. Wheatstone and his older brother, William, took over the business. Although Charles disliked the commercial side, he used his creativity to improve existing instruments and design new ones. One of his most famous inventions was the Wheatstone concertina, a six-sided instrument with 64 keys arranged for easy playing. The English concertina became popular during his lifetime but reached its peak of popularity in the early 20th century.

In 1827, Wheatstone introduced the 'kaleidophone,' a tool that made the vibrations of a sound source visible. It used a metal rod with a silvered bead that reflected a light spot. When the rod vibrated, the light spot created complex shapes in the air. His photometer, which compared the brightness of two lights, was likely inspired by this invention.

In 1828, Wheatstone improved the German wind instrument called the Mundharmonika, creating the symphonium, a mouth-blown instrument with a logical key layout. He patented it on December 19, 1829, and it resembled the later English concertina. He also invented the portable harmonium, which won a prize at the Great Exhibition of 1851. Wheatstone improved the speaking machine made by De Kempelen and agreed with Sir David Brewster’s belief that by the end of the century, machines that could sing and speak would be possible.

In 1834, Wheatstone, who had already gained recognition, was appointed to the Chair of Experimental Physics at King’s College London. His first lectures on sound were not successful because he disliked speaking in public. He struggled to speak clearly, sometimes facing away from the audience or muttering at diagrams. However, in the laboratory, he felt comfortable and focused on demonstrating experiments rather than giving lectures.

Velocity of electricity

In 1834, a scientist became famous for conducting an important experiment to measure how fast electricity traveled through a wire. He cut the wire in half to create a gap where a spark could jump across. Then, he connected the ends of the wire to the poles of a Leyden jar filled with electricity. This setup produced three sparks: one at each end of the wire and one in the middle. To study the sparks, he attached a tiny mirror to the works of a watch, allowing the mirror to spin very fast. He observed the reflections of the sparks in the mirror. The wire was arranged so that if the sparks happened instantly, their reflections would appear in a straight line. However, the middle spark appeared slightly delayed because it occurred a moment later. This delay showed that electricity took time to travel from the ends of the wire to the middle. By measuring the delay and comparing it to the known speed of the spinning mirror, he calculated the time it took for electricity to travel. Then, he divided the length of half the wire by this time to find the speed of electricity. His results suggested a speed of 288,000 miles per second, which was faster than the speed of light known at the time (299,792.458 kilometers per second or 186,000 miles per second). Although this was not the exact speed of light, it was a useful estimate.

At the time, some scientists already knew that the speed of electricity depended on the material and environment of the conductor. In 1816, Francis Ronalds noticed delays in electrical signals traveling through a buried telegraph cable, which he attributed to induction. As a young man, Charles Wheatstone observed these experiments, which inspired his later work on telegraphy. Years later, after telegraphs became widely used, Michael Faraday explained that the speed of an electric field in a submarine wire, covered with insulation and surrounded by water, was slower—only 144,000 miles per second (232,000 kilometers per second) or even less.

Wheatstone’s spinning mirror device was later used by Léon Foucault and Hippolyte Fizeau to compare the speed of light in air and water. This method eventually helped scientists measure the speed of light more accurately.

Spectroscopy

Wheatstone and others helped develop early spectroscopy by discovering and using spectral emission lines.

As John Munro wrote in 1891, "In 1835, at the Dublin meeting of the British Association, Wheatstone showed that when metals were vaporized in an electric spark, their light, viewed through a prism, revealed specific light patterns unique to each metal. This allowed scientists to identify the metals used in the spark by studying the light. This method became very important in spectrum analysis. Scientists like Robert Bunsen and Gustav Kirchhoff used it to find new elements, such as rubidium and thallium. It also helped scientists learn more about the stars and other celestial objects."

Telegraph

Charles Wheatstone gave up his idea of sending messages by moving rods with machines and instead focused on the electric telegraph. In 1835, he talked about a system created by Baron Schilling and said that the tools needed to build a useful electric telegraph already existed. He tested his own plans, suggested building a test line across the Thames, and proposed using the London and Birmingham Railway for the telegraph. Before these plans began, William Cooke visited Wheatstone at his home on 27 February 1837, which changed Wheatstone’s future.

Cooke was an officer in the Madras Army who was on leave and studying medicine at the University of Heidelberg. On 6 March 1836, he saw a telegraph demonstration by Professor Georg Munke and became so interested that he stopped studying medicine and focused on the telegraph. He returned to London and showed a telegraph with three needles in January 1837. Knowing he needed more scientific knowledge, he asked Michael Faraday and Peter Roget (then secretary of the Royal Society) for help. Roget directed him to Wheatstone.

During a second meeting, Cooke told Wheatstone about his plan to build a working telegraph and explained his method. Wheatstone said the method would not work and showed his own experimental telegraph. Eventually, Cooke proposed a partnership, but Wheatstone was hesitant at first. Wheatstone was a well-known scientist who wanted to share his findings without seeking profit. Cooke, however, wanted to make money from the invention. In May 1837, they agreed to work together, with Wheatstone providing scientific knowledge and Cooke handling organization. Their partnership agreement was signed on 19 November 1837. They jointly patented their inventions, including Wheatstone’s five-needle telegraph and an alarm system using a relay.

The five-needle telegraph, mostly Wheatstone’s idea, worked like Schilling’s system and used a principle discovered by Ampère. A battery’s current was sent through a wire using a key, and at the other end, the current passed through a coil around a magnetic needle. Depending on which side of the battery was connected, the needle turned left or right. Five separate circuits controlled five needles. The needles were attached to a diamond-shaped dial with letters arranged so that two needles would point to a letter when the current passed through.

An experimental telegraph line was set up between Euston and Camden Town stations on 25 July 1837. The distance was 1.5 miles, but extra wire was added to make the line longer. Wheatstone operated the telegraph in a dim room at Euston, and Cooke at Camden Town. Wheatstone sent the first message, and Cooke replied. Wheatstone later said he felt a strong sense of achievement when the needles clicked and spelled out the message.

Despite this success, railway directors ignored the telegraph and asked it to be removed. However, in 1839, the Great Western Railway supported the invention and built a line from Paddington to West Drayton, 13 miles long. Later, the line was extended to Slough and displayed at Paddington as a scientific marvel. It could send 50 signals per minute over 280,000 miles. The admission fee was a shilling (about 5 pence), and in 1844, one visitor wrote about its impact.

The public began to accept the telegraph after it helped arrest John Tawell, the first person caught using telecommunications in 1845. That same year, Wheatstone improved the telegraph with single- and double-needle instruments. The single-needle version, needing only one wire, is still used today.

The telegraph’s progress is shown by two events: In 1855, news of Emperor Nicholas’s death in St. Petersburg reached the House of Lords hours later. In 1890, the result of The Oaks horse race was received in New York 15 seconds after the race ended.

In 1841, Cooke and Wheatstone disagreed about who deserved credit for inventing the telegraph. They asked Marc Isambard Brunel and Professor Daniell to decide. Brunel gave Cooke credit for introducing the telegraph as a useful project, while Daniell credited Wheatstone for his research. They concluded that both men’s combined efforts led to the telegraph’s success.

From 1836 to 1837, Wheatstone studied underwater telegraphs and in 1840 gave evidence to the House of Commons about laying a cable from Dover to Calais. He designed the tools for this work. In 1844, he tested an insulated wire in Swansea Bay, sending signals from a boat to a lighthouse. The next year, he suggested using gutta-percha to coat the cable for the English Channel.

In 1840, Wheatstone patented an alphabetical telegraph, or "Wheatstone A B C instrument," which moved step-by-step and displayed letters on a dial. His 1841 type-printing telegraph was the first to print telegrams in type. It used two circuits to press letters onto paper.

By 1845, the telegraph had advanced enough that on 2 September 1845, the Electric Telegraph was officially opened.

Optics

Stereopsis was first described by Wheatstone in 1838. In 1840, he received the Royal Medal from the Royal Society for his work on binocular vision. This research led him to create stereoscopic drawings and build a device called a stereoscope. He explained that our brain combines two separate images of an object, seen from slightly different angles by each eye, to create the sense of depth and solidity. The stereoscope uses lenses or mirrors to combine two photographs of the same object taken from different positions, making the object appear three-dimensional. Sir David Brewster later improved the stereoscope by removing the mirrors and using only lenses, creating the version of the device still used today.

In 1852, Wheatstone introduced a device called the pseudoscope. The name comes from the Greek words for "false" and "to look." The pseudoscope works oppositely to the stereoscope, making solid objects appear hollow and causing closer objects to look farther away. For example, a statue might seem like a mask, and a tree outside a window might look like it is growing inside the room. Wheatstone created the pseudoscope to test his ideas about 3D vision and to study how the brain processes visual information, which is now part of the field of experimental psychology.

Measuring time

In 1840, Charles Wheatstone created a device called the chronoscope, which measured very short time intervals. This tool helped scientists find the speed of a bullet or track the movement of a star. The chronoscope used an electric current to activate an electromagnet, which marked the exact moment of an event by drawing a line on moving paper. It could measure time as small as 1/7300 of a second (137 microseconds), such as how long it took an object to fall from one inch (25 mm) high.

On November 26, 1840, Wheatstone showed his electromagnetic clock at the Royal Society’s library. He also proposed a plan to share accurate time from a main clock to other clocks in different places. The clocks would be connected through electrical circuits controlled by a key linked to the main clock. Their hands would be adjusted using electromagnetism. In January 1841, Alexander Bain received a patent for an electromagnetic clock. He later claimed that Wheatstone used his ideas. Bain had worked for Wheatstone as a mechanic from August to December 1840 and said he shared the idea of an electric clock with Wheatstone during that time. Wheatstone, however, said he had already been experimenting with similar ideas in May 1840. Bain also accused Wheatstone of copying his design for an electromagnetic printing telegraph, but Wheatstone proved that his device was a different version of his own telegraph.

In 1840, Alexander Bain told the editor of Mechanics Magazine about his financial struggles. The editor introduced Bain to Wheatstone. Bain showed his models to Wheatstone, who said, “I wouldn’t spend time on these—they don’t have a future.” Three months later, Wheatstone demonstrated an electric clock to the Royal Society, claiming it was his invention. However, Bain had already applied for a patent. Wheatstone tried to stop Bain’s patents but failed. When Wheatstone helped create the Electric Telegraph Company through a law passed by Parliament, the House of Lords asked Bain to testify. Eventually, the company paid Bain £10,000 and gave him a job as manager, leading Wheatstone to resign.

One of Wheatstone’s most clever inventions was the “Polar clock,” shown at a British Association meeting in 1848. This device used a discovery by Sir David Brewster that sunlight reflects off the sky in a specific direction, always at a right angle to the sun’s position. By measuring this direction and comparing it to north, scientists could determine the sun’s position even when it was below the horizon and calculate the time of day.

The Polar clock had a spyglass with a Nicol prism (a special glass that splits light) in the eyepiece and a thin selenite plate in the lens. When the spyglass was pointed toward the North Pole (aligned with Earth’s axis) and the prism was turned until no colors were visible, the angle of the turn, shown by a pointer on a marked circle, indicated the current hour. While this device was not useful in places with accurate watches, it was used by Captain Nares during the 1875–1876 North Polar expedition.

Wheatstone bridge

In 1843, Wheatstone shared an important paper with the Royal Society. The paper was called "An Account of Several New Processes for Determining the Constants of a Voltaic Circuit." It explained a method for measuring the electrical resistance of a conductor, which is now known as Wheatstone's Bridge or balance. However, this method was first created by Samuel Hunter Christie, who taught at the Royal Military Academy in Woolwich. Christie published his work in the Philosophical Transactions in 1833. Wheatstone later made this method widely known.

His paper included many simple formulas for calculating electrical current and resistance using Ohm's law. He introduced a unit of resistance, defined as a copper wire that is one foot long and weighs 100 grains (6.5 grams). He also showed how this unit could be used to measure the length of a wire based on its resistance. For his work, the Royal Society gave him a medal. That same year, Wheatstone invented a device that allowed the temperature from a thermometer or the air pressure from a barometer to be recorded from a distance using an electric connection with mercury. In May of that year, Cooke and Wheatstone also patented a sound telegraph that used the ringing of a bell to send signals.

Cryptography

Charles Wheatstone showed great creativity by inventing ciphers. He created the Playfair cipher, named after his friend Lord Playfair. This cipher was used by military groups in several countries during World War I and was also used by British intelligence during World War II.

At first, the Playfair cipher was difficult to break using code-breaking methods, but techniques were later developed to decode it. Wheatstone also helped interpret coded messages at the British Museum. He designed a device that could turn messages into ciphers, and only a matching machine could be used to decode them.

As an amateur mathematician, Wheatstone wrote a math proof in 1854 (see Cube (algebra)).

Electrical generators

In 1840, Wheatstone introduced a machine that used magnetism and electricity to create continuous electric currents.

On February 4, 1867, Wheatstone shared the principle of reaction in a dynamo-electric machine through a paper presented to the Royal Society. However, Mr. C. W. Siemens had shared the same discovery ten days earlier, and both papers were presented on the same day.

Later, it was found that Werner von Siemens, Samuel Alfred Varley, and Wheatstone each discovered the principle independently within a few months of each other. Varley received a patent for it on December 24, 1866. Siemens brought attention to it on January 17, 1867. Wheatstone demonstrated how it worked at the Royal Society on the same date.

Disputes over invention

Charles Wheatstone had disagreements with other scientists throughout his life about his contributions to various technologies. Sometimes, he took more credit than he should have. Other scientists involved in these disputes included William Fothergill Cooke, Alexander Bain, David Brewster, and Francis Ronalds at the Kew Observatory. Many people wrongly believed that Wheatstone created the tools for studying atmospheric electricity that Ronalds invented and developed at the observatory in the 1840s. Additionally, it was mistakenly thought that Wheatstone installed the first automatic recording weather instruments there (see, for example, Howarth, p158).

Personal life

Charles Wheatstone married Emma West, an unmarried woman and the daughter of John Hooke West, who had passed away. The ceremony took place at Christ Church in Marylebone on February 12, 1847, and was conducted with a special legal document called a licence.

Legacy

In 1994, British Rail Telecommunications named a British Rail Class 20 locomotive with the number 20187 Sir Charles Wheatstone.