John Michell facts for kids

John Michell (/ˈmɪtʃəl/; 25 December 1724 – 21 April 1793) was an English scientist and clergyman. He made amazing discoveries in many areas of science. These included astronomy, geology, optics, and gravitation.

Many people consider him "one of the greatest unsung scientists of all time." He was the first person known to suggest that black holes might exist. He also first proposed that earthquakes travel in waves. Michell realized that double stars orbit each other because of gravity. He was also the first to use statistics to study the universe.

He invented a special tool to measure the mass of the Earth. He also explained how to make an artificial magnet. Because of his work, he is sometimes called the father of seismology (the study of earthquakes) and magnetometry (the study of magnetism).

A science journalist once said that some of Michell's ideas sound like they came from a modern astronomy textbook. The American Physical Society (APS) noted that Michell was "so far ahead of his scientific contemporaries." This meant his ideas were forgotten until they were discovered again over a century later. The APS also said that even though he was brilliant, Michell is still mostly unknown today. This is partly because he didn't do much to share his own groundbreaking ideas.

Early Life and Education

John Michell was born in 1724 in Eakring, England. His father, Gilbert Michell, was a priest. John went to Queens' College, Cambridge, for his education. He later became a Fellow there, which means he was a senior member of the college.

He earned his M.A. degree in 1752 and his B.D. degree in 1761. Michell taught at the college from 1751 to 1763. He also held a special position as the Woodwardian Professor of Geology from 1762 to 1764. He had to leave this job when he got married.

There are no pictures of Michell that we know of today. People who knew him said he was "a little short Man, of a black Complexion, and fat." They also said he was "a very ingenious Man, and an excellent Philosopher."

A scientist named Sir Edmund Whittaker noted in 1910 that Michell was the only important scientist at Cambridge after Isaac Newton died. However, Michell's work didn't get much attention from others at Cambridge. His discoveries were sometimes even given credit to other people.

In 1767, Michell became the rector (a type of priest) of St. Michael's Church in Thornhill, England. He stayed there for the rest of his life. Most of his important scientific work was done while he lived in Thornhill. He died there on April 21, 1793, when he was 68 years old. He is buried in Thornhill. A special blue plaque is now on the church wall to remember him.

Scientific Discoveries

Michell made many important scientific discoveries. He wrote about magnetism, earthquakes, and even predicted black holes.

Magnets and Light

In 1750, Michell wrote a book called "A Treatise of Artificial Magnets." In this book, he explained an easy way to make magnets that were better than natural ones. This method is still named after him. The book also had many accurate observations about magnetism. It clearly explained how magnets work.

Michell also tried to measure the pressure of light. He focused sunlight onto a compass needle. However, the experiment didn't work as planned because the needle melted!

Earthquakes and Geology

Michell is very important for his work on geology. His most important paper on geology was written after the big 1755 Lisbon earthquake. This paper was called "Conjectures concerning the Cause and Observations upon the Phaenomena of Earthquakes."

In this paper, he suggested that earthquakes spread out as waves through the Earth. He also said that earthquakes cause shifts in the Earth's layers, which we now call faults. He was able to guess where the Lisbon earthquake started and how deep it was. He might also have been the first to suggest that a tsunami is caused by an earthquake under the sea.

Michell's paper also helped people understand the Earth's crust better. He realized that the Earth is made of "regular and uniform strata" (layers of rock). Some of these layers have been broken by movements in the Earth. He showed amazing knowledge of the Earth's layers in England and other places. He was the first to describe the Mesozoic layers in the U.K.

Because of this important work, he was chosen to be a member of the Royal Society in 1760.

Gravity and the Earth's Mass

Michell's torsion balance, used in the Cavendish experiment

Michell designed a special tool called a torsion balance. This tool was meant to measure the mass of the Earth. However, he died before he could use it. His friend Henry Cavendish got the tool. In 1798, Cavendish used it to do an experiment now called the Cavendish Experiment.

Cavendish hung a six-foot rod horizontally with two 1-kilogram lead balls at its ends. He then placed two much larger lead balls next to the small ones. The gravity from the large balls pulled on the small ones, making the rod turn. By measuring how much the rod moved, Cavendish could figure out the force of gravity between the balls. From this, he could accurately estimate the gravitational constant and the mass and average density of the Earth. Cavendish always gave Michell full credit for inventing the torsion balance.

A gravity scientist named A. H. Cook said in 1987 that Michell's torsion balance was the most important step forward in gravity experiments. It has been used as the basis for almost all important gravity experiments ever since.

Double Stars

Michell was the first person to use statistics to study stars. In a paper from 1767, he showed that many more stars appear in pairs or groups than would happen by chance. He studied the Pleiades star cluster. He calculated that the chance of finding such a close group of stars by accident was about one in half a million.

He concluded that the stars in these pairs or groups were pulling on each other with gravity. This was the first proof that binary stars (two stars orbiting each other) and star clusters exist. His work on double stars might have influenced his friend William Herschel's research on the same topic.

Black Holes

In a paper read on November 27, 1783, Michell was the first to suggest the existence of black holes. He called them "dark stars." He believed in Newton's idea that light was made of tiny particles. He thought that if a star was very heavy, its gravity would slow down the light particles it sent out. He reasoned that a star's gravity could be so strong that light couldn't escape it at all.

Michell calculated that a star more than 500 times the size of the Sun would have this effect. Since light couldn't escape, the star would be invisible. He wrote:

If there should really exist in nature any bodies, whose density is not less than that of the sun, and whose diameters are more than 500 times the diameter of the sun, since their light could not arrive at us; or if there should exist any other bodies of a somewhat smaller size, which are not naturally luminous; of the existence of bodies under either of these circumstances, we could have no information from sight.

Michell suggested there might be many "dark stars" in the universe. Today, astronomers believe that black holes do exist at the centers of most galaxies. Michell also proposed that astronomers could find "dark stars" by looking for star systems that acted like two stars, but where only one star could be seen. This was an incredibly accurate prediction! Most of the black holes we've found in our galaxy are in binary systems where they orbit another visible star.

Michell's ideas about gravity and light interested William Herschel. Herschel tried to test them with his powerful telescopes. A few years after Michell, the French mathematician Pierre-Simon Laplace suggested a similar idea in his 1796 book.

Michell was so far ahead of his time with black holes that his idea "made little impression" on scientists then. He died quietly, and his idea of a "dark star" was forgotten. It wasn't until the 1970s that his writings were rediscovered.

Telescopes

Michell built telescopes for his own use. One of them was a large reflecting telescope with a 10-foot focal length. After Michell's death, the famous astronomer William Herschel bought this telescope. Michell and Herschel had many interests in common and wrote letters to each other. Herschel visited Michell in 1792 and saw his telescope, which was in need of repair. Herschel bought it the next year for £30.

Other Activities

Michell also wrote a paper about surveying, which is the process of measuring land. His biographer called it "elegant" in its theory.

He was elected a member of the Royal Society, a famous group of scientists. He first attended their meetings as a guest in 1751. His paper on earthquakes was read to the Society in 1760, and he was invited to join. He became a member on June 12, 1760.

Michell's letter to Cavendish in 1784, about gravity's effect on light, was rediscovered in the 1970s. It is now recognized for predicting several astronomical ideas that were thought to be 20th-century inventions. Michell is now credited as the first to study an object so massive that light cannot escape it. He also suggested using a prism to measure what is now called gravitational redshift. This is the weakening of starlight due to the gravity of the star. Michell knew that some of these ideas were not possible to test at the time. But he hoped they would be useful to future generations.

Personal Life

Michell was described as a man with "wide latitude in religious belief." He was also called "a little short man, of black complexion, and fat." People thought he was "a very ingenious Man, and an excellent Philosopher."

While living in Thornhill, he welcomed many famous visitors. These included Benjamin Franklin, Joseph Priestley, Jan Ingenhousz, and Henry Cavendish. Michell wrote to Franklin in 1767 about his first visit to Thornhill.

Priestley lived nearby for a while. He and Ingenhousz met for the first time at Michell's rectory. At the same meeting, John Smeaton met Benjamin Franklin. Together, they looked at a canal that Smeaton had just finished building. Michell also helped Smeaton improve his book about the Eddystone Lighthouse.

Michell married Sarah Williamson in 1764. She was "a young lady of considerable fortune" but sadly died only a year later in 1765. On February 13, 1773, he married Ann Brecknock. They had one child, a daughter named Mary.

Michell's younger brother, Gilbert, was a merchant. He later lived with John in Thornhill. The two brothers were involved in buying and selling many properties in the area.

More Information

John Michell is the subject of a book called Weighing the World: The Reverend John Michell of Thornhill (2012) by Russell McCormmach.

Selected Publications

• Observations on the Comet of January 1760 at Cambridge, Philosophical Transactions (1760)
• Conjectures Concerning the Cause and Observations upon the Phaenomena of Earthquakes, ibid. (1760)
• An Inquiry into the Probable Parallax and Magnitude of the Fixed Stars, ibid. (1767)

Images for kids

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  Michell's torsion balance, used in the Cavendish experiment

See also

In Spanish: John Michell para niños