John Perry (engineer) facts for kids

John Perry (born February 14, 1850 – died August 4, 1920) was an amazing engineer and mathematician from Ireland. He helped create new ideas and inventions that changed how we understand the world.

Early Life and Career

John Perry was born in a place called Garvagh in County Londonderry. He was the second son in his family. His brother, James, also became an engineer. James helped start an electric light company. John's niece, Alice, was one of the first women in the world to earn an engineering degree!

John Perry worked with some very famous scientists. He was an assistant to Lord Kelvin at the University of Glasgow. Later, he became a professor of mechanical engineering at Finsbury Technical College. He also taught in Japan at the Imperial College of Engineering from 1875 to 1879. He was a professor of mathematics in London too.

Perry was a very respected scientist. He became a Fellow of the Royal Society, which is a big honor for scientists. He also led important groups like the Institution of Electrical Engineers and the Physical Society of London.

Spinning Tops and Gyro-Compasses

John Perry really admired his old boss, Lord Kelvin. He even wrote a special thank you to Kelvin in his book about spinning tops. This book, Spinning Tops and Gyroscopic Motions, was about how spinning objects behave.

Perry also worked on developing practical gyrocompasses. These are special compasses that use spinning wheels (gyroscopes) to always point north, even on a moving ship. He worked with Sidney Brown on this. Together, they even got a patent for their "Gyro-compass" in 1919!

In 1901, the University of Glasgow gave John Perry an honorary degree. This was to recognize all his important work.

Challenging Old Ideas

John Perry was not afraid to question big ideas, even those from famous scientists like Lord Kelvin.

Earth's Age: A Big Debate

In 1895, Perry disagreed with Lord Kelvin about how old the Earth was. Kelvin thought the Earth was only 20 to 400 million years old. He based this on how fast he thought heat escaped from the Earth's core.

Perry believed that the inside of the Earth was more like a fluid, or partly melted. He argued that if the Earth's core was fluid, heat would move through it much faster than Kelvin thought. This would mean the Earth could be much, much older. Perry said that "much internal fluidity would practically mean infinite conductivity for our purpose."

Kelvin didn't agree. He thought that if the Earth's inside was fluid, we would see more changes in its shape from tides. But Perry argued that even solid rock can change shape over a very long time. He compared it to how passages in a mine slowly close up. He said, "10⁹ years is a long time, and the forces are great."

How Perry's Ideas Were Proven Right

At first, many scientists didn't accept Perry's idea of a fluid Earth. But later, new discoveries proved him right! In 1903, scientists found out that radioactive decay inside the Earth releases heat. A few years later, they developed radiometric dating, which is a way to find the true age of rocks. These discoveries showed that the age of Earth was indeed much, much older, just as Perry had argued.

Perry's ideas about the Earth's fluid interior were very important for geology. They helped scientists understand things like continental drift, which is how continents move slowly across the Earth's surface. Even though it took a while, John Perry's brave challenge to a famous scientist eventually helped us understand our planet better.