John Pratt (archdeacon of Calcutta) facts for kids
John Henry Pratt (born June 4, 1809 – died December 28, 1871) was a British church leader, astronomer, and mathematician. He joined the British East India Company in 1838 as a chaplain, which is like a priest who serves in a special organization. He later became the Archdeacon of Calcutta, a high-ranking church position. Pratt was a very talented mathematician who studied problems about the Earth's shape and gravity. He was asked by the Surveyor General of India to look into errors in land surveys. These errors were caused by the pull of gravity from the huge Himalayas mountains on survey tools. This led Pratt to create an important idea about how the Earth's crust balances itself, which is now known as isostasy. He sadly died in India from cholera during a visit to Ghazipur.
Contents
Who Was John Henry Pratt?
Early Life and Education
John Henry Pratt was born in London, England, and was baptized on June 30, 1809. He went to Oakham School and later studied at Caius College, Cambridge. He was a student of William Hopkins, a famous mathematician. In 1833, Pratt graduated as the third-best math student in his class, a title called a "wrangler." He stayed at Cambridge for a while, teaching students privately. One of his students later became a bishop. While at Cambridge, Pratt wrote a book called Mathematical Principles of Mechanical Philosophy (1836). This book explained how math could be used to understand gravity and physics.
Life and Work in India
In 1838, Pratt became a chaplain for the East India Company, a powerful British trading company that governed parts of India. He became a close assistant to Bishop Daniel Wilson. In 1850, Pratt was made Archdeacon of Calcutta. His work in India gave him time to continue his math studies. He often shared his ideas with scientific groups in Britain.
When Bishop Wilson died in 1858, Pratt was considered for the role of Bishop. However, after a major uprising in India in 1857, it was decided that someone known for missionary work should not be appointed. Instead, George Cotton became the new Bishop. Pratt and Bishop Cotton respected each other greatly.
Pratt was supposed to retire in 1867, but Bishop Cotton asked for him to stay longer. Pratt continued his service until 1869. After Bishop Cotton died in 1866, Pratt helped set up a fund to support Bishop Cotton's idea of creating schools in the cooler hill areas of India. These schools were for children of poorer English families living in India who couldn't afford to send their children to England for education.
In 1854, Pratt married Hannah Maria Brown in Bhagalpur, India. He became a Fellow of the Royal Society in 1866, which is a very respected group of scientists. Pratt also served as president of the Calcutta Society for Prevention of Cruelty to Animals. He died from cholera in Ghazipur, India, on December 28, 1871. A memorial was built for him in St. Paul's Cathedral in Calcutta.
Understanding Earth's Gravity
Pratt wrote another important book called On Attractions, Laplace's Functions and the Figure of the Earth (1860). This book explored whether the Earth got its current shape from once being a fluid. It used Newton's law of universal gravitation to calculate the force of gravity from different shapes, from a perfect sphere to the irregular shape of the Earth.
The Mystery of the Himalayas
While traveling to India in 1838, Pratt even did experiments to study ocean currents and temperatures. In India, he was asked by Andrew Scott Waugh, the Surveyor General, to solve a puzzle. Surveyors were finding errors in their measurements near the Himalayas. These errors were caused by the mountains' gravity pulling on their survey tools, which use a weighted string called a "plumb-line" to find true vertical.
Pratt calculated how much the plumb-line should be pulled by the Himalayas. He used an estimate of the mountains' density (how much matter is packed into them). But the actual pull observed was much less than he expected!
Pratt's Idea of Isostasy
To explain this, Pratt suggested a new idea: the mountains themselves were less dense than the land beneath them. He thought that under mountains, the Earth's material was lighter, balancing out the huge mass of the mountains above ground. This idea became known as isostasy, which means a state of balance in the Earth's crust.
Another scientist, George Biddell Airy, had a similar but different idea. Airy thought that mountains had deep "roots" that went far into the Earth, like a block of wood floating in water. The higher the wood sticks out, the deeper its root goes. Pratt disagreed with Airy's idea because it suggested the Earth's crust was much thinner than other scientists believed.
Pratt also used his knowledge of physics and math to help engineers in India. He studied how arches work, the physics of large water movements like floods, and even calculated the iron needed for cantilever bridges.
Other Scientific Interests
Pratt was very interested in ancient Indian astronomy. He supported the translation of an important Indian astronomy text called the Siddhānta Shiromani. He also looked into how an earlier scholar, Henry Thomas Colebrooke, had estimated the age of the Vedas (ancient Indian texts) using astronomical clues. Pratt found some errors and suggested different dates. However, Pratt felt that both Indian and Arab astronomy had not developed a strong mathematical or physical framework, and their main achievement was limited to predicting eclipses, which he still found imprecise.
In 1856, Pratt published a book called Scripture and Science not at Variance (meaning "not in conflict"). He wrote this book to show that science and the Bible could agree, especially against ideas that seemed to conflict with religious beliefs, like the early theories of Evolution.
His Legacy
A school for girls, the Pratt School for Girls, was founded in his memory in Calcutta in 1876. It is now known as the Pratt Memorial School and is located in Kolkata, India.
