James Prescott Joule (1818-1889)

James Prescott Joule

So, who was James Prescott Joule?

James Prescott Joule was born on 24th December 1818 in Salford, Lancashire, England. He came from a wealthy family who were involved in the brewing industry. As befitting his perceived status, along with his elder brother Benjamin, he was educated at home by private tutors. At the age of sixteen he was taught by the Manchester scientist John Dalton for around three years.

In 1837, James went to work in the family brewery. He had developed an interest in science and began to study electric motors. He was able to carry out his experiments in his laboratory housed in the cellar of his parents' home. Funding for his work came from the family fortune.

What did James Prescott Joule do?

Joule had the idea that he could use the electric motor to convert the family brewery from steam power to electric power. As a course of his experiments he decided that it would be too expensive to do this, as the work done by the motor did not come out very highly when the cost of the zinc used in the batteries that powered it was taken into consideration. It was still cheaper to produce the steam power by burning coal.

James Joule was very painstaking and paid great attention to detail. He spent a great deal of his life in determining the mechanical equivalent of heat, inspired from his belief that heat was derived from work.

In 1840, he established that the heat produced in a wire by an electrical current is proportional to the resistance of the wire multiplied by the square of the current, which is known as Joule's Law.

Still with the idea that it was possible to convert mechanical work directly into heat without any electrical steps, Joule experimented from 1842 to 1878 on such conversions. Around 1845, he was able to demonstrate in a paddle-wheel experiment, which involved the shaft and paddles being driven by a falling weight suspended from a pulley, that the same amount of work, however done, always produced the same amount of heat. This enabled Joule to conclude that heat was a form of energy. The mechanical equivalent of heat is a constant and is designated by the symbol J in honour of James Joule.

What else do we know about James Prescott Joule?

James Joule married Amelia Grimes in 1847 and whilst on honeymoon in the Alps continued his science experiments. He had always wanted to show that when water falls through 778 feet that it rises one degree Fahrenheit in temperature (FPS units were the ones Joule used). The opportunity came when he visited Chamonix and armed with a huge thermometer, he attempted this exploit. He was unsuccessful, as the water did not fall through that distance and also produced too much spray to allow his experiment to work.

Joule and his wife had three children, Benjamin Arthur (b.1849), Alice Amelia (b.1852) and a son who died in 1854 along with his wife. Joule did not remarry.

William Thompson (later to be Lord Kelvin) worked with Joule between 1852 and 1862 on experiments which led to the discovery known as the Joule-Kelvin cooling effect.

James Prescott Joule died on 11th October 1889 at Sale, Cheshire, England.