James Prescott Joule was born on December 24, 1818, in Salford, Lancashire, England.
His father, Benjamin Joule, and grandfather before him, were successful brewers and the business, in due course, descended to James and his elder brother, also named Benjamin. They carried on with the family brewing business untill they sold it in 1854.
James was the second of 5 children, Benjamin, the eldest, James, and John and two daughters Alice and Mary.
Young Joule was a delicate child and was not sent to school. His early education was commenced by his mother's half sister, and was carried on at his father's house, Broomhill in Pendlebury, by tutors until 1834 when he was sent, with his elder brother, to study with John Dalton at the Manchester Literary and Philosophical Society.
The pair only received two years' education in arithmetic and geometry when Dalton was forced to retire owing to a stroke. However, Dalton's influence made a lasting impression on the young Joule. It appears that Joule was fascinated by electricity. He and his brother experimented by giving electric shocks to each other and to the family's servants.
At fifteen, while still being tutored, he commenced working in the brewery, which, as his father's health declined, fell entirely into the hands of his brother Benjamin and himself. Science was a hobby but he soon started to investigate the feasibility of replacing the brewery's steam engines with the newly-invented electric motor.
Joules' first investigations were in the field of magnetism. In 1838, at the age of nineteen, he constructed an electro-magnetic engine, which he described in Sturgeon's "Annals of Electricity" for January of that year. In the same year, and in the three years following, he constructed other electro-magnetic machines and electro-magnets of novel forms; and experimenting with the new apparatus, he obtained results of great importance in the theory of electro-magnetism. In 1840 he discovered and determined the value of the limit to the magnetization communicable to soft iron by the electric current; showing for the case of an electro-magnet supporting weight, that when the exciting current is made stronger and stronger, the sustaining power tends to a certain definite limit, which, according to his estimate, amounts to about 140 lb (about 63.5 kg) per square inch of either of the attracting surfaces. He investigated the relative values of solid iron cores for the electro-magnetic machine, as compared with bundles of iron wire; and, applying the principles which he had discovered, he proceeded to the construction of electro-magnets of much greater lifting power than any previously made, while he studied also the methods of modifying the distribution of the force in the magnetic field. He also became interested in measuring the work done and the heat generated by electricity and, again in 1840, he discovered that the rate of generation of heat by an electric circuit was proportional to the square of the current multiplied by the resistance. This led him, by 1847, to measure the heat produced through the action of falling weights, his famous "paddle wheel" experiment. His conclusion was that all systems contain energy which can be converted from one form to another but the total energy of a closed system remains constant. Although his lack of advanced mathematical training compelled him to leave the development of the new science of energetics to Kelvin, Clausius, Rankine, Hirn and Gibbs, Joules' skilful and accurate experimental work was primarily responsible for the general acceptance of the subject.
His contribution to the theory of the velocity of sound in air was likewise of great importance, and is distinguished alike for the acuteness of his explanations of the existing causes of error in the work of previous experimenters, and for the accuracy, so far as was required for the purpose in hand, of his own experiments. His determination of the specific heat of air, pressure constant, and the specific heat of air, volume constant, furnished the data necessary for making Laplace's theoretical velocity agree with the velocity of sound experimentally determined. On the other hand, he was able to account for most puzzling discrepancies, which appeared in attempted direct determinations of the differences between the two specific heats by careful experimenters. He pointed out that in experiments in which air was allowed to rush violently or "explode" into a vacuum, there was a source of loss of energy that no one had taken account of, namely, in the sound produced by the explosion. Hence in the most careful experiments, where the vacuum was made as perfect as possible, and the explosion correspondingly the more violent, the results were actually the worst. With his explanations, the theory of the subject was rendered quite complete.
In 1847 Joule married Amelia Grimes, daughter of the Liverpool Comptroller of Customs. Joule spent much of his honeymoon in the Alps studying a waterfall. He found the temperature of the water at the base of the waterfall higher than the temperature of the water at the top. This proved that the energy of the falling water was being converted into heat. This was a major step in proving the theory of energy conservation. Taking time out of his own honeymoon to conduct an experiment shows his dedication to his hobby: physics. Joule had a son, Benjamin Arthur, in 1849 and a daughter, Alice Amelia, in 1852. Joules' wife and a second son died in 1854 and he remained a widower for the rest of his life.
As is characteristic of many researchers, Joules' accomplishments were not limited to those things we today associate with the word "research." Much of what comes from experimental investigations results in practical devices and new technologies. In this respect one can note that James Joule was also an inventor.
Amongst many of his inventions are "arc" or electrical welding, and the displacement pump.
Much of his research was funded by himself, and the funds finally ran out in 1875and the following years were ones of continuous illness.
Joule died as a result of a form of degeneration of the brain on October 11 1889 at home in Sale and is buried in Brooklands cemetery there. The gravestone is inscribed with the number "772.55", his climacteric 1878 measurement of the mechanical equivalent of heat. h2>Honours and tributes: