James Prescott Joule (1818–89) is now rightly revered as one of the greatest scientists in the history of physics, due to his groundbreaking work in thermodynamics. However, this was not always the case—in his younger years, Joule struggled to be taken seriously by the scientific establishment.
Who was James Joule?
Born in Salford in 1818, James Prescott Joule was the son of a renowned local brewer and grew up fascinated by all things scientific. He became particularly interested in electricity and was fortunate enough to be tutored by John Dalton, one of the leading chemists of the day and a pioneer of atomic theory.
This expert tutelage, combined with Joule's personal obsession and some brewing know-how (as well as access to some specialised beer-making equipment) would ultimately lead to one of the most ground-breaking (and at the time, controversial) discoveries in the history of science: that heat is a form of energy.
Joule's First Law
In 1837 Joule followed in his father's footsteps and became the manager of the family brewery; however, his fascination with and passion for science and experimentation continued in parallel with his day job. He continued carrying out experiments at home with the intention of finding out if it would be more efficient to power the brewery using an electric battery than the steam power that was traditionally used.
In 1841 he discovered what became known as Joule's First Law. This defined the relationship between the amount of heat produced and the current flowing through a conductor.
Resistance from the establishment
At this time, things seemed to be going well for Joule; he was still an amateur scientist but had been accepted as a member of the London Electrical Society. However, following the acceptance of Joule's First Law, he decided to look into the wider question of how much work can be extracted from a given source and soon found that the scientific establishment was strongly opposed to his ideas.
Joule's experiments showed that heat could be generated by an electric current; however, this went against the prevailing theory of the time, known as the caloric theory.
In 1843 Joule presented his results to a meeting of the British Association for the Advancement of Science, in Cambridge, but contemporary anecdotes claim that he was met by a stony silence.
Undeterred, he continued his experiments. In 1844, believing he had compelling evidence, he submitted his paper to the most prestigious scientific group of all, the Royal Society… who refused to publish his work.
Why were people slow to believe in him?
The accepted theory of the time, caloric theory, considered heat to be a material—a type of fluid that flowed from warmer to cooler bodies—while Joule's ideas posited that heat was a form of molecular motion and that it would continue without dying out.
However, the very existence of atoms and molecules was not widely accepted until much later in the century. The atomic theory pioneered by John Dalton may seem inarguable to us now, but at the time that it was first suggested it was deeply controversial.
Joule's theory was a huge step for the scientists of the day to take; simply too huge for many of them.
(It was later found that Joule's rejection of caloric theory went too far, and later scientific theories, including those put forward by Lord Kelvin, sought to find ways to unify the two seemingly contradictory theories).
Another reason many of Joule's contemporaries were quick to reject his theories was because they simply didn't believe that he could carry out his experiments with the level of accuracy that he claimed. Joule said he could measure temperatures to within 1/200 of a degree Fahrenheit, something that was simply unthinkable with the majority of scientific equipment available at the time.
However, Joule had two secret weapons. One was his background as a brewer, which meant he had ways to measure much more precisely, as the finely tuned measurement of temperatures is critical to the brewing process. The other was John Benjamin Dancer, an exceptionally talented instrument-maker who created custom equipment for him (featured in more detail below).
Joule in the Science Museum Group collection
Some of Joule's belongings are currently on display in our exhibition Electricity: The spark of life, while others are held in the wider Science Museum Group collection:
Friends in high places
In 1845 Joule successfully published his paper in a less prestigious publication, the Philosophical Magazine. He also presented his most famous paper, On The Mechanical Equivalent of Heat, to the British Association in Cambridge. Despite the establishment's indifference to his ideas, it was enough to bring him to the attention of scientists including Michael Faraday and William Thompson—later Lord Kelvin—and Joule's fortunes began to turn.
Revenge is sweet
In 1847 Joule once again presented his ideas, this time to the British Association at Oxford, which was attended by both Faraday and Kelvin. Eventually his ideas would become the cornerstone of one of the most fundamental scientific laws ever discovered, the First Law of Thermodynamics.
Joule's revenge was indeed sweet: in 1850, he was made a fellow of the Royal Society, in 1852 he was awarded the Royal Medal, and in 1872 he was named President of the British Association for the Advancement of Science, the same group that had rejected his ideas back in 1843.