The Great Experimenter

James Prescott Joule was born at Salford, near Manchester, England, on December 24, 1818. He was the second of five children born to a wealthy brewery owner. As a child, James was weak and shy, and suffered from a spinal disorder. Because of these limitations, he preferred studies to physical activity. Although his spinal problem later improved, it affected him throughout his life.

James was educated at home until he was 15. He then went to work in the family brewery. However, he and his older brother continued their education part-time with private tutors in Manchester.

From 1834 until 1837, they were taught chemistry, physics, the scientific method, and mathematics by the famous English chemist John Dalton. (Like James Joule, Dalton was a Bible-believing Christian.) James gratefully acknowledged the key role that Dalton played in his becoming a scientist. “It was from his instruction that I first formed a desire to increase my knowledge by original researches, ” Joule said.

When their father became ill, James and his brother took over running the brewery. James therefore did not have the opportunity to attend university. However, his great desire was to continue to study science, so he set up a laboratory in his home and began experimenting before and after work each day. James saw this desire to study science as a natural consequence of his Christian faith. As he later wrote, “it is evident that an acquaintance with natural laws means no less than an acquaintance with the mind of God therein expressed.”

In 1839, Joule began a series of experiments involving mechanical work, electricity and heat. In 1840, he sent a paper entitled “On the Production of Heat by Voltaic Electricity” to the Royal Society in London—probably the most prestigious association of British scientists.

In this paper, he showed that the amount of heat produced per second in a wire carrying an electric current equals the current (I) squared multiplied by the resistance (R) of the wire. The heat produced is the electric power lost (P). (That is, P=I²R.) This relationship is known as Joule’s Law. The Royal Society showed little enthusiasm for Joule’s paper, and published only a brief summary of his findings.

In 1843, Joule calculated the amount of mechanical work needed to produce an equivalent amount of heat. This quantity was called “the mechanical equivalent of heat.” Again he presented a paper on his findings—this time to the British Association for the Advancement of Science. Again the response was unenthusiastic. Several leading journals also declined to publish papers on Joule’s work.

Many British scientists were hesitant to accept his work, but Joule patiently persisted. New ideas often take time to gain acceptance, especially if they are put forward by an amateur in that field. Joule’s findings challenged the caloric theory of heat which most physicists believed in at that time. In the caloric theory, heat was believed to be a fluid substance.

Another stumbling block to the acceptance of Joule’s findings was a disbelief of the incredible accuracy of his measurements. But Joule was patient and ingenious in his experiments. These attributes greatly assisted him in avoiding errors and in obtaining results far more accurate than those of previous experimenters.

Joule’s work on the relationship of heat, electricity and mechanical work was largely ignored until 1847. His work then came to the attention of William Thomson. (Thomson, who was later known as Lord Kelvin, was another famous scientist who was a committed Christian.)

Although only 23 years old at the time, Thomson was already Professor of Physics at the University of Glasgow. Thomson recognized that Joule’s work fitted in with the unifying pattern that was beginning to emerge in physics and he enthusiastically endorsed Joule’s work. (In fact, Joule’s work made a significant contribution to the process of unifying the fragmented sections of physics.)

Other enthusiastic supporters of Joule’s work were Michael Faraday and George Stokes. Both were famous scientists who were committed Christians. This endorsement by a few eminent supporters opened doors which previously had been closed to Joule. The Royal Society was now prepared to give him another hearing. In 1849, Joule read his paper entitled “On the Mechanical Equivalent of Heat” to the Royal Society, with Faraday as his sponsor. In the following year, the Royal Society published Joule’s paper and he was elected a member of its prestigious ranks.

The principle of energy conservation involved in Joule’s work gave rise to the new scientific discipline known as thermodynamics. While Joule was not the first scientist to suggest this principle, he was the first to demonstrate its validity. Although Thomson and a number of other scientists later made significant contributions to thermodynamics, Joule is correctly recognized as the chief founder of thermodynamics. He showed that “work can be converted into heat with a fixed ratio of one to the other, and that heat can be converted into work.”

Joule’s principle of energy conservation formed the basis of the first law of thermodynamics. This law states that energy can neither be created nor destroyed, but it can be changed from one form into another.

In a landmark paper published in 1848, Joule became the first scientist to estimate the velocity (speed) of gas molecules. This early work on the kinetic theory of gases was later extended by others, especially outstanding Scottish mathematical physicist James Clerk Maxwell.

Joule was one of the first scientists to recognize the need for standard units of electricity, and he strongly advocated their establishment. This standardization was later done by the British Association for the Advancement of Science under the direction of Maxwell. Joule became president of the British Association in 1872 and 1887.

In recognition of Joule’s contribution in relating heat and mechanical motion, the unit of energy (or work) in physics was later named the “Joule.”

In 1852, Joule began working in cooperation with Thomson. The two scientists complemented each other perfectly—Joule, the accurate and resourceful experimenter with only limited training in mathematics, and Thomson, the mathematically talented physicist concerned with extending the theory underlying physics.

Tragically, Joule’s wife died in 1854 after only six years of marriage, leaving him with their young children. Shortly afterwards, Joule’s family sold the brewery. Joule then led a relatively secluded life. He was now able to devote himself more fully to his scientific work.

For the next eight years, Joule worked with Thomson on a number of important experiments to confirm some of the predictions being made in the new discipline of thermodynamics. The most famous of these experiments involved the decrease in temperature associated with the expansion of a gas without the performance of external work. This cooling of gases as they expand is known as the “Joule—Thomson effect.” This principle provided the basis for the development of the refrigeration industry.

During his association with Thomson, Joule humbly took on the practical role of experimentally investigating theoretical issues raised by Thomson. This was the less prestigious role in the fruitful partnership, but Joule was more concerned with achieving worthwhile results than with gaining recognition.

Joule displayed an amazing clarity in conceiving, executing, describing and explaining his experiments. Unlike many scientists, it was rare for Joule to follow blind alleys or make incorrect observations. In most cases, his original notes were almost clear enough for publication without subsequent revision. This demonstrated his extraordinary clarity of mind.

From 1872 onwards, Joule’s health deteriorated and he did little further work. He died at Sale, Cheshire, England, on October 11, 1889.

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1. Who is James Prescott Joule?

2. What is “the mechanical equivalent of heat”?

3. What were the stumbling blocks to the acceptance of Joule’s findings?

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5. What is Joule—Thomson effect?