James Prescott Joule Biography

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World of Scientific Discovery on James Prescott Joule

James Joule was perhaps the greatest amateur scientist of all time. He was the proprietor of a successful brewery who never held an academic post--in fact, he never completed an undergraduate degree. Today he is recognized as an important contributor to the field of thermodynamics.

Joule was born in Manchester, England, in 1818. He was a sickly child who suffered from a chronic spinal injury. His father, a wealthy brewer, was eager to please his young son; he provided as many books as the child could read and eventually built for him a home laboratory. Joule was entirely self-educated, taking from his books only the information that interested him. He quickly gained a working knowledge of physics and chemistry. At the age of seventeen he briefly attended Manchester University but left shortly thereafter to pursue his own studies.

During his early years, Joule had developed a passion for measurement, and as he became an adult that passion turned to fanaticism. It is often told that he spent the bulk of his honeymoon comparing the temperature of water at the top of a nearby waterfall to its temperature at the bottom. (The purpose of this experiment--the transformation of kinetic energy into heat energy--would not be fully appreciated for several years.) Joule's scientific was slowed in 1833 when his father's illness forced him to take greater control of the family brewery; even so, within seven years he made his first important scientific discovery.

It was well known at that time that a wire would heat up when an electrical current was passed through it. However, no scientist had determined the principles that governed this process. In 1840, Joule announced that the heat produced was proportional to the square of the current's intensity as multiplied by the circuit's resistance. This formula has come to be known as Joule's Law.

At this time, Joule had become fascinated by heat and set out to measure the heat produced by every process he could construct in the laboratory. Using paddles, he churned water and measured its temperature increase. He forced water through small holes and measured the heat caused by friction. In his most famous experiment he used a falling weight to drive a paddle that would stir water; by measuring the distance the weight dropped, Joule could calculate the precise amount of work that went into raising the temperature of water.

It was this experiment upon which he based his calculation for the mechanical equivalent of heat. Joule determined that 41,800,000 ergs of work were required to increase the temperature of 1 gram of water by 1 degree celsius (this amount of heat is called a calorie). This was a landmark discovery, since no other scientist had achieved so accurate a measurement.

He set out to publish his findings in 1847. Unfortunately, no science journal would accept Joule's essay, principally due to the fact that Joule was a brewer and a wealthy eccentric, not a scientist. He ultimately introduced his research at a very small public lecture in Manchester, afterward begging a local paper to reproduce it. Several months later he was allowed to speak before a crowd of doubtful academicians, all but one of whom took little or no interest. The only one to recognize the importance of Joule's work was a young scholar named William Thomson, who would go on to become the preeminent physicist Lord Kelvin. Even at twenty-three, Thomson's opinion was held in high regard by his peers, and with his support Joule's research was quickly accepted.

Though Joule was not the first to come up with a figure for the mechanical equivalent of heat, his was considered the most precise. In his honor the principle unit of work was named the joule, equal to 10,000,000 ergs (so that 4.18 joules is equal to one calorie, as per his findings).

The determination of the mechanical equivalent of heat was an important step in the eventual development of the concept of conservation of energy. For example, researchers could compare the amount of potential energy in a weight held aloft to the amount of kinetic energy as that weight falls to the ground. In previous experiments, a small amount of energy was lost during the experiment, probably to friction. After the announcement of Joule's number, a researcher could calculate precisely the amount of work that was converted into heat, and it was realized that the amount of potential energy always equaled the amount of kinetic: energy was, indeed, conserved. However, the final proof of this would be provided by the German physicist Hermann von Helmholtz.

Joule was at least partially responsible for two other important discoveries. Along with his new friend Thomson he showed that a gas, when allowed to expand, would drop in temperature--sometimes significantly. They conducted a number of experiments with low temperatures, succeeding in the liquefaction of certain gases. This discovery is known as the Joule-Thomson effect, and it forms the basis of the modern science of cryogenics. Using techniques based upon Joule and Thomson's work, scientists can now liquefy hydrogen, helium, and other gases.

In 1846, Joule also discovered that an iron bar, when magnetized, would change in length. He called this phenomenon magnetostriction, and it has since been used in connection with the formation of ultrasonic sound waves.

Joule was elected to the prestigious British Royal Society in 1850 and received its highest honor, the Copley medal, in 1866. He also served as president of the British Association for the Advancement of Science. He remained a brewer all his life, however, and when his business failed in 1878 he was given a pension by Queen Victoria.