Lord Kelvin

Mathematical Physicist

• Born: June 26, 1824
• Birthplace: Belfast, Ireland (now in Northern Ireland)
• Died: December 17, 1907
• Place of death: Netherhall, Ayrshire, Scotland

Irish Scottish physicist

Lord Kelvin, born William Thomson, devoted himself to the study of thermodynamics. He devised an absolute temperature scale that measured temperature according to a general standard and went down to absolute zero. He is sometimes credited with the formulation of the second law of thermodynamics.

Also known as: William Thomson

Primary field: Physics

Specialty: Thermodynamics

Early Life

William Thomson was born on June 26, 1824, in Belfast, Ireland. He was the son of mathematics professor James Thomson, who assumed sole responsibility for raising Thomson and his siblings after their mother, Margaret, died in 1830. Shortly following her death, the family relocated to Glasgow, Scotland.

When he was ten years old, Thomson enrolled in the University of Glasgow, which provided elementary education for gifted children. By the age of fourteen, he was taking university-level courses in astronomy and chemistry. At fifteen, after studying natural philosophy (an early form of physics), he wrote an essay on the figure of the Earth, a geodetic concept, which earned him a gold medal in astronomy from the university.

In 1841, Thomson transferred to St. Peter’s College, Cambridge, where he developed an interest in thermodynamics, or the science of heat. The consensus among physicists of the period was that heat took the form of a weightless fluid called caloric, which flowed from hotter to colder objects. The laws of thermodynamics had yet to be formulated, although caloric was believed to be governed by the law of conservation of matter, the precursor to the first law of thermodynamics, which states that matter can change form but cannot be created or destroyed.

Thomson graduated from Cambridge in 1845. Later, during a brief stay in Paris, he read about the Carnot engine, a hypothetical heat engine designed by Nicolas Léonard Sadi Carnot in 1824 that consisted of a cold area and a hot area. According to the design, heat (caloric) could be transferred from the hot area to the cold area unchanged in quantity and turned into mechanical work. Some of that mechanical work would then move the heat from the cold area back to the hot area, reversing the engine and starting the process over. Although the Carnot engine could never be realized due to inherent design flaws, Thomson found the logic behind it sound.

Upon returning to Scotland, Thomson was elected chair of natural philosophy at the University of Glasgow. In 1847, at a meeting of the British Association for the Advancement of Science, Thomson heard controversial British physicist James Prescott Joule speak on the nature of heat. Joule’s unconventional theory that heat is not a fluid and can actually be created by mechanical work such as the lifting of a weight sparked his curiosity. Thomson, however, subscribed to the Carnot school of thought, believing that mechanical work transferred heat but did not create it. Many years would pass before Thomson reconciled his beliefs with those of Joule.

Life’s Work

In the course of his work in thermodynamics, Thomson became dissatisfied with contemporary methods of thermometry. Gas-filled thermometers were the norm, and they measured temperature by means of the ideal gas law, which defines the relationship between the pressure, volume, and temperature of a gas. In a gas thermometer that is kept under constant pressure, the volume of the gas will increase or decrease in proportion to its temperature. The problem with gas thermometers, Thomson found, is that different gases exhibit different amounts of expansion when subjected to the same temperature. Thomson wanted to create an objectively defined absolute temperature scale that could quantitatively define temperature according to a uniform physical standard.

In 1848, Thomson reflected upon such a temperature scale in an article he wrote about the Carnot engine. Basing his scale on Carnot’s theory that the maximum work the engine could produce from a specific amount of heat depended only on the high and low temperatures within the engine, he stated that the amount of work produced would be the same no matter what the high and low temperatures were, as long as there was a one-degree interval between them. Thus, each degree in his temperature scale had the same value. Thomson had to revise his scale when he learned that temperature variation within the Carnot engine affected its efficiency. He presented his revised scale (the old scale was a logarithm of the new one) in his work “On the Dynamical Theory of Heat” (1851). The revised scale was more practical to use than the original, as it corresponded to the temperature scale of gas thermometers.

One striking feature of Thomson’s revised temperature scale was the presence of absolute zero. His first temperature scale descended to minus infinity because an equal amount of work was produced at each degree, regardless of how low. Thomson explained the concept of absolute zero in his revised scale in the essay “On a Universal Tendency in Nature to the Dissipation of Mechanical Energy” (1852). Based on his knowledge that having a cold reservoir of zero degrees would enable a Carnot engine to run at 100 percent efficiency, he claimed that any temperature lower than zero would be impractical.

In the papers he wrote between 1848 and 1852, Thomson proposed new ideas about the nature of heat and its transition between objects. He stated that heat transferred from a hot to a cold object without producing work is not destroyed but wasted, and that when converting heat to work, the sum of both quantities remains equal. This is the first law of thermodynamics, which had been formulated independently by other scientists. Thomson went on to state that the extent to which energy, or heat, is wasted remains the same in a reversible system such as Carnot’s heat engine. In an irreversible system, however, entropy continues to rise. This concept became known as the second law of thermodynamics.

Thomson had reconciled Carnot’s and Joule’s theories on heat by deciding that heat was a form of motion, not a fluid, and, although dynamic, still behaved like caloric in a Carnot engine. Thomson and Joule established a friendship, collaborating with each other on an experiment in 1852 that led to the discovery of the Joule-Thomson effect: the temperature of a gas in a vacuum declines as the gas expands.

Soon after his marriage to Margaret Crum in 1852, Thomson turned his attention to electricity and magnetism. He improved the functionality of the Atlantic Telegraph Company’s transatlantic telegraph cable by determining that the signal the cable carried would travel faster with lower voltage and a larger conductor. Due to his scientific expertise, Thomson was appointed to the board of the Atlantic Telegraph Company in 1856. Over the course of a decade, he made many botched cable-laying trips across the ocean. His team finally laid a working cable in 1866, thanks in large part to his input and his invention of the mirror galvanometer, a device used to detect extremely subtle electric currents. He was knighted in November 1866 for his contributions to the transatlantic telegraph.

Patenting inventions (mainly instruments used to measure electricity), consulting, and lecturing earned Thomson both notoriety and a fortune. His wife died in 1870; in 1874, he married Frances Anna Blandy, whom he had met the previous year. They spent much of their time sailing, inspiring Thomson to invent an adjustable compass that compensates for magnetic deviation caused by the presence of iron ships.

In 1892, Queen Victoria granted Thomson the title of Baron Kelvin of Largs, Kelvin being the river near Glasgow University and Largs the township in Scotland in which he lived. Known as Lord Kelvin, Thomson became a sought-after engineer and helped design the Niagara Falls power plant in 1893. He remained professor of natural philosophy at the University of Glasgow until 1899. Thomson continued to write and consult almost until his death on December 17, 1907, at Netherhall, his residence in Largs.

Impact

Over the course of his life, Thomson wrote more than six hundred papers, patented countless inventions, and was elected to numerous societies, including the Royal Society and the Royal Swedish Academy of Sciences. He presided over the British Association for the Advancement of Science in 1871 and the Royal Society from 1890 to 1895. In addition to attaining knighthood and the title of baron, Thomson received honors such as the Royal Society’s Copley Medal and the American Association of Engineering Societies’ John Fritz Medal.

Thomson had a significant influence on science and technology during his lifetime, particularly in the areas of telegraphy and thermodynamics. While improvements in technology over time led some of his work, such as that related to the transatlantic telegraph cable, to become obsolete, his publications and research on thermodynamics continued to have a significant impact. Many years after his death, his absolute temperature scale was renamed the Kelvin scale in his honor. It was found to be accurate even after heat was discovered to be the product of the motion of atoms, and it came to be widely used in a variety of scientific fields, including chemistry and astronomy.

Bibliography

Chang, Hasok. Inventing Temperature: Measurement and Scientific Progress. New York: Oxford UP, 2007. Print. Provides a history of the measurement of temperature, discussing the development of Thomson’s concept of absolute temperature.

Lindley, David. Degrees Kelvin: A Tale of Genius, Invention, and Tragedy. Washington, DC: Henry, 2005. Print. Chronicles Thomson’s life and career, focusing in particular on his work in thermodynamics and his role in the establishment of the transatlantic telegraph cable.

Smith, Crosbie, and M. Norton Wise. Energy and Empire: A Biographical Study of Lord Kelvin. Cambridge: Cambridge UP, 1989. Print. Discusses Thomson’s life and work and provides historical and social context for his discoveries.