William Thomson (1824-1907) was an Irish mathematician, physicist and engineer. He did seminal work on thermodynamics and mathematical analysis of electricity. He developed what is now known as the Kelvin scale (named after him, when he was made the Baron Kelvin) of absolute temperature measurement.
Thomson’s greatest work was in heat. Apparently, he was set into motion by Joules demonstration of the mutual convertibility of heat and mechanical work and their mechanical equivalence. Thomson was intrigued and set out to see if there were theoretical explanations of Joules experimental conclusions.
Building on the work of Carnot-Clapeyron, Thomson predicted that the melting point of ice must fall with pressure otherwise its expansion could be exploited in perpetual motion.
Further work on gas thermometer provided Thomson with insights that led to his proposition that:
“absolute temperature scale in which a unit of heat descending from a body A at the temperature T of the scale, to a body B at the temperature (T-1), would give out the same mechanical effect (work), whatever be the number T. Such a scale would be quite independent of the physical properties of any specific substance.”
These analyses led Thomson to the second law of thermodynamics, that seeming lost heat was apparent but not real (lost to man but is in a different form of energy, is elsewhere).
Later Thompson speculated on how the universe would die, as he sees it, from lost heat:
“I believe that no physical action can ever restore the heat emitted from the sun, and that this source is not inexhaustible; also that although the motions of the earth and other planets are losing vis viva which is converted into heat; and that although some vis viva may be restored for instance to the earth by heat received from the sun, or by other means, that the loss cannot be precisely compensated and I think it probable that it is under compensated.”
His speculations on how the universe would end aside, Thomson showed that heat is a form of energy and that it is convertible to other forms of energy (such as mechanical, electrical etc).
Thompson, working with Tait, published books that unified the various branches of physics (heat, mechanics, sound, light, electricity) into energy.
Thomson’s greatest contribution to science is the demonstration that energy changes form, and in some forms are called heat, in others light etc.
His work shade light on the measurement of temperature (heat).
Thomson, in a paper titled “Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light” pointed out that there were unsatisfactory explanations in physics, viz, the Michelson-Morley experiment and black body radiation.
This problem spurred the two major discoveries of the twentieth century, relativity and quantum mechanics.
Thomson made many pronouncements that turned out false, such as his effort to prove James Clerk Maxwell’s contention that there was aether in space that made the conduction of electromagnetism possible. Einstein showed that radiation phenomenon did not have to depend on a medium to conduct it through space.
In sum, Thompson made contributions to pure and applied science (engineering). He made some contributions to transatlantic telegraph.
However, his main contribution is in heat, pressure and temperature and his recognition that energy can be translated into different forms while remaining the same amount (Laws of Thermodynamics).
William Thomson. Mathematical and Physical Papers. (1911)
William Thomson. Collected Papers in Physics and Engineering. (1912)