William Thomson (Kelvin) (26.06.1824-17.12.1907) was an English physicist, one of the founders of thermodynamics, and a Fellow of the Royal Society (1851), its president in 1890-95. In 1892 he received the title of Lord Kelvin. He was born in Belfast. He graduated from the University of Cambridge (1845). In 1846-99 he was a professor at the University of Glasgow (in 1846 he organised one of the first physical laboratories), and from 1904 its president.
His research was in the fields of thermodynamics, hydrodynamics, electromagnetism, elasticity, heat, mathematics and engineering. In 1851 he formulated (independently of R. Clausius) the second law of thermodynamics: “in nature there can be no process whose only result is mechanical work performed at the expense of cooling a heat reservoir”. In accordance with this formulation of the second law (Thomson's formulation) the impossibility of a perpetual motion machine of the second kind was proved. However, starting from the law he had discovered and applying it to the Universe as a whole, he reached (1852) the mistaken conclusion that the “heat death of the Universe” was inevitable (the hypothesis of the heat death of the Universe). The invalidity of this approach and the error of the hypothesis were demonstrated by L. Boltzmann.
He made wide use of the thermodynamic method to explain various physical phenomena. In 1848 he introduced the concept of absolute temperature and the absolute temperature scale named after him (the Kelvin scale). He showed how the boiling point of a liquid, as a function of pressure, is related to the heat of vaporisation, the volume of the liquid and the vapour formed from it, and established in 1870 that the vapour pressure depends on the shape of the liquid's surface. Together with J. Joule he established in 1853-54 the change in temperature of a gas as it flows slowly and steadily, adiabatically, through a porous partition (the Joule-Thomson effect). The use of this effect is one of the main methods of obtaining low temperatures.
In 1856 he discovered a third thermodynamic effect (the Thomson effect): if a temperature difference exists along a conductor carrying an electric current, then, in addition to Joule heat, a further quantity of heat is released or absorbed in the volume of the conductor, depending on the direction of the current (Thomson heat). He constructed a thermodynamic theory of thermoelectric phenomena.
He worked fruitfully in the study of electric and magnetic phenomena, in particular studying the magnetic properties of crystals. In 1851 he discovered the change in the resistivity of ferromagnets when they are magnetised (the Thomson effect). He designed a number of highly sensitive electrometers and galvanometers, a universal compass and other instruments. He calculated electric oscillations in a circuit, deriving in 1853 the formula for the dependence of the period of natural oscillations in a circuit on its capacitance and inductance (the Thomson formula). He established (1856) the change in the resistance of metals in a magnetic field perpendicular to the current. Thomson's theoretical studies of electromagnetism and a number of his technical inventions contributed substantially to the practical realisation of telegraph communication, in particular by the transatlantic cable, in the laying of which he took an active part.
His studies of heat conduction are well known; he tried to use them to calculate the age of the Earth. He studied the problem of the Earth's rotation about its axis and concluded that the ocean tides affect this rotation. He put forward (1902) a hypothesis on the structure of atoms, carried out calculations of the sizes of molecules, and so on.
He was a member of many academies of sciences and learned societies, among them the St Petersburg Academy of Sciences (1896).