Macquorn Rankine and the Laws of Thermodynamics

William John Macquorn Rankine (1820-1872)

William John Macquorn Rankine (1820-1872)

On July 5, 1820, Scottish mechanical engineer William John Macquorn Rankine was born. He was a founding contributor, with Rudolf Clausius and William Thomson (Lord Kelvin), to the science of thermodynamics, particularly focusing on the first of the three thermodynamic laws.

Born in Edinburgh as second son to British Army lieutenant David Rankine and Barbara Grahame, Rankine was due to bad health initially educated at home in a strictly religious environment. Rankine‘s interests were divided between music and mathematics. Later he attended Ayr Academy and, very briefly, the High School of Glasgow. Around 1830 the family moved to Edinburgh and in 1834, Rankine studied at a Military and Naval Academy with the mathematician George Lees, followed by the study a spectrum of scientific topics at the University of Edinburgh in 1838, including natural history. During vacations, he assisted his father who, from 1830, was manager and, later, effective treasurer and engineer of the Edinburgh and Dalkeith Railway which brought coal into the growing city. Rankine decided not to take a university degree but chose to leave university and become an apprentice to the engineer John Benjamin MacNeill, perhaps because of straitened family finances. Sir John Benjamin Macneill was at the time surveyor to the Irish Railway Commission, involved with, including river improvements, waterworks, railways and both harbours. During his pupilage Rankine developed a technique, later known as Rankine‘s method, for laying out railway curves, fully exploiting the theodolite and making a substantial improvement in accuracy and productivity over existing methods. In fact, the technique was simultaneously in use by other engineers – and in the 1860s there was a minor dispute about Rankine‘s priority.

The year 1842 also marked Rankine‘s first attempt to reduce the phenomena of heat to a mathematical form. Probably his interest in heat and heat engines developed from his early work with railroads. Though his theory of circulating streams of elastic vortices whose volumes spontaneously adapted to their environment sounds fanciful to scientists formed on a modern account, by 1849, he had succeeded in finding the relationship between saturated vapour pressure and temperature. The following year, he used his theory to establish relationships between the temperature, pressure and density of gases, and expressions for the latent heat of evaporation of a liquid. He accurately predicted the surprising fact that the apparent specific heat of saturated steam would be negative, which was later confirmed experimentally. Rankine then began to generalize his equations to include solids and liquids. Suggesting that his previous equations were probably valid only for perfect gases, he removed any restrictions on the shape of the atoms and vortices, except to demand that the matter in the vortices move in closed paths. By clever approximations, Rankine obtained the same equations as before and immediately concluded that they therefore applied to all substances, whether in the solid, gaseous, or liquid state.[3]

At this time Rankine turned his attention to the problem of calculating the efficiency of heat engines. Like Clausius and William Thomson, who had been working independently on the theory of heat, Rankine attempted to derive Carnot’s law. Rankine used his theory as a basis to deduce the principle, that the maximum efficiency possible for any heat engine is a function only of the two temperatures between which it operates. Though a similar result had already been derived by Rudolf Clausius and William Thomson, Rankine claimed that his result rested upon his hypothesis of molecular vortices alone, rather than upon Carnot‘s theory or some other additional assumption. The work marked the first step on Rankine‘s journey to develop a more complete theory of heat. He developed a general theory of energy that was independent of all mechanical hypotheses. The sum of the actual and potential energies of the universe was assumed constant—a law already familiar as the conservation of energy. Rankine then proposed a law that determined the amount of energy transformed during any change of state of a substance. By 1855, Rankine had formulated a science of energetics which gave an account of dynamics in terms of energy and its transformations rather than force and motion. The theory was very influential in the 1890s. In 1859 he proposed the Rankine scale of temperature, an absolute or thermodynamic scale whose degree is equal to a Fahrenheit degree.

In 1855, Rankine was appointed to the Queen Victoria chair of civil engineering and mechanics at the University of Glasgow. Rankine conducted pioneering research in the fields of railway engineering, molecular physics and thermodynamics. He wrote more than 150 scientific papers and manuals as well as textbooks which became standard works of reference for students. He was elected a Fellow of the Royal Society in 1853 and he was the first President of the Institution of Engineers in Scotland.

At yovisto, you may learn more about Thermodynamics in ‘The Flow of Heat‘ by Rick Prellinger.

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