<P> Temperature is one of the principal quantities in the study of thermodynamics . </P> <P> The Kelvin scale is called absolute for two reasons . One is that its formal character is independent of the properties of particular materials . The other reason is that its zero is in a sense absolute, in that it indicates absence of microscopic classical motion of the constituent particles of matter, so that they have a limiting specific heat of zero for zero temperature, according to the third law of thermodynamics . Nevertheless, a Kelvin temperature does in fact have a definite numerical value that has been arbitrarily chosen by tradition and is dependent on the property of a particular materials; it is simply less arbitrary than relative "degrees" scales such as Celsius and Fahrenheit . Being an absolute scale with one fixed point (zero), there is only one degree of freedom left to arbitrary choice, rather than two as in relative scales . For the Kelvin scale in modern times, this choice of convention is made to be that of setting the gas--liquid--solid triple point of water, a point which can be reliably reproduced as a standard experimental phenomenon, at a numerical value of 273.16 kelvins . The Kelvin scale is also called the thermodynamic scale . However, to demonstrate that its numerical value is indeed arbitrary, it is useful to point out that an alternate, less widely used absolute temperature scale exists called the Rankine scale, made to be aligned with the Fahrenheit scale as Kelvin is with Celsius . </P> <P> The thermodynamic definition of temperature is due to Kelvin . </P> <P> It is framed in terms of an idealized device called a Carnot engine, imagined to define a continuous cycle of states of its working body . The cycle is imagined to run so slowly that at each point of the cycle the working body is in a state of thermodynamic equilibrium . There are four limbs in such a Carnot cycle . The engine consists of four bodies . The main one is called the working body . Two of them are called heat reservoirs, so large that their respective non-deformation variables are not changed by transfer of energy as heat through a wall permeable only to heat to the working body . The fourth body is able to exchange energy with the working body only through adiabatic work; it may be called the work reservoir . The substances and states of the two heat reservoirs should be chosen so that they are not in thermal equilibrium with one another . This means that they must be at different fixed temperatures, one, labeled here with the number 1, hotter than the other, labeled here with the number 2 . This can be tested by connecting the heat reservoirs successively to an auxiliary empirical thermometric body that starts each time at a convenient fixed intermediate temperature . The thermometric body should be composed of a material that has a strictly monotonic relation between its chosen empirical thermometric variable and the amount of adiabatic isochoric work done on it . In order to settle the structure and sense of operation of the Carnot cycle, it is convenient to use such a material also for the working body; because most materials are of this kind, this is hardly a restriction of the generality of this definition . The Carnot cycle is considered to start from an initial condition of the working body that was reached by the completion of a reversible adiabatic compression . From there, the working body is initially connected by a wall permeable only to heat to the heat reservoir number 1, so that during the first limb of the cycle it expands and does work on the work reservoir . The second limb of the cycle sees the working body expand adiabatically and reversibly, with no energy exchanged as heat, but more energy being transferred as work to the work reservoir . The third limb of the cycle sees the working body connected, through a wall permeable only to heat, to the heat reservoir 2, contracting and accepting energy as work from the work reservoir . The cycle is closed by reversible adiabatic compression of the working body, with no energy transferred as heat, but energy being transferred to it as work from the work reservoir . </P>

Who invented the standard unit of measuring temperature