Page:Elementary Text-book of Physics (Anthony, 1897).djvu/262

248 temperature of the source and refrigerator, and the efficiency depends only on the temperatures of the source and the refrigerator, or is a function of these temperatures. If the temperatures be represented on any conventional scale, the form of this function may be found by experiment; on the other hand, the assumption of a form of this function will determine a scale of temperatures. The proposal to form such a scale, which is dependent only on the efficiency of the reversible engine, and is therefore independent of the properties of any particular body, was made by William Thomson.

The scale of temperatures which is most convenient for application in thermodynamics, and which is so distinguished by its simplicity from all others that might be formed that it is called distinctively the absolute scale of temperatures, is formed by assuming that the efficiency of a reversible engine is equal to the ratio of the difference of temperature between the source and the refrigerator and the temperature of the source, that is, by assuming This assumption may also be stated in the form  The maximum efficiency of an engine is attained when all the heat which is received from the source is transformed into work, so that no heat is transferred to the refrigerator; on the scale of temperatures just assumed this condition is attained when $$R = 0.$$ This zero is an absolute and not an arbitrary zero. It depends on the general properties of bodies, and not on the particular properties of any one body. It is the lowest temperature attainable in Nature, for, if it were possible to have a refrigerator at a lower temperature than this, the efficiency of an engine working with that temperature as the temperature of its refrigerator, would be