A diagram illustrating the thought process of William Thomson (Lord Kelvin) to design his second temperature scale. A Carnot engine working in between the temperatures of 1000K and 500K rejects 1000/500 = 50% of the heat it receives. If the lower temperature is a fourth of the top temperature, this wasted heat is 1/4th of the received heat, and so on.
Own work, part of Thermodynamique de l’ingénieur
Olivier Cleynen