Additional laws have been suggested, but have not achieved the generality of the four accepted laws, and are generally not discussed in standard textbooks. Gradually, this resolved itself and a zeroth law was later added to allow for a self-consistent definition of temperature. In some fields, the second law was considered to deal with the efficiency of heat engines only, whereas what was called the third law dealt with entropy increases. While the numbering of the laws is universal today, various textbooks throughout the 20th century have numbered the laws differently. Later, Nernst's theorem (or Nernst's postulate), which is now known as the third law, was formulated by Walther Nernst over the period 1906–12. By 1860, as formalized in the works of scientists such as Rudolf Clausius and William Thomson, what are now known as the first and second laws were established. The first established thermodynamic principle, which eventually became the second law of thermodynamics, was formulated by Sadi Carnot in 1824 in his book Reflections on the Motive Power of Fire. The laws of thermodynamics are the result of progress made in this field over the nineteenth and early twentieth centuries. The history of thermodynamics is fundamentally interwoven with the history of physics and history of chemistry and ultimately dates back to theories of heat in antiquity. See also: Timeline of thermodynamics and Philosophy of thermal and statistical physics The first and second laws prohibit two kinds of perpetual motion machines, respectively: the perpetual motion machine of the first kind which produces work with no energy input, and the perpetual motion machine of the second kind which spontaneously converts thermal energy into mechanical work. With the exception of non-crystalline solids ( glasses) the entropy of a system at absolute zero is typically close to zero. The third law of thermodynamics states that a system's entropy approaches a constant value as the temperature approaches absolute zero. Another form of the statement is that heat does not spontaneously pass from a colder body to a warmer body. The second law of thermodynamics states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. The first law of thermodynamics states that, when energy passes into or out of a system (as work, heat, or matter), the system's internal energy changes in accord with the law of conservation of energy. The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature: If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. A more fundamental statement was later labelled as the zeroth law, after the first three laws had been established. Traditionally, thermodynamics has recognized three fundamental laws, simply named by an ordinal identification, the first law, the second law, and the third law. In addition to their use in thermodynamics, they are important fundamental laws of physics in general, and are applicable in other natural sciences. They state empirical facts that form a basis of precluding the possibility of certain phenomena, such as perpetual motion. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. The laws of thermodynamics define a group of physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems in thermodynamic equilibrium.
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