This law describes the statistical distribution of energies of molicules in a gas. First presented by James Clerk Maxwell in 1859, the law was generalized by Ludwig Boltzmann in 1871. In simplest terms, the distribution function for a Maxwell-Boltzmann classical gas (*f*_{M-B}) can be written as *f*_{M-B}=C*e^{-E/(k*T)}, where C is the normalizing constant (chosen so that the integral of all probibilities is unity), e is the base for all natural logarithms, E is the total energy of the system, k is the Boltzmann's constant (1.38e-16 erg/K), and T is the absolute temperature of the system. The function implies that the probibility *dP* that any particle has an energy between E and E+dE is given by *dP=f*_{M-B}dE. All systems observed to date obey this law provided that quantum-mechanical effects are not important.