I N T R O D U C T I O N T O V O L U M E 1 4 l x v i i tromagnetic-mechanical analysis, which led to (*), is incompatible with quantum theory, and it is not surprising that Planck himself and all theoreticians who work on this topic incessantly tried to modify the theory so as to base it on noncontradic- tory foundations” (Einstein 1916j [Vol. 6, Doc. 34], p. 318). In his 1916/17 papers, Einstein had made an advance on this problem by assum- ing that the resonators are Bohr atoms that interact with the radiation field accord- ing to Bohr’s frequency condition, and by introducing coefficients for induced absorption and spontaneous emission as well as induced emission (negative ab- sorption). This allowed him to derive an expression for ρ as a function of the coef- ficients and the temperature. But in order to recover Planck’s law, he had to invoke the validity of Wien’s law, and conceded that “it will be possible to compute the constants […] when we have an electrodynamics that has been modified in the sense of the quantum hypothesis” (Einstein 1916j [Vol. 6, Doc. 34], p. 322). In his manuscript, Bose took seriously the assumption that light quanta are par- ticles with energy and momentum, and derived the relation (*) on the assumption that their phase space was quantized into cells of size , where h is Planck’s con- stant, in the same way as had been done for material oscillators.[36] On the basis of this assumption, he succeeded in deriving Planck’s formula by a straightforward application of Boltzmann’s principle by maximizing an expression for the entropy, i.e., by maximizing an expression for the probability of distributing the light quanta over the discrete cells of the phase space volume. Einstein immediately realized the importance of Bose’s procedure as being the first derivation of Planck’s radiation law using statistical mechanics for a system of light particles. He quickly set out to translate the paper into German and submitted it only a few days later to the Zeitschrift für Physik, not without adding a comment: “In my opinion Bose’s derivation of the Planck formula signifies an important ad- vance. The method used also yields the quantum theory of the ideal gas, as I shall work out in detail elsewhere.”[37] Einstein’s decision to apply the same statistical method to an ideal gas of mole- cules was probably the motivation for his quick action regarding Bose’s paper. On 10 July 1924, he presented to the Prussian Academy a paper in which he applied Bose’s procedure to the case of a monatomic ideal gas and derived its equation of state (Einstein 1924o [Doc. 283]). He verified that in this framework the relation- ship between pressure and kinetic energy is the same as in the classical theory, and he looked at the classical limit of the expressions obtained. He observed that in this new approach Nernst’s theorem would automatically be satisfied, since for vanish- ing temperature the entropy, too, would vanish. He concluded by pointing out that the method did not allow him to solve Gibbs’s paradox, the solution of which he posed as an open problem. h3