DOCUMENT 490 DECEMBER 1913 579 tity x, so that q = ))(x), then very satisfactorily, the equation takes on the same form in x. With this equation we first investigated whether Maxwell's distribution function corresponds to the radiation formula of Rayleigh and Jeans (which is needed for the calculation of R). We did not achieve agreement as long as we assumed R to be equal to zero. This seemed so plausible to us. We eventually realized though that it was not so and I have succeeded in calculating the value of R. Agreement has now been achieved. Subsequently, I started to calculate the distribution function that corresponds to the radiation formula of Planck. It has an awkward form. If co is the angular velocity and L the moment of inertia of the dipole, and if consequently the distribution func- tion for co is written down, h(ü 4n2LkT 2nL Wda = Kd(ü . e h2 e + (0 h If one puts - = x and if the exponent is written as -T])(x), the average energy be- comes[7] oo E = =T2- x2e~ Tp (x) dx OO J dx 0 Differentiation with respect to T yields the specific heat. As far as I can tell, though, the curve representing this as a function of T has a vertical tangent for T = 0, while Eucken's measurements of the specific heat of hydrogen require this tangent to be horizontal.[8] This is the result which, of course, I would have liked to be different.- We have not spoken much yet about the theory of gravitation, but I think that will gradually have its turn. Einstein mentioned his plan to travel to Haarlem in order to hear your opinion and criticism of his theory, which would be very important to him. This would occur next spring after he arrives in Berlin[9] when his time will be all his own. With Dr. Stern[10] I get along well. With the other physicists, for that matter, I will also get along fine, I think. I try to keep working, sometimes successfully, other times not. There are many books on the table in front of me, which I definitely want to work through, but which are still waiting. Time passes quickly! It is almost Christmas al- ready!