Einstein's blackboard from a lecture given in Oxford on 16 May 1931. The lecture was about redshift. In the first line D is the measure of expansion in the universe, defined in terms of the expansion factor P. In the third line, the density of matter in the universe (\rho) is derived from the field equations. The last four lines give values for density, radius and age of the universe. "L.J." stands for "Licht Jahr" (light year), and "J" for Jahr (year). (From the exhibition ......)