  Neither is there any hostile attitude in the famous ‘reversibility objection’ by Loschmidt in 1875. Loschmidt was Boltzmann's former teacher and later colleague at the University of Vienna, and a life-long friend. He had no philosophical reservations against the existence of atoms at all. (Indeed, he is best known for his estimate of their size.) Rather, his main objection was against the prediction by Maxwell and Boltzmann that a gas column in thermal equilibrium in a gravitational field has the same temperature at all heights. His now famous reversibility objection arose in his attempts to undermine this prediction. Whether Boltzmann succeeded in refuting the objection or not is still a matter of dispute, as we shall see below (section 4.1).