The famous Boltzmann equation, S=k ln Ω, is inscribed on Boltzmann's tombstone in Vienna, Austria. Boltzmann did not write it in this form, however, Planck did. Boltzmann also has two other equations named for him, the first is a diffusion equation used in neutron transport theory and the second describes particles in a gravitational field. In 1904, Boltzmann gave several lectures on mathematics at the World's Fair in St. Louis. He was also a popular lecturer in philosophy at the University of Vienna. Boltzmann is considered the founder of statistical mechanics, and a strong proponent of the "atomistic" view that underscored the importance of understanding the behavior of atoms and molecules in order to understand the bulk.