  This note is based on a relatively unknown paper of Albert Einstein published
in 1941 in the Revista de la Universidad Nacional de Tucuman. That work can be
regarded as the prequel of the one written in 1943 in collaboration with
Wolfgang Pauli, where, along the same lines, a proof of the non-existence of
certain non-singular solutions in Kaluza-Klein theory was given. More
generally, disproving the existence of regular solutions in classical unified
field theories became, specially after 1930, an important criterion leading
Einstein's investigations on unified field theory. This is the context in which
Einstein's paper of 1941 and its generalizations of 1943 and 1948 become
important.
