Pirani performed post-doctoral research at the
Institute for Advanced Studies in Dublin, Ireland. In 1958, he started teaching at King's College London, where Bondi was also teaching, and in 1968 became professor of rational mechanics there. In 1957, Pirani independently discovered what was later called the
Petrov classification (also Petrov–Pirani–Penrose classification) and separately discovered by
Petrov in 1954. Pirani's work with Bondi and Robinson resulted in correspondence between Pirani and
Albert Einstein, some of whose partially expressed views on the subject had been challenged by the paper. In 1972, Pirani,
Jürgen Ehlers and Alfred Schild showed that the space-time geometry of general relativity can be constructed from simple measuring processes with light beams and free-falling particles. ==Popular books==