Peierls a research project on ferromagnetism. It was known that this was caused by the spin of the electrons in the metal aligning; but the reason for this was unknown. Heisenberg suspected that it was caused by a quantum mechanical effect, caused by the Pauli exclusion principle. Peierls was unable to develop the theory, but work on Hall effect was more productive. The anomalous Hall effect could not be explained with the classical theory of metals, and Heisenberg sensed an opportunity to demonstrate that quantum mechanics could explain it. Peierls was able to do so, resulting in his first published paper. Heisenberg left in 1929 to lecture in America, China, Japan and India, and on his recommendation Peierls moved on to ETH Zurich, where he studied under Wolfgang Pauli. Pauli set him a problem of investigating the vibration of atoms in a crystal lattice. Peierls explored—and named—the phenomenon of umklapp scattering. He submitted this work as his DPhil thesis, Zur kinetischen Theorie der Wärmeleitung in Kristallen (On the Kinetic Theory of Heat Conduction in Crystals), which was accepted by the University of Leipzig in 1929. His theory made specific predictions of the behaviour of metals at very low temperatures, but another twenty years would pass before the techniques were developed to confirm them experimentally. Early career Peierls accepted an offer from Pauli to become his assistant in place of Felix Bloch. Lev Landau was there at this time on a scholarship from the government of the Soviet Union, and Peierls and Landau became friends. They collaborated on deriving a series of wave equations similar to the Schrödinger equation for photons. Unfortunately, their equations, while complicated, were nonsensical. In 1930, Peierls travelled to the Netherlands to meet Hans Kramers, and to Copenhagen to meet Niels Bohr. In August 1930 Pauli and Peierls attended a physics congress in Odessa and met a young physics graduate, Eugenia (Genia) Nikolaievna Kannegiesser, who, like Landau, came from Leningrad. Since he did not speak Russian and she did not speak German, they conversed in English. During a subsequent visit by Peierls to lecture in Leningrad they were married on 15 March 1931. However, she had to wait for a passport and exit visa. They finally left for Zürich that summer. They had four children: Gaby Ellen (b.1933), Ronald Frank (b.1935), Catherine (Kitty; b.1948), and Joanna (b.1949). Peierls assisted Egon Orowan in understanding the force required to