Memories of early days in solid state physi orld War ll. None- ploration of its form through this same effect starting before extensive e heless, we often implicitly assumed it. For instance, in bristol my research student Baber(a) showed in 1937 that collisions between electrons, all in states within an energy ca kT of the Fermi surface, yielded a term in the resistivity proportional to T2; the proof assumed that the wavenumber k near the Fermi energy was a quantity with physical reality, and this was equivalent to assuming the existence of the Fermi surface. Peierls's memorandum shows that this result was anticipated by landau Interaction between electrons plays an essential role in our understanding of ferromagnetism. This was of course first shown by Heisenberg6) in his paper of 1928, which was essentially a theory of a non-metallic ferromagnetic material hich ascribed ferromagnetism to between two atoms. In Bristol, in the period 1933-8, our interest in metals made us start from the Pauli theory of the paramagnetism of a metal; here the electrons excited above the Fermi energy, of which the number per unit volume was N(EF)kT per unit volume, each contributed pB2/ kt to the paramagnetism, giving a total susceptibility x equal to N(EF)B. Here N(E)is the one-electron density of states b the Bohr magneton and Ef the Fe ergy. In Bristol, influenced by the experimental work of Potter and Sucksmith, I put forward in 1935 a model6) for the transition metals in which a narrow d-band overlaps a wide s band, as in figure 2 so that the density of states at the Fermi energy could be large, and in ferromagnets the saturation moment a non-integral multiple of the Bohr magneton. This was supported by results already existing on the effect on the paramagnetism of palla dium of alloying it with certain metals, such as silver with one extra electron which could be expected to displace the Fermi energy in figure 2 to the right, thus of Bohr B N(Er)and x. Ferromagnetism, and particularly the non-integral number magnetons per atom shown by nickel, cobalt and iron, was in our thinking the result of a 'Weiss molecular field 'which in nickel and cobalt, at any rate, polarized the spins of as many d-electrons as possible in one direction. The Weis field arose because two electrons of which the spins pointed in the same direction must have an antisymmetrical orbital wavefunction, so that the probability that two electrons approached within a distance rr2 of each other tended to zero for small les of r12. This idea goes back to Bloch's paper of 1929. This meant a decrease in the energy contributed by the repulsion e /r12 between each pair of electrons with parallel spins. f Stoner(B)in 1938 published the first of a series of papers using this model, and developing its consequences in detail, which came to be called the Stoner model t His obituary notice published by the Royal Society says that this t blocham in 1929 first saw that exchange correlations (as distinct from correlations of ntiparallel electrons) would enhance paramagnetism, and should give ferromagnetism fo a very extended lattice. Wigner pointed out that this was not likely to occur for nearly free electrons(see for instance Mott Jones(%), p. 141, and Seitz(o, p 602). The use of the equation for the susceptibility X=X/(1-X01) th I an exchange term, is due to the post-war work of Anderson and Hubbard t See note on Stoner's work at the end of this article