Opportunities missed and opportunities seized quanta. 'Dirac's mistake, like Fermis, is, of course, the omission of the spin of the electron. But whereas the electron was considered to be a structureless mass point in 1925, in 1926 the hypothesis of G. E. Uhlenbeck S Goudsmit, that the electron possessed an intrinsic spin, was generally accepted, and it therefore followed that the eigenfunctions of an ideal spinless gas should be symmetrical functions of the space coordinates, and that Fermi-Dirac statistics is not applicable to such a gas The first practical as distinct from theoretical problem to which the Fermi- Dirac statistics was correctly applied was that of the behaviour of White Dwarf stars. In what is probably his most important paper, published late in 1926 and entitled'On dense matter,R. H. Fowler put forward the hypothesis that matter in a White Dwarf consists of bare nuclei and free electrons, and that the ultimate fate of a White dwarf is to become a Black Dwarf similar to a single gigantic molecule in its lowest quantum state, the specific heat of the condensed electron (and nuclear) gas being effectively zero. This major step forward, though acclaimed by astrophysicists, received scant attention by physicists, and a paper by Pauli, published early in 1927 and entitled Uber Gasentartung und Paramagnetismus', received little more. Pauli wrote Die,. von Fermi herruihrende Quantenstatistik des einatomigen idealen Gases wird auf den Fall von Gasatomen mit Drehimpuls erweitert. Betrachtet man die Leitungselektronen im Metall als entartetes idealen Gas-was gewiss nur als ganz provisioned anzusehen ist-so gelangt man auf Grund der entwickelten Statistik zu einen wenigstens qualitativen theoretischen Verstandnis der Tat- sache, dass trotz des Vorhandenseins des Eigenmomentes des Elektrons viele Metalle in ihrem festen zustand keinen oder nur einen sehr schwachen und annahernd temperaturunabhangigen Paramagnetismus zeigen e. This paper was largely taken up by a discussion of the difference between instein-Bose and Fermi-Dirac statistics, and, except for the derivation of the paramagnetic susceptibility, contained very little of physical interest. It will be seen that in this paper Pauli is far from insisting that the conduction electrons in a metal should definitely be treated as a degenerate gas, but anyone really familiar with the Drude-Lorentz theory of metallic conduction could have seen in a com bination of Fowler's and Pauli's papers a key to the solution of the difficulties that had beset the theory. The most outstanding stumbling block(there were many more)was, on the one hand, the necessity for the number of the conduction electrons to be of the order of one per atom, and, on the other hand, for the number to be negligibly small. The first requirement arose from the magnitude of the Hall coefficient, while the second was the basis for one explanation of the fact that the specific heat per atom was the same for insulators and conductors. These require ments could now be reconciled, but it was not until a year later(1928)that Sommer old published his paper 'Zur Elektronentheorie der Metalle auf grund der Fermi- schen Statistik, which is the real starting point for the major developments that were to follow Why had it taken so long to arrive at this point? So far as Fermi and Dirac areOppoγt侃侃ities missed and 'portunitics seized 41 quanta.' Dirac's mistake, like Fermi's, is, of ∞"""' he omi ion of he spin of the electron. But whereas the electron was considered to be a structureless mass point in 1925, ìn 1926 he hypothesis ofG. E. Uhlenbeck & S. Goudsmi hat the electron posse鸣幽 an intrinsic spin, was generally accep and it herefore followed that he eigenfunctions of an ideal spinIess should be symmetrical functions of he space coordinates, and at Fermi Dirac atistic8 is not applicable to such a ga.s The firs practical as distinct from heoreticaI problem to wruch Fcrmi￾Dirac statistics was rre tly applied was hat of the behaviour of White Dwarf stars. In what is probab!y his mos importan paper published late in 1926 and enti led ' On dense matter' , R. H. Fowler put forwaro he hypo eSls hat mat in a Whi Dwarf consÎsts of bare nuclei and free electrons, and hat he ultimate fate of a. White Dwarf is to become a Black Dwa.rf similar to a single gigantic molecule in its lowes qu a.ntum state, the specific heat of the condensed electron (a.nd nuclear) gas being effectively zero This 坷。 step forwaI址， though acclaimed by 剧也rophysicists ，目。eived sca.nt attention by physicis恤， and a er by Pauli, published early in 1927 a.nd entitled 'über Ga8entartung und Paramagnetismus', received little more. Pauli wro Die ... von Fermi herrührende Quan nsta.tistik des eina.tomigen idcalen Ga wird auf den Fa.ll von atomen mi Drehimpuls erwe crt ... Betrach阳也 man die Leitungselektronen im Metall als en rtetes idealen Ga8 - was gewi nm ganz provisioncl anzusehen ist - 80 gelangt man a.uf Grund der entwickelten 阳岛istik zu cincn wenigstens qua. litativen heoretischen Ve tändnis der Tat. sache, das.s trotz Vorhanden ins des Eigenmomen des Elektron8 viele Meta.lle in ihrem fcs zustand keinen oder nur einen hr schwa.chen und annähcrnd tempera.turunabhãngigen Paramagnetismus zcigen This 叩时 was largely taken up by a discussion of the differen between Einstein-Bose a.nd Fermi- Dirac atisti曲， and, except for the derivation of he paramagnetic suscep bili conta.ined very little of physical in erest. It will be en at in thi8 paper Pauli i8 far from insisting that the conduction electrons in a meta.1 should del1nitely be 也， 也阻 as a degcnerate gas, but anyone really fami Jia.r wi仙也he Drude-Lorentz ~ory of metallic conduction could have 8een in a com. bination of Fowler's and Pauli's papers a key to the solution of the di culties hat had beset the theory. The mo outstanding umbling block (there were many more)w剧， on the one hand, the necessity for he numberofthe conduc nelectrons b