Murray Gell-Mann, at Caltech, proposes in 1964 that hadrons — the family of subatomic particles including protons, neutrons, and dozens of other particles discovered in accelerators during the 1950s and 1960s, whose disorderly proliferation was frustrating physicists — are not fundamental particles but combinations of more basic constituents, which he calls "quarks", taking the term from a word with no clear meaning in James Joyce's novel Finnegans Wake. Gell-Mann postulates the existence of three types of quarks with fractional electric charges — something never observed before in nature, where every known charge was an integer multiple of the electron's charge — whose combinations of two or three quarks neatly explain the whole variety of known hadrons according to a mathematical pattern Gell-Mann calls "the eightfold way", by analogy with Buddhism. George Zweig, also at Caltech, proposes the same idea completely independently and almost simultaneously. The quark hypothesis, initially met with skepticism by the particle-physics community given how strange it was to posit fractional charges never observed in isolation, is progressively confirmed through deep inelastic scattering experiments at SLAC in the late 1960s and decisively so with the discovery of the charm quark in 1974, becoming established as a fundamental pillar of the standard model of particle physics.