No. 15: Spring 1981
There's no escaping it, those fractionally charged niobium balls just can't be swept under the rug. In fact, more recent experiments have served only to accentuate the anomaly. Researchers at Stanford University have been magnetically suspending superconducting niobium spheres in a modern version of Millikan's oil-drop experiment. With the niobium spheres thus suspended, their net electrical charges can be measured. The trouble is that several of the spheres have fractional electrical charges -- +1/3 or -1/3 electronic charges.
For decades the charge on the electron was supposed to be the basic, indivisible natural unit of electrical charge. In 1964, however, theorists began muddying the waters with talk of new fundamental constituents of matter called quarks, which could possess 1/3 or 2/3 electron charges. No one really expected that quarks, if they existed at all, would be floating around free. But the niobium balls tell us that not only are quarks free but that we could have detected them with relatively simple experiments decades ago if we had not been so blinded by the idea of integral electronic charges.
(Robinson, Arthur L.; "Evidence for Free Quarks Won't Go Away," Science, 211:1028, 1981.)