 Holt and Pipkin completed in 1973 (Holt 1973) an experiment very much like that of Freedman and Clauser, but examining photon pairs produced in the \(9^1 P_1 \rightarrow 7^3 S_1\rightarrow 6^3 P_0\) cascade in the zero nuclear-spin isotope of mercury-198 after using electron bombardment to pump the atoms to the first state in this cascade. The result of Holt and Pipkin was in fairly good agreement with the CHSH Inequality, and in disagreement with the quantum mechanical prediction by nearly 4 standard deviations—contrary to the results of Freedman and Clauser. Because of the discrepancy between these two early experiments, Clauser (1976) repeated the Holt-Pipkin experiment, using the same cascade and excitation method but a different spin-0 isotope of mercury, and his results agreed well with the quantum mechanical predictions but violated Bell’s Inequality. Clauser also suggested a possible explanation for the anomalous result of Holt-Pipkin: that the glass of the Pyrex bulb containing the mercury vapor was under stress and hence was optically active, thereby giving rise to erroneous determinations of the polarizations of the cascade photons.