Electric Neutrality of Matter

With the use of a new feedback levitation electrometer (with an increase in sensitivity by ${10}^3$ in comparison to our previous graphite experiments) iron objects of mass ∼ 2 × ${10}^{-4\mathrm{}}$ g have been explored for fractionally charged quarks and/or a possible electron-proton charge difference. Upper limits found were $\frac{N\left(\mathrm{quarks}\right)}{N\left(\mathrm{nucleons}\right)}<3\mathrm{}\times {10}^{-21\mathrm{}}$ and $\frac{(Q_p-|Q_e\mathrm{}\left|\right)\mathrm{}}{Q_p}<{10}^{-21\mathrm{}}$. The present "sensitivity" is ∼ ${10}^7$ times that of the original Millikan experiment.