By 1799 the number of Martha Washington's dower slaves had grown to 153; George Washington owned 124 people, and at least a dozen Washington-owned slaves intermarried.
Hund's rule of maximum multiplicity is a rule based on observation of atomic spectra, which is used to predict the ground state of an atom or molecule with one or more open electronic shells.
Heisenberg's Uncertainty Principle. The uncertainty principle is one of the most famous (and probably misunderstood) ideas in physics. It tells us that there is a fuzziness in nature, a fundamental limit to what we can know about the behaviour of quantum particles and, therefore, the smallest scales of nature.