This relationship is called Gauss’s law after the scientist who first deduced it, the nineteenth-century German mathematician and physicist Carl Friedrich Gauss. In honor of Gauss, a closed surface used to enclose charge in order to apply Gauss’s law is referred to as a Gaussian surface. Equation 16-9 holds true for any Gaussian surface (Figure 16-19), no matter what its shape or size and no matter where the charges are located inside the surface. As we mentioned previously, such surfaces are imaginary: The surface does not need to be made of any physical substance.