Experimentally, the polarity of molecules is measured indirectly by measuring
the dielectric constant, which is the ratio of the capacitance of a cell filled with the substance
to be measured to the capacitance of the same cell with a vacuum between the
electrodes. Orientation of polar molecules in the electric field partially cancels the effect
of the field and results in a larger dielectric constant. Measurements at different
temperatures allow calculation of the dipole moment for the molecule, defined as