This section of the article by C. F. von Weizsäcker discusses the problem of nuclear mass theory. It highlights that protons and neutrons are likely the only elementary building blocks of atomic nuclei. Given their high rest energies compared to nuclear binding energies, these particles should be described using non-relativistic quantum mechanics. However, due to the difficulty in directly determining the forces between elementary particles, the approach is to derive nuclear forces from empirically known mass defects. The mass defects of the lightest nuclei (H₁², H₁³, He₂³, He₂⁴) increase rapidly with particle number, while those of heavier nuclei grow linearly. The packing fractions (mass defects per particle) of lighter nuclei (up to Fe) are not strictly constant but increase slowly, while those of heavier nuclei decrease slowly after a nearly constant period. Nuclei with even proton and neutron numbers are more strongly bound than those with odd numbers. Wigner showed that the rapid increase in mass defects for light nuclei can be explained by a specific choice of force model, which implies an increase in particle density in the nucleus. This is contrasted with the behavior of heavier nuclei, which suggest a constant density. Gamow phenomenologically described this behavior with his "drop model," while Majorana's model suggests an exchange force between protons and neutrons, leading to a constant density and binding energy proportional to particle number. However, this force law does not match Wigner's findings. Heisenberg formally represented the third observation by assuming a progressive worsening of Majorana's approximation with decreasing particle number in the nucleus. Wick noted that this can be explained within the drop model by considering a surface tension of the nucleus. The current work aims to explore the existence and magnitude of this surface tension through an extension of the Thomas-Fermi method.This section of the article by C. F. von Weizsäcker discusses the problem of nuclear mass theory. It highlights that protons and neutrons are likely the only elementary building blocks of atomic nuclei. Given their high rest energies compared to nuclear binding energies, these particles should be described using non-relativistic quantum mechanics. However, due to the difficulty in directly determining the forces between elementary particles, the approach is to derive nuclear forces from empirically known mass defects. The mass defects of the lightest nuclei (H₁², H₁³, He₂³, He₂⁴) increase rapidly with particle number, while those of heavier nuclei grow linearly. The packing fractions (mass defects per particle) of lighter nuclei (up to Fe) are not strictly constant but increase slowly, while those of heavier nuclei decrease slowly after a nearly constant period. Nuclei with even proton and neutron numbers are more strongly bound than those with odd numbers. Wigner showed that the rapid increase in mass defects for light nuclei can be explained by a specific choice of force model, which implies an increase in particle density in the nucleus. This is contrasted with the behavior of heavier nuclei, which suggest a constant density. Gamow phenomenologically described this behavior with his "drop model," while Majorana's model suggests an exchange force between protons and neutrons, leading to a constant density and binding energy proportional to particle number. However, this force law does not match Wigner's findings. Heisenberg formally represented the third observation by assuming a progressive worsening of Majorana's approximation with decreasing particle number in the nucleus. Wick noted that this can be explained within the drop model by considering a surface tension of the nucleus. The current work aims to explore the existence and magnitude of this surface tension through an extension of the Thomas-Fermi method.