Abstract
It is shown that the primary contribution to the field-emission current comes from electrons with total momentum equal to zero in a direction parallel to the metal surface and that the field-emission current measures the density of states at a point several angstroms from the metal surface. An explicit expression is derived for the error made in using the transfer-Hamiltonian technique to calculate the tunneling probability of an electron through a one-dimensional barrier, and it is pointed out that the error is small in the case of field emission.