A simple, nondispersive spectrometer has been used to study the binding energies of core electrons at solid surfaces. The spectrometer consists of a photomultiplier which measures the soft x-ray fluorescence of an electron-bombarded surface. The derivative of the multiplier current as a function of target potential rises abruptly at the threshold energies at which core electrons can be excited to unoccupied states. This produces a comparatively simple spectrum for metals with each level being represented by a sharp peak, followed by an abrupt step. For nonmetals, however, the spectrum of a single level can consist of a series of sharp peaks spread over as much as 30 eV.