The energy of an electrostatic accelerator is modulated over a range of 50 kev by applying an alternating potential of 50‐kv amplitude to an insulated target at a frequency of 10 cps. A sample of the modulating voltage and the signals from a nuclear detector are fed to a so‐called ``function sampler,'' which furnishes an output pulse whose height is proportional to the instantaneous value of the target voltage. Analysis of the pulse‐height spectrum by means of a 100‐channel analyzer then affords a presentation of the spectrum of nuclear events as a function of accelerator energy over a 50‐kev range, each channel of the analyzer corresponding to an energy width of 500 ev. Advantages of this system are discussed for high resolution work with an electrostatic accelerator.