Abstract : An experiment is described in which the interval distribution of photoelectric counts is examined, under conditions where light from a low pressure Hg198 gas discharge falls on a photomultiplier. The rate of two-photon counting is measured when the interval lies within the range tau-1 and tau-1 + 7.5 nsec, and it is shown that the two-photon counting rate exceeds the corresponding rate for random pulses when tau-1 approx. < 3 nsec. The measurements yield information on the spectral profile of the light, which is shown to be non-Lorentzian and to have a width somewhat greater than 200 Mc/sec. (Author)