A particle sizing instrument has been developed as part of a research program in particle sizing interferometry conducted by the Arnold Engineering Development Center. The instrument, which uses fringe visibility to size particles, has been applied to determination of water droplet size distributions in a wind tunnel employed for icing studies. Droplets were sized in the range from 8 to 80 micrometers, while droplet velocities in the air flow were in excess of 100 meters/second. Number densities ranged up to a few hundred droplets per cubic centimeter. Design features of the system are described, including on-axis, forward scatter light collection optics which use a specialized lens mask to reduce the dynamic range of signal magnitudes. The variation of the sample volume with particle size is discussed. The electronics are outlined and signals are described in both the time and frequency domains.