“…For large, single particles, the last two terms are indistinguishable and considered as one group, which is proportional to the projected area of the particle or that portion of it in the control volume. Various techniques based on this principle are described in the literature (see: Ritter et al, 1974;LaFrance et al, 1974;Schleusener and Reed, 1967;Schleusener, 1968;Shuster and Knollenberg, 1972;Rhodes et al, 1976). The general approach involves the use of a light beam having a rectangular cross section, with the particle moving across the longer side.…”