In a series of papers (7a, b, c, d, e) Pettersson has described the construction and use of a transparency meter and has given the results of transparency measurements at several stations in Swedish waters. Two of the main difficulties in determining the transparency of sea-water by measuring submarine daylight arise from fluctuations of the surface intensity and from the rapid decrease of intensity with depth. The transparency meter uses an artificial source of light, thus ensuring constant intensity. The present paper reports transparency measurements for 23 stations off the coast of Southern California.