deviations of 1.68 to 1.98 (Nathans, Thews, end Russell, 1970). With the larger particles thus deposited as local fallout, smaller particles vr remain in the cloud. One cloud 1.5 hours after a megaton range of explosion «t the surface of a coral island was found to have a particle size distribution made up of two lognormal functions, the larger particle group being dominant in abundance. Ninty-one percent of the particles were in the larger group, which was centered around 37 microns in diameter, and nine percent were in the smaller group centered around 2.9 microns in diameter (Heft, 1970, p. 264). The Bravo test at Bikini Atoll in 1954 produced fallout whose size and composition was studicd (Suito, 1956). 15-megaton surface explosion. The test was a The fallout on the Japanese fishing vessel Fukuru Maru consisted of calcite grannies af annravimotaly 300-microns in diameter with sizes ranging mostly between 100 and 400 microns. As is expected, for subsurface bursts the particle sizes of local fallout are again found to be larger than the particle sizes of the cloud. This was true even for one particular measurement for whicn Again, lognormal distribtuions of sizes were observed, the dominant part of the distribution in the early cloud centered around 18-micron diameter. In contrast, the local fallout particles centered around 290-micron diameter (Heft, 1970, p. 271). For nuclear explosions in the air, the cloud does not contain ~~ surface materials. Essentially all particles then consist of metal 10 ARENe IR Fare eer ne Se ete ema nuclear explosion. ee Ae SaterRR aN Ree the cloud was sampled at the early time of only 15 minutes after the