indications that the arbitrary system was in error, the activity was reassigned to the appropriate burst. In the case of observationa in the Pacific and adjoining regions, it was usually possible to deterstine the burst responsible for the activity from an examination of the trajectories of the debris in conjunction with observed increases in radioactivity, Elsewhere in the world, it was ordinarily necessary to use the arbitrarily assigned burst. All maps of daily fallout values indicate the burst assignment used in computing the decay correction. Unless otherwise indicated, all radioactivity is reported in units of disintegrations per minute per square foot of “1,2 gummed film, decayed to 100 days after the day of the burst, The t law for the decay of fission product activity has beenused throughout. The mans of daily fallout include only the data from the land stations, since there is considerable uncertainty in the ship date. The locations of the ships were imperfectly known and the procedures for avoiding cross-contamination of samples in handling and mailing, particularly on ships exposed to heavy fallout at some time during their voyage, were not adequate. The ship dats were utilized in the drawing of isolines of activity on the fallout maps and in the intercretation of the land station data.