The original measurements were extremely simple as only the total mixed fission product beta activity was required, These data gave in- formation on the arrival of fallout and to some extent on the relative fallout contribution at different locations, In the first network of 10 stations set up for the United States in the spring of 1951, the collector was a metal tray having an area of about <A layer of water was maintained in the tray and every twenty- se 9 square feet, four hours the contents were filtered to obtain the particulate activity. The water, including any rainfall, was collected in a polyethylene bottle. These samples were prepared for beta counting and measured with Geiger tubes against Radium D+E standards, For the fall 1951 tests the network was expanded to 61 stations and 20 of these had gummed paper samplers as well as trays. These stations were operated for the Atomic Energy Commission by the U. S. Weather Bureau, The gummed papers were forwarded to the Health and Safety Laboratory for ashing The results on these stations were reported by the Health and ben neneg and counting. Safety Laboratory in 1952, (2) The network in the United States for the spring 1952 tests included 109 deposition stations with gummed paper samplers. The data were reported in 1953 by Eisenbud and Harley, (3) During the fall 1952 Pacific tests the network consisted of 51 gummed paper stations in the continental United States and 60 elsewhere in North America and overseas. All later samplings were with a gummed acetate film instead of gummed paper which gave a smaller amount of ash, In the spring 1953 Nevada series, 96 U.S, stations and 29 others were in operation, and rea re in the spring 1954 Pacific series, the network was 39 U. S. stations plus