ia | 1. The gummed film results tend to be low when compared to pot analyses, 2. Results from composite samples are even lower with respect to the pot analyses than the summed daily values compared in adjoining months. 3. 4. r | The highest daily pot/film ratios are found in 1954, and the next highest are found in 1958 and 1959, The daily pot/film ratios are generally good during 1955, 1956 and 1957. Since the composite gummed film resultswere excessively low, a comparison was made for the months of February through June of 1955 where the samples from stations in the United States were run by both methods, This comparison showed the summed daily values to be 5 times as high as the composites on the average, This value may not be generally applicable and has not been used in preparing the summary tables for individual stations, The most probable causes are loss of sample in compositing and insufficient correction for self-absorption, The monthly pot samples collected in New York City from 1954 through 1958 were analyzed for total B activity as well as for sr? , These total B : activity values have been treated by the present model, assuming the monthly collection to have been a single sample taken on the 15th of the month, (Pot samples before January 1957 were collected weekly and the effective date was taken as mid-week), This computation allows comparison of calculated and measured sr? from the same collector, The data in Table 5 show a marked improvement over the comparison made in Table 4. This is surprising, since they are based on the same model and a factor (1.6) has been included to correct for gummed film efficiency. The difference is very marked for 1958, and an inspection of the - 17 - .