-to justify a monthly summary. in the data tables, we have arbitrarilytaken the reporting of less than 10 days in the-month to be an insufficient sample. ..As it is desirable to obtain an estimate of cumulative values for comparison with soil data and to approximate the total deposition where other data are sacking, missing months have been filled.in by geographic interpolation. In the arbitrary system selected, the three closest stations are averaged for before and after the missing month, ¥ These interpolated estimates are marked req geographic interpolation with some weight being given to the months immediately as such in the summary tables for each station, ComparisonDuplicate Since duplicate films were exposed daily at most of the netwark stations, there is a considerable body. of data on paired samples at the same location, .A statistical treatment of the duplicates is planned as an exercise in methematical statistics, but this project will not be complete for some time, It might be noted that visual inspection shows remarkable agreement for the most part. This may be taken as an indication that we are usually dealing with a statistically valid number of particles deposited on each film, It is possible to compare results from two stations in the same city for a few cases, Such data have been tabulated for New York City (Table 1) barry and for Tokyo and Durban (Table 2). While it is not necessarily true that such paired stations will give identical results, they should be close, The tables indicate a mumber of differences, but the overall agreement is reasonable. It is not possible te attribute errors individually Pe to sampling, analysis, or computation,