a 29 A larger sampling program was initiated in the summer of 1965 for the : purposeof extending our knowledge of strontium-90 fallout and precipitation : over the sea. Ion-exchange column collectors and rain gauges have been placed on the 23 Coast Guard vessels assigned to Ocean Station duties; these vessels maintain continuous weather observation stations at four locations in the Atlantic Ocean. These locations are: Latitude 56° 30' N, Longitude 51° 00' W; Latitude 52° 45' N, Longitude 35° 30' W; Latitude 44° 00" _N, Longitude 41° OO" W; Latitude 35° 00! N, Longitude 48° 00° W. Normal scheduling of the ships results in "on station" periods of about 21 days; thus, the deposition samples are not monthly as is usual for land sampling. The factor of ten difference between the data reported by the Canadian Air Surveillance Network and that of the U. 5S. Publie Health Service Radiation Alert Network is a result of difference in equipment and procedures used by the two countries in making these measurements. Air filter samples collected at sampling stations in the United States are surveyed with field instruments and a field estimateof the gross beta concentration in air is made. Samples collected for the Canadian Air Surveill _ ance Network are mailed to a central laboratory for analysis. Levels of , gross beta concentration in air, identified by laboratory equipment >» are consistently lower than field estimates of gross beta concentration in air made By field instruments. Prior to August 1967, all air filter samples collected for the USFHS Radiation Surveillance Network (presently the Radiation Alert Network) were sent to the Radiation Surveillance Network Laboratory for analysis. The