An interesting observation was made independently by a British group during the summer of 1954 in flying aircraft over England at various altitudes. It is not known exactly how the samples were col- lected, but the assumption is made that they were obtained in a manner similar to those obtained by our jet aircraft as mentioned above. Their data are: TABLE } (fect) 3 1,600 11,000 18,500 27,000 35,000 40,000 4,000 48,000 Fissions/Kg Air (x10°) Fissions/Cu. M. Air (x10°) 58 70 41h 475 1,632 2,388 1,400 1,600 9,320 3,460 2,808 1, 400 33,714 9,900 85,145 131,814 20,650 26,400 This group by some method of extrapolation has estimated that fission products from 20 M? fission yield, with several Mf in the troposphere, are present in the total atmosphere. There are therefore at least some qualitative data available which tend to show the presence of low levels of radioactivity due to fission products in both the stratosphere and the troposphere. The New York Operations office of the Atomic Energy Coumission has been sampling fall-out at the earth's surface for the past five years. The method has been to place gummed paper, one foot square, at many points in the United States and at several locations throughout the world. The sample points in the United States are at Weather Bureau Stations and Atomic Energy Commission installations, while our foreign samples are taken lergely at embassies and legation buildings. There are 41 sampling stations in the United States where about 250,000 samples have been collected since 1951. The number of samples from foreign stations is much lower than this and many of the stations aT