ay transparent brown stains against the sky at sampling time, This transparent cloud was almost impossible to see without the aid of the special brown glasses or helmet visors, which were invaluable in keeping the target in sight. The cloud separated into three layers before plus 1 hour; a very puny layer at 21,000 feet; a middle layer at 19,000 to 20,000 feet which seemed to contain the majority of visible bomb material, although quite thin; and a lower layer at 16,000 feet which was very thin and wide spread and quite difficult to see at all, It was found that all of these thin pieces of cloud could be seen best by breaking. off about 20 miles and then flying straight in watching radiation instruments to pick out the activity, as the clouds almost disappeared to the eye, when approached closely or penetrated, SAMPLING MISSION Red One was brought out a little early, because of the meagre appearance of the cloud, and at plus 38 minutes was put in the top; Red Two at plus 70 minutes was put in the middle; White Flight at plus 84 minutes was put in the bottom; Blue Flight at plus 91 minutes was put in the middle; and Cassidy at plus 108 minutes was put in the top. In line with visual appearance, the top cloud was somewhat low in radiation readings, the middle about normal and the bottom very low. Decay of the top between Red Two readings and Cassidy readings (70 and 108 minutes) was over 50%, The special penetration by Cassidy was an experiment to check COPIED/DOE LANL RG cross contamination effects if two separate samples were to be gathered with one aircraft. One sampler pod was, opened in the cloud and the as