When the explosion went off, I was first dazzled by this indirect light which was much stronger than I anticipated, and I was not able to concentrate upon the view through the dark glass and missed, therefore, the first stages of the explosion. When I was able to look through the dark glass I saw flames and smoke of an estimated diameter of 1000 yds. which was slowly decreasing in brightness seemingly due to more smoke development. At the same time it rose slightly above the surface. After about three seconds its intensity was so low I could remove the dark glass and look at it directly. Then I saw a reddish glowing smoke ball rising with a thick stem of dark brown color. This smoke ball was surrounded by a blue glow which clearly indicated a strong radioactivity and was certainly due to the gamma rays emitted by the cloud into the surrounding air. At that moment the cloud had about 1000 billions of curies of radioactivity whose radiation must have produced the blue glow.
