anticipation of a severe shock. The arrival of the air shock at T +45 on my stop-watch came as an anti-climax. I noticed two deep thuds which sounded rather like a kettle drum rhythm being played some distance away. I remember the sound as being without any important high frequency components as cracks, etc. There was no earth tremor perceptible to me at any time. The ground on which I was lying was a very loosely packed dike of mud.
3. Appearance of the smoke cloud
After the passage of the shock I stood up to watch the end of the mushroom. The red glow died out and the mushroom appeared as a column of smoke or cloud hanging over Zero. In a matter of another minute or so the smoke had arranged itself in three rather well defined oblique clouds forming roughly a vertical Z. The lowest cloud was quite well defined, and stretched north at a slight angle. At
