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