I was kneeling between the pilot and co-pilot in B-29 No. 384 and observed the explosion through the pilot's window on the left side of the plane.  We were about 20 to 25 miles from the site and the cloud cover between us and the ground was approximately 7/10.  About 30 seconds before the object was detonated the clouds obscured our vision of the point so that we did not see the initial stages of the ball of fire.  I was looking through crossed polaroid glasses directly at the site.  My first sensation was one of intense light covering my whole field of vision.  This seemed to last for about 1/2 second after which I noted an intense orange red glow through the clouds.  Several seconds later it appeared that a second spherical red ball appeared but it is probable that this apparent phenomenon was caused by the motion of the airplane bringing us to a position where we could see through the cloud directly at the ball of fire which had