I observed the Trinity shot looking toward Zero from a position on the south bank of the base camp reservoir directly beside the larger water tank.  There were three distinct stages in the process I saw, which I describe consecutively as follows: 

1.  Instantaneous glow and ball of fire 

At time T = -45 seconds I lay prone facing Zero wearing ordinary sun glasses and holding in one hand a stop watch and in the other the welding glass issued by the stockroom.  I watched the second-hand until T = -5 seconds when I lowered my head onto the sand bank in such a way that a slight rise in the ground completely shielded me from Zero.  I placed the welding glass over the right lens of my sun glasses, the left lens of which was covered by an opaque cardboard shield.  I counted seconds and at zero began to raise my head just over the protecting