I shall try to describe the Trinity test as seen from the "Hill Station", twenty miles from the event.  None of my estimates of times or magnitudes can be considered very accurate, as I have found by comparison with others a wide variation, illustrating the difficulty of personal judgment without instruments.  

The shot went off at about 5:30 a.m., just before sunrise.  I was watching the shot through a piece of dark glass such as is used in welders' helmets.  An exceedingly bright light appeared and expanded very rapidly.  I was aware of a sensation of heat on my face and hands, which lasted about a second.  After about two seconds, I took the glass away.  The sky and surrounding landscape were brightly illuminated, but not as strongly as in full sunlight.  The "ball of fire" was still too bright for direct observation, but it could be seen to be rising and expanding and slowly fading out.  At some time during this stage, the layers of clouds visible