The daughter of Richard Feynman, one of the greatest scientists of the 20th century, published her father’s letters. From the introduction:
When I was very young, I thought my father knew everything. Indeed, Omni magazine once declared him “The smartest man in the world”. Upon hearing this, his mother exclaimed,”If Richard is the smartest man in the world, God help the world!” My father was the first one to laugh.
Here’s how he experienced the first atomic explosion:
I was blinded by a terrific silver-white flash — I had to look away. Wherever I looked an enormous purple splotch appeared: it was just as bright when I closed my eyes. “That,” said my scientific brain to my befuddled one, “is an after-image caused by looking at a bright light — it is not the bomb you are looking at.” So I turned back to look at the bomb.
The sky was lit up with a bright yellow light — the earth appeared white. The yellow gradually became darker, turning gradually to orange. In the sky I saw white clouds from above the gadget caused by the sudden expansion following the blast wave — the expansion cools the air and fog clouds form — we had expected this. The orange got deeper, but where the gadget was, it was still bright, a bright orange, flaming ball-like mass. This started to rise, leaving a column of smoke behind, below looking much like the stem of a mushroom. The orange mass continued to rise, the orange to fade and flicker. A great ball of smoke and flame three miles across it was, like a great oil fire billowing and churning, now black smoke, now orange flame. Soon the orange died out and only churning smoke, but this was enveloped in a wonderful purple glow.
Another after-image I thought, but on closing my eyes it did disappear, and appeared on opening them again. Others said they saw it too, probably caused by ionised air produced in the great heat. Gradually this disappeared, the ball of smoke rising majestically slowly upward, leaving a trail of dust and smoke.
Then suddenly there was a sharp loud crack followed by resounding thunder. “What was that?” cried the man at my left, a war department representative. “That is the thing,” I yelled back.