From: Richard Rhodes. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986.HIROSHIMA AND AFTER."The hour was early, the morning still, warm, and beautiful," a Hiroshima physician, Michihiko Hachiya, the director of the Hiroshima Communications Hospital, begins a diary ofthe events Little Boy entrained on August 6. "Shimmering leaves, reflecting sunlight from a cloudless sky, made a pleasant contrast with shadows in my garden." The temperature at eight o'clock was 80 degrees, the humidity 80 percent, the wind calm. The seven branches of the Ota flowed past crowds of citizens walking and bicycling to work. The streetcars that clanged outside Fukuya department store two blocks north of Aioi Bridge were packed. Thousands of soldiers, bare to the waist, exercised at morning calisthenics on the east and west parade grounds that flanked Hiroshima Castle a long block west of the T-shaped bridge. More than eight thousand schoolgirls, ordered to duty the day before, worked outdoors in the central city helping to raze houses to clear firebreaks against the possibility of an incendiary attack. An airraid alert at 7:09 - the 509th weather plane - had been called off at 7:31 when the B-29 left thearea. Three more B-sans approaching just before 8:15 sent hardly anyone to cover, though many raised their eyes to the high silver instruments to watch. "Just as I looked up at the sky," remembers a girl who was five years old at the time and safely at home in the suburbs, "there was a flash of white light and the green in the plants looked in that light like the color of dry leaves." Closer was more brutal illumination. A young woman helping to clear firebreaks, a junior-college student at the time, recalls: "Shortly after the voice of our teacher, saying 'Oh, there's a B!' made us look up at the sky, we felt a tremendous flash of lightning. In an instant we were blinded and everything was just a frenzy of delirium." Closer still, in the heart of the city, no one survived to report the coming of the light; the constrained witness of investigative groups must serve instead for testimony. A Yale Medical School pathologist working with a joint American-Japanese study commission a few months after the war, Averill A. Liebow, observes:
Accompanying the flash of light was an instantaneous flash of heat. . . Its duration wasprobably less than one tenth of a second and its intensity was sufficient to cause nearby flammable objects. . . to burst into flame and to char poles as far as 4,000 yardsaway from the hypocenter [i.e., the point on the ground directly below the fireball]. . . .At 600-700 yards it was sufficient to chip and roughen granite. . .. The heat also produced bubbling of tile to about 1,300 yards. It has been found by experiment that toproduce this effect a temperature of 3,000˚ F acting for four seconds is necessary, but under these conditions the effect is deeper, which indicates that the temperature was higher and the duration less during the Hiroshima explosion.