...

In point of fact it is possible to tell the
difference between a small nuclear explosion and
a large one by a very simple method. The calling
card of a nuclear bomb is the blinding flash that
is far more dazzling than any light on earth--brighter
even than the sun itself--and it is by the duration
of this flash that we are able to determine the size
of the weapon. After the flash a fireball can be
seen to rise, sucking up under it the debris, dust
and living things around the area of the explosion,
and as this ascends, it soon becomes recognisable
as the familiar "mushroom cloud". As a demonstration
of the flash duration test let's try and count the
number of seconds for the flash emitted by a very
small bomb; then a more substantial, medium-sized
bomb; and finally, one of our very powerful,
"high-yield" bombs