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Trinity Test, July 16 1945

Eyewitness Report by Philip Morrison

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 convered by an
opaque cardboard shield. I counted seconds and at zero began to raise my
head just over the protecting rise. During this motion the gadget went off
while I was looking at it or possibly a small fraction of a second before.
What I saw first was a brilliant violet glow entering my eyes by reflection
from the ground and from the surroundings generally. I had not raised my
head quite enough to provide a clear vision of Zero. Immediately after this
brilliant violet flash, which was somewhat blinding, I observed through the
welding glass, centered at the direction of the tower an enormous and
brilliant disk of white light. The sensation lasted for such a short time
and the light was so great that I cannot be sure of the shape observed. I
remember it only as a well-marked vaguely round pattern. This disk was a
true white in color, even through the welding glass which makes the sun's
disk distinctly deep green. On subsequently looking at the noon sun through
these glasses I have been led to estimate this initial stage of the gadget
as corresponding to a color much whiter or bluer and a brightness several
times greater than that of the noon sun. I felt a strong sensation of heat
on the exposed skin of face and arms, lasting for several seconds and at
least as intense as the direct noon sun.

It should be noted that my eyes were adapted to twilight or perhaps even to
somewhat brighter light because of the use of the radio dial light I had
made just previous to the T -45 second signal.

2. Growth of the mushroom

For a time which I guess to be less than two seconds the bright disk
produced an after effect in my eyes which spoiled the details of the
following process. I quickly realized that my vision was improving, that the
image was becoming much fainter and less white. I then took off the welding
glass and several seconds later the sun glasses as well. Beginning at T = +2
to 3 seconds, I observed the somewhat yellowed disk beginning to be eaten
into from below by dark obscuring matter. Meanwhile the whole surface of the
plain was covered with matter being thrown up into the air as the motion
continued outward from Zero. In a matter of a few seconds more the disk had
nearly stopped growing horizontally and was beginning to extend in a
vertical direction while its appearance had transformed into that of a
bright glowing distinctly red column of flame mixed with swirling obscuring
matter. The column looked rather like smoke and flame rising from an oil
fire. This turbulent red column rose straight up several thousand feet in a
few seconds growing a mushroom-like head of the same kind. This mushroom was
fully developed and the whole glowing structure complete at about 15,000
feet altitude. I do not recall whether this stage was reached before or
after the arrival of the shock. At T +30 I realized the shock was due very
soon and I huddled closer to the ground in anticipation of a severe shock.
The arrival of the air shock at T +45 on my stop-watch came as an
anti-climax. I noticed two deep thuds which sounded rather like a kettle
drum rhythm being played some distance away. I remember the sound as being
without any important high frequency components as cracks, etc. There was no
earth tremor perceptible to me at any time. The ground on which I was lying
was a very loosely packed dike of mud.

3. Appearance of the smoke cloud

After the passage of the shock I stood up to watch the end of the mushroom.
The red glow died out and the mushroom appeared as a column of smoke or
cloud hanging over Zero. In a matter of another minute or so the smoke had
arranged itself in three rather well defined oblique clouds forming roughly
a vertical Z. The lowest cloud was quite well defined, and stretched north
at a slight angle. At a couple of thousand feet, it appeared to bend around
almost double and to stretch about southeast for a somewhat greater
distance. This second cloud again seemed broken off rather sharply and a
large cloud gradually spread with less and less well defined shape from the
upper end of the second step. This process was nearly complete when the
upper cap was spread over most of the bowl at a height of about 30,000 feet.
There was a strong impression of definite layers in the wind structure, and
there were even some water vapor clouds which seemed to mark the boundaries
between winds of different directions. The completion of this stage took
many minutes until finally the cloud was rather well dispersed toward north
10,000 at a rather low level, had overspread at an intermediate level all
the way to the Oscuro mountains, and on a higher level was drifting slowly
south and southeast.

Other observations:

After T = +50 seconds, I distinctly smelled upon standing up a faint but
marked odor of ozone or corona discharge ionization.

At T +15 minutes or more I observed Zero through a battery commander's
periscope set of 8-power. Not much detail was visible in this region. A sort
of dust haze seemed to cover the area. A remarkable amount of heat shimmer
was noticed on the horizon directly above the Zero area. It was shortly
after this that I saw the Jumbo tower was missing.

Size and distance figures mentioned here are based on judgments of angular
size and the assumption of 18,000 yards distance from Zero to base camp.