"Surely You're Joking, Mr. Feynman!" - unam.

"This is the place," the receptionist replied.
The man asks if his group can come to the lectures.
"I don't think you'd like 'em much," I say. "They're kind of technical."
Pretty soon the woman, who was rather clever, figured it out: "I bet you're
Professor Feynman!"
It turned out the man was John Lilly, who had earlier done some work with
dolphins. He and his wife were doing some research into sense deprivation, and had built
some tanks.
"Isn't it true that you're supposed to get hallucinations under those
circumstances?" I asked, excitedly.
"That is true indeed."
I had always had this fascination with the images from dreams and other images
that come to the mind that haven't got a direct sensory source, and how it works in the
head, and I wanted to see hallucinations. I had once thought to take drugs, but I got kind
of scared of that: I love to think, and I don't want to screw up the machine. But it seemed
to me that just lying around in a sense­deprivation tank had no physiological danger, so I
was very anxious to try it.
I quickly accepted the Lillys' invitation to use the tanks, a very kind invitation on
their part, and they came to listen to the lecture with their group.
So the following week I went to try the tanks. Mr. Lilly introduced me to the
tanks as he must have done with other people. There were lots of bulbs, like neon lights,
with different gases in them. He showed me the Periodic Table and made up a lot of
mystic hokey­poke about different kinds of lights that have different kinds of influences.
He told me how you get ready to go into the tank by looking at yourself in the mirror
with your nose up against it ­­ all kinds of wicky­wack things, all kinds of gorp. I didn't
pay any attention to the gorp, but I did everything because I wanted to get into the tanks,
and I also thought that perhaps such preparations might make it easier to have
hallucinations. So I went through everything according to the way he said. The only thing
that proved difficult was choosing what color light I wanted, especially as the tank was
supposed to be dark inside.
A sense­deprivation tank is like a big bathtub, but with a cover that comes down.
It's completely dark inside, and because the cover is thick, there's no sound. There's a
little pump that pumps air in, but it turns out you don't need to worry about air because
the volume of air is rather large, and you're only in there for two or three hours, and you
don't really consume a lot of air when you breathe normally. Mr. Lilly said that the
pumps were there to put people at ease, so I figured it's just psychological, and asked him
to turn the pump off, because it made a little bit of noise.
The water in the tank has Epsom salts in it to make it denser than normal water, so
you float in it rather easily. The temperature is kept at body temperature, or 94, or
something ­­ he had it all figured out. There wasn't supposed to be any light, any sound,
any temperature sensation, no nothing! Once in a while you might drift over to the side
and bump slightly, or because of condensation on the ceiling of the tank a drop of water
might fall, but these slight disturbances were very rare.
I must have gone about a dozen times, each time spending about two and a half
hours in the tank. The first time I didn't get any hallucinations, but after I had been in the
tank, the Lillys introduced me to a man billed as a medical doctor, who told me about a