Also:

William James describes a man who got the experience from laughing-gas; whenever he was under its influence, he knew the secret of the universe, but when he came to, he had forgotten it. At last, with immense effort, he wrote down the secret before the vision had faded. When completely recovered, he rushed to see what he had written. It was: "A smell of petroleum prevails throughout.”

-- Bertrand Russell, A History of Western Philosophy

I wonder if both stories are real, or one is a memetic mutation of the other.