Transcript of the letter for better searchability:
Dear Miss Cox:
Your instructor was right not to give you any points for your answer was wrong, as he demonstrated using gauss’ law. You should, in science, believe logic and arguments, carefully drawn and not authorities.
You also read the book correctly and understood it. I made a mistake, so the book is wrong. I probably was thinking of a grounded conducting sphere, or else of the fact that moving the charges around in different places inside does not effect things outside. am not sure how I did it, but I goofed. And you goofed too, for believing me.
We both had bad luck.
For the future I wish you good luck in your physics studies.
Richard P. Feynman