Thursday 10th September 1942

Today we had the last practice lectures before the exam. My subject was “The Diode and Triode Valves” and I began by talking of the Earth and how it was flung off the sun. I told of “that envelope of air which we call the atmosphere,” of gases, liquids and solids; and then, a bit reluctantly, I revealed that electrons were the negative part of an atom. Just as I was about to commence discussing diode and triode valves, I was stopped by the instructor.

“That'll do,” he said, “Quite good. But I didn't expect you to go so deeply into the subject.

So, once again, I hardly mentioned the subject of my lecture.