Thanks for the link to the downloadable versions. I have the Feynman Lectures loaded on an old iPod and I find them to be an amazing sleep aid. This is not a criticism, they are engaging enough to take my mind off of whatever is keeping me up while also being baffling enough that I fall asleep during the extended sections of blackboard writing sounds. My current set of files is not as good as the recently re-edited Caltech set but I don't want an active Internet device by my bed. Unfortunately they occasionally lead to somewhat stressful dreams of being in college again. It's a risk I am generally willing to take.