You can take a look at this article james.padolsey.com/javascript/special-sc....
YNhat's link will describe how to do it correctly. However, in case you want to know why yours doesn't work. If you look at your code, the fadeIn is completely outside of any event.
This means that it will run initially when the browser interprets it and never again. The fadeOut will run every time you scroll but fadeIn will not run so it will just stay hidden.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.