I am always gobsmacked at the knowledge contained in these halls, but I thought I would call a Lt.Cmdr friend of mine who is in the US Navy based in San Diego.
His e-mail says "The "ball" refers to the fresnel light on the left side of the deck that shows the pilot if he is at the correct altitude on the glide slope".
There ya go AC, they all got there before me! But such knowledge! I sure as hell didn't know.