This is just a sketch of a thought...When I first read the mad jmens rantings about the world being double sided and always spinning, what first came to me was, when you are in like 2nd grade and you learn about christopher colombus and how he sailed to the New World to prove that the Earth wasn't flat, (of course we know this not to be true cuz every educated person of the time knew the earth to be round) that made me think that the journal writer might have believed that there was nothing outside of his known world. And the Jman who not only tellls the journal writer of the cycal between light and dark, but also tells him that there are other lands beyond those occupied by the Legion.
Edge of Nothingness- could be an area beyond the cycles control or an area unrecognized and therefore deemed...well nothing, cept the unknown, and untraveled.
Like a coin spining in the air, it not only shows a cycle of 2 sides, but in a continuous spin represents a globe of sorts.
Heh I think this theory would have been better if the Mad Jman had thrown up a sphere and explained this...but hey I'm flexible :)