[kosta50]

For me the symbolism illustrates that the light increases when it travels westward, as the Sun dawns out of the darkness in the east and moves toward a brighter zenith in the west

Zenith is as high as it will go (zenbith it's straight up, not west); after zenith it all down hill... :)

[Dr. Eckleburg]

As I said, the movement is all east to west...