On the Right Track...
This view of the tracks from the over-pass at the Belmont station has much to reveal.
Looking north from Belmont, the tracks split off for the Brown Line. I lived in the black building in the distance from 2000 to 2003 (and didn't realize that I actually had a view of this).
Looking south from Belmont. When you look closely at the tracks you can see how un-even they are. This would explain why the trains rock back and forth as much as they do.
Side note: I quit smoking on July 2nd. This is a pretty big deal for me, as I have been smoking since many of my readers were under the age of 10. I have had my moments in the last week, but thanks to Nicoderm CQ (annoying site), and the support of my close friends and co-workers, I am managing to hang on. I put a li'l java script on my sidebar to keep track of the number of day's since my last smoke.