Today’s classic article, http://www.straightdope.com/classics/a4_015b.html , says that the low-light-level reflection off of the center rear-view mirror is a reflection off the front of the glass.
This would mean there should be one, and only one, position the mirror can be in where you can see the headlights behind you dimly reflected.
However, every car I’ve driven has TWO mirror positions that give a dim reflection. One is about one rear-window-height above the main reflective (silvered) viewing angle, and the other is about one rear-window-height below it. I can even adjust the mirror so that the “dim” mirror-switch position is showing me the bright, silvered reflection, and the normal “daytime” position shows me the dim reflection.
What’s causing the second dim reflection? Is the mirror’s reflection getting bounced off the inside of the glass’s front surface, and then bouncing off the mirror again before it reaches my eyes? Or what?