Why do I see two reflections?

Dave - This probably means that you're using a standard back-silvered mirror...

So, a normal mirror is made up of a sheet of glass and then they deposit aluminium onto the back of it, which is shiny. So the main reflection you see is from the layer of aluminium at the back of the mirror. But the front of a sheet of glass also has a weak reflection. If you look at any window, especially if it's darker on the other side, you will see a reflection of yourself in that. And so, there will be a second reflection there. Because of the thickness of the glass, it won't be in exactly the same place, so there are two reflections, the main one from the silvering at the back, and a front one from the sheet of glass in the front.

Chris - I think the other place where you see this manifest is if you had one of those car rear-view mirrors that you can flick down to stop the person who's got very bright headlights behind from dazzling you at night time. You flick the mirror down and, bizarrely, although the mirror is now pointing downwards and out of your line of view, you can still see an impression of the headlights of the car behind in that mirror - and that will be that reflection off of the glass surface rather than the silver one?

Dave - They actually put a second piece of glass at a different angle, so then you're seeing the reflection in the glass, not in the mirror itself.