How do “night” rear view mirrors work? One flick of the switch and it seemingly dims all. –Chris Gaffney, Toronto
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The trick is that the two reflecting surfaces are the front and back of the same piece of glass. Said glass is specially ground so that the back surface is slightly tilted relative to the front one. (In other words, the glass looks wedge shaped from the side.) The back surface is coated with silver, like a bathroom mirror, making it highly reflective. The front surface isn’t coated, but it’s still slightly reflective, just as all glass is.
At night the situation is reversed. When you flip the dim switch, the silvered surface tilts so it’s showing you the car’s ceiling, which is so dark you don’t notice it. But now the non- silvered surface is showing you the road. Because the headlights of the cars behind you are so bright, the nonsilvered surface reflects enough light to let you see what’s behind you, but not so much that you’re blinded.
- Pre-Charmin toilet paper substitutes (cf. More of the Straight Dope)–my parents tell me peach season was considered a real treat in the old days because the semi-soft paper each peach was wrapped in was far preferable to the Sears catalog or a corncob.
The stuff I get in the mail these days is just unbelievable. The fellow in the pictures goes by the witty moniker of Long Dong Silver (no, he’s not Oriental). Though no official measurements are supplied–pornmongers just have no grasp of science–18 inches appears to be in the ballpark.
