Glass fogs up pretty easily. It’s normally not a problem, unless you want to see through it, for example the windscreen of your car. Or your bathroom mirror, if you’re shaving.
How can do you stop it fogging up? It’s actually a lot easier than you think. Get some dishwashing detergent, squirt some onto a cloth, and rub it on the glass. It will of course smear initially, but just keep rubbing until it becomes clear again. You now have a very thin coating of detergent all over the glass surface.
Now try fogging it up with your breath. Works well, doesn’t it?
Here’s how it works. Mist is formed by tiny droplets of water beading up on the surface of the glass. the tiny drops act like little lenses, and scatter the light, you therefore can’t see through it. The detergent breaks the surface tension of the water and allows it to a flatten out on the surface.
And no, you won’t find this in the book anywhere – I thought it up myself. It’s a Dr chemical special!
PS. For any motorcyclists out there, it also works on plastic, and is a great way to stop the inside of your fighter fogging up