Sitting in a status meeting this morning, I found myself staring at the particles of dust illuminated by the beam of the overhead projector. They were all moving in the same direction — toward the lens, like moths drawn to the light. And I realized that when I’ve watched dust in a projector beam in the past, it has always moved in that direction. There must be a physical reason for this.
Here’s my theory: The projector heats the air around it, which rises. Cooler air then flows toward the projector to replace the departed warm air. Therefore, once a projector has been on long enough to heat up, the air in front of it will always be moving toward the lens, carrying dust with it.
Unfortunately, I haven’t had the opportunity to test this theory. The simplest way would be to light a couple of cigarettes, hold them near the projector, and observe the behavior of the smoke. But you can’t do that where I work. A bowl of dry ice would probably work just as well, but how do I explain bringing that to a status meeting? Guess I’ll have to figure out another method.

Like many people in post-9/11 America, I’ve experienced a renewal of interest in displaying the flag. One place to do this, of course, is on your car. You have several options: attach a flag to your radio antenna, paste a flag sticker on the rear bumper, get one of those flag brackets that mounts in a window, or opt for a flag made of that flexible magnetic plastic that some refrigerator magnets are made of.
I decided on the magnets, and each of our vehicles now has one. They seem to me to be the best solution: the antenna-mounted flags get tattered too quickly, bumper stickers are impossible to remove, and the brackets make your windows leak. The magnets have all of the advantages of a bumper sticker and none of the flaws: they can easily be removed, repositioned, or even moved to another vehicle; if they collect dirt, you can take them off and clean under them; and they don’t fade like paper stickers do. Sure, they’re a bit more expensive, but not enough to matter.
So why aren’t all bumper stickers made of this stuff? For that matter, why aren’t license plates made out of it? Car dealers figured out the advantages of magnetic license plates years ago; you’ve probably noticed the special magnetic frames they use, so they can quickly switch dealer plates from one vehicle to another. The rest of us don’t need to do that, but it would still make sense for license plates to stick to your car on their own without having to be mounted in a special holder.
I know what you’re thinking: wouldn’t that make it too easy for people to steal your plate? Not really. Anyone with a screwdriver can steal your plate right now. It only takes a minute to undo the screws and walk off with it. Yet few license plates ever get stolen. It won’t make any difference if doing so no longer requires the screwdriver.
I suspect the real reason why neither license plates nor bumper stickers are magnetic is simply that no one has thought of doing it. This is probably also the reason why the full potential of refrigerator magnets hasn’t been tapped. Refrigerator magnets are a brilliant advertising ploy, because they’re actually useful. You can never have too many of them. And so people tend to hang onto them for years (sometimes long after the company they advertise has ceased to exist). You may not give the advertiser your business, but their phone number is right there on your refrigerator door if you ever decide to.
Yet when a business hires people to put advertisements on parked cars, they always use paper flyers and stick them under your windshield wiper. This never works, because a piece of paper is worthless. Those flyers end up on the ground or in the nearest trash can. Why not hire people to stick refrigerator magnets to your car? You’re more likely to put that magnet in your pocket than in a trash can, and odds are it will end up on your fridge for the next decade or so.