By Patrick Clinton

What is it that pushes lemmings over the edge?
--Joe Marotta, Steubenville, Ohio

Ah, the legendary mass plunges of the lemmings, all those furry rodents hurling themselves off the cliffs. Is it pack behavior run amok? Is it some kind of self-sacrifice for the sake of the species? Or is it, as some have theorized, the lemmings' effort to return to their ancestral home in Atlantis?

If you're like me, the image of the lemmings' group belly flop was burned into your brain by the Disney film White Wilderness. But Disney got it wrong. In fact, the lemming-suicide thing is a myth that was started long ago, most likely in Scandinavia. Like their cousins the voles, lemmings have a boom-and-bust population cycle. When a boom gets really out of hand, lemmings swarm out of the hills, presumably in search of less populated territory. Some undoubtedly tumble into the fjords by accident. After such migrations, people began to notice that there were no more lemmings around, and this gave rise to the speculation that they must snuff themselves en masse.

The weird thing is, although lemmings don't commit suicide, they do commit murder on a fairly big scale: Current research shows that lemmings respond to overcrowding with infanticide and other Caligulalike frenzies of intraspecies violence. But being a nice family-values outfit, Disney didn't want to get into that.

If hot air rises, why is it always cooler in the mountains?
--William Conway, Louisville, Kentucky

Hot air rises, but it doesn't stay hot. On its way skyward, decreasing atmospheric pressure causes it to expand and, consequently, gradually grow colder in a process called adiabatic cooling. Eventually, the formerly hot air becomes so chilly that it stops rising altogether.

We all know now that the Greek myth of Daedalus and Icarus got it exactly backward: It's cooler in the higher altitudes. This is because air is warmed for the most part by sunlight hitting the surface of the Earth. The farther you get from the radiant effects of the ground, the lower the temperature--about 3.6 degrees Fahrenheit lower for every thousand feet of ascent. (Of course, mountains are "the ground," too, but while sunlight warms peaks just as it warms valleys, mountains are surrounded by brisk, breezy, high-altitude air, which keeps them refrigerated.) All things being equal, the summit of Mount Everest ought to be an invigorating 104 degrees cooler than sea level.

By the way, hot air doesn't always rise. Anyone who's spent a summer in, say, Washington, D.C., knows that under certain atmospheric conditions, hot air can just lie around for weeks at a time, slow-cooking the citizens and making them yearn for the mountains.

Why aren't acorns just called oak nuts?
--Margaret Bird, Mobile, Alabama

Acorn was originally a generic term for all the varieties of nuts that accumulate on the forest floor at this time of year. In Chaucer's day, if you wanted to be specific, you'd have to say "acorns of oak."

Acorn comes from the same family of words as acre. However, it just so happens that the Old English word for "oak" is ac. Because of this phonetic similarity, people in the British Isles began to make the not unreasonable assumption that acorns must specifically be the seeds--"corns," in Old English--of ac trees, and by the sixteenth century the original meaning of the word had been lost.

There's no end to linguistic evolution, of course. In parts of the United States today, in fact, people call oaks "acorn trees." I like that. It puts the chicken before the egg, but at least it's consistent.

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