Mary Boudreau, age 11, of Fairfield, Conn., for her question:

WHAT EXACTLY IS A WAPITI?

You know the wapiti under another name, so let's make this a guessing game. He stands 5 feet tall and may weigh half a ton. His thick, hairy coat is brownish gray, fading to a paler yellowish tone around his rump and stubby tail. His head and long, slim legs are dark brown, and there is a dark brown shawl around his neck and throat.

He has the gentle face of a dark eyed deer  and through most of the year he wears a spreading crown of antlers on his head. In older males, the proud antlers may be 5 feet wide, with 12 pointed branches. This handsome deer belongs to North America. His correct name is the wapiti  though most people call him the elk.

We do not notice this speed variation as we travel, but it does cause strange things to happen to moving objects above the rotating surface. North of the equator it causes draining water to veer to the right, while south of the equator it veers to the left.

This odd happening was figured out by a French mathematician named Gaspard Coreolis, which is why we call it the Coreolis effect. It works equally well on moving water, winds and flying arrows. For example, suppose you launch a long¬ distance arrow 1,000 miles southward toward the equator. You would expect it to land due south of where you are standing, but it does not.

The earth rotates eastward, carrying a point on the equator at a faster pace than at points north and south. While your arrow is traveling due south, the solid earth beneath it is moving faster toward the east. Hence its path is veered to the right  and it lands somewhat farther to the west. This is the Coreolis effect at work north of the equator, veering all moving objects to the right in a clockwise direction.

This is what causes the drain water in your bathtub to turn clockwise. South of the equator, the rotating earth causes bath water and other moving objects to veer left in the opposite

The Coreolis effect also causes the winds to veer off course. For example, the north and south trade winds blow toward the equator. North of the equator they veer right as the northeast trades. South of the equator they veer left and become the southeast trades.