Joe Harvey, age 10, of Lake Jackson, Texas, for his question:

What is a gyroscope?

The heart of a gyroscope is a solid metal wheel and the magic works when the wheel spins. You can test its talents with a toy model. The trick is the central wheel that refuses to tip over as long as it spins. Bigger gyros use the same trick fn balancing and direction finding instruments.

The simplest gyroscope is a solid wheel set neatly inside a circle and the whole gadget is made of sturdy metal. An axle through the center of the wheel is fixed into the metal circle by smooth bearings. You can stand the circle upright with one of the bearings on a table and start the gyro wheel spinning. The wheel will be in a flat position and it will stay in this horizontal position as long as it spins. If you tip it, it will try to right itself. You can spin it on your finger and it will keep its balance, even if you point your finger in another direction.

A gyro has a mind of its own. In whatever position you start it spinning, it stays that way until it runs down. This amazing trick is related to a spinning top and to the wheels on your bicycle. Gently tip a fast spinning top and it will try to straighten itself. When you start to pedal, the wheels of your bike are upright. They stay upright all by themselves as they begin to turn    which is why you can balance as long as the bike is in motion    and can't when the bike stops.

These tricks are possible because a rotating wheel tends to stay on its plane of rotation. Rotation, of course, is spinning and a plane is a level surface or direction. The plane of the rotating gyro is the angle at which it starts to spin and tends to keep on spinning. If you start it in a vertical position, it stays on this plane. If some force tips it to one side, it moves itself back to the original position.

You can see how this wondrous talent can be very useful. Big, heavy gyros exert a lot of strength. They are set in outer rings and sturdy frames and fixed to many useful instruments. The spinning wheel points always in the same direction. •A gyro does not yield to magnetic pull or to the earth's rotation. In long trips, it is more dependable than a magnetic compass, but a magnetic compass is used to set the correct direction of the rotating wheel. The directional talents of the gyroscope are used in many other compasses and guiding 4.nstrumetxtg,

In the gyrostabilizer, the balancing talents of the gyro are put to work. When a plane h=is bumpy weather, a heavy gyroscope tries to counteract the sway and makes the flight smoother than it would be without this stabilizing influence. Ocean liners carry gyrostabilizers that work their hardest when the sea is rough. As the ship pitches and rolls. the rotating gyros are tipped. Being gyros, they strive to get back into balance and this effort is geared and guided to balance the ship also.

Gyros of many kinds are very useful to surveyors. Mounted on trains and trucks they help to chart accurate maps of the rails and roads. An oilman also needs a gyro. He uses it when, drilling a deep well to show whether the shaft is straight down or crooked. Other gyros are used in warfare. When firing heavy artillery, the important thing is the correct aim. Various  range finding instruments are used to line up the target and the directional talents of a gyro help to make the aiming job accurate.