Ever wonder what kind of instrument made the eerie, vibrating pitch changes in '50s science-fiction thrillers?

It's called a theremin, and your young maestros can play this interesting instrument at the Magic Music Factory, a new exhibit opening today at the Rainbow Children's Museum in Cleveland.

The factory is full of colorful music-makers that have been constructed of plumbing and machine parts and are therefore impervious to the punishments of children.

That's not the point, of course. The point is to introduce the very young (kids up to 8 years old) to concepts such as rhythm, musical intervals, tone, pitch, synchronization and melodies.

Children can't see the invisible forces such as lasers, solenoids and photo cells that make things happen in the factory. When they wave a hand, press a button, pull a rope or walk through a tunnel, they make music. Cause and effect is played to perfection.

The exhibit consists of 10 interactive stations. When kids rearrange the Musical Building Blocks, the blocks light up and vibrate and play a succession of tones and rhythms. When they are moved again, they play a different tune.

Kids can wave their hands through the empty frame of the Light Harp and produce heavenly harp music, which fills the air as if by magic.

Walking through the Tempo Tunnel at different speeds will produce different songs. Playing the keys of the Air Organ will produce notes of different durations -- quarter notes, half notes, sixteenth notes and so forth.

The Center Piece is an assemblage of motors, lights, valves and buzzers that demonstrate how parts of a whole work together.

The Instrument Machine is a computer interactive in which the user can make new instruments from different parts and then play the parts. What? Like a trumpet-guitar-saxophone. See?

The exhibit was constructed by a brother and sister team, Chris Yewell and Tracy Douglas, both of Aurora, who have masterminded exhibits for the Great Lakes Science Center and other venues. It will remain at the museum until Dec. 3.

Another new exhibit, Adventures into Books: Gumby's World, will open Sept. 29. In it, Gumby goes on a prehistoric adventure in a giant book in which kids can help solve mysteries and dig for artifacts.

They can also create their own books, adding and subtracting text and illustrations, making bookmarks and writing their own stories. Children are free to take home their creations. That exhibit will run through Feb. 14.

A final note on age appropriateness: All the activities at the museum are geared for ages 8 and younger, so worry not that Gumby will be beyond your young ones, providing they are within the prescribed ages.

Other exhibits include the popular Over and Under Bridges and Water-Go-Round -- glorified fun with bridges and fun with water exhibits -- and The Little Nest. The nest is a resting place for weary moms with toddlers or babies. A mirror near the floor should keep crawlers intrigued.

The museum has different activities every day of the week, so feel free to call and ask what's doing. Last year, 81,000 visitors tromped through. The museum's mission is ``to encourage children and families to discover the world of play together.''

The museum, 10730 Euclid Ave. at University Circle, is open from 10 a.m. to 5 p.m. Monday through Sunday. Admission is $5; $4.50 for seniors and $4 for children (ages 18 months to 15 years). The phone number is 216-791-7114.