Joseph P. Giblin, age 10, of Staten Island, N.Y., for his question:

WHAT IS THE COLOR SPECTRUM?

We see the color spectrum in the rainbow and also when a sunbeam goes through the sloping sides of a glass prism. In both cases we see a series of colored rays, always arranged in the same order. This orderly arrangement is the color spectrum of ordinary light. The red ribbon merges with orange, which merges with yellow, then comes green and blue which merge to deep violet.

Ordinary light is invisible, though scientists call it white light. It's hard to believe that colorless light is a blend of the rainbow colors called the light spectrum.

This is possible because light is electromagnetic energy, a mysterious blend of electricity and magnetism. X rays and radio are other forms of electromagnetic,energy.

All these amazing energies pulse along in longer or

shorter waves called wavelengths. X rays are much shorter than light waves, and radio waves are much longer. All of them pulse along at the fantastic speed of 186,000 miles per second. The wavelengths of light are measured in angstrom units. It takes 100 million angstrom units to equal a centimeter, which is slightly less than half an inch. The lengths    of light waves range all the way from 4,000 to 7,000 angstroms.

When a beam of light passes through a glass prism, its longer and shorter waves are bent at different angles. Shorter waves are bent most, longer waves are bent least. From here the different waves separate and angle off in different directions. The beam of light is separated into strands, and each strand reveals its true color.

The longer waves, in the 7,000‑angstrom range, are bent least. They separate and angle off to reveal bands of red. Shorter and still shorter waves in the 6,000 range are bent more, and angle off in bands of orange and yellow. Still shorter waves reveal bands of green. The shortest waves, in the 4,000 range, bend at sharp angles and streak off in bands of blue.

Altogether, these rainbow ribbons reveal the color spectrum of ordinary light.  The colors always appear in the same order for a good reason. Each one depends on certain wavelengths of energy‑‑and different wavelengths angle off in different directions.