Brenda Thomas, age 12, of Flushing, New York, for her question:

What exactly is meant by “subatomic particles” ?

The word "atom" began its career in ancient Greece. Thoughtful scholars deduced that the earth's solids, liquids and gases are made and remade from small, indivisible units of matter. The theoretical particle was the atom. And for almost 2,000 years, scholars assumed that no unit of matter was sub sized to the tiny atom.

Andy's mail shows that many future scientists are confused by the term "subatomic particle." Math, we are told, is the language of science. But the human brain cannot form logical thoughts without the language of words. Sometimes our adult generation of scientists unintentionally confuse younger future scientists with overlapping terms such as "subatomic particles," "primary particles" and "elementary particles."

Science Age students already know that solids, liquids and gases are made and remade from basic units of matter called atoms. The basic meaning of "atom" is "uncut" or "indivis¬ible." Scientists of the 19th century sorted and charted the different atoms of the basic chemical elements. For this job, the old concept of the indivisible atom seemed sound. But early in the 1900s, new studies of radioactivity shattered the notion that the atom could never be broken into smaller particles of matter.

Radioactive atoms shoot off energetic particles of themselves. They become different atoms, but these also are whole atoms. Obviously the atom is. built from still smaller parti¬cles. Nuclear research discovered a growing list of these atomic building blocks. A term was needed for this group of midgets and a sensible term was chosen. Sub, meaning "smaller," was borrowed to name them "subatomic particles." Sensible terms were used to name the positively charged proton, the neutral neutron and the energetic, negatively charged electron.

Meson, meaning "middle," was used to name a new medium sized particle. The Greek alpha¬bet, known to scientists of ail nationalities, was used to name the "pion" and other members of the meson family and also the "muon" and "lambda," the "sigma" and the "xi" families of subatomic particles. This is a sensible naming system.

In any case, the term "subatomic particle" was challenged by two new terms. Units smaller than the atom may also be called "primary particles" or "elementary particles." The detailed roles of all these particles is not fully understood. But all of them are directly or indirectly related to atoms and all are smaller than atoms. All of them, then, are subatomic particles.

The submicroscopic world of atoms is a busy place teeming with energetic particles. At present, we cannot explain the details of energy exchanges that go on inside the dynamic atom. Swarms of the earth's electrons are unattached to atoms and throughout the universe only a small percentage of all atomic particles are used as atomic building blocks. We need to know more about them and to find interrelated patterns in their behavior. Some sub¬atomic particles are units of smaller particles and we may learn that most of them are made from unimaginably smaller building blocks.