Jean Bertrand, age 11, of Sioux City, Iowa, for her question:

WHAT IS THE CELSIUS SCALE?

The Celsius scale is based on the metric system and designed to measure temperature. Its middle section grades the difference between freezing and boiling water in 100 equal degrees. Degrees of exactly the same size are used to measure temperatures below freezing and above boiling water.

For a long time a temperature scale of this sort was called the centigrade scale. But in 1948, an International Conference on Weights and Measures decided to change the word centigrade. Instead, the members of the conference renamed the neat metric scale for Andor Celsius of Sweden, who invented it way back in 1742. The old Fahrenheit scale also measures the difference between freezing and boiling water. But it is more clumsy because freezing point is 32 degrees and boiling point is 212 degrees. Someday we may drop this old system altogether, in favor of the much simpler Celsius scale.