Sion Zucker, age 15, of Fairfield, Conn., for his question:

WHAT IS THE FOURTH DIMENSION?

We usually say that space has three dimensions, as in a cube: length, width and height. But many problems can't be solved by considering only three dimensions.

The fourth dimension is used in the study of all spheres in space. The four dimensions, or quantities, are three distances used to fix the position of the center of the object, and the radius of the sphere.

Temperature can be the fourth dimension if the problem involves making an airplane fly. And time is often the fourth dimension.

Four dimensional geometry has the same relation to solid geometry as solid geometry has to plane geometry. The language of geometry is used even though a fourth dimension cannot be visualized.