Faith Sorbo, age 10, of Two Harbors, Minnesota, for her question:

Could the earth possibly be hollow?

A lot of people wonder about this, especially when they learn that nobody has ever been more than a few miles down to check the inside of the earth. However, there are ways to check things without on the spot investigations. Our earth scientists are clever at this sort of thing, and several of their indirect investigations are very reliable. For instance, they have weighed the whole earth. Its total weight is 5 1/2 times heavier than an equal amount of water. The surface rocks of the crust are much lighter than this    so the inside cannot be hollow. It must indeed be packed full of heavier materials than those in the outer crust.

Another test makes use of the vibrations that travel on and on from earthquake shocks. The speed of vibrations vary through lightweight and denser materials. Certain earthquake vibrations go down, down, right through the earth. They prove that the inside is not hollow. It is full of heavier materials than those on the surface.