Bobby Cornett, age 10, of Nashville  Tenn. for his question:

Why does mercury roll in little balls?

Breaking a thermometer may cost the better part of a dollar. But the fun you get from the mercury that runs out of the little tube is worth it, The gleaming silver metal runs down hill and collects in shimmering pools, Poke it, and it separates into little round silver balls. They roll along and join up with each other when they meet.

Mercury is the only metal that is a liquid at ordinary temperatures. It freezes solid at minus 37,96 degrees Fahrenheit. That temperature puts a stop to those merrily rolling little silver balls.

Particles of liquid have attraction for each other, They tend to cling together. Particles of water cling together to make the raindrops. Liquid mercury acts the same way. A small amount of it clings together to form a little round ball, A larger amount will rest in a hollow and form a little pool.