Tomas was ten years old and quite sure of one thing: air has weight. His older sister Elisa laughed so hard that she nearly dropped her toast. "Air is nothing!" she said. "That is the whole point of it." Tomas said nothing, which in a boy of ten is a sign of serious intent. He took a flat football from the garage, set it on the kitchen scale and wrote the number on the back of his hand, like a man recording a verdict. Then he pumped the ball until it was hard as a stone and weighed it again.
The number was a few grams higher. Elisa picked up the ball, put it back on the scale and frowned. She checked the scale twice, once with a spoon on it, to make sure that it was not lying on his behalf. It was not. Their father, who had been listening from the doorway with a cup of coffee, explained that the same air presses on everything around us, on the table and the toast and the doubting sister, even though we never feel it.
Tomas took the football to school and showed the class, and at the science fair he won a ribbon. Elisa, who had never in her life admitted that she was wrong, became his assistant and awarded herself the title "Head of the Air Department," which she wrote on a card and wore, to his considerable annoyance, for a week.