Danny Kelley, age 10, of Spokane, Wash., for his question:

Can air be weighed?

It would be a tricky job to weigh the air, say, in a shoebox. But it can be done. Two identical containers would be weighed on a perfect pair of delicate scales. Both would seem empty, but one would be full of ordinary air, and the other would be a vacuum from which the air had been removed. The difference in weight would be a mere fraction of a gram. It would equal the weight of air in the air filled container. The air in an average room weighs only one or two pounds.

The airy atmosphere reaches hundreds of miles above our heads, and it presses down upon the Earth with terrific weight. An instrument called the barometer is used to weigh the air from the very bottom at ground level to the very top where it merges with outer space. The barometer weighs the air pressing down upon one square inch of the Earth's surface. The weight varies, depending upon the height, temperature and moisture. At sea level, the average weight of a column of air above one square inch is about 14.5 pounds.