Barbara Ann Boston, age 11, of Philadelphia, pa., for her question:

What is an altimeter?

The name of this gadget means height measurer, and the job of an altimeter is to measure height or altitude. There are several types of altimeters for measuring the height above sea 1eve1, and there is an up to date type that gives the exact altitude above the ground. An altimeter is a useful and often a necessary instrument to take along on a trip.

The air becomes thinner above sea level at a given rate, and the atmospheric pressure decreases at a given rate. This is measured by the barometer, and a barometer is part of the aneroid or barometric type altimeter. It measures the altitude above sea level. Another type uses a radio device. It computes the exact distance above the earth by timing the returning echoes from radio signals.