Mike Mitchell, age 9, of St. Louis, Missouri, for his question:
How do they measure the weather?
The weather is a mixture of sunshine and showers, wild winds and gentle breezes. It brings clouds and clear skies, warm air and cool air, foggy days and dewy mornings. The weather is a mixture of different ingredients. The weatherman has different ways to measure them. For example, he uses one gadget to measure the temperature and a different gadget to measure the wind.
They use a rain gauge to measure the rain and a weather vane to measure the wind. They take the air's temperature with a thermometer and measure how heavy it is with a barometer. They use a hydrograph or some other instrument to measure the moisture in the air. Every weather station takes these different measurements. All the facts are put together to show what the weather is doing outdoors.
But, as we know, the weather outdoors is always changing. Today's weather moves overhead and tomorrow's weather arrives from somewhere else. So we need to know what the weather is doing in faraway places. The weathermen send up balloons to check the high flying clouds and winds. They use telephones and radio to swap their local reports with other weather stations, near and far. They also tune in to get the wide range pictures from weather satellites, miles above the earth.
Wide range pictures show weather changes on the way. But, as usual, the most important work depends on a lot of small chores. These are the careful measurements that weather stations take all the time. The thermometer measures degrees that tell how warm or cold the air is. The barometer measures its weight, or pressure. As'a rule, heavy high pressure air brings pleasant weather. Light, low pressure air usually brings a spell of nasty weather.
A rain gauge is a special can with a funnel to trap the drops as they fall. Its side is marked with inches and parts of inches. After a shower, the rain gauge shows exactly how deep the water would be if none ran away or sank into the ground. A wind vane may look like a propellor or a set of metal cups spinning around at the top of a pole. It shows the wind's direction and measures how fast it is blowing.
Naturally the weathermen cannot be checking these changeable details every minute. So some of their instruments are fitted up to keep their own records, day and night.
The pen touches a roll of squared graph paper around a drum. The moving meters move the pen and the drum turns in step with a clock. The pen writes a zig zag line on the graph to show how the weather events change, minute by minute.
Humidity is the invisible water vapor in the air. This tricky chore measures the gaseous vapor in a sample of air from outdoors. The amount of vapor is weighed and compared with a chart. The result shows how damp or how dry the air is. It also shows just how much more vapor the air can hold before some of it turns to dewy moisture.