Gary Hopkins, age l0, of Glendale, Calif., for his question:

How can they measure the amount of rainfall?

There are thousands of weather stations spotted across our land where weather watchers measure such events as temperature and pressure, wind and rain. News from the local points is flashed to a central Weather Bureau to be analyzed. Then the weatherman can tell exactly how much rainfall was doused upon our town by yesterday's shower.

Suppose the weatherman reported that more than 32. million tons of water had been dropped upon the city of Los Angeles. This, surely, would be a deluge and We would expect to find the city knee deep in floods. Not at ail  it is merely the weight of one inch of rainfall on the entire area of the city. Most of this water, of course, would drain away or sink into the soil, leaving wet streets and a few puddles to dry up in the sunshine.

Normally the amount of rainfall is measured in inches and fractions of an inch. An inch of rainfall would cover a solid, level area with a layer of water one inch deep. However, as they fall, most of the raindrops drain away down the slopes or sink into the ground. To measure the exact amount of rain dumped by a cloud We must not let any of it escape. Weathermen Use a contraption called a rain gauge that accurately measures the downpour to l/l00th of an inch.

The simplest rain gauge is a tin can with an open top to catch and hold the raindrops as they fall. The usual rain gauge looks like an overgrown can hoisted on metal legs. Its open mouth catches the rain and funnels it down to a narrow tube inside the can. This makes it possible to measure the depth in detail.

You can measure the depth of trapped water in a plain open can with a ruler. But it would be hard to measure accurately every l/l0th or l/l00th inch. In a rain gauge, the water collected by the open top is funneled down inside to a narrower tube. The top is 3 inches wide, the tube only 2.53 inches wide. In area, the top is just l0 times bigger than the tube so one inch of rainfall in the top puts l0 inches of water into the tube and l/l0th inch funnels down a whole inch.

The tube is 20 inches tall and marked with a ladder of lines to Measure each l/l0th inch. The weather watcher can Measure a sprinkle from a small shower in accurate detail merely by dividing by l0. If the water in the tube reaches l/l0th inch, the actual rainfall was l/l00th inch.

Some gages keep written records of the rain as it falls. One type has two buckets that take turns at filling and tipping themselves empty. It can be left to keep its own records for several days. And one type measures the weight of the rain. An inch of rainfall drops 72,000 tone of water on every square mile. so if our city covers 450 square miles, a one inch shower doused us with a watery deluge of more than 32 million tons.