Maria Viscera, age 10, of Phoenix, Ariz., for her question:
How do they measure rainfall?
A sudden shower fills the gutters with running rivulets and leaves ankle deep puddles in the hollows. You might guess that it covered the ground with i0 inches of water. Not at all. At news time, the Weatherman reports that we got only one inch of rainfall and he is not guessing. He knows the exact rainfall in inches and fractions of inches.
It is fun to guess the rainfall from a sudden shower. But we need a rain gage to get a true picture of matter. Some people spell this measuring gadget as rain gauge, but gage and gauge both rhyme with the word age. A rain gage measures the water, which fell on a patch of ground before any sank in or ran away. It measures the depth of this water in inches and fractions of inches.
There are several types of rain gages, and all of them look like tall. Wide tin cans standing on metal legs. You can Use an ordinary tin can to make a rain gage of your own. Take off the top and place your can outdoors on level ground. It must stand in the open, away from sheltering walls and dripping trees. The idea is to find the amount of water, which fell on an average patch of ground.
When the shower is over, use a ruler to measure the water trapped in your rain gage. If it is one inch deep, then the shower brought about one inch of rainfall. The weatherman's more elaborate rain gage gives more exact measurements. The most common one is the eight inch rain gage, which stands about three feet tall.
The metal cylinder is exactly eight inches wide, and the top is a funnel, which slopes down to a round hole. This hole leads into a metal tube, which is 20 inches long and exactly 2.53 inches wide. The measurements of the outer cylinder and the tube inside are important. The area of the eight inch circle is just 10 times greater than
The area of the 2.53-inch circle. Ten times more rain falls onto the bigger circle
If the top of the rain gage collects one inch of rainfall, the water runs down and fills the tube inside to a depth of 10 inches. One tenth of an inch of rainfall puts a whole inch of water in the tube. This makes it easy to measure rainfall in small fractions of an inch. The weatherman notes the depth of water in the tube and divides it by 10. The answer gives the exact amount of rain that fell down upon the ground.
Another type of rain gage has a tipping bucket. A wall divides the tube inside. When one side fills, it tips over and empties, and then the other side fills. Each time the bucket tips, the rain gage sends a signal. Another rain gage measures the rainfall from the weight of the water. A very fancy rain gage can write a steady record of the falling rain onto a revolving drum.