What are cosmic rays?

   About 100 years ago scientists noticed that odd things were happening to some of their experiments. Rays of a strange kind were reaching them. They were much like X rays, but they were not X rays. The scientists set out to track down the strange rays. They found that these rays came from far outside the earth. The rays were named cosmic rays.
   Cosmic rays do not seem important to most of us. We do not see them or feel them. But scientists, of course, wanted to find out much more about them as soon as they found out there were such things. They went here, there, and everywhere to study them. They went into coal and iron and copper mines. They went into caves and into the great cracks in glaciers. They went deep down under the sea and up to the tops of high mountains. In balloons they went higher in the air than anyone had ever gone before. They even went into such out-of-the-way places as the mouth of a big cannon and under great piles of salt. Many turned diver or miner or mountain climber or airman. Some of these scientists even lost their lives exploring.
   Cosmic rays are still mysterious. Scientists are not yet sure exactly where they come from. But what they have found out helps them to understand better the great universe around us.