The atmosphere. When you hear the word explore, perhaps you think of an expedition to some distant, unknown land. Perhaps you think of explorations in Africa or at the south pole. Explorations at or near home, however, are constantly being made by scientists. Among the most important of these are explorations of the atmosphere.
Until recent times little has been known about the nature of the atmosphere or about how deep it is. Even today it has been explored for only a few miles above the ground. Before the invention of balloons and airplanes the atmosphere was studied chiefly near the earth’s surface. By climbing mountains men learned something about what the air is like a few thousand feet above sea level. They learned that when they climbed high mountains, it was hard for them to get enough air for breathing.