dipper@utastro.UUCP (Debbie Byrd) (10/15/86)
The man who discovered outer space -- after this. October 15 Evangelista Torricelli Long ago people took the air we breathe for granted. They assumed that Earth's atmosphere extended all the way to the moon and beyond. Then on today's date in the year l608, a man was born who in a sense discovered outer space. Evangelista Torricelli invented the first barometer, a device which measures changes in air pressure. This device ultimately showed that Earth's air gets thinner as you go up from the surface -- and finally tapers off entirely into the vacuum of space. Torricelli invented the first crude barometer when he took a piece of glass tubing and filled it with mercury. He placed the open end of the tube upright in a shallow basin. Some of the mercury spilled out, but about 30 inches of mercury stayed in the tube -- because the weight of the air pressing down on the mercury in the basin pushed the rest of mercury up the tube. Torricelli was then able to get a rough estimate of the height of Earth's atmosphere. Mercury weighs more than ten thousand, five hundred times as much as air -- so the height of the atmosphere had to be about ten thousand five hundred times the height of the mercury in the tube. That would have made the atmosphere about five miles high. Actually, it's higher -- since the air closest to Earth's surface is thicker than the air higher up. There are still traces of atmosphere several hundred miles above Earth's surface -- enough to drag satellites slowly down from their orbits. But by several thousand miles up, it's fair to say that we've reached outer space! Script by Diana Hadley and Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin