National Geographic : 1926 Jan
MEASURING THE SUN'S HEAT AND FORE CASTING THE WEATHER The National Geographic Society to Maintain a Solar Station in a Remote Part of the World to Cooperate with Smithsonian Institution Stations in California and Chile BY C. G. ABBOT, ASSISTANT SECRETARY, SMITHSONIAN INSTITUTION RIDING, one day, between Salt Lake and Los Angeles, my newly met seat mate, learning that my business is to observe the heat of the sun, said that he did not believe the sun is hot. "For," said he, "the higher one goes on a moun tain or in a balloon, the colder it gets." What would you say to that? Plausi ble, isn't it? The secret is the same as that which keeps a windowpane cold. If you sit inside the room in the sun, your black coat and your shoes soon become very warm, while the windowpane, through which the sunbeam comes, keeps its win try chill. Sun rays are not heat. They are of another form of energy which we call radiation. It is a wave motion, like radio waves, only enormously shorter in wave length. Most radio programs come in on waves of 200 to 5oo meters; visible sun rays come in on waves of 0.0000004 to o.oooooo6 meter, or about 500,000,000 times as short. Clear air and clear glass are very transparent to sun rays, which pass through these substances almost without absorption of energy; but black shoes or clothes, and lampblack still more, absorb sun rays, and their energy is di verted from its beautiful wave-play to promoting the irregular vibrations of the molecules which we call heat. The upper air is so very transparent that it stays cold, for it absorbs almost no solar energy of radiation, and although a person or a blackened object absorbs even more of solar radiation at high alti tudes than at the earth's surface, yet, being surrounded by the very cold air, which is carried along by the winds, his temperature is kept low for the same rea son that a fan cools the radiator of an automobile. Besides charming us in the rainbow, the sunset, and the blue of the sky, sun rays keep the earth warm enough to live on. They maintain the inimitable chem ical processes by which plants grow; dis till into the clouds all of the ocean water that comes to us as rain;* cause all the weather; and, when we get wise enough, they will furnish us a trillion horsepower for mechanical, electrical, and heating purposes, if we need so much power by that time. No wonder that "Uncle Joe" Cannon once said in the Appropriations Commit tee of Congress: "I don't care so much about the stars that are so far away that if they were all abolished to-night our great-grandchildren would never know the difference; but everything hangs on the sun, Sherley, and it ought to be in vestigated. I think this appropriation is all right !" A GRANT TO INVESTIGATEE T ill' SUN" This is just what the National Geo graphic Society has given me a grant to undertake-to measure the radiation of the sun. But since I have been in this work for the Smithsonian Institution for more than 30 years, members of The Society have a right to know what more is expected to be found out with the aid of this generous grant. The fact is, we have discovered that the sun is a variable star. Mr. H. IT. Clayton, the eminent American meteorol ogist, who has been cooperating in the work, has proved that very distinct changes of barometer, temperature, and rainfall are caused by these changes of * See "Toilers of the Sky," by McFall Kerbey. in the NATIONAL GEOGRAPHIC MAGAZINE for August, I925.